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The corporate ABB technical journal review Greater power 18 Integrating renewables 22 All components from a single source 44 Trends and outlook 60

Special Report 60 years of HVDC 60 years ago, ABB’s predeces- sor company, ASEA, laid the cable for the world’s first commercial HVDC subsea power link, ­Gotland 1, connect- ing mainland Sweden to the island of Gotland. This ground- breaking event was the begin- ning of the modern era of HVDC transmission. Today, ABB remains the market leader in HVDC and is the only company in the world that can supply the complete range of products for an HVDC system.

The picture here and on page 5 shows a cascaded two-level valve arm, rated at 320 kV DC, from the HVDC Light installa- tion Dolwin1 in Germany.

2 ABB review special report Contents

6 Powering the world Impact of HVDC ABB is the global leader in HVDC transmission

13 High impact 60 years of HVDC has changed the power landscape

18 Corridors of power HVDC at work Next-generation UHVDC will send more power through existing transmission corridors

22 Strong winds, high yield HVDV Light® technology goes farther out to sea

26 From far away Efficient and cost-effective long-distance power transmission with HVDC

30 Steps beyond ABB’s HVDC Light® provides a range of expanded benefits for its customers

34 AC/DC Backing up AC grids with DC technology

37 Offshore power With HVDC Light® ABB offers the offshore industry an alternative way to provide electrical power to platforms

40 First-class service Components of Service and upgrades lengthen HVDC equipment lifetime and maximize performance

HVDC 44 A single-source supplier From semiconductors to surge arresters, ABB can supply it all

60 Trend lines Breakthroughs and developments

Contents 3­ Editorial 60 years of HVDC

Dear Reader, This year, we celebrate the 60th anniversary of semiconductors, and extruded cables with the first commercial subsea high-voltage direct solid polymer insulation. By embedding HVDC current (HVDC) power transmission link – a Light functionalities into an AC network, groundbreaking project that used mercury-arc voltage support, reactive power compensa- converters and mass-impregnated high-volt- tion, black start, and the performance of age cables to bring electricity from mainland existing grid assets can be reinforced. Sweden to the island of Gotland in the Baltic Sea. Over the course of 25 years, Dr. Uno HVDC connections are currently point-to- Lamm and his team at ASEA had researched point, so a logical next step is to network previously unexplored fields to overcome the them. This will optimize network reliability challenges of HVDC transmission – work that as well as enable balancing of loads, integra- Claudio Facchin culminated in the commissioning of the tion of intermittent renewables, lowering of Head of Power Systems division Gotland link in 1954. Since then, more than transmission losses and energy trading across 170 HVDC projects have been installed around borders. The missing link here has always the world, bringing bulk power from distant been a low-loss HVDC breaker that acts fast locations to where it is needed. enough to interrupt current and isolate faults. ABB has now developed a solution for this HVDC is the technology of choice for trans­ century-old challenge. mitting power efficiently and reliably over long distances. It is ideally suited for integrating Today, ABB remains the market leader in renewable energy sources situated in remote HVDC, with more than half the global installed and challenging locations. The benefits of base and the unique distinction of being the reliable, long-distance transmission with only company in the world with in-house manu- minimum losses, combined with features like facturing of key components like converters, the ability to connect unsynchronized power cables and semiconductors, as well as grids, have opened new opportunities for this switchgear, transformers and products along versatile technology. the entire power value chain. This special edition of ABB Review showcases how ABB Classic HVDC power transmission technology keeps its HVDC pioneering heritage alive by Hanspeter Fässler has come a long way: from the first 20 MW, remaining at the forefront of this technology Global Business Unit Manager, 100 kV transmission in Gotland to ultrahigh- and continuing to shape the grid of the future. Grid Systems voltage DC links like the 800 kV Hami-Zheng- zhou transmission link in China, with a capacity Join us on this journey. Happy reading! of 8,000 MW. As part of this ongoing journey, ABB has developed new technologies – eg, line-commutated converters using thyristor- based HVDC valves (up to 1,100 kV) that make low-loss DC power transmission of 10 GW Claudio Facchin Hanspeter Fässler over distances up to 3,000 km viable.

A major advance came in the late 1990s, when ABB introduced HVDC Light. With well over a dozen projects completed, this tech­ nology is being successfully deployed in an increasing number of applications, thanks to the parallel development of higher converter voltage and power ratings, IBGT-based

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­4 ABB review special report Editorial 5­ Powering the world

ABB is the global leader in HVDC transmission

MAGNUS CALLAVIK, MATS LARSSON, SARAH STOETER – The installation of the world’s first commercial high- voltage direct current subsea power link, Gotland 1, in 1954 was the beginning of ABB’s lifetime commit- ment to HVDC. Since then, generations of ABB engineers have, together with ABB’s customers, pushed the envelope of HVDC technology, resulting in more powerful links at greater distances. Today, as much as 8,000 MW can be transmitted – the 2,210 km, ± 800 kV Hami-Zhengzhou UHVDC link commissioned in early 2014 is one example. ABB has had many other firsts over the years, not least of which is the groundbreak- ing development of the world’s first hybrid HVDC breaker, resolving the largest roadblock in the develop- ment of an HVDC grid. As more electricity is generated from renewable sources in remote areas and requires long-distance transmission, there is a greater push toward DC power. ABB, the only supplier to offer the complete range of products for an HVDC system, remains committed to HVDC.

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­6 ABB review special report 1 The limitations of AC transmission

I=I0- IC U=U0- UL

L I U G 0 Load G 0 Load

C IC= wCU0 UL= wLI0

1a Underground cable 1b Overhead line

1,200

1,000

800

600

400

Transmission capacity (MW) Transmission 200

0 0 50 100 150 Length of cable (km)

AC 500 kV AC 345 kV AC 230 kV DC ±320 kV

1c Transmission capacity of AC and DC with cables

5,000

4,000

3,000

2,000 ack in the early days of electric- 1,000 ity supply, AC (alternating cur- capacity (MW) Transmission rent) was adopted for power 0 transmission because it could 0 200 400 600 800 1,000 B Length of transmission line (km) be stepped up or down as needed by HVDC 800 kV HVDC 500 kV HVAC 765 kV HVAC 500 kV transformers, and because it could be interrupted more easily than DC (direct current). High-voltage AC grids evolved 1d Transmission capacity of AC and DC with overhead lines as an efficient way to connect existing islands of distribution grids and large valves in 1954. Now, 60 years later, ABB generate a lot more reactive power than generation units with industrial and resi- has supplied, or has been a subsupplier they consume, and require a large reac- dential loads. It was not until some de- to, more than 90 HVDC connections. tive current to charge and discharge the cades later that the technology for high- The company has helped transform cable as the grid voltage changes polar- voltage DC (HVDC) power advanced HVDC from being a relatively specialized ity 50 or 60 times per second. This cur- sufficiently for the first commercial HVDC application to a key technology enabling rent is added to the active current need- link to be established. The pioneering both low-loss, high-power connections ed to transport the energy from one end work by Uno Lamm at one of ABB’s pre- between power markets and remote of the cable to the other. decessor companies, ASEA, began in renew­able generation. 1929 and resulted in the first subsea Both active and reactive current use the HVDC link using mercury-arc converter Why HVDC? thermal capacity of the cable. Due to the In DC, as opposed to AC, electrons flow generation of reactive power, high-volt- through the circuit in one direction only, age AC cable transmission links have and, as a result, do not generate reactive a maximum practical length of about Title picture power. AC cables have primarily capaci- 50 to 100 km ➔ 1. In underground cables The new HVDC Light technology is increasingly tive characteristics ➔ 1a, whereas over- longer than 50 km, most of the AC cur- being used as the power range increases and losses decrease. Shown here is the reactor hall head lines have primarily inductive rent is required to charge and discharge for an HVDC Light installation at 320 kV. characteristics ➔ 1b. Long AC cables the capacitance (C) of the cable ➔ 1a. In

Powering the world 7­ ABB has supplied 2 DC power has lower losses on longer distances. more than half of

HVAC: 2 x 400 kV the world’s HVDC 10

HVDC connections. HVAC

HVDC: 1 x ± 400 kV VSC HVDC 1,200 A 5 1,620 mm2 conductors Energy losses (%) HVAC 2 x 1,200 mm2 conductors

AC/DC conversion losses

0 0 500 1,000 Transmission distance (km)

3 There is a critical distance at which DC becomes more cost effective.

Investment costs

Total AC costs

TotalTotal DCDC costscosts

DC line costs

AC line costs

DC terminal costs

AC terminal costs

Distance Critical distance

overhead lines longer than 200 km, most ferent frequencies (asynchronous grids). of the AC voltage is needed to overcome This can be done via a power line the voltage drop and phase shift due to ­between two converter stations or in a the inductance (L) of the line ➔ 1b. C and back-to-back arrangement with both L can be compensated for using reac- converters in the same location. tors/capacitors or FACTS (flexible alter- nating current transmission systems), or An HVDC system takes electrical power by the use of DC power. from an AC network via a transformer, converts it to DC at a converter station HVDC is the most efficient method of and transmits it to the receiving point by transmitting power over substantial dis- overhead lines or underground cables, tances by cables ➔ 2. HVDC has a higher where it is turned back into AC using an- initial cost – the converter stations – but other converter ➔ 4. because the overhead lines and cables are less expensive, there is a critical dis- The conversion is carried out using high- tance above which DC is more cost power semiconductor valves. Because effec­tive ➔ 3. Furthermore, transmitting HVDC transmits only active (real) power, DC power over long distances with over- no line capacity is wasted on transmit- head lines is more efficient than AC trans- ting reactive power. Therefore, the same mission and is a cost-effective method power can be transmitted over fewer of connecting two grids operating at dif- transmission lines than would be required

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­8 ABB review special report 4 Overview of an HVDC system 5 Different transmission technologies

F c

E Overhead line with AC b

Overhead AC line with FACTS G d

D HVDC overhead line a

a HVDC converter station rectifier b HVDC converter station inverter Underground line with VSC HVDC or AC cable c AC c F d DC

6 Comparison of HVDC Light and HVDC Classic

HVDC Light (power from 50 to 2,500 MW) HVDC Classic (power up to 8,000 MW) – Each terminal is an HVDC converter, which – Most economical way to transmit power can support the AC network as a Statcom over long distances (SVC Light) – Long submarine cable connections – Suitable for both submarine and land cable – Around three times more power in a connections right-of-way than overhead AC – Advanced system features to enhance the – Footprint (eg, 600 MW): 200 x 120 x 22 m performance of the AC network – Footprint (eg, 1,200 MW): 100 x 150 x 20 m

using AC, so less land is needed to HVDC Light® cables, used together with prefabricated ­accommodate the lines. HVDC induces HVDC Light, introduced by ABB in 1997, joints, enable long underground trans- minimal magnetic fields, so the power is used to transmit electricity where the mission. Because HVDC Light uses the lines may be safely built closer to human power involved exceeds 50 MW. It uses IGBT as the power electronics device for habitation ➔ 5. Upgrading an AC trans- IGBTs (integrated-gate bipolar transis- the conversion, superior independent mission line to carry DC can substantially tors), which, unlike thyristors, offer fully controllability can be achieved. HVDC increase its loadability and provide con- controllable power semiconductor switch- Light offers the same benefits as tradi- trollability that can be used to protect the ing. The link with the highest power rating tional HVDC systems, but also provides power networks against blackouts. in operation to date is the 500 MW / ±200 kV more secure power control and quick East-West interconnector between Ireland power restoration in the event of a black- HVDC Classic and the United Kingdom. Major advances out. Because of its ability to stabilize AC HVDC Classic is one of two HVDC tech- in switching loss reduction have been voltage at the terminals, it is the ideal nologies used today ➔ 6. Based on thy- ­accomplished – from an initial 3.7 per- technology for wind parks, where the ristor power semiconductors, it is used cent to less than 1 percent – while HVDC relative compactness of HVDC Light primarily for bulk electrical transmission Light technology has expanded the oper- converter stations compared with HVDC over long distances and for interconnect- ating power ranges up to about 2 GW Classic converter stations is a key ing separate power grids where conven- based on present voltage and current ­enabler for remote offshore wind power tional AC methods are not suitable. ­capability. HVDC Light can be used for generation. HVDC Classic transmission typically has a grid interconnections, offshore links to power rating between 100 and 8,000 MW. wind farms, strengthening power net- Converter stations and transformers It uses overhead lines (for distances over works, and powering oil and gas plat- Electricity generated in a power station 600 km) or subsea cables (for distances forms. Thanks to the superior reactive must first be stepped up to the appropri- of 50 to 100 km), or a combination of power control capability of an HVDC ate voltage and converted from AC to DC cables and lines. Thyristor power semi- Light terminal, it can increase the transfer for long-distance transmission, and then conductors are line commutated, mean- capacity of the AC network surrounding stepped down and converted back to AC ing that the turn-off signal is controlled the terminal. for distribution to consumers. The step- by the AC line voltage reversal. ping up and down is performed by trans- ABB’s HVDC Light features oil-free poly- formers. ABB is one of the world’s leading mer-insulated extruded cables or mass- suppliers of transformers and transformer impregnated cables. The lighter, extruded components – including insulation materi-

Powering the world 9­ In 2012, ABB 7 HVDC cable technology ­announced a major breakthrough in the development – XLPE plastic insulation – Oil-impregnated insulation of the DC grid – – Lightweight land cable at 10 kg/m – Heavyweight land cable at 25 kg/m – Low number of joints for land installations – High number of joints for land installations the hybrid HVDC – Prefabricated joints – Tailored joints – Flexible, allowing coiling and installation – Requires special ship for installation (three circuit breaker. from a barge (over 200 barges available) such ships available globally) – Flexible production (ie, AC and DC cables – Dedicated production line for DC cables in the same production line) – Maximum cable voltage of 500 kV – Maximum cable voltage of 320 kV

7a Extruded polymer HVDC cables 7b Mass-impregnated HVDC cables

8 ABB’s hybrid HVDC breaker

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8a Normal operation: Power flow in path with 8b Power electronic breaker blocks upper least resistance (results in lower losses) current path to direct the flow into lower path

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8c Mechanical breaker opens to block 8d Main electronic breaker block in upper path lower path

als and kits, tap changers, bushings and world’s longest subsea cable, NorNed, electronic control equipment – as well as which connects Norway to Holland via a service for transformers. 580 km mass-impregnated cable, and the world’s longest underground cable, the The core element of an HVDC system is Murray link, which uses two 180 km long the power converter, which serves as the extruded cables to connect the Riverland interface to the AC system. The conver- region in South Australia and Sunraysia sion from AC to DC and vice versa is car- region in Victoria. ried out in a converter station using valves, which can carry current in one Mass-impregnated submarine cables direction only. This feature is needed for Mass-impregnated cables have been in both rectification and inversion. use since 1895. ABB has delivered more than 1,700 km of such HVDC ca- Cables bles all over the world. The 580 km long, HVDC makes it possible to stretch the 700 MW / 450 kV cable link between Nor- transmission distance for subsea or under­ way and the Netherlands represents a ground cables ➔ 7, as has been shown milestone in both power and length for by two world-record installations – the this cable type.

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­10 ABB review special report 9 ABB has supplied more than half of the world’s 170 HVDC projects.

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Extruded polymer land and subsea cables Service and upgrades large power station – in less than 5 ms. (HVDC Light) As the installed base of HVDC links This innovation is paving the way for New HVDC Light cables have insulation grows older, the number of upgrades to a more efficient and reliable electricity consisting of extruded cross-linked poly- the system components increases. After supply system. ethylene polymer. The insulation is triple about 20 years of operation it is common extruded together with the conductor to upgrade valves and control systems. Since the introduction of the first com- screen and the insulation screen. Often, after another 20 years, the whole mercial subsea HVDC link, ABB has be- link or station is upgraded or replaced come – and remains – a leader in HVDC The extruded DC cables are an impor- with new HVDC solutions. To date no technologies, and is the world’s leading tant part of the HVDC Light concept. commercial HVDC link has been shut supplier of HVDC projects to date ➔ 9. Typically, a link will have two cables, with down, which demonstrates the reliability one carrying voltage of positive polarity and long lifetime of the equipment and and the other negative. The strength and the market relevance of these links. flexibility of HVDC Light cables make ­Requests for service are growing, and them suitable for submarine use as well. ABB is commonly chosen as a turnkey service supplier. Control and protection system ABB has its own powerful, flexible and The hybrid DC breaker reliable control and protection system, One of the major disadvantages of HVDC which uses state-of-the-art computers, and one of the main reasons today’s grid microcontrollers and digital signal pro- is primarily an AC grid, is the inability to Magnus Callavik cessors connected by high-performance to interrupt the flow of power and DC ABB Power Systems, Grid Systems industrial standard buses and fiber-optic fault currents. The lack of ultra-fast DC Västerås, Sweden communication links. The system is breakers has been a huge roadblock to [email protected] called MACH (Modular Advanced Con- using HVDC beyond point-to-point links. trol for HVDC and SVC) and is designed That is, however, until very recently. Mats Larsson specifically for converters in power appli- ABB Corporate Research cations. All critical parts of the system In 2012, ABB announced a major break- Baden-Dättwil, Switzerland have inherent parallel redundancy and through in the development of the DC [email protected] use the same switchover principles that grid – the hybrid HVDC circuit break- have been used by ABB for HVDC appli- er ➔ 8. This breaker combines mechani- Sarah Stoeter cations since the 1980s. cal and power electronic switching that ABB Review enables it to interrupt power flows of up Zurich, Switzerland to 1 GW – equivalent to the output of a [email protected]

Powering the world 11­ 12­ ABB review special report High impact

60 years of HVDC has changed the power landscape

BO PÄÄJÄRVI, MIE-LOTTE BOHL – We are he developed world relies on Mercury-arc valves so used to the convenience of merely inter-regional and international Early HVDC experiments based on me- having to flick a switch to illuminate a transmission lines to deliver the chanical, moving-contact devices were room that few of us stop to think where T power that energy-hungry cit- unsuccessful so pioneers soon turned the power that lights the lamps actually ies and industries consume in such vast their attention to the potential of mer­ comes from. It may be generated quantities. As the world urbanizes and cury-arc valves. At the end of the 1920s, locally, but, equally well, it may have becomes more industrialized, and as ASEA embarked on the development been carried from a generator hundreds more dispersed generators appear on and manufacture of static converters and of miles away – perhaps even in a differ- the network, the demand for, and on, mercury-arc valves for voltages up to ent country. The infrastructure that such power distribution infrastructure about 1 kV, and the possibility of devel- makes such widespread distribution of will only increase. It has long been rec- oping valves for even higher voltages power possible is the spider’s web of ognized that power is more efficiently ­began to be investigated. In 1933, an high-voltage direct current (HVDC) transmitted using DC than AC and early ­experimental valve was produced that transmission lines that interlink many visionaries worked hard at perfecting confirmed the validity of the principle. regions and countries in the developed the valves neces- world. Though having roots in the sary for converting 1920s, the modern era of HVDC the high-voltage AC Early HVDC experiments based transmission really began in 1954 when produced by gen- ASEA linked the mainland of Sweden erators into HVDC, on mechanical, moving-con- and the island of Gotland with an HVDC and vice versa. tact devices were unsuccessful connector. In the intervening 60 years, This conversion is HVDC technology and performance the key challenge so pioneers soon turned their have improved at a remarkable rate – for HVDC transmis- and are set to continue to do so. sion and the HVDC attention to the potential of story can be divid- ed into two con- mercury-arc valves. version technology eras – one domi- nated by mercury-arc valves and a later In 1944, Dr. Uno Lamm, “the father of Title picture one in which they were supplanted by HVDC” ➔ 1, successfully operated a recti- The modern era of HVDC began in 1954, but its thyristor-based valves. fier and an inverter in his laboratory in Lud- roots extend back several decades further. Shown is vika, Sweden at a power rating of 2 MW a mercury-arc valve laboratory at the Trollhättan test station, which was established in 1945 and run and voltage of 60 kV. The time was now jointly by the Swedish State Power Board and ASEA. ripe for service trials at powers higher than

High impact 13­ those that could be accommodated at 1 Dr. Uno Lamm, “the father of HVDC” The 20 MW / 200 A / Ludvika so a test station, run jointly by the Swedish State Power Board and ASEA, 100 kV Gotland link was established in 1945 at Trollhättan and marked the begin- a 50 km power line was made available for service trials ➔ title picture. ning of the modern Further technical development of the era of HVDC and mercury-arc valve – as well as other com- ponents in the converter stations and the concept was transmission equipment such as trans- so successful that it formers, reactors, switchgear, and pro- tection and control equipment – resulted has remained basi- in a completely new approach that was implemented by ASEA in the 1954 HVDC cally unchanged link to the island of Gotland ➔ 2. This since. 20 MW / 200 A / 100 kV line marked the beginning of the modern era of HVDC and the concept was so successful that it has remained basically unchanged since.

ASEA’s second order for HVDC transmis- sion equipment – for a 160 MW / ± 100 kV Anglo-French cross-channel link – fol- the second technology era – that of thy- lowed soon after and the stage was set ristors – was about to dawn. for the development of converters that could handle twice the voltage and Thyristor-based converters would have 10 to 20 times higher power Mercury-arc-valve-based HVDC had come than would be required by subsequent a long way in a short time, but was a installations. technology that still harbored some weaknesses. One of these was the diffi- Following the English Channel project, culty in predicting the behavior of the several further HVDC links using mercury- valves themselves – for example, because arc valves were built during the 1960s: they could not always sustain the reverse Konti-Skan (250 MW) between Sweden voltage, they suffered from arc-backs. Also, mercury-arc valves require reg- The invention of the thyristor ular maintenance, during which abso- in 1957 had presented indus- lute cleanliness is try with a host of new oppor- critical. A valve that avoided these draw- tunities and HVDC transmis- backs was needed.

sion was seen as one The invention of the thyristor in 1957 promising area of application had presented in- for these new devices. dustry with a host of new opportu­ nities and HVDC and Denmark; Sakuma (300 MW) in Japan; transmission was seen as one promising the inter-island connection in New Zea- area of application for these new devic- land (600 MW); and the Italy – Sardinia es. All through the first half of the 1960s, (200 MW) link. The largest mercury-arc work continued on the development of valve transmission built by ASEA was the high-voltage thyristor valves as an alter- Pacific HVDC Intertie in the United native to the mercury-arc type. In the States, a 1,440 MW (later re-rated to spring of 1967, one of the mercury-arc 1,600 MW) / ± 400 kV transmission from valves used in the Gotland HVDC link The Dalles, Oregon to Los Angeles, Cali- was replaced with a thyristor valve ➔ 4. It fornia ➔ 3. In fact, this was the last mer- was the first time anywhere that this kind cury-arc valve project commissioned as of valve had been put into commercial

14 ABB review special report 2 Gotland control room in the 1950s 3 Pacific Intertie mercury-arc valve in Sylmar, Los Angeles

4 Mercury-arc valves and thyristor valves installed at Gotland 1 The largest mer­ cury-arc valve transmission built by ASEA was the ­Pacific HVDC Inter- tie – 1,440 MW, ­later ­re-rated to 1,600 MW.

operation for HVDC transmission. Thyris- showed that it could and this cable was With thyristor valves, convertor stations tor technology had ushered in a new era subsequently operated at an electrical became much simpler, cheaper and more of HVDC and rendered the mercury-arc- stress of 28 kV/mm, which is still the reliable and semiconductors have been based approach obsolete. After a trial of worldwide benchmark for large HVDC used in all subsequent HVDC links. just one year, the Swedish State Power cable projects. Board ordered a complete thyristor valve Other companies now entered the field: group for each Gotland link converter The new valve groups were connected in Brown Boveri (BBC), which later merged station and increased the transmission series with the two existing Gotland mer- with ASEA to form ABB, teamed up with capacity by 50 percent at the same time. cury arc valve groups, thereby increasing Siemens and AEG in the mid-1970s to In parallel, tests were carried out on the the transmission voltage from 100 to build the 1,930 MW / ± 533 kV Cahora Gotland submarine cable, which had 150 kV. This higher-rated system – the Bassa HVDC link between Mozambique been operating without any problems at new rating being another world first for and South Africa ➔ 5. The converter valves 100 kV, to see if its voltage could be in- the Gotland transmission link – was for this transmission were oil-immersed. creased to 150 kV – the level needed to brought into service in the spring of The same group then went on to build the transmit the higher power. The tests 1970. 2,000 MW / ± 500 kV Nelson River 2 link in

High impact 15­ 5 Oil-insulated and oil-cooled thyristor outdoor valves in the Cahora Bassa HVDC link 6 600 kV valve test for Itaipu between Mozambique and South Africa

Canada. This was the first project to em- ground, with opposite polarity. Since ploy water-cooled HVDC valves. these conductors must be insulated for the full voltage, transmission line cost is The mid-1970s saw the completion of higher than a monopole with a return further projects: The Skagerrak link be- conductor, but this is more than com- tween Norway and Denmark, Inga-Shaba pensated for by its advantages, such as in the Congo, and the CU Project in the negligible earth-current flow, lower abso- United States. The converter valves in lute current rating (each line carries only these projects were air-cooled. The half the current for the same power), fault ­Pacific Intertie was also extended twice tolerance and so on. Gotland 2 and 3, in the 1980s, each time with thyristor with a total rating of 2 × 130 MW / ± 150 kV converters, to raise its capacity to featured new water-cooled converters. 3,100 MW at ± 500 kV. This bipolar link has provided extremely good availability with no interruption of In 1983, Gotland was revisited with a power transmission in 10 years. new 130 MW / 150 kV cable being laid – Gotland 2. Gotland 1 and Gotland 2 op- Itaipu erated independently, but Gotland 3, an The contract for the Itaipu HVDC link in additional link laid in 1985 to satisfy Brazil was awarded to the ASEA-PRO- ­increasing demand and allay supply MON consortium in 1979. The sheer scale and technical complexity of the In 1967, one of the mercury- Itaipu project pre- sented a consider- arc valves used in the Gotland able challenge, and HVDC link was replaced with it can be seen as the start of a new a thyristor valve – the first chapter in the HVDC story. The commercial use in HVDC power rating was the highest ever transmission. seen in HVDC – two bipoles at safety fears, usually works with Got- 6,300 MW / ± 600 kV ➔ 6. The project was land 2 to form a bipolar link (though it too completed and put into operation in sev- can operate independently). In bipolar eral stages between 1984 and 1987 ➔ 7. transmission, a pair of conductors is It played a key role in the Brazilian nation- used, each at a potential with respect to al power infrastructure, supplying a large

­16 ABB review special report 7 12,600 MW power station at Itaipu The Itaipu power rating was the high- est ever seen in HVDC – two bipoles at 6,300 MW / ± 600 kV.

portion of the electricity for the city of bulk power transmission and is able to São Paulo. The experience gained in the send vast amounts of electricity over very course of the completion of the Itaipu long distances with low electrical losses. HVDC project has paved the way for all But HVDC technology is constantly chal- later HVDC high-power transmissions. lenged to achieve higher ratings for volt- age and current, conquer even longer Some milestones here are: ­distances with overhead lines, cables or − The 2,000 MW / ± 500 kV Québec to a combination of these, and to further New England link. This was among the ­reduce transmission losses. first large multiterminal HVDC trans- mission systems to be built anywhere. ABB’s 1992 vision to create a DC grid − The 1,920 MW / ± 500 kV Intermoun- that solves the problem of renewable tain Power Project in the United ­energy generators often being situated States. The high earthquake-proofing far from the users they serve is now close requirements were met by suspended to being realized by the multiterminal valve structures – used here for the HVDC links being built on land and off- first time and the standard solution shore. HVDC has become an established since. technology and an integrated part of − The 6,400 MW / ± 800 kV Xiangjiaba- AC grids, as well as the key for a future Shanghai transmission link. This sustainable grid based on renewables. record-breaking link uses UHVDC (ultrahigh-voltage direct current) – the technology used in the longest and most powerful transmission links. The introduction of the 150 mm, 8.5 kV PCT (phase control thyristor) was a major factor in enabling performance improvements in this technology, the next generation of UHVDC.

HVDC – key for a sustainable grid based on renewables HVDC is now the method of choice for Bo Pääjärvi subsea electrical transmission and the Mie-Lotte Bohl inter­connection of asynchronous AC grids ABB Power Systems – providing efficient, stable transmission Ludvika, Sweden and control capability. HVDC is also the [email protected] technology of choice for long-distance [email protected]

High impact 17­ Corridors of power

RAUL MONTANO, BJORN JACOBSON, DONG WU, LILIANA AREVALO – With a Next-generation forecasted average annual growth rate of 9 percent [1], the world’s UHVDC will send voracious hunger for clean, reliable electrical power is set to continue for many years to come. Power utilities struggle to keep up with this more power through surging demand. Indeed, in order to cope, they would need to increase their power generation base by an average of 11 percent each and every existing transmission year for the foreseeable future [1]. A further complication arises in that much power generation capacity is situated at some distance from corridors those places where it is consumed – a trend exacerbated by increasing urbanization and industrialization. To ensure future supply, power transportation corridors will have to increase their voltage- and current- carrying capabilities. Despite the maturity of ultrahigh-voltage direct current (UHVDC) technology, these new ratings represent major techno- logical steps that will have to be taken in a very short time.

­18 ABB review special report 1 World energy forecast from EIA [1]

45

40

35

30

25

20

15

10

5

World electricity generation by fuel (trillion kWh) World 0 2010 2015 2020 2025 2030 2035 2040 Year

Coal Nuclear Nonhydropower renewables

Natural gas Hydropower Liquids

1a World electricity generation by fuel (2007-2035) in trillion kilowatt-hours

900 Projections )

15 800

700

600

500

400

orld energy consumption 300

and the power generation 200

to match it are set to con- 100 tinue to rise for the fore- energy consumption (Btu x 10 World W 0 seeable future [1] ➔ 1. Unfortunately, the 1990 2000 2010 2020 2030 2040 bulk of the energy resources needed to Year satisfy rising demand are not located near the load centers. For example, in 1b World market energy consumption (1990-2035) in quadrillion (1015) Btu China, large resources of untapped hy- droelectric power – up to 500 GW – are quirements to minimize routes through power throughput per line as possible. available in the west of the country, in forests and other sensitive ecosystems, For shorter distances, the utility in China ­Sichuan, Xizang and Yunnan provinces. and the general protection of flora, fauna has been considering an increase of the In addition, additional significant coal- and people. If a transmission corridor rated current of 800 kV DC systems. fired generation capacity is planned in is long, the chance of exposure to one ­Despite the maturity of HVDC techno­ the Xinjiang area. The distance of these or more of these factors is increased. logy, these new ratings – of voltage or generation sources from the heavily in- current – represent dustrialized regions along the coast in major technologi- eastern China (Beijing, Shanghai) and The bulk of the energy cal steps that will southern (Guangzhou) China is between have to be taken in 1,000 and 3,000 km. resources needed to satisfy a very short time.

All over the world, diverse factors make rising demand are not located Technical-eco- the construction of new transmission near the load centers. nomical solution lines ever more complex: public resis- In recent years, tance, narrow transmission corridors, 800 kV DC trans- limited availability of rights of way, re- Often, the best solution is to increase mission systems, capable of transmitting the power-carrying capacity of existing more than 7 GW over 1,400 km, have routes. been in operation ➔ 2. However, when

Title picture the transmitted power is increased above Rising demand and the difficulty of building new China, for example, is investigating the 10 GW, 800 kV systems become much HVDC transmission lines means new technology possibility of using a voltage rating of less economic because it is not possible has to be developed to allow existing lines to carry 1,100 kV for power transmissions of 10 to transmit these power levels over a more electrical power from distant generators to centers of consumption. Shown is the valve hall in to 13 GW per line for distances over single UHVDC transmission line – two the Xiangjiaba-Shanghai Fengxian UHVDC station. 2,000 km in order to achieve as much lines are needed.

Corridors of power 19­ 2 HVDC systems evolution 3 Cost comparison of various options in percentage of the total cost of an 800 kV DC transmission link

900 8,000 Yunan Jingping 180 Guangdong Sunan 800 7,000 160 Xiangjiaba Shanghai 700 140 6,000 Itaipu 600 120 Cabora Bassa 5,000 Nelson River 100 500 4,000 Pacific Intertie 80 400 New Zealand 60 3,000

300 Rated power (MW)

Rated voltage (kV DC) 40 2,000 200 20 Gotland 100 1,000 cost of an 800 kV DC transmission link (%) Total 0 Cross Channel 800 kV DC 1,100 kV DC 1,200 kV DC 800 kV AC 1,000 kV AC 0 0 Station Lines Losses 1953 1960 1962 1970 1978 1979 1985 2010 2010 2012 Year Rated power Rated voltage HVDC: one 10 GW line HVAC: three 3,167 MW lines

There is no question that using higher Electromechanical design and equipment ments is of critical importance – elec- voltages reduces losses and allows tar- transport trode size, corona shielding, terminal get energy costs to be achieved ➔ 3. Outdoor high-voltage insulators face forces, etc. all need to be properly de- However, for power lines to be able to many challenges, among which is the signed and tested to guarantee a cost- cope with the higher-voltage demands risk of flashover – atmospheric pollution, effective solution with the reliability that that will soon be put upon them, new for example, can lead to excessive con- the new generation of UHVDC systems system components, especially thyristor tamination of the insulator and thus to requires ➔ 4. valves, will have to be developed. flashover if creepage length and general design is not adequate. Insulators de- Indoor vs. outdoor DC yard Challenges signed for higher voltages have to be Today, both outdoor and indoor DC yards ABB has worked for many years in high- longer – necessitating a diameter in- have been adopted by different 800 kV voltage power transmission and this expe- crease to provide the required mechani- UHVDC projects. However, operational rience is exploited in the development of cal stability and this, in turn, decreases experience at this voltage level is still lim- products that meet the challenges faced flashover performance. The battle to rec- ited [2]. One reason for selecting an indoor when transporting power over very long oncile insulation, mechanical and electri- solution is to minimize the footprint of distances at very high voltages. Several cal requirements can quickly spiral into a the converter station ➔ 5. For equipment aspects become critical when designing runaway situation if great care is not inside this weather-protected building, UHVDC systems: availability and reliability, taken in the design phase [2]. the creepage distance needed and the electromechanical design and equipment mechanical strength required can be transport, and the type of DC yard. The equipment subjected to the new, ­reduced. Switching impulse voltage will higher voltages will be larger, which be the dimensioning parameter. There- Availability and reliability brings further challenges. For example, fore, smooth electrodes with a larger UHVDC systems designed to transmit converter transformers are assembled, ­diameter can be adopted to reduce the power levels above 10 GW need to cope tested and shipped to site. Shipment required air clearance [2]. with higher requirements on availability and reliability. After all, one single-pole The cost of the trip will disconnect energy equivalent to All over the world, diverse building makes the half of the installed capacity of a very indoor approach large hydroelectric power plant – eg, the ­factors conspire to make the more expensive than 12 GW Itaipu plant in Brazil. This will also the outdoor. In ad- impose a high strength requirement on construction of new transmis- dition, depending the AC systems at both ends of the sion lines ever more complex. on the requirements ­UHVDC transmission. Also, thorough in- on the ambient con- vestigations are necessary to ensure that ditions inside the single, small events that occur in regions might be no longer possible with larger- hall, auxiliary equipment, such as a humid- into which multiple UHVDC systems feed sized transformers, so on-site manufac- ity controller, may be required [2]. How­ do not escalate into something more turing and the reliability issues this entails­ ever, part of the building costs will be dramatic. This all means that reliability is have been assessed. returned by the reduced cost of the a very important issue and represents a ­apparatus itself and the costs saved by major design parameter. Reliability throughout the entire range of reducing outages will usually more than products and components destined for cover the rest. A reduced risk of failure is use in these new, higher-voltage environ- the major benefit of the indoor solution.

­20 ABB review special report 4 High-voltage test laboratory 5 Indoor DC yard

ABB technology development systems in both the AC and DC realms. It In 2010, ABB started research into and was the first country to commission and development of the key components for fully operate 800 kV DC transmission sys- the next generation of UHVDC transmis- tems and more than 21,000 GW of trans- sion systems, ie, those exposed to the mission capacity is now installed at this new rated voltage (1,100 kV DC). By rated voltage. Further economic growth means of advanced electromagnetic is expected in the coming years – and simulations, transient studies and high- with it further demand for high-voltage voltage testing, ABB has developed transmission systems. ­prototypes for the converter valve, valve hall design, converter transformer, by- After 2020, a further seven hydroelectric pass switch, radio interference capacitor, power projects, with a total rating of surge arrester, transformer bushing and 110 GW, are planned in Xizang. The power from these will be transmitted to the eastern and southern provinces of China is investigat- China. To enable the bulk transmission from these and from other projects, even ing using 1,100 kV further development of UHVDC systems will be required – either at 1,100 kV DC for power trans- or at existing voltage ratings with higher missions of 10 to current-carrying capabilities. Presently, there is no immediate market interest for 13 GW per line for the new UHVDC transmission systems outside of China. However, this may distances over change with the emergence of future hy- Raul Montano 2,000 km. droelectric and solar generation sources Bjorn Jacobson in Africa, India, the United States and Dong Wu South America that are far removed from Liliana Arevalo wall bushing. Also, conceptual designs the centers of consumption and that are ABB Power Systems for station layout and indoor DC yards needed to satisfy the world’s apparently Ludvika, Sweden have been completed. insatiable hunger for power. [email protected] [email protected] New UHVDC applications [email protected] The Chinese economy has exhibited an [email protected] average annual growth rate of around 12 percent over the last 30 years. Improve- ment in affluence and economic growth is References closely associated with increased energy [1] EIA, International Energy Statistics database, requirements. To cope with the increas- available March 2014, http://www.eia.gov/ forecasts/ieo/more_highlights.cfm ing electricity demands, and to keep the [2] D. Wu, et al., “Selection between indoor or costs reasonable, China has pioneered outdoor DC yards,” article submitted to CIGRE the implementation of new high-voltage 2014.

Corridors of power 21­ Strong winds, high yield

HVDC Light® technology goes farther out to sea

PETER SANDEBERG – Under pressure to decrease the environ- exploited these winds to produce clean energy. Given that the mental impact of generating electrical power, coupled with higher average offshore wind speeds can result in an energy continuously increasing demand, energy producers must yield of up to 70 percent higher than that generated on land, utilize more of the earth’s natural resources to harvest it is no wonder that the next 15 years will see an increase in additional power. While many parts of the world bask in the number of offshore plants. However, the farther out to glorious sunshine, northern Europe tends to experience sea, the greater the challenge of ensuring the transmission of winds that can wreak havoc. On the flip side, the construction a stable energy supply to the mainland. This challenge is of onshore and offshore wind power plants have successfully being met with ABB’s HVDC Light technology.

­22 ABB review special report 1 Alternative HVDC and HVDC/HVAC connection schemes

Offshore

DC

P DC P AC P AC

Onshore Onshore grid Onshore grid grid

Onshore

1a Direct connection solution 1b Back-to-back solution 1c Parallel solution combines HVAC and HVDC

he United Nation’s Intergovern- of the mainland grid, particularly consid- To begin with, given that each wind ­power mental Panel on Climate Change ering the intermittent nature of wind. The plant will typically be in range of a few (IPCC) has predicted that clean tendency toward long distances in com- hundred MW up to several GW, HVDC is T energy will have to at least tre- bination with often weak coastal connec- capable of transmitting power levels of ble in output in order to avoid catastrophic tions mean that tough technical chal- between 100 MW and 1,200 MW with climate change [1, 2]. Over the past few lenges need to be overcome: only one cable circuit. It is considered an decades, wind power generation has – The power level of the connected park economically viable solution especially in been making a vital contribution to the – The distance to the connection point situations where the distance to the con- global effort of lowering the environmen- – The type of transmission necting AC grid exceeds 70 to 120 km. tal impact of electrical power generation. – The AC network strength at the Championed as an increasingly important connection point Closer to shore, a wind power park could source of renewable energy, its contribu- – The fault ride-through capability in be connected with either AC or DC tion is set to increase over the next 15 case of AC grid faults transmission or a combination of these years with the construction of large off- – The start-up of the wind power park systems. It offers support to meet oner- shore wind parks in Northern Europe with – The environmental impact of the ous grid access requirements and helps a planned capacity of up to 40 GW of transmission system to improve power quality issues at the power. One of the main attractions of connection point. ­going offshore is the frequency of very Its technology pro- strong winds, which in turn can yield up vides superior con- to 70 percent more energy than onshore Average offshore wind speeds trol and quick wind parks. Even though it is costlier to power restoration construct offshore wind power parks, this can result in an energy yield during and after increase in yield combined with the fact of up to 70 percent higher disturbances and that many renewable energy technolo- contingencies in- gies have substantially advanced in terms than that generated on land. cluding blackouts. of performance and cost, could offset And it supports these costs in the long run. weak grids with In addressing each of these challenges, black-start capability, fine-tuning of AC As well as growing in terms of rated ABB has, using its HVDC Light transmis- voltage and reactive power and the abil- power, offshore wind power plants are sion technology, developed a detailed ity to energize wind power parks at zero being located farther from the coasts design for offshore HVDC (high-voltage or low wind conditions. Last but not least, and the grid entry points. The impact of direct current) systems that can safely this transmission system is ideal for stabi- large-scale offshore wind power pene- and reliably integrate large-scale wind- lizing irregular electricity flows by quickly tration may potentially affect the stability power production. compensating for power fluctuations.

Strong winds, high yield 23­ Offshore wind 2 Offshore wind projects connected by HVDC Light

Rated System DC cable Company / Year of power plants are Project power voltage length location completion growing in terms of (MW) (kV) (km)

TenneT DC: ±150 SM*: 2x125 rated power and BorWin1 400 2009 (Germany) AC: 155/400 UG*: 2x75 are being located TenneT DC: ±320 SM*: 2x75 DolWin1 800 2014 farther from the (Germany) AC: 155/400 UG*: 2x90

TenneT DC: ±320 SM*: 2x45 coasts and the DolWin2 900 2015 (Germany) AC: 155/380 UG*: 2x90 grid entry points. *SM = Submarine; UG = Underground

Capturing offshore wind with HVDC immune against transient disturbances solutions originating from the onshore grid. For A variety of different transmission schemes ­example, during onshore AC network are possible using HVDC technology alone faults the onshore converter station can and in combination with HVAC ➔ 1. bypass the surplus energy from the wind power plant into a braking resistor. Once The direct connection solution shown the network fault is cleared the resistor is in ➔ 1a and the back-to-back solution ­ disconnected and normal power flow is illustrated in ➔ 1b can use a frequency in re-established. This practice protects the the wind power park that is not synchro- wind turbines and other equipment from nized with the onshore grid. The wind stresses which, in the long term, helps power park is also isolated from electri- extend their life cycle. cal disturbances in the onshore grid, meaning that significant “fault ride- From an environmental point of view, through” capability is achieved. HVDC Light transmission systems pro- vide many benefits, including: The parallel case demonstrated in ➔ 1c – An underground, oil-free extruded shows how HVAC and HVDC can be cable system from the shore to the combined and is an example of a step- AC connection point wise expansion approach that enables – Twin cable installation, which in turn transmission capacity to be added in neutralizes magnetic fields stages. The advantages of such a scheme – An enclosed converter station to include higher energy availability, the ­ efficiently suppress noise poten­tial to include changes and incorpo- – A smaller station footprint rate new technology as the wind power park develops and, from a business point Offshore platforms with dual of view, incremental investments. functionality The trend nowadays is toward large off- At startup, an HVDC Light converter sta- shore power plants located remotely in tion provides fast and efficient voltage a harsh and unforgiving environment that control as the offshore grid is being ener- can accommodate both HVDC convert- gized. The voltage is ramped up smooth- ers, as well as operations and mainte- ly at a rated frequency (to prevent tran- nance personnel. The first two platforms sient overvoltages and inrush currents) built for offshore wind HVDC converter after which the wind turbine generators stations were based on a conventional are safely connected to the offshore grid. topside jacket solution. In close cooper- The onshore (receiving) converter station ation with a Norwegian yard, ABB devel­ is located either near the shore or farther oped a flexible, highly innovative, robust inland. Even though the grid is often and scalable platform for greater pro- weak along the coastline, HVDC Light duction efficiency and ease of instal­ technology is designed to enhance the lation (no heavy-lift vessels or jack-up system by providing voltage stability operations are required). This platform support. Moreover, this technology will is based on a combination of semisub- literally make the offshore grid, including mersible and gravity-based designs – the connected wind turbines, electrically ie, it acts as a semisubmersible platform

24 ABB review special report 3 Dörpen West onshore station for the DolWin1 wind farm 4 The DolWin2 offshore platform for the North Sea

3a Back view

3b Side view during transport and installation, after DolWin1 neutral electromagnetic fields. Compact which it is ballasted down to sit solidly Another example of this type of solution converter stations will help reduce car- on the seabed. is the 800 MW DolWin1 HVDC Light con- bon dioxide emissions by more than nection, which will bring power to the 3 million t per year by replacing fossil- HVDC in action grid connection point at Dörpen West in fuel-based generation. The increasing number of wind power Germany, about 90 km inland ➔ 3. ABB is parks combined with the growing distance responsible for system engineering, in- between offshore power generation and cluding design, supply and installation of onshore consumption are two of the main the offshore converter station, including driving factors for the adoption of HVDC the platform, 75 km of DC submarine Light. In fact, HVDC has been and will be cables, 90 km of underground cables and used in some major European projects, all the onshore converter station. Sched- of them in the North Sea ➔ 2. uled to be operational in 2014, this net- work of offshore wind power parks is

BorWin1 ­expected to reduce CO2 emissions by In 2007 ABB received an order from 3 million t per year. E.ON-Netz (now TenneT) to integrate one of the largest and most remote offshore DolWin2 wind power parks into the German grid by For the DolWin2 project, the wind power Peter Sandeberg means of a 400 MW HVDC Light ­system. parks will be connected to an HVDC ABB Power Systems, Grid Systems The project order, known as BorWin, is converter station installed on an offshore Västerås, Sweden the world’s first offshore wind HVDC platform in the North Sea ➔ 4. The gener- [email protected] connection. Full grid code compliance ated power will be transmitted through ensures a robust network connection of a 45 km long DC submarine cable and the wind power plant, which consists of a 90 km long underground cable to the References 80 wind generators rated at 5 MW each; HVDC onshore station at the grid con- [1] D. Carrington. (2014, April 12). IPCC report: offshore and onshore converter stations; nection point of Dörpen West. world must urgently switch to clean sources and 75 km of underground and 125 km of energy [Newspaper article]. of submarine cables. The wind energy The transmission system will have a total Available: http:// www.theguardian.com/ environment/2014/ apr/12/ipcc-report-world- feeds into a converter substation at ­Diele, capacity of 900 MW at ± 320 kV, which must-switch-clean-sources-energy near Papenburg, on the German main- will make it the world’s largest offshore [2] R. McKie and T. Helm. (2014, April 12). land where the power is injected into HVDC system. This HVDC Light connec- UN urges huge increase in green energy to the 400 kV grid. This project reduces tion provides numerous environmental avert climate disaster. [Newspaper article]. Available: http://www.theguardian.com/ CO2 emissions by nearly 1.5 million t per benefits, such as electrical losses of less environ-ment/2014/apr/12/un-urges-increase- year. than 1 percent per converter station and green-energy-avert-climate-disaster-uk

Strong winds, high yield 25­ From far away

Efficient and cost-effective long-distance power transmission with HVDC

ABHAY KUMAR, ALF PERSSON – As the VDC technology uses thyris- trolled cascade tripping of lines is avoid- energy needs of the world increase, the tors for conversion and typi- ed. For example, during the massive demand for long-distance energy cally has a power rating of sev- 2003 blackout that affected the entire transmission also rises. Areas needing H eral hundreds of megawatts, northeastern United States, the HVDC electrical energy are often located far though many are in the 1,000 to 3,000 MW connections shielded the Quebec sys- away from the source of energy, be it range, and some even as high as tem in Canada from frequency swings.1 water, solar or wind. ABB’s HVDC 8,000 MW. HVDC is suitable for over- Classic technology serves as a cost- head lines as well as undersea/under- HVDC lines use the right of way (m/MW) effective alternative to AC transmission ground cables, or a combination of cables very effectively and can also be operated for long-distance and bulk-power and lines. It can also be configured as at reduced voltage in case some section transmission as well as for intercon- back-to-back HVDC stations. This con- of a line has issues with insulation with- necting asynchronous AC networks. figuration enables two asynchronous stand capability. HVDC technology en- For connecting remote and large-scale grids to exchange power and ensures ables long underwater transmission links generation to load centers HVDC is that in the event of a disturbance in one, with low losses. Traditional AC transmis- an attractive solution with extremely the other supports it. sion systems with underwater cables low transmission system losses. cannot be longer than about 60 to 100 km ABB continues to create HVDC solu- The interconnection through HVDC does as it would require massive ­reactive tions to suit the many scenarios not add to the short-circuit capacity of compensation en-route. encountered in the transmission world. the networks. This allows for less-fre- quent replacement The configuration enables of the heavy-duty switchgear equip- two asynchronous grids ment, keeps grids to exchange power and immune from dis- turbances and mini- ­ensures that in the event of a mizes affected ar- eas. By controlling disturbance in one, the other its power flow, an HVDC system sta- supports it. bilizes the grid in the interconnected networks and in- Footnote creases the security of supply. As HVDC 1 http://energy.gov/sites/prod/files/oeprod/ systems cannot be overloaded, uncon- DocumentsandMedia/BlackoutFinal-Web.pdf

­26 ABB review special report 1 The NorNed station The interconnection, which is based on market coupling, has led to power trading between the two countries and increased the reliability of electric- 2 A selection of ABB’s HVDC commissions ity supply in both. – The Itaipu project in Brazil supplies 50 Hz – The Rihand-Delhi project in India transmits power into a 60 Hz system and economically bulk thermal power (1,500 MW) to Delhi, transmits large amounts of hydropower ensures minimum losses, least amount of (6,300 MW) over long distances (800 km). right-of-way, and better stability and control.

– The Leyte-Luzon project in the Philippines – The Garabi project in Argentina is an supplies bulk geothermal power across an independent transmission project transfer- island interconnection and improves stability ring power from Argentina to Brazil. The to the Manila AC network. back-to-back HVDC system ensures a supply of 50 Hz bulk power (1,100 MW) to a 60 Hz system under a 20-year power supply.

Sustainability showcase: NorNed Dutch grid to be optimized by using The 580 km NorNed HVDC monopolar hydropower­ to cover peak loads during transmission link with a 700 MW / the day. At night, power can be trans- ± 450 kV transmission capacity, is the ported back to Scandinavia, thereby longest underwater high-voltage cable saving electric energy in the dams. The in the world ➔ 1. Commissioned in 2008, result is a more stable output from the the converter stations are located at the fossil-fuel-fired plants, thus minimizing Feda substation in Norway and at the emissions. Additionally, the stabilized Eemshaven substation in the Nether- grid allows integration of new renewable lands – a span of 580 km. The intercon- generation in the form of wind power. nection is jointly owned by the two state power grid companies, TenneT in the The security of supply has improved Netherlands and Statnett in Norway. since production resources in a larger The interconnection, which is based on area are available as a backup in the market coupling, has led to power trading event of network disturbances. The elec- between the two countries and increased tricity market has benefitted as the link the reliability of electricity supply in has enabled electricity trading between both. two distant, isolated markets.

To optimize cable costs and cable loss- The link demonstrates that HVDC tech- es, NorNed has two fully insulated DC nology offers the unique capability to cables at ± 450 kV although it is a mono- build long underwater or underground polar link. This makes the DC current cable transmission lines with low losses. small and creates low cable losses, but The NorNed link has losses of only about requires a higher converter voltage and 4 percent. has a record voltage of 900 kV for a 12-pulse converter. North-East Agra ABB has built HVDC transmission projects Scandinavia has a largely hydro-based all around the world ➔ 2. A unique project production system whereas the Nether- is currently under construction in India. lands and surrounding countries have a When commissioned in 2016, the North- system based largely on fossil fuels. East Agra HVDC link, officially known as Hydropower­ is easily regulated and ± 800 kV / 6,000 MW HVDC Multi Termi- stored in existing dams. This allows the nal NER/ER-NR/WR Interconnector-I, will

From far away 27­ ABB’s HVDC trans- 3 The North-East Agra HVDC link will cover a distance of 1,728 km.

Agra mission system Alipurduar Biswanath was chosen in large Chariali part because of the advantage of the technology needing INDIA only a minimum right of way. be the first multiterminal HVDC project at the technology needing only a minimum 800 kV. The link comprises four terminals right of way. in three converter stations with a 33 per- cent continuous overload rating, enabling The system will have two ± 800 kV con- an 8,000 MW conversion. It will be the verter poles in Biswanath Chariali and largest HVDC transmission system ever two ± 800 kV converter poles in Alipur­ built, having the highest converter capac- duar, whereas Agra will have four ity at 8,000 MW and the first one having ± 800 kV converter poles. As each con- 800 kV indoor DC halls. verter pole has a nominal rating of 1,500 MW with a continuous overload Power Grid Corporation is constructing rating of 2,000 MW, it is possible to com- this HVDC link to transmit clean hydro- pensate for the loss of any conver- ter pole. If for in- stance Pole 1 in The solution also acts as a Agra is lost, Poles 2, 3 and 4 can still firewall, isolating disturbances supply the rated and preventing them from 6,000 MW to the Agra region ➔ 4. spreading from one network At full capacity, the to the other. North-East Agra HVDC link will be able to supply electric power from India’s northeast enough electricity to serve 90 million ­region to Agra, the city of the Taj Mahal, people based on average national con- over a distance of 1,728 km ➔ 3. sumption.

One converter station (Biswanath Chari- Multiterminal HVDC links are unique to ali) will be in the state of Assam, and a ABB. The North-East Agra HVDC link will second (Alipurduar) in the state of West be the second ABB-built multiterminal Bengal in eastern India. The other end of HVDC link. The first of this kind was built the DC line will terminate at Agra, where by ABB in North America in the early two bipolar converters will be connected 1990s. The Québec-New England HVDC in parallel. The 800 kV equipment yard at link is a large-scale three-terminal trans- Agra will be indoors. mission link (2,000 MW / 450 kV) com- missioned in 1992. ABB recently received Northeast India has abundant untapped a contract to refurbish the 20-year-old hydropower resources of the order of control and protection systems of the 50 to 60 GW scattered over a large area, link with the newest modular advanced but load centers are hundreds or even control systems (MACH). thousands of kilometers away. Transmis- sion lines must pass through a very nar- Railroad DC Tie row patch of land (22 km × 18 km) in the The Sharyland station, located at the state of West Bengal, which has borders border of Mexico and the southern tip with Nepal and Bangladesh. ABB’s of Texas in the United States, was the HVDC transmission system was chosen first 150 MW back-to-back DC tie sta- in large part because of the advantage­ of tion ➔ 5. It was commissioned in 2007.

28 ABB review special report 4 Multiterminal arrangement in North-East Agra HVDC link

-432 km -1,296 km

3,000 MW 3,000 MW +800 kV 3,000 MW 3,000 MW

400 kV 400 kV 400 kV

Pole 1 Pole 3 Pole 1 Pole 3

Pole 2 Pole 4 Pole 2 Pole 4

Bipole 1 Bipole 2 Bipole 1 Bipole 2 Biswanath Alipurduar Agra Chariali +800 kV

5 Sharyland station ABB is currently constructing a second 150 MW back-to-back HVDC converter station adjacent to the existing site. The two stations, part of the Railroad DC Tie Expansion project, will work in parallel to provide a transmission capacity of up to 300 MW. This will further increase the power transfer capacity between Texas and Mexico and secure the reliability of power in the Rio Grande Valley.

To learn more about ABB’s reference projects, please visit www.abb.com/hvdc

national grid, operated by the Comisión ABB designed Federal de Electricidad (CFE), and in- creases power reliability in the Rio a solution that Grande Valley. HVDC technology en- ables bidirectional power flow between ­includes unique both grids, thereby allowing each grid black-start emer- to rely on the other in times of emer- gency assistance. gencies or peak demand. ABB designed a solution that, in addition to the normal properties of an HVDC sta- The Mexican and the Texan AC net- tion, includes unique black-start emer- works are not synchronized so con- gency assistance. The solution also acts Abhay Kumar necting them as a normal AC intercon- as a firewall, isolating disturbances and Alf Persson nection was not possible. The Sharyland preventing them from spreading from ABB Power Systems, Grid Systems station enables power exchanges be- one network to the other. Ludvika, Sweden tween the Electric Reliability Council of [email protected] Texas (ERCOT) grid and the Mexican [email protected]

From far away 29­ Steps beyond

® PETER LUNDBERG, MIKE BAHRMAN – Using advanced convert- ABB’s HVDC Light er technology developed by ABB, the world’s first HVDC provides a range of transmission with voltage source converters began transmit- ting power in 1997. This technology was introduced as HVDC expanded benefits for Light. The new transmission link ran along a 10 km route between the Swedish towns of Hellsjön and Grängesberg. its customers It was rated at 3 MW / ± 10 kV DC. Due to its unique charac- teristics, HVDC Light has expanded the range of system applications beyond that possible with HVDC Classic. New uses include remote offshore applications, weak system interconnections, long land cables and black start. A look at a few of the significant HVDC Light projects tells the story of how ABB has linked the development of this technology to meeting customer needs.

­30 ABB review special report 1 Shoreham HVDC Light converter

evelopment of the new HVDC The result was the development of de- AC/DC VSC stations connected by a pair Light technology has continued vices with voltage and current ratings of 40 km DC submarine cables ➔ 1 - 2. at a rapid rate, with voltage lev- suitable for transmission. This semicon- Dels and power ratings steadily ductor development formed the basis for Transmission capacity over the CSC increasing as power losses decrease. HVDC Light. project was offered to market partici- Since the first transmission ABB has un- pants through an open season process dertaken 20 HVDC Light projects globally. Within five years of its inaugural project, and a firm capacity purchase agreement. HVDC Light is currently available for rat- ABB commissioned two HVDC Light com- A key feature of the HVDC Light technol- ings of 2,000 MW / ± 500 kV in bipolar mercial projects – Gotland Light in Sweden ogy in the CSC project is the ability to configuration and 1,200 MW / ± 320 kV in 1999 and Directlink in Australia in 2002 precisely control power transfers with in symmetrical monopolar configuration. – where the technology was proven at a scheduled transactions by those who Voltage source converter (VSC) techno­ voltage level of ± 80 kV and a power rat- have purchased rights to its capacity. logy provides superior dynamic features ing of 55 MW per that go beyond pure power transmission. circuit. The next They have no reactive power demand or step was the intro- Both interconnected networks associated need for reactive power com- duction of systems pensation. They appear to the network as at the ± 150 kV lev- benefit from active and a virtual synchronous machine but with- el. A power rating out inertia. Therefore the converters can of 330 MW was ­reactive power control and help control the AC voltage. reached in 2002 AC voltage control. with the Cross- A brief history Sound Cable (CSC) In the development of power electronic project connection in New Haven and Additional benefits for the HVDC Light technology for industrial drive systems Long Island in the United States, and the technology in the project were reactive thyristors were replaced with VSCs 200 MW Murraylink project in Australia. power and AC voltage control at each where the semiconductors could be converter to support the connected AC switched off as well as on. The advan- Cross-border trading networks and a compact layout with the tages this change brought to controlling With the CSC project, ABB showcased majority of all equipment inside the con- industrial drive systems could also be the ability for cross-border trading as verter building. Modular design allowed applied to transmission technology. well as excellent dynamic voltage sup- for comprehensive factory testing, which port with HVDC Light. CSC was the first led to short field testing and commis- merchant transmission project in the sioning. Title picture ABB continues to develop HVDC Light transmission United States consisting of a bidirection- throughout the world. al 330 MW transmission system with two

Steps beyond 31­ 2 The Cross-Sound Cable project links southern New England with 3 Estlink 1 HVDC Light cable laying Long Island, New York.

Canada

New Haven

Shoreham New York United States

The cross-border trading feature in this ­national grids of Estonia and Finland. tinue to operate in supplying its own aux- instance works well because the opera- Commissioned in December 2006, this iliary power, supplied through the DC tor can continuously control the power was the first time electric power was from the Finnish station. The converter transfer in either direction between 0 and ­exchanged between the Baltic states can also be started manually in black- 330 MW independent of the AC voltage and the Nordel electric systems. With the start mode, if needed. control. CSC manages the steady-state goals of creating electricity trading and AC voltage regulation at the connecting increasing secure supply in the Baltic The network restoration sequence starts stations to improve the dynamic stability. ­region, HVDC Light was an obvious with the converter station running with- During the first year of operation a testi- choice due to the asynchronous net- out load. The voltage and frequency are mony to the quality of the feature was works and the long distance under water decided by the converter, which in this seen when a severe thunderstorm on between the two systems ➔ 3. case operates in voltage and frequency Long Island created multiple AC faults, control. The AC network is then connect- yet voltage up to its reactive power limit Both interconnected networks benefit ed with a small load, and ramped up to of 125 MVAr was supported and active from active and reactive power control the rating of the link. The black-start fea- power kept relatively constant. and AC voltage control. Additional con- ture makes it possible to start up parts trol features are emergency power con- of the Estonian network in only minutes Following the massive blackout of the trol, frequency control and rapid active after a total blackout. In the network res- northeastern portion of North America on power flow to support either of the con- toration scenarios determined by the grid August 14, 2003, CSC was instrumental nected grids. On the Finnish side a operator, Estlink 1 would provide aux­iliary in restoring electric power to customers damping control is designed to damp the power to selected power units. Estlink 1 on Long Island, being one of the first inter-area oscillations that can occur in and the connected generators will share transmission links to the area brought into the Nordel electric system to increase the load through the use of frequency service after the blackout. The link trans- operational security. droop. When a sufficient amount of gen- ported 330 MW to the area, enough power eration is feeding the network, the mode to restore electric service to over 330,000 HVDC Light converters are able to gen- of operation of the converter can be homes. Furthermore, CSC’s AC voltage erate a voltage that can be changed very changed from frequency/voltage control control feature proved valuable by stabi- quickly in amplitude and phase and offer to normal power/voltage control. lizing the AC system voltage in Connecti- the possibility of energizing a network cut and on Long Island during the net- ­after a blackout. This has been imple- Caprivi Link work restoration. mented in Estlink 1 for the Estonian side. Many of the electricity networks in the ­developing part of the world, such as Estlink 1 The transformer is equipped with a spe- ­Africa, span vast distances and are often Supply security and black-start capabili- cial auxiliary power winding for self-sup- characterized by relatively weak AC net- ty are additional benefits ABB has pro- ply of the converter station, and the con- works. ABB’s Caprivi Link project 1 was vided with HVDC Light. The Estlink 1 trans- trol system has schemes for detecting able to meet these challenges in order to mission system, operating at 350 MW / a network blackout. If such a blackout connect the Zambezi converter station in ±150 kV DC, has been able to provide occurs, the converter will automatically the Caprivi strip in Namibia, close to the these features while connecting the trip the connection to the grid, and con- border of Zambia, and the Gerus converter

­32 ABB review special report 4 Gerus HVDC Light station Additional custom- er benefits are the system’s black- start capability and active AC voltage support.

station, about 300 km north of Windhoek and the DC line by opening the AC and As part of the solution, ABB extended in ­Namibia ➔ 4. The Caprivi transmission DC circuit breakers to interrupt the fault the previous rating record for an HVDC link is a 2 × 300 MW interconnection with currents. Immediately after clearing the Light cable from 150 kV to 200 kV. The the converter stations joined by a 950 km fault currents, the breakers are re-closed higher voltage enables a higher trans- long, bipolar ± 350 kV DC overhead line. and the transmission resumed. Reactive mission capacity of 500 MW. This was the first HVDC Light project to power support is resumed within 500 ms combine VSCs with overhead lines. and power transmission within 1,500 ms.

The weak networks have a high likeli- Intergration of onshore renewable hood of becoming islanded with passive generation AC networks when critical lines are HVDC Light transmission technology is tripped. The converter controllability with of particular interest for power transfer AC voltage and frequency control pre- between asynchronous AC grids in order vents tripping of about 100 MW of gen- to increase the security of supply be- eration at Victoria Falls island close to tween grids with wind farm generation. the Zambezi converter. A similar condi- The EirGrid East-West Interconnector tion can occur on the Namibian side project (EWIP), is a benchmark example. when the AC link to South Africa is lost Commissioned in 2012, EWIP links the and the Gerus converter station islands high-voltage power grids of Ireland and together with the Ruacana hydropower Great Britain by means of an HVDC Light station. Similarly both sides can experi- interconnection. The project is ABB’s ence passive network conditions where most recent, and largest HVDC Light no generation is present. Without the project undertaken. HVDC Light link the outage of critical lines can lead to a blackout due to the Ireland is expanding its wind power gen- extremely weak AC network. eration and the 500 MW / ± 200 kV EWIC Peter Lundberg HVDC Light transmission system pro- ABB Power Systems, Grid Systems The HVDC Light solution has enhanced vides an opportunity to export excess Ludvika, Sweden stability and assisted with the prevention power into the UK market. [email protected] of blackouts. The Caprivi Link converter stations can provide up to ± 200 Mvar Additional customer benefits, due to the Mike Bahrman ­reactive power capability throughout choice of the HVDC Light technology, are ABB Power Systems, Grid Systems nearly the entire power transfer range the system’s black-start capability and Raleigh, NC, United States from 0 to 300 MW. The solution is pre- active AC voltage support. In addition, [email protected] pared for providing n-1 network security by connecting to the UK national grid, when the full bipole is implemented. Dur- Ireland can now access power from con- Footnote ing a DC line fault, the converter stations tinental Europe (via an interconnector 1 See also figure 3 on page 35 of this issue of are temporarily isolated from the AC grid from Great Britain to the continent). ABB Review.

Steps beyond 33­ AC/DC

Backing up AC grids with DC technology

STEFAN THORBURN, TOMAS JONSSON – VDC transmission is starting rate AC systems ➔ 1 – 2. In the embed- As the demand for energy grows, so to evolve into a grid of its own ded HVDC grid, the AC frequency is too does the demand for reliable where very fast HVDC break- the same in all HVDC stations. A power supplies of energy. When power grids H ers help maintain high avail- imbalance in the AC grid cannot be were established, AC transmission ability of the meshed HVDC grid. The ­alleviated by HVDC control since both was the preferred choice, overcoming existing AC system is utilized to trans- ends of the HVDC link are in the same DC’s inability to be quickly interrupted form power between different voltage grid. With DC and AC grids in parallel, and transformed. Now, more intelli- levels and to use the less costly AC the AC frequency is the same in the gent, better-controlled networks are breaker for local fault clearance, mini- HVDC stations, but the HVDC system is needed. How can these be created? mizing the impact of an electrical fault. in a strong position to mitigate an exist- The key lies in combining existing AC ing bottleneck on the AC side. With and DC technologies, making use of Reinforcing the AC grid separated AC grids, the AC frequency the best of both. HVDC (high-voltage The existing point-to-point HVDC links differs between the HVDC stations; a direct current) transmission will be already show many examples of support power imbalance in one of the AC grids embedded inside the AC grid and will functions, which can, even today, be- can be alleviated by applying proper reinforce the operation of the whole come part of a wider HVDC grid [1]. HVDC control. The size of the HVDC grid with its controllability, speed and These support functions address four support can easily be limited to the low losses. At designated locations main constraints in the AC system: present capacity (spinning reserve) of the HVDC system will operate as a – There must be a power balance the other AC grid. “firewall,” supporting the AC system between production and consump- during disturbances. tion (including losses). HVDC as a firewall in the AC grid – Thermal overloading of the circuits An HVDC system can be placed be- must be avoided. tween AC grids as a firewall to prevent – The synchronous generators must be disturbances spreading from one AC in synchronism. If they are not, there grid to another. The HVDC system can may be difficulty maintaining the be set up such that loop flows are integrity of the AC system after an avoided and market power exchange electrical fault or avoiding oscillations can be fulfilled. Should a power imbal- between the generators. ance occur on the AC side, HVDC con- – Availability of local reactive power trol can mitigate the imbalance and control must be ensured. Losing this ­borrow spinning reserve from the control may result in a voltage neighboring AC systems in a controlled instability, which could spread and manner. endanger the whole power network. Frequency stability There are also different ways in which An imbalance between the produced AC and DC systems can be connected. and consumed power will show up as a The HVDC system can be embedded in frequency deviation. Many HVDC sys- the AC system or it can connect sepa- tems can mitigate the frequency devia-

­34 ABB review special report 1 Connecting AC and DC systems 2 Level of support possible from an embedded HVDC system during disturbances

Embedded Separated HVDC grid AC grids

VSC Classic VSC Classic

Operate as a firewall + 0 +++ ++ during contingencies

Maintain frequency N/A N/A +++ +++ stability

Separated Artificial inertia N/A N/A +++ + Embedded

Maintain ++ + + + synchronism

Improve voltage +++ + ++ + stability

Improve power ++ + ++ + oscillation damping Parallel Merchant links ++ ++ +++ +++

Black start + 0 +++ 0

technology will start to back up the 3 Case study: Caprivi Link AC system. When the fault is cleared, the reactive power output from the For islanded network situations, the converter HVDC system will support the power Zambezi station has a characteristic comparable to an infinite AC source, ie, a slack bus. The link transfer in the AC grid. This will reduce Gerus automatically­ converts the active power needed the risk of falling out of step and losing to maintain the power balance of the system. It synchronization. Special schemes can also automatically converts the reactive power Namibia needed to keep the AC voltage at the desired be set up in the HVDC system to help level. Under normal AC network conditions, the quickly restore a viable power flow after converter resembles an electrical machine to a fault. generate or consume active and reactive power. The Caprivi Link interconnects the Namibian and Zambian/Zimbabwean AC systems ➔ 4. Performance under islanded AC network It is also possible to control the HVDC The overhead HVDC line has a length of 952 km. in Namibia system in such a way that inadvertent The first stage of the project was a monopole On June 3, 2010, a high-power transmission power flow changes in the AC grid are scheme with a nominal power of 300 MW and was planned from Namibia to Zambia. Dur- automatically compensated for so that a nominal DC voltage of -350 kV DC. ing the process of ramping up power, when the power exported from Namibia was about safe power transfer can be maintained At the initial stage, the AC networks at both 80 MW, an overload protection tripped a 220 kV in the AC system. The active power sides are extremely weak and the short-circuit line in Nampower’s 220 kV bus zone, which led control can, alternatively, be set up such ratio (SCR) at the connection points may be to an islanded condition in Namibia. that it resembles the phase-angle de- below 0.8. Normally, the AC networks at both sides of the HVDC link are connected to the This unplanned event was observed and pendency of an AC line (possibly with AC grid of South Africa, resembling a parallel automatically recorded in both converter sta- reactive power support at each end). AC structure as in ➔ 1. However, if an AC line is tions ➔ 5. The Gerus substation (shown on lost it can lead to an islanded network situation page 33 of this issue of ABB Review) immedi- Power oscillation damping in either end of the HVDC link. ately reduced the power to almost zero (see the lower plot in ➔ 5a). About 1s after the line A stressed AC system is prone to elec- tripped, the Namibian grid restored stable AC tromechanical oscillations of the rotors voltage and frequency [2]. in the synchronous machines. This is an unwanted situation since it wears down the governor systems of the turbines tion if one of the converters is connect- link in such an AC system can be con- and indicates an operating working ed to a separate AC grid. Assuming trolled to provide additional inertia in point close to the stability limit related to that the separate AC grid has spinning ­order to strengthen the local stability. maximum power transfer. By modulat- ­reserve available, the stressed grid can Such functionality has been implement- ing a control signal to the HVDC sys- be automatically supported to restore ed in the Caprivi Link project in southern tem, oscillations can be damped and a frequency stability. Africa ➔ 3. safe power transfer limit can be main- tained in the AC system. This damping Artificial inertia Maintaining synchronization functionality has been implemented in In very weak AC systems, frequency To maintain synchronization, the HVDC several links, including the Pacific DC variations may be a problem due to the system will support the AC system in Intertie and the Fenno-Skan link. low ratio of rotating mass (inertia) relat- several ways. For example, during a ed to synchronous machines. An HVDC fault, the VSC (voltage source converter)

AC/DC 35­ requires precise, controllable power 4 Network map of the Caprivi Link project flows in order to operate effectively in

3x80MW 100MW Otjikoto line with the market-derived schedules. Ruacara Kafue Power scheduling on an hour or minute Town Mazuma basis is a common situation. The con- Zambia Omburu SVC Namibia Walmund Omburu Sasheke trollability of active power flow in the Gerus Zambezi To South Rössing AC AC Africa HVDC system compensates for the Osona DC DC Khan 3x27MW Caprivi link Victoria Livingstone power flow in the AC system that would Van Falls P/S Eck follow the physical laws rather than the

Botswana Victoria S/S prearranged commercial deals. Hwange P/S

Auas Zimbabwe AC/DC: the grid of the future Kuiseb Hardap The HVDC system will alleviate power 400 KV

Auas SVC 330 KV imbalances in the AC system and give

Walvis Bay Kokerhoom 220 KV operators full control over the power 65 KV Obib Future line flow. With the introduction of VSC tech-

Karis nology, HVDC is also able to operate as Harib a FACTS1 device. The HVDC system Oranjemund Aries South Africa Aggeneis can consist of a back-to-back convert- er, a point-to-point connection, a multi- terminal connection, or a meshed HVDC grid with parallel paths enhancing the 5 AC voltage, frequency and converter P/Q loadings for Zambezi and Gerus availability of the HVDC system.

450 400 For more information, please visit 400 350 www.abb.com/hvdc

350 300

300 250 UPCC_RMS (kV) UPCC_RMS (kV)

250 200 0 1 2 3 4 0 1 2 3 4 5 5

0 0

-5 -5

F_DEV (Hz) -10 F_DEV (Hz) -10

-15 -15 0 1 2 3 4 0 1 2 3 4 100 100 Stefan Thorburn 50 50 ABB Corporate Research 0 0 Västerås, Sweden P (MW) P (MW) Q (Mvar) Q (Mvar) [email protected] Q Q -50 -50 P P

-100 -100 Tomas Jonsson 0 1 2 3 4 0 1 2 3 4 ABB Power Systems, Grid Systems Time (s) Time (s) Västerås, Sweden 5a Gerus 5b Zambezi [email protected]

Black start its smooth control of both active and References In some AC grids, black-start function- ­reactive power. As the AC grid is rather [1] S. G. Johansson, et al., “Power System Stability Benefits with Vsc Dc-Transmission Systems,” ality is very valuable. The restoration weak and often has reduced short-cir- CIGRE, Paris, 2004. process (black start) of an AC system cuit power during a black start, high [2] Y. Jiang-Häfner, M. Manchen, “Stability following a contingency related to loss requirements­ are put on reactive power Enhancement and Blackout Prevention by VSC of crucial AC lines, islanding or blackout control to maintain voltages. ABB has Based HVDC,” CIGRE, Bologna, 2011. has some critical requirements, which, implemented and tested this for the in certain cases, can be fulfilled with an ­Estlink 1 project. HVDC link. VSC transmission techno­ Footnote 1 FACTS, or flexible alternating current transmis- logy is particularly suitable. The VSC Merchant links sion systems, are technologies that enhance the link can follow the cold load pickup and The coupling of electricity markets and security, capacity and flexibility of power the pickup of the power production with growing commercial interconnections transmission networks.

­36 ABB review special report Offshore power

® With HVDC Light MATS HYTTINEN – Traditionally, offshore platforms generate their own electricity by burning fossil fuels to run onboard gas turbines and/or ABB offers the off- diesel-powered generating units. This inefficient method has come shore industry an under increasing scrutiny and criticism because it creates substan- tial greenhouse gas emissions, particularly CO2; consumes large alternative way to amounts of fuel; and adversely impacts the health and safety of

platform workers. Some regions also put a high tax on CO2 emis- provide electrical sions, adding to the steep operating costs of platform generating power to platforms systems. ABB’s HVDC Light is a proven technology providing more efficient power from shore for customers who need reliable power in remote places. As the offshore industry searches for alternative ways to provide platforms with electrical energy, ABB is ready with a solution.

Offshore power 37­ 1 The Troll A was the first HVDC Light transmission system installed in an offshore platform.

40 years, which is higher than a local workers. The reduced risk of a fire or ex- ­generation solution. Efficiency rates vary plosion, as well as decreased noise levels ­depending on the transmission distance and vibrations, are also important work- and cable type. With an HVDC Light place improvements. transmission system there is often more than a 90 percent efficiency rate, com- Technical background pared with the typical range of 15 to Initially power-from-shore solutions were 25 percent for a local generation unit. limited to AC cable systems over short distances (50 to 100 km), or conventional Coupled with the requirement of high line-commutated HVDC systems. The in- availability is the cost-effectiveness of the troduction of HVDC Light with voltage transmission system. Each potential user source converter (VSC) technology in the BB’s HVCD Light is a robust of HVDC Light for offshore power is late 1990s opened up the market seg- transmission system with a unique in terms of power rating, distance ment, because VSC technology enables a long life cycle that reduces op- from the platform to the mainland, sea cost-effective supply of large amounts of A erating and maintenance costs. depth, etc. Initially the cost to install gen- power over long distances using robust, Such a power-from-shore system helps eration on the platform can be lower than lightweight, oil-free cables. Beyond 50 to make the platform a safer, cleaner place the cost to install a power-from-shore 100 km, HVDC Light is the only techni- to live and work by lowering greenhouse system, especially when power ratings cally feasible solution. gas (GHG) emissions, risk of fire and are low, the sea route is deep and the dis- ­explosions on the platform, and noise and tance from the mainland is long. However, HVDC Light does not need any short-cir- vibrations, while maintaining the highest by using an electricity supply from the cuit power to operate, which makes it an standards of reliability and availability. mainland weight and volume on the plat- ideal technology to start up and energize form are greatly reduced, enabling signifi- offshore platforms and allows for fully Ensuring high availability and lower cant savings in the long term. A small and inde­pendent control of both active and costs compact HVDC Light solution may also reactive power. The technology ensures The offshore industry’s main requirement enable a complete onshore assembly, smooth energization and startup, and of any power supply solution is high avail- with shorter installation and commission- precise control of the platform’s power ability, since an emergency shutdown ing time, thus further reducing costs. system. means loss of production capacity and income. In terms of operating costs power-from- During a black start, active and reactive shore alternatives require less mainte- power is automatically adjusted accord- An HVDC Light installation typically has nance and shorter maintenance shut- ing to the ongoing power need of the 99 percent availability per year, taking into downs. Power-from-shore solutions pro- ­platform. The HVDC Light link will balance account both scheduled and forced out- duce no emissions, so an emissions tax the load generation automatically as new ages. The lifetime is on average 30 to is not paid. loads are connected, instantly changing the transmitted power according to the From a health and safety perspective, size of the load. power-from-shore eliminates all hazards

Title picture associated with gas-fired rotating equip- Valhall HVDC Light field platforms ment operating in the vicinity of platform

­38 ABB review special report 2 Troll A and Valhall transmission links Each potential user of HVDC Light

Sweden for offshore power Norway is unique in terms Troll A Kollsnes of power rating, distance from the Lista platform to the Valhall mainland, sea depth, etc.

The optimum balance between the size The system eliminates GHG emissions other 40 years of service. Improvements of the platform module, equipment cost, from the Troll A platform. ABB’s HVDC include a new production and hotel plat- engineering work and risks must be eval- Light solution was selected because of its form that require more electric power than uated in each specific installation. Specif- positive environmental effects, the long is currently available. ABB is responsible ic arrangements and optimizations of the cable distance under water and the com- for the system engineering and the design,­ main circuit equipment may be necessary pactness of the converter achieved on and is supplying the HVDC Light system. to achieve desired compactness. the platform. According to BP the benefits gained from In addition, the system design must ensure The electrical drive system that Statoil using ABB’s HVDC Light power-from- that maintenance activities have an abso- and ABB developed has met all perfor- shore technology, as opposed to conven- lute minimum effect on system operation. mance expectations. The ABB motor- tional gas-turbine generators, are consid- With HVDC Light, maintenance time – formers – a very-high-voltage motor and erable. Operating and maintenance costs ­especially work that requires interrupting generator – installed on a platform com- have been significantly lowered. Each the power transmission – can be minimized pressor skid have performed well and year 300,000 t of CO2 and 250 t of NOX by exchanging whole modules or compo- ­operate at lower than expected vibration emissions have been eliminated. Working nents, instead of repairing them, and by levels. conditions have improved and no emis- introducing redundant systems whenever sions tax is applied. Maintenance is mini- technically or economically justified. In 2011, ABB was awarded a second mal, simple, remote and safe, which power-from-shore contract from Statoil ­reduces the need for the constant pres- Troll A for the Troll A platform, this time to pro- ence of offshore crews. The Troll A precompression project deliv- vide 100 MW to power two additional ered to Statoil in the North Sea and com- compressor drive systems. This HVDC missioned by ABB in 2005 was the first Light transmission system is scheduled to HVDC Light transmission system ever go into operation in 2015. ­installed in an offshore platform ➔ 1. It is located in the Troll oil and gas field about Valhall 65 km west of Kollsnes, near Bergen, The Valhall HVDC Light power-from-shore Norway ➔ 2. This field contains almost transmission system was commissioned 40 percent of total gas reserves on the in October 2011 to replace gas turbines Norwegian continental shelf, and is the on British Petroleum’s (BP) linked multi- cornerstone of Norway’s offshore gas platform complex in the North Sea, about production. 294 km from the Norwegian mainland ➔ 2. The Valhall HVDC Light system is capable The groundbreaking solution delivers two of delivering 78 MW to run the offshore independent systems, each producing oil-and-gas field facilities, though most 42 MW of power from the Norwegian customers need only roughly half the mainland to power a high-voltage vari- power. able-speed synchronous machine instal­ Mats Hyttinen led on the platform to drive compressors The project is part of a redevelopment ABB Power Systems, Grid Systems that maintain gas delivery pressure, com- scheme to increase production at the Ludvika, Sweden pensating for falling reservoir pressure. 30-year-old complex and equip it for an- [email protected]

Offshore power 39­ First-class service

ANNA JANSSON, HANS BJÖRKLUND – High-voltage direct current (HVDC) Service and upgrades transmission links are being used all over the world to efficiently and lengthen HVDC cost-effectively transmit large amounts of power from generators to distant centers of consumption. But such links represent significant equipment lifetime and investments for the utilities who own them. Also, HVDC assets typically have an expected lifetime that runs into decades. These two aspects of maximize performance HVDC mean that properly servicing and upgrading these assets is of major importance. ABB has extensive experience with HVDC service – covering regular maintenance and support as well as major service and upgrades. Control system upgrades, which can be done with a relatively short system outage, are, in particular, an efficient way to prolong the high performance of an HVDC link. Service, maintenance and upgrades have been applied by ABB in many cases to maximize output, increase functionality and extend the lifetime of HVDC assets.

­40 ABB review special report 1 ABB has many years of experience in HVDC and has maintenance and service agreements with many HVDC systems operators.

− 24/7 standby Midlife upgrades of HVDC − Spare parts and other additional installations services When built, most HVDC installations had − Control system maintenance a long operational life - typically 30 years – as a design target. When the end of hen an HVDC transmission Assessments maximize system this design life nears, it often turns out asset has a lifetime of lifetime and reduce downtime that the installations are still running very many decades, then very In order to put a coherent service and efficiently and delivering substantial eco- W often newer, better tech- upgrade plan in place for HVDC equip- nomic benefit to their owners. Often, nology has come along by the time the ment, it is usually necessary to perform a many important parts – usually repre- asset has reached the middle of its ex- lifetime assessment of certain systems senting the bulk of the investment – are pected lifetime. Carrying out an upgrade or items of equipment. Such an assess- still in good working order and can at this point can add many years to the ment is available for all HVDC-specific be used for many more years to come. asset’s lifetime as well as further increase equipment provided by ABB – eg, con- Examples of these are overhead lines, its availability and reliability. ABB has a verter transformers, thyristor valves, cables, buildings, switchyards and trans- long experience with HVDC and is trusted IGBT valves and control equipment. Sim- formers. When elements of these assets, by many operators of HVDC systems with such as breakers, maintenance and service agreements ➔ 1. parts of a cable or One recent example of a long-term ser- ABB has a long experience single-phase trans- vice undertaking that typifies this sort of formers, fail, they arrangement is found in the Estlink 1 with HVDC and is trusted can often be re- HVDC Light project, where ABB has been by many operators of HVDC placed on compo- First-class service providing services since the commission- nent basis. How- ing of the link in 2006. systems with maintenance ever, there are some parts of an These consist of: and service agreements. HVDC installation − HVDC converter station operation that need to be support, eg, weekly inspection of viewed as an inte- unmanned stations ilar assessments can also be carried out grated system and for these it is advan- − Regular preventive and corrective on conventional AC equipment included tageous to look at a more coordinated maintenance in the HVDC scheme – eg, breakers, dis- upgrade activity. − Annual planned maintenance connectors, filter reactors and ca- bles ➔ 2. These assessments provide the Upgrades of control and protection systems owner with a firm foundation upon which The lifetime of an HVDC control and pro- Title picture planning for future upgrades, service and tection system can be expected to be at HVDC equipment, like this converter station in operation can be based. least 30 years. The actual life is often lon- Finnböle, Sweden, represents a significant ger, perhaps 40 years, but for installations investment. Servicing and upgrading can ensure that the operator gets the most out of the that will operate for 50 to 60 years it is equipment as well as extend its life. wise to plan for one replacement of the

First-class service 41­ 2 Breakers at Porto Velho HVDC station 3 Control and protection upgrades

Year Station commis- sioned New Zealand pole 1 and 2 1992

CU 2004

Square Butte 2004

Sylmar converter station, Pacific DC Intertie 2004

Skagerrak 1 and 2 2007

Apollo converter station, Cahora Bassa HVDC link 2008

Blackwater 2009

Chateauguay 2009

IPP 2010

Highgate 2012

FennoSkan 1 2013

The following stations are currently being prepared for control upgrades:

Eel River 2014

Skagerrak 3 2014

Inga Kolwezi 2014

Celilo converter station, Pacific DC Intertie 2015

Quebec New England multiterminal HVDC 2016-17

control equipment during the lifetime of upgrade and ABB has therefore focused the plant – perhaps after about 20 to both the design of new control and pro- 35 years. In this way, an optimal return on tection systems and the organization of investment for the new controls can be the upgrade work on keeping outage achieved. If the plan is to retire the com- times to a minimum. plete plant after 40 years, the control equipment can most likely be used during One example of this type of work is the the entire operational lifetime of the plant recent successful upgrade and testing if the spare part supply is monitored on Great River Energy’s CU HVDC proj- closely during the last years of operation. ect – a 1,000 MW / ± 400 kV DC bulk power transmis- sion corridor be- tween Underwood, Some parts of an HVDC North Dakota and ­installation need to be viewed Dickinson, Minne- sota, that was built as an integrated system and and commissioned by ABB in 1978. for these it is advantageous to Here, the controls look at a more coordinated­ were changed with just a two-week upgrade activity. outage of one pole at a time while the other pole of the These assumptions are supported by bipole was running. Thus, the complete data from the large number of plants bipole could be upgraded in one month, around the world that have long service during which time the HVDC link could histories and by the different reasons for still carry 50 percent of its rated power. upgrading their control and protection systems. In the Intermountain Power Project (IPP) in the United States, commissioned in A complete control equipment upgrade 1986 to bring power from a 1,600 MW essentially means replacing the brain coal-fired generating plant in Utah to of the converter; this will inevitably result Southern California, a similar approach in power transmission being interrupted was used but here a three-week outage at least for one pole at a time. The cost per pole was needed because not just of this period of unavailability may be the control system, but also the valve as much as, or higher than, the actual cooling and the transformer cooling sys-

­42 ABB review special report 4 MACH control system In due course, upgrades of IGBT valves will be avail- able in ways similar to that of thyristor valves.

tems were upgraded to handle higher Kolwezi converter stations. ­Future valve powers. upgrades are being prepared for the Eel River and Celilo HVDC converter In Skagerrak 1 and 2 – HVDC links ­stations. ­between Norway and Denmark – a differ- ent approach was used because mainte- So far, IGBT valves (the successor nance work on the overhead line was to thyristor valves) have only been in needed and this required a bipolar out- ­operation for 15 years. In due course, age. A three-week bipolar outage was upgrades of IGBT valves will be available planned, but the installation activities went in ways similar to that of thyristor valves. very smoothly and power transfer was restarted after an outage of just 15 days. The further development and improve- ment of ABB’s HVDC service product There are many such examples of portfolio is very important and is an ­completed control and protection up- ongoing exercise. For example, ABB is grades ➔ 3. ABB’s long experience in placing great emphasis on Web-based HVDC and the very advantageous struc- systems that speed up support and ser- ture of the MACH control system ➔ 4 vice information exchange between cus- stands ABB in good stead when such tomers and ABB. Further, an annual upgrades are executed. ­users’ conference (celebrating its 21st anniversary this year) ensures that cus- Thyristor and IGBT valve upgrades tomer feedback is clearly understood Remarkably, most of the HVDC thyristor and mutual proposals for service im- converters ever supplied by ABB/ASEA provements can be heard. These and are still in operation. From the technical many more measures that enhance up- data available, it can be concluded that grades and service ensure a commit- the lifetime of a thyristor valve is very ment to quality throughout the entire life long, probably around 50 to 60 years. cycle of a product.

Because thyristor technology has ad- vanced so dramatically in the last 40 years, replacing an old thyristor valve with a new one may be a good business Anna Jansson proposition for the customer, resulting in Hans Björklund life extension, lower losses and decreased ABB Power Systems, Grid Systems maintenance. ABB has a leading position Ludvika, Sweden in this area and has conducted valve [email protected] ­upgrades in the Sylmar, Apollo, Inga and [email protected]

First-class service 43­ A single-source supplier

ABB enjoys a unique position in HVDC systems technol- power semiconductors, cooling equipment, transformers, ogy, being the sole company able to supply all key compo- bushings and other DC and AC power products, and in nents. An HVDC substation includes converter valves with many cases, cable connections.

Heart of the converter High-voltage power semiconductor devices

MUNAF RAHIMO, SVEN KLAKA – Silicon- wide range of possibilities in terms of dependent on technologies devel- based high-voltage semiconductor controlling the way electrical energy is oped for lower power applications, devices play a major role in megawatt transported and used. At the heart of which were then scaled to handle power electronics conversion. In this revolution lies the power semicon- higher voltages and currents. In particular, advances in ultrahigh-volt- ductor device: This device performs HVDC applications today, the two age semiconductors have over the the actual task of modulating the main types of switching devices are past few decades led to tremendous energy flow to suit the demands of the the phase-controlled thyristor (PCT) improvements in high-voltage direct application. The main trend in the and the insulated-gate bipolar current (HVDC) transmission. The development of power devices has transistor (IGBT). Also important is power device is considered a main always been increasing the power the power diode found in a range of enabler for the growing demands of ratings while improving overall device applications spanning rectification, modern grid systems in terms of performance in terms of reduced snubber and freewheeling. increased power levels, improved losses, increased robustness and efficiency, greater control and better controllability, and improving Different power-semiconductor-based integration of renewable energy reliability under normal and fault circuit topologies such as current sources. conditions. source converters (CSCs) and voltage source converters (VSCs) are em- The power electronics revolution, The HVDC-applications market is ployed for the AC/DC conversion which over the past few decades has small but important for semiconduc- process. For long-distance and swept across the power delivery and tors. Progress in the domain of power multi-gigawatt power transmission, automation sectors, has opened up a devices has in the past largely been PCT-based CSC topologies are widely

44 ABB review special report 1 Power device evolution and basic structures

IGBT PCT/IGCT

Cathode (Metal) 1,E+08 PCT/Diode 150 mm Bipolar Insulator 125 mm 100 mm technologies GTO IGCT Bipolar IGCT gate layer BJT 1,E+07 n MOS p n MOSFET gate layer p GTO MOS based 1,E+06 technologies IGBT Switching power (VA) N-base N-base Ge Si

1960 19701980 19902000 2010 1,E+05 p p 1960 1970 1980 1990 2000 2010 2020 Year Anode (metal) Year Thyristor Insulated

Carrier concentration GTO/IGCT PressPack

IGBT

2 PCT evolution and 150mm PCT rated at 8.5 kV / 4,000 A for UHVDC The power elec- tronics revolution has opened up 10,000 200 ) ETT 2 a wide range of 8,000 160 possibilities in 6,000 120 Wafer area (cm area Wafer Blocking rating (V) 4,000 80 terms of control-

2,000 40 ling the way elec-

0 0 1970 1975 1980 1985 1990 1995 2000 2005 2010 trical energy is Year transported and Blocking capability Wafer area used. used due to the overall low system low n-doped base region at the losses. For relatively shorter distances pn-junction to support the high and lower power levels, IGBT-based electric fields required for the high VSC conversion is becoming the voltage ratings. For current-carrying system of choice due to a number of capability with low losses, they advantageous integration and control require large active areas and highly features (especially when taking into doped contact regions to provide account the introduction of renewable high minority carrier (holes) injection energy into the grid). Despite the levels for modulating the low doped existence of optimized high-voltage n-base, and good ohmic contacts to devices with attractive electrical the outside world. Current normally characteristics, the main development flows in the vertical direction (per­ trend continues to seek higher power pendicularly to the wafer surface) and superior overall performance. in devices whose voltage range exceeds 1 kV. Today, silicon-based Power semiconductor devices for devices can be designed with good HVDC applications overall performance parameters up to High-voltage power semiconductors 8.5 kV for a single component. It is differ from their low-voltage counter- important to note here that power part in a number of structural as- semiconductors employed in grid pects. First, they include a wide and systems do not differ from those

A single-source supplierTopic 45­ 3 Evolution of IGBT technology and modern structures

Enhanced planar IGBT Trench IGBT Planar Cathode MOS cells Cell design Enhancement

Trench IGBT High SOA n-enhancement technologies temp. p p layer NPT Bulk design SPT/FS PT 6,500 V 4,500 V n-base n-base 3,300 V Ratings 2,500 V n-buffer (SPT) 1,700 V 1,200 V 600 V p p

1990 1995 2000 2005 2010

Anode

employed in other power electronics bipolar device, which is mainly For relatively applications such as traction and characterized by its favorable excess industrial drives. carrier distribution for low on-state shorter distances losses in conduction mode. The IGBT, Nevertheless, for HVDC applications on the other hand, is a MOS (metal- and lower power operating in the hundreds of kilovolts oxide semiconductor)-controlled levels, IGBT- range, devices are normally connect- device with a bipolar effect for ed in series to support the total achieving low on-state losses. based VSC DC-line voltage. The choice of the single device voltage rating employed The PCT ­conversion is in these systems depends largely on In contrast to the IGBT, the PCT is ­becoming the the performance/cost calculation for not a turn-off device. It is nevertheless a given topology and operational the device of choice for line-commu- system of parameters. Devices rated for lower tated CSC HVDC systems due to its voltages normally have favorably exceptionally low on-state losses and choice. lower overall loss figures but imply very-high-power handling capability. that a larger number of components Until very recently, state-of-the-art are needed. single devices were rated at 8.5 kV with a total diameter of 125 mm. The basic structure of a PCT and With the increase in demand for even IGBT is shown in ➔ 1 as is its evolu- higher power HVDC system ratings, tion over the years along with other larger area 150 mm, 8.5 kV PCTs with current ratings up to The PCT is the device of 4,000 A were developed choice for line-commutated for the latest Ultra HVDC CSC HVDC systems due to systems its exceptionally low on-state operating at ± 800 kV with losses and very-high-power total transmis- sion power handling capability. exceeding 7 GW. The device concepts such as the integrat- PCT evolution, including the new ed gate-commutated thyristor (IGCT). 150 mm PCTs and the UHVDC system The historical increase in the switching valves consisting of series connected power levels of high-voltage devices is PCTs, is shown in ➔ 2. also shown. The PCT is a thyristor

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­46­ ABB review special report 4 High-voltage IGBT technologies on-state losses Vce(sat) 5 IGBT application from single chip to system valve

7 Wafer 6

5 System valve

4 Today Sub-module section (V)

ce(sat) 3 V 2

1 85 A/cm2 75 A/cm2 60 A/cm2 50 A/cm2 40 A/cm2 30 A/cm2 0 IGBT 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 V (V) ce Module Planar NPT Enhanced trench SPT limit

Planar SPT BiMOS thyristor

Enh. planar or trench SPT BiMOS thyristor limit or IGCT

Enhanced trench SPT

Further technology developments are on an enhanced-planar cell design underway to increase current ratings (EP-IGBT), which has enabled the Today, high-­power to exceed 6,000 A while lowering establishment of a new technology conduction losses. curve benchmark over the whole IGBT press-pack IGBT voltage range from 1,200 V up and insulated The IGBT to 6,500 V as shown in ➔ 4. Future The IGBT is a MOS-controlled bipolar higher power densities and loss modules have rat- switch and presents the inherent reductions are possible by implement- advantages of that technology includ- ing Enhanced Trench ET-IGBT cell ings ranging from ing a controlled low-power driving designs, Emitter Switched Thyristor requirement and short-circuit self-limit- EST structures as shown in ➔ 4 and 1,700 V / 3,600 A ing capability. The IGBT has experi- integration solutions such as the to 6,500 V / 750 A. enced many performance break- bi-mode insulated-gate transistor throughs in the past two decades ➔ 3. (BIGT).

The fast progress in IGBT cell designs A customized press-pack module (Stak- (planar, trench, enhancement layers) Pak) was developed for series connec- and bulk technologies such as punch- tion of IGBT and diode chips to be used through (PT), non-punch-through (NPT) in grid applications. The mechanical and soft-punch-through (SPT) has led design is optimized to clamp the press to their widespread deployment in packs in long stacks. The module many high-voltage applications. Today, remains fully functional due to its design high-power IGBT press-pack and with individual press-pins for each chip insulated modules have ratings ranging as shown in ➔ 5. Furthermore, the from 1,700 V / 3,600 A to 6,500 V / choice of materials is optimized to 750 A. The most recent trends have achieve high reliability. targeted lower losses by using thinner n-base regions (SPT) and plasma enhancement layers and/or trench cell designs as shown in ➔ 3 accompanied by higher SOA and higher operating temperature (HT) levels. Similar development efforts targeted an improved diode design to match the latest IGBT performance. The free- Munaf Rahimo wheeling diodes play a very important Sven Klaka role in the application during normal ABB Semiconductors switching and under surge current Lenzburg, Switzerland conditions. The current IGBT platform [email protected] employed in grid applications is based [email protected]

A single-source supplierTopic 47­ Crossing land and sea

High-voltage 1 Laying the Gotland cable in 1954 DC cables

THOMAS WORZYK, TORBJÖRN SÖRQVIST, OLA HANSSON, MARC JEROENSE – It is notable that Gotland 1, the very first modern HVDC project of the 1950s, featured an underwater link. Following this 2 An extruded HVDC cable for submarine application, equipped with optical fibers for 1954 breakthrough, further HVDC temperature monitoring cables were installed across the world. ABB has as of today deliv- ered 2,300 km of mass impregnated DC cables.

The Gotland 1 link ➔ 1 did not only feature the first submarine MI (mass- impregnated) HVDC cable, but it also heralded an era of onshore connec- tions. A new link was built at Gotland in 1999 using an 80 kV extruded installed more than 5,000 km of HVDC cable system. Three years later The Murray Link extruded HVDC cable ➔ 2 – 3. ABB installed the Murray Link at the antipodes using almost twice the is still today the Almost all modern HVDC cables are voltage (150 kV) and more than double single-core. The simplicity of the the length (180 km). The Murray Link longest land- design is one of the reasons for the is still today the longest land-based based high-volt- significant reduction in required high-voltage cable in the world. The investment compared with HVAC. contracting of a number of extruded age cable in the HVDC cables can be manufactured in HVDC cable projects for offshore many varieties. Round copper or wind farms at ± 320 kV is a clear world. aluminum conductors of large sizes indication for the confidence in this can be used. There are two different technology. As of 2015, the energy section, NordBalt will be the longest insulation types used for HVDC supply of Lithuania will be supported extruded high-voltage cable in the cables: Mass-impregnated cables (MI) by the record-breaking NordBalt world. Once the DolWin2 cable have a layered insulation made of project. With its 400 km submarine system is complete, ABB will have special paper and impregnated with a

48 ABB review special report 3 Cable history

HVDC and HVDC cables have always had a were expected to grow after the war. At the – Solid 90 mm2 solid copper conductor flavor of fascination – from the War of Currents same time, the work of Dr. Lamm in Ludvika in order to reduce disadvantageous between AC and DC at the end of the 19th resulted in mercury-arc valves with acceptable conductor expansion under cable torsion century to the German “Energiewende,” reliability. in manufacturing or submarine laying engineers and even the public continue to – 7 mm mass-impregnated insulation, discuss the fantastic possibilities of HVDC As so often happens in technical development, comfortably exceeding physical require- cables to transport large amounts of power not only ingenuity but its combination with ments over virtually unlimited distances. During the pioneering spirit and a certain market situation – Extra-dense insulation paper in order to first half of the 20th century, HVDC research in lead to the breakthrough – and to the Gotland avoid partial discharges or ionization countries such as Sweden, the United States project. The Swedish State Power Board as it was called at that time and Germany focused on converter stations. decided in 1951 to connect the Swedish Island – Double lead sheath. Liljeholmens AB later The development of high-voltage cables of Gotland electrically to the mainland – a developed a continuous lead sheathing principally served the widespread AC tech- distance of 100 km. No other technology but machine, which improved the quality and nology. Although some of the peculiarities a submarine HVDC cable could solve the task. emerged as a virtual standard in high-volt- surrounding HVDC cables were understood It was a bold decision – nobody had done this age cable sheathing early on, manufacturing experience remained before. – Double armoring in the landfall cables scarce. An HVDC cable system was built during WW II in Germany but was never commissioned Bjurström, the mastermind of Liljeholmens AB The cable design was so successful that the due to the turmoil of war. It was later re-erected at that time, presented the Gotland cable original Gotland cable link could be upgraded in Russia as an experimental line. A submarine at the 1954 Cigré conference, in a paper from 100 to 150 kV when power demand HVDC connection between Norway and the humbly titled “A 100 kV DC cable.” The increased. A piece of the original cable Netherlands was proposed as early as 1933, Gotland cable was a masterpiece of its time, was analyzed after decommissioning a few 75 years before ABB realized this link. engineered to be reliable. While it is quite decades later and showed no signs of aging. easy to produce a few hundred meters of ABB’s predecessor cable factory (Liljeholmens cable, the production and installation of Today, only the double-lead sheath would be AB) performed HVDC tests on mass-impreg- extreme lengths is a very different business. manufactured differently. nated cable in the 1940s, maybe sensing the Bjurström and his colleagues put all the best upcoming interest in the market where grids into the Gotland cable:

high-viscosity compound. The other type, the extruded insulation, com- The simplicity of the HVDC prises a polymeric insulation made by continuous extrusion of ultra-clean ­cable design is one of the polymeric material. MI cables are a ­reasons for the significant good choice for the highest ratings but extruded cables are catching up. ­reduction in required investment Both insulation types are solid, ie, no harmful oil is spilled should the cable when compared with HVAC. be damaged.

Since the insulation must be pro- Characteristics of HVDC cables temperature. A loaded cable gener- tected from water, submarine HVDC At first sight there is not much ates heat in the conductor, which will cables always feature a metallic difference between an HVAC and an typically result in a temperature drop sheath serv­ing as a water block HVDC cable. Both contain a conduc- across the insulation. The tempera- and path for short-circuit currents. tor, insulation, a water barrier and in ture distribution will have a corre- Extruded underground HVDC cables the case of the submarine cable, sponding effect on the resistivity can instead use a lightweight metallic armor. The main difference lies in the distribution. As a result, the electrical laminate sheath and a copper wire electrical high-voltage insulation. field distribution may be inverted in a screen. loaded HVDC cable compared with From an electrical point of view, HVAC (where the electric field is The HVDC cable can be dressed with HVDC insulation behaves differently always the highest at the conductor tough outer plastic sheaths, or wire than its HVAC counterpart. While screen and decreases toward the armoring for, eg, subsea applications. the electrical field – an important insulation screen). The effect of field The extruded HVDC cable can be design and operational parameter – inversion is a well-known peculiarity installed in the most challenging is defined by the permittivity in an of both mass-impregnated and environments, such as the deep sea HVAC cable, it is (also) controlled extruded cable. and vertical shafts ➔ 4. by the resistivity in the HVDC case. The resistivity of the insulation material depends in part on the

A single-source supplier 49­ 4 Selection of ABB’s groundbreaking HVDC cable projects 5 The PEA technique presents a reliable method to quantify space charge Project Location DC voltage Insula- Year Remarks name tion Cable screen Guard ring Cu-foil Ferrite First submarine HVDC Semicon Gotland 1 Sweden 100 - 150 kV MI 1954 cable ever

Baltic Sweden- Highest Voltage, longest 450 kV MI 1994 Cable Germany length at that time

Longest underground UA Murray Link Australia ± 150 kV XLPE 2002 ­cable system of all times. PEA 580 km. Longest Norway- NorNed ± 450 kV MI 2008 power cable system, Netherlands all categories

First extruded HVDC SouthWest Sweden ± 320 kV XLPE 2015 system with combined Link cables and OH line.

Longest HVDC Light Pulse generator Sweden- system, 400 km submarine NordBalt ± 300 kV XLPE 2015 Lithuania cable route with cost- saving Al conductor

The development of the extruded (such as lightning and switching The main differ- cable took time: The physics of the impulses). DC field control is achieved polymer insulation under DC electric by a continuous layer of nonlinear field ence between stress was a new area, and proper grading material (FGM) connecting full non-destructive measurement potential to ground. HVAC and technology was not available. In the HVDC cable lies 1960s, theorists had predicted that so-called space charges would impact in the electrical the electric field and therefore possibly have a negative effect on the perfor- high-voltage mance of the cable. Space charges, insula­tion. as the term suggests, are charges that are present inside the insulation. These charges will affect the local field strength and “distort” the distribution of the electrical field. In the 1980s Tatsuo Takada in Japan presented a reliable measurement technology to quantify space charge in both magni- tude and space. The measurement principle is called the pulsed electro- acoustic (PEA) method. ABB was one of the first companies to use it ➔ 5.

Applying this tool as well as a wide technology base in physics, chemistry and high-voltage engineering, ABB was able to develop 80 kV extruded Thomas Worzyk cable systems. The technology has Ola Hansson since been boosted to 320 kV. Marc Jeroense ABB Power Systems Cable accessories for HVDC Light Lyckeby, Sweden extruded cables utilize a combination [email protected] of geometric and refractive field [email protected] grading for capacitive field distribu- [email protected] tions and nonlinear resistive field grad- ing for DC field distributions. The Torbjörn Sörqvist accessories are designed to ensure an ABB Power Products appropriate electric-field level when Alingsås, Sweden subjected to time-varying voltages [email protected]

50 ABB review special report Topic 50­ Conversion

HVDC valves 1 Valve suspended from the ceiling of the valve hall

JONATAN DANIELSSON, BAOLIANG SHENG – The heart of the converter is the valve, which comes in two basic designs for HVDC Classic and HVDC Light®, based on thyristors and IGBT semiconductors, respectively.

Two different designs of thyristor- based line-commutated valves have been developed by ABB: a conven- tional base-mounted design with support insulators standing on the floor, and another (more frequently For the sake of reliability they have a ing voltages and currents, while also used) design with the valve suspended minimum of electrical components reducing conducting and switching from the ceiling of the valve hall ➔ 1. and connections. The main compo- losses. The first HVDC valves designed The latter design is particularly suitable nents are thyristors and their voltage by ABB were for the upgrading of the for withstanding seismic stresses, but dividers, control units and heat sinks. Gotland transmission – they used also offers cost advantages. thyristors with an area of The design uses a modular concept The design uses a modular 5 cm2. The to ensure high reliability while retaining next valve the flexibility to design valves accord- concept to ensure high design (used ing to customer requirements and for the preferences. A valve is built up with ­reliability while retaining the Skagerrak one or several layers depending flexibility to design valves transmission) on the required voltage withstand featured capability ➔ 2. Each layer consists of ­according to customer require­ double-sided series-connected thyristor modules cooling of the with intermediate current-limiting ments and preferences. thyristors, reactors, corona shields and piping which had for the cooling liquid. The individual The modules are of compact design an area of 8 cm2. Today thyristors have parts are supported by a mechanical for easy access during maintenance. an area of up to 130 cm2 capable of structure with a central shaft running The design allows components to be withstanding continuous currents up vertically through the structure with exchanged without opening the water to 4,500 A and short-circuit current ladders and working platforms for cooling circuit ➔ 3. up to 50 kA, eg, for the Xiangjiaba- easy access. Shanghai ± 800 kV Ultra-HVDC Each module contains a number project [1]. Thyristor modules of thyristors connected in series. Thyristor modules are of a mechani- Continuous thyristor development cally standardized compact design. enables them to handle ever-increas-

A single-source supplierTopic 51­ 2 Single layer of a valve 3 Thyristor module

Reactor

Thyristor module

4 Voltage across thyristor level

Service platform Current busbar

Aluminum shields Water pipes

Light guide channel

Protected area

A switching position is built up from IGBT-based voltage source type mainly depends on the appli­ a thyristor with two parallel circuits, converter valves cation. each consisting of a damping circuit The use of IGBT-based voltage source and a DC grading circuit, as well a converters (VSCs) in HVDC power A switch-type valve has a close TCU (thyristor control unit). The TCU transmission was a breakthrough. apparent resemblance to conventional converts the optical firing pulses Its first application was in a 3 MW thyristor valves: A large number of from the control system to electrical HVDC Light test installation in Hällsjön series-connected IGBT devices are signals to trigger the gate that fires in 1997. Since then, 20 VSC HVDC switched simultaneously. Pulse-width the thyristor. The TCU includes modulation state-of-the-art built-in functions (PWM) is used that protect it against overvoltages The liquid in the closed to achieve a during the reverse recovery period good approxi- (after a thyristor turns off) as well as valve cooling system is mation of a from high voltages in the forward ­continuously passed through sinusoidal blocking state ➔ 4. output voltage a deionizing system to keep (AC volt- By using this hybrid technique, ABB age) ➔ 5. is able to provide a very compact its conductivity low. TCU. ABB’s service record is also A CTL unbreakable: Of the more than 19,000 converter thyristors installed since 2000, only power transmissions have been integrates the DC capacitors into the four thyristor failures have been installed or are under construction by valve. The valve consists of series- reported. This demonstrates the supe- ABB alone [2]. connected voltage cells that can rior design of electrically triggered produce a sinusoidal voltage ➔ 6. thyristors. Two types of VSCs have been devel- The greater the number of cells con- oped for HVDC transmission: the nected in series, the more sinusoidal “switch” type and the cascade two- the waveform. A CTL converter valve level (CTL) or “controllable voltage for the DolWin1 HVDC trans­mission source” type. The choice of converter project is shown in figure 3 page 25.

52 ABB review special report 5 Voltage and current in a switch-type VSC valve with PWM 6 Voltage output of a CTL-type converter with seven voltage cells in series connection

200 (kV)

ac(t) 100

0

-100 1 + ⁄2U (kV) and U dc v(t)

U -200 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 time (s) 4 U

2

1

(kV) 0 2 - ⁄ Udc v(t) I -2

-4 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 time (s)

7 StakPak IGBT used in ABB’s VSC valves 8 Overview of a typical valve cooling system 9 Typical skid-based modularized redundant cooling system Main pumps Shunt valves Deaeration vessel M

Outdoor Expansion coolers vessel Con- verter Mechanical filters valve

Deionizer filters Replenishment system

Mechanical filters

In this project, one valve consists of tors. This efficiently transports heat thirty-six voltage cells. away from the device to be cooled through heat exchangers using either The modular design concept for air or a secondary circuit. The liquid in valves is found in both switch and the closed-valve cooling system is CTL types. ABB’s VSC valves use continuously passed through a StakPak IGBTs ➔ 7. These switching de-ionizing system to keep its modules create an internal short conductivity low. circuit should they fail, making them similar to thyristors. This function A typical valve cooling system is Jonatan Danielsson allows a current to continue to con- shown in ➔ 8 and ➔ 9. ABB Power Systems, Grid Systems duct through a faulty IGBT device Raleigh, NC, United States without calling for an external bypass [email protected] circuit (as is the case for other IGBT types). The decreased deployment Baoliang Sheng of components at high potential can ABB Power Systems, Grid Systems therefore augment the valve’s avail- Ludvika, Sweden ability, reliability and compactness. [email protected] StakPak follows the conventional press-pack design advantages such as better cooling and robust mechani- References cal module structure [3]. [1] J. Waldmeyer and W. Zhengming, “Six Inch Thyristors for UHVDC,” in Proc. 2006 International Conference on UHV Transmission Valve cooling Technologies, Nov. 27–29, 2006, Beijing, China. The purpose of the cooling system is [2] G. Asplund, “Application of HVDC Light to to dissipate the power losses gener- Power System Enhancement,” IEEE/PES Winter Meeting, Singapore, January 2000. ated in the valves. Coolant fluid is [3] B. Jacobson, et al., “VSC-HVDC Transmission circulating through the heat sink in with Cascaded Two-Level Converters,” B4-110, close contact with the semiconduc- CIGRE 2010, Paris, France.

A single-source supplierTopic 53­ Converter 1 An early converter transformer transformers

A 60-year journey

MATS BERGLUND – ABB’s HVDC- 2 The function of the HVDC converter transformer transmission transformer technology has evolved from the 1954 Gotland Voltage and dielectric separation integral part of the control of the HVDC In all HVDC systems (regardless of the system, both from an active and reactive link ➔ 1. ABB’s predecessor com- converter topology) the HVDC converter power perspective. Compared with other pany, ASEA, broke new ground with transformer serves as an interconnection transformers, the HVDC converter its 400 kV DC technology used in the between the AC grid and the converter transformer often displays a large regulation 1,000 MW CU project (Coal Creek valve. Besides converting AC voltage and range – a consequence of its role as an current to a level suitable for the converter integrated regulating function of the Station to Underwood, ND, United valve, the HVDC converter transformer fulfills HVDC system. States) in 1977. The company additional roles in the HVDC system. For asserted its undisputed technology many converter topologies (HVDC Classic Short-circuit current limitation and leadership with the Itaipu (Brazil) and asymmetric HVDC Light®) the most system properties important function of the transformer is to In the early days of converter valves, a key project of 1982 (3,150 MW / 600 kV keep the DC-voltage offset created by the feature of the transformers was to provide an DC). This was to be a cornerstone in converter valve out of the AC network. impedance to limit the short-circuit current HVDC converter-transformer history. This results in AC and DC stress being to the semiconductor valve. As the capability To realize this record-breaking superimposed in the winding of the of semiconductors grew, this property transformer. lessened in importance. The transformer still milestone, ASEA built on the fulfills basic functions in enabling correct knowledge it accumulated delivering Power and voltage regulation interaction between the HVDC transmission high power transformers to the The HVDC converter transformers is an and the AC network. booming AC-networks during the 1970s. 3 Design aspects for the HVDC-converter transformer It was not until the end of the 1990s that anything close to Itaipu would be High power, high voltage and DC Reactive loading attempted in terms of transmission HVDC converter transformers are among For HVDC transformers, reactive power the largest transformers in terms of power, capability of the complete transmission is power. The next records were set by voltage and complexity. On top of this come translated into the transformer’s ability to transmission projects in China: The the requirements dictated by the need to handle the reactive load. first two major HVDC links were from handle DC voltages. the Three Gorges hydropower station Short-circuit-like duty Impact from current harmonics The mercury-arc valves of the early HVDC to the load centers in eastern China, For some applications, the load current seen days sometimes “backfired,” subjecting for which ABB was a key supplier. by the transformers is not perfectly smooth. the transformers to a condition close to This implies extra care for the thermal short circuit. Apparently, the ABB design was A diversification of HVDC-transmis- dimensioning of the HVDC converter sufficiently robust as there is no history of transformer as well as its accessories, short-circuit incidents – but this was not sion configurations into the Light and bushings and tap changers. formally proven until 2007 when ABB Classic variants started at the end of short-circuit tested an HVDC converter the 1990s. The thyristor-based HVDC transformer for the first time. Classic has built on its strengths –

54 ABB review special report 4 HVDC transformer configurations The ultrahigh All HVDC systems need transformers, but direct consequence of HVDC-transmission how these are arranged can vary quite power capability and the transformer DC-transmission substantially between projects depending on topology. the specification of the project. In their basic voltage is highly forms, each pole of an HVDC Classic system For HVDC Classic, the transformer needs to be fed by six phases of transform- alternatives are shown below. challenging to ers while HVDC Light needs a three-phase supply. Typically, more transformers are needed the insulation when transmission power and transmission The HVDC-transformer configuration of an voltage are high. The spare transformers abilities of the individual project is unique to the project and strategy in the converter station also plays determined by the sheer size of transformers an important role in the selection of converter in relation to the limitations in the transport transformer solution. infrastructure between the place of manu- transformers. facture and the HVDC converter station. For HVDC Light, the transformer solutions The main driver behind size of the converter possible often are limited to the choice of transformer is the rated power, which is a single-phase and three-phase transformers.

transmission voltage of 1,100 kV DC. 3-phase, 3-winding 3-phase, 2-winding 1-phase, 3-winding 1-phase, 2-winding This means that the transformers transformers transformers transformers transformers must have a very high power rating, Y Y Y Y and thus a substantial physical size Y Y – weighing in excess of 600 t ➔ 6.

Y Y Y Y Y Y Y Y The ultrahigh DC-transmission voltage Y Y is highly challenging to the insulation Y Y Y abilities of the converter transformers. Y These are subjected to extreme test 1 unit per 2 units per 3 units per 6 units per 12-pulse bridge 12-pulse bridge 12-pulse bridge 12-pulse bridge voltages before delivery. Besides the voltage stresses often appearing in HVDC Classic, these transformers often claim superlatives in terms of 5 Project execution power rating as well. The largest HVDC converter transformers built

Technical and scientific proficiency is one China are examples where ABB has set have single-phase power ratings in important aspect of HVDC converter industry records. In the project between excess of 600 MVA – the largest in the transformers, but equally important is the Hami and Zhengzhou ABB delivered all world of transformers ➔ 7. way projects are executed and how HVDC converter transformers to the technology is implemented. HVDC projects 8,000 MW, 800 kV DC mega-project in often need a long series of HVDC converter 17 months. This should be compared with HVDC Light transformers being manufactured in a timely the delivery times of the Three Gorges HVDC Light systems share certain manner to complete the supply for an projects where the complete time schedule features with HVDC Classic systems, individual project. As lead times for delivery ranged over 36 months. These improve- while others are less prominent. of projects are gradually reduced, this aspect ments could very well stem from the Depending on the system configura- becomes more and more important. abundance of projects delivered: ABB was responsible for more than 50 percent of all tion, the converter transformers are ABB has taken the lead in this important the projects realized – far more than any of sometimes exposed to a DC stress development. The deliveries to SGCC in its competitors. similar to that of the HVDC Classic systems, while in some system configurations they are not. The ­expanding into ultrahigh transmission To understand what contemporary further the capability of HVDC Light voltages enabling very efficient power HVDC transmission means for the advances, the greater the DC stress transmission over long distances. HVDC converter transformers a that the converter transformer must HVDC Light, which started off as a complete view of the technologies and face ➔ 8. moderate power application, has their applications are given below. grown into a medium-power transmis- A clear contrast to the HVDC Classic sion system that nowadays can do HVDC transformers today systems is found in the load current what HVDC Classic could do at the HVDC Classic has in recent years that the converter transformers for end of the 1990s ➔ 2 – 5. seen rapid expansion in terms of HVDC Light are subject to. For HVDC performance. HVDC Classic can now Light, the load current is in most transmit up to 11,000 MW at a cases free from current harmonics,

A single-sourcesingle source supplierTopic 55­ 6 800 kV UHVDC (ultrahigh voltage direct current) converter transformer 7 Power rating references

Project Rated power Year

Itaipu 314 MVA 1982

Quebec-New 404 MVA 1987 England

Sylmar 625 MVA 2007

Rio Madeira 630 MVA 2011

Celilo upgrade 785 MVA 2014

The thyristor- based HVDC Classic has built on its strengths – expanding into ultrahigh trans- mission voltages enabling very efficient power 8 Converter transformers and the spare transformer at Woodland HVDC Light® station in Ireland. transmission over long distances.

HVDC converter transformers will need to connect HVDC systems directly to AC networks at even higher voltages than are used today. An HVDC-transformer technology for interconnecting the highest voltage DC transmissions to 800 kV AC sys- tems already exists and there will soon be commercial applications. Beyond this, interconnections to even higher AC voltages, such as the 1,000 kV AC networks in China, are a possibility.

whereas in HVDC Classic the trans- reactive, something that needs to formers must cope with the thermal be carefully considered in the trans-­ stress originating from the extra losses former design. incurred by current harmonics. The future Mats Berglund One consequence of the reactive It is not only the DC voltage level on ABB Power Products power capability of HVDC Light is that the HVDC transmission itself that is Ludvika, Sweden a large portion of the load can be being increased. Another trend is that [email protected]

56 ABB review special report Capacitors

A key component 1 Capacitor bank at Porto Velho HVDC station in Brazil in HVDC systems

BIRGER DRUGGE, PETER HOLMBERG – Capacitors have multiple functions in HVDC systems ➔ 1. They cover aspects such as reactive power compensation, DC filtering, AC filter- ing and power-line carrier coupling. Capacitor technology for HVDC has gone through the various shifts in technology from impregnated mixed dielectrics (paper/film) to full-film dielectrics with highly specialized capacitor fluids. The latest technology used in HVDC Light® applications features dry solutions based on special metallized film dielectrics.

ABB’s technology is based on its long experience and deep understanding of specific DC phenomena such as space charges. An example of ABB’s prowess is the internally fused capacitor used to maintain high levels of power quality and availability.

HVDC’s increasing voltage levels have introduced special mechanical challenges in the design of the capaci- As a technology leader, ABB also tor stacks, not the least of which drove the technology shift to dry concern seismic requirements. HVDC capacitors for HVDC Light, required to handle unit voltage ratings Capacitors are part of the output filter above 150 kV. ABB’s dry DC capacitor that reduces harmonics. One chal- technology is based on metallized film Birger Drugge lenge faced is that these harmonics with self-healing properties. With Peter Holmberg generate sound in the components. ABB’s dry technology, customers ABB Power Products, Special patented sound-attenuating benefit from higher availability and High Voltage Products solutions have been developed to reduced footprint of the link, also Ludvika, Sweden keep the sound level low and meet improving the eco-aspect of the [email protected] environmental requirements. solution. [email protected]

A single-source supplierTopic 57­ 1 ABB’s HVDC arresters 2 Comparison of gapped SiC arrester and gapless ZnO surge arrester

6- to 12-pulse valve AC bus

Neutral bus HVDC AC filter arrester applications

DC breaker

DC filter DC bus

2a XDL 280 A surge 2b ZnO surge arrester (1970s) arrester (1980s) Surge arresters

60 years of HVDC protection

LENNART O. STENSTROM, JAN-ERIK The various arresters normally used in A short history of ABB (and predeces- SJÖDIN – An HVDC station features an HVDC project are shown in ➔ 1. sor company ASEA) HVDC surge different types of surge arresters to arresters is shown in ➔ 3 and ➔ 5. protect the equipment from overvol- Historically HVDC stations were first tages caused by lightning and/or protected by gapped SiC surge ABB has a number of designs for switching events. In some equipment arresters until the late 1970s when HVDC arresters optimized for thermal, such as DC breakers, surge arresters gapless ZnO surge arresters were electrical and mechanical stresses, also may form an integral part of the introduced. The last generation of the safety requirements and cost depend- apparatus. gapped arresters were quite complex ing on the application. and comprised a vast number of The stresses the arresters have to be components such as spark gaps, To date, tens of thousands of ABB designed for, compared with normal SiC blocks, grading capacitors and HVDC arresters have been delivered AC arresters, are characterized by, for grading SiC resistors. The design worldwide with an excellent service example: became even more complex when record. – Special voltage waveforms compris- parallel columns had to be used to ing frequency components ranging meet high energy demands or low Instrument transformers – from pure DC, and power frequency protection levels ➔ 2 shows how the reliable metering and protection to several kHz introduction of the ZnO material ABB has been producing instrument – Very low protection levels required remarkably simplified the internal transformers by the thousands for – High energy demands – eg, for valve design of the surge arresters com- more than 70 years ➔ 4. Their applica- arrester, neutral-bus arresters and pared with the previous gapped tions range from revenue metering, arresters for DC breakers HVDC arrester. control, indication and relay protec- – High ambient temperature, eg, for tion. One field of application in HVDC valve arresters is the use of capacitor voltage

58 ABB review special report 3 Surge arrester 4 420 kV cap. 5 The first gapless HVDC arrester and the first 500 and 1,100 kV DC bus arresters with history at ABB volt. transf. polymer housings

Pre-1979: Gapped SiC arrester 1979: First gapless ZnO surge arrester (probably the world’s first) delivered to a 250 kV HVDC station in Denmark ➔ 5a 2000: First 500 kV arrester with polymer-housing delivered to the 3GS project in China ➔ 5b 2006: First 800 kV arrester type tested and energized for a China project 2012: First 1,100 kV arrester fully type tested ➔ 5c

5a Gapless HVDC line 5b 500 kV DC bus arrester 5c 1,100 kV DC bus arrester (1979) (2000) arrester (2012)

of a capacitor voltage transformer ABB has been incorporates an inductive reactor, connected in series between the producing instru- capacitive voltage divider and the ment transform- high-voltage end of the primary winding, to compensate for the shift ers by the thou- in phase angle caused by the capacitive reactance of the capaci- sands for more tor’s voltage divider. This type of than 70 years. compensation allows simple con- struction to obtain high accuracy for high loads. However, the reactance transformers to obtain the source and capacitance form a tuned circuit voltage for converter control, as well that gives relatively low accuracy at as to obtain signals for the protec- frequencies outside the nominal tion of the converter station. The frequency. output from the capacitor voltage transformers is used to trigger the In an HVDC application, the capacitor thyristor valves at a certain time, voltage transformer that is used to based on the previous zero crossing obtain the source voltage for special of the AC voltage. Because even requirements in converter control for minor disturbances can be disas- transient and frequency response trous to the operation of the HVDC uses an electromagnetic unit without station, special requirements must be a separate compensation reactor. For met for transient and frequency this special type, the function of the response. compensation reactor and the primary winding of the intermediate Lennart O. Stenstrom The first capacitor voltage transform- transformer are combined into one Jan-Erik Sjödin ers were produced by ABB in the device. This arrangement gives a ABB Power Products, 1950s for delivery to the 1,000 km, substantially increased operating High Voltage Products 400 kV AC transmission line from frequency range, and highly improved Ludvika, Sweden Harsprånget to Hallsberg in Sweden. transient response. [email protected] The electromagnetic unit in the base [email protected]

A single-source supplier 59­ Trend lines

The first high-voltage direct current (HVDC) pioneers the last few years have seen a steady stream of world- started work in the early 1920s, but it was not until 1954 record-breaking achievements in both the classic that ASEA, a predecessor of ABB, was able to develop line-commutated converter (LCC) and in the more recent and commission the first commercial subsea HVDC link, voltage source converter (VSC) areas. HVDC progress to the island of Gotland, in Sweden. Since then, HVDC has, to a large extent, been made possible by the technology has been characterized by rapid and evolution of a particular set of key technologies and continuous advances driven by new and demanding products and it is likely that these will continue to drive customer needs. Despite the maturity of the technology, the field for the foreseeable future.

1 HVDC is the technology of choice for bringing distant Future offshore wind power to shore. directions in HVDC transmission Technologies for bulk power transmission are evolving fast

PER SKYTT – Advances in HVDC In addition, HVDC makes it more cost for the user during its entire life technology in recent years have straightforward to interconnect cycle – which in HVDC can span been breathtaking: Bulk transmis- asynchronous AC networks and it decades. The initial investment, driven sion for extremely long distances can effectively be used in very long by equipment and plant size, and has reached levels of 8 GW using subsea cables that connect AC engineering and commissioning ± 800 kV ultrahigh-voltage DC and systems. HVDC is also ideal for efforts, can be considerable and ratings above 10 GW are envisioned powering offshore oil and gas installa- improved technology and processes within a few years; world-record tions with clean electricity from shore. can contribute significantly to cost subsea transmission cable projects Further, embedding HVDC in AC reduction here. HVDC also saves cost have opened the door to the further systems is an effective way to rein- during operation because total expansion of the global power cable force bulk transfer and strengthen the electrical system losses, a major network; and new VSC tech­nology AC system operation. factor for many operators, are lower will simplify the job of con­necting than in other solutions. weak AC networks as well as Customer values making it easier to transfer power As in many technology areas, one of Other aspects are important too: from offshore wind generators and the most important aspects of the As HVDC is a part of critical national other remote renewables ➔ 1. product is a continuous reduction of electrical infrastructure, reliability and

60 ABB review special report 2 HVDC lines in Brazil. HVDC meets many criteria for bulk electrical power transport. 3 Evolution of HVDC Classic power and voltage ratings

Voltage Power Valve type Year (kV) (MW) Mercury 1954 100 20 arc Mercury 1968 533 1,440 arc

Thyristor 1970 50 10

Thyristor 1977 250 500

Thyristor 1978 500 560

Thyristor 1979 400 1,000

Thyristor 1985 500 2,000

Thyristor 1987 600 3,150

Thyristor 2003 500 3,000

Thyristor 2010 800 6,400

Thyristor 2013 800 7,200 availability become essential consider- decisive steps will be taken. The ations. In addition, less-easily defin- improvements being made to indi- Thyristor 2014 1,100 10,000 able requirements often come into vidual components and the way they play, such as an efficient approval are used within HVDC systems process for the system, the supplier’s suggest that HVDC transmission and computer memory have pushed experience, simplicity of updates and systems will continue to gain in material and processing limits beyond upgrades, and project execution functionality and capacity for the what many thought possible. The time ➔ 2. foreseeable future. industry has gone from 4-inch to 5-inch and now 6-inch thyristors, Performance improvements increasing current ratings. Voltage Even though HVDC technology has Breaking DC cur- ratings have been increased by many reached a point at which many vital kilovolts purely with enhanced and demanding applications can be rents has been a processing ability and material quality. satisfied, there is a need for further The IGBT has seen an even more enhancement in capabilities and major challenge drastic development in the past few performance: when applying years that has enabled VSC HVDC to − Increased power ratings and lower reach the 1 GW level. This develop- losses for bulk transfer using LCCs HVDC on a large ment looks set to continue for many − Increased power ratings for VSCs years to come, until silicon-based – enabling connections to remote scale. However, technology reaches its theoretical renewable generators or the ABB’s new hybrid limits. Already, however, other even interconnection of weak AC more capable semiconductor materi- networks HVDC breaker als, principally silicon carbide, are − Further reduction in HVDC station emerging as the basis of new compo- size – allowing applications offshore has changed this. nents. Indeed, silicon carbide devices and in constrained urban areas have already started to appear in Power semiconductors lower power applications. These enhancements will come about The core of an HVDC system is a by developments in key enabling-tech- silicon-based power semiconductor Insulation nology areas ➔ 3. device: a thyristor in an HVDC Classic The DC voltage withstand of HVDC system, or a more controllable tran- components and systems is a critical Enabling technologies sistor device, an IGBT (insulated- factor to consider when designing The advances in HVDC have, to a gate bipolar transistor), for HVDC reliable and compact electrical large extent, been made possible by Light ➔ 4 – 5. This technology benefits systems. DC voltage withstand limits the evolution of a particular set of key from the astonishing progress that has have been pushed ever higher in technologies and products. These been made in the mainstream semi- recent years and systems operating same technologies and products conductor business – where fabrica- at 1,100 kV have recently been made provide the arena in which future tion processes for microprocessors possible. But better DC voltage

Trend lines 61­ 4 Assembly of thyristors at ABB’s semiconductors facility 5 ABB StakPak with four and six submodules

withstand has advantages other than DC breakers The latest systems use, as their basis, higher operating voltages and capaci- Breaking DC currents has, for many advanced electronics that are tailored ties – converter stations can be made years, been seen as a major challenge for HVDC. smaller, for example. Gas-insulated when applying HVDC on a large scale. solutions for DC will play a major role However, ABB’s new hybrid HVDC Trends as will further expansion of the air- breaker has changed this and has From day one, pioneering technology insulated switchgear design envelope. thus ushered in a new era of HVDC has ensured ABB’s leading position in transmission networks. This paves the the HVDC field. This leadership will be Cable technology way for large multiterminal systems of great importance in the planning of A key enabling product for HVDC is and a future supergrid HVDC system future electrical transmission systems the lightweight polymer-insulated that will be superimposed on the – in which HVDC will play a major role. cable, which allows systems with existing AC network. In addition, the theoretical limits of higher transmission capabilities to be HVDC’s core technologies have not built. Recent history shows a dramatic Control systems yet been reached, so HVDC holds evolution of the cross-linked poly­ An HVDC system comprises a collec- great potential and is set to become ethylene (XLPE) DC cable, for instance. tion of controllable equipment that an even more dominant technology for The first HVDC Light systems oper- needs constant monitoring and con- bulk power transmission. ated with a system voltage of 80 kV trol. The semiconductor valve itself, and projects currently under construc- for example, relies on a very fast and tion will operate at ± 320 kV, enabling reliable automatic control regime to 900 MW of power to be transmitted. fire the thyristors in the HVDC Classic And there is scope to expand cable product, or to fire the on and off signals for the IGBTs in HVDC Light. The DC voltage withstand Apart from of HVDC components and this, the entire electrical systems is a critical factor and auxiliary systems to consider when designing need to be reliable and compact electri- constantly monitored and cal systems. controlled to ensure all components development much further: Theo­retical work in harmony. ABB has developed limits are well above current ratings such dedicated control and protec- Per Skytt and this points to the possibility of tion systems – starting with ones ABB Power Systems, Grid Systems future cables performing at levels far based on vacuum tubes that then Ludvika, Sweden above current ones. evolved into relay-based solutions. [email protected]

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­62 ABB review special report 1 ABB’s new hybrid HVDC breaker will revolutionize the HVDC field by making Breaking ­multiterminal HVDC grids possible. step

ABB’s unique hybrid­ HVDC breaker is a key component for future grids

JÜRGEN HÄFNER, REZA DERAKHSHAN- The hybrid HVDC breaker melds reliable Building multiterminal HVDC systems FAR, PETER LUNDBERG – The best way power electronics already used in with more than one protection zone to transport large quantities of electri- HVDC converter stations and fast-dis- would increase the robustness of the cal power over long distances with connecting gas-insulated switchgear system during DC faults and would be minimal losses is to use high-voltage technology to fill a gap in the products of great value to the customer. However, direct current (HVDC) technology. needed to build large multiterminal the absence of a suitable breaker has, Because more, and more remote, systems with multiple protection zones. until now, limited the feasibility of this. renewable power sources are coming online and urban centers of consump- The hybrid HVDC breaker opens up a DC breakers are required to protect tion are pulling in power from further new era not only for the transport of voltage source converters from line and further afield, the importance of renewable energy but also for all other faults in DC grids and to enable a HVDC is growing rapidly. However, types of generated power that has to reactive power compensation mode for since the dawn of HVDC technology, voltage stabiliza- almost a century ago, one major tion in point-to- com-ponent has been missing – a This 100-year-old electrical point and low-loss breaker that is appropriate multiterminal for the high voltages and high speeds engineering problem has HVDC applica- required. The absence of this critical tions. The component has confined HVDC topol- now been solved by the relatively low ogy to point-to-point configurations; ­introduction of ABB’s new impedance of an HVDC grid has remained infeasible. HVDC systems All this has changed with the launch hybrid HVDC breaker. presents a of ABB’s new hybrid HVDC breaker. challenge when short-circuit The many HVDC transmission lines be transmitted over long distances, faults occur in a DC link because the scattered around the globe have one including under large bodies of water. fault penetration is faster and deeper thing in common: They are all point-to- Further, the ability to create HVDC grids compared with the AC equivalent. point connections. There is no HVDC will improve overall grid reliability and Consequently, ultrafast HVDC breakers grid. The reason for this has been the enhance the capability of existing AC are needed to isolate faults and avoid a absence of a breaker that could handle networks. collapse of the common HVDC grid the high voltages and high response voltage. In DC systems, fault currents speeds involved, and that could operate Technical background and system grow steadily in one direction. The lack within acceptable loss limits. requirements of (naturally occurring) zero crossings Until now, protecting a multiterminal and the response speed requirements This 100-year-old electrical engineering HVDC grid in the event of a fault would have long been the main challenges [1]. problem has now been solved by the demand a coordinated operation by all introduction of ABB’s new hybrid HVDC the terminals to abort the active power breaker ➔ 1. flow in the entire multiterminal system.

Trend lines 63­ 2 Hybrid IGBT DC breaker

Hybrid DC breaker

a b c

h d e

g

f

a Main current branch (when current is flowing) consisting of: d Main HVDC breaker consisting of: g Residual current breaker b Ultrafast disconnector e Semiconductor interrupter h Current limiting reactor c Load-commutation switch (semiconductor-based) f Arrester bank

3 The ultrafast disconnector kilowatts of on-state losses and a size mode in case of component failure. that increases the footprint of an HVDC Individual resistor-capacitor-diode (RCD) converter station by only 5 percent. This snubbers across each IGBT module breaker is a milestone in the history of ensure equal voltage distribution during electrical transmission and solves a current breaking. Optically powered central problem of HVDC grids. gate units enable operation of the hybrid HVDC breaker independent of How it works current and voltage conditions in the The hybrid HVDC breaker consists of HVDC system. a main breaker branch made up of semiconductor switches and a bypass A cooling system is not required for the branch composed of a semiconductor- main breaker, as the semiconductors based load-commutation switch (LCS) are not exposed to the line current in series with a mechanical ultrafast during normal operation – then, the disconnector (UFD) ➔ 2. current will only flow through the bypass. The LCS opens proactively at a The main breaker path is separated into certain fault current level in order to several sections with individual arrester commutate the fault current, almost banks that are dimensioned for full instantaneously, into the main breaker. voltage- and current-breaking capability. Thereafter, the UFD opens in less than The LCS is dimensioned for a lower 2 ms to disconnect the load commuta- DC breakers should have negligible voltage and energy capability. After tion switch from the main breaker. After transmission losses and be easy to fault clearance, a disconnecting circuit the UFD is opened, the main circuit integrate into a converter station breaker interrupts the residual current breaker is ready for operation. design. Mechanical breakers have very and isolates the faulty line from the low losses, but developing a very fast HVDC system in order to protect the One IGBT for each current direction mechanical HVDC breaker is a chal- arrester banks from thermal overload. is sufficient for the LCS to fulfill the lenge. Semiconductor-based HVDC requirements of the voltage rating. The breakers, on the other hand, easily Each main breaker section contains transfer losses of the hybrid HVDC surmount the limitations of switching semiconductor stacks composed of breaker are thus significantly reduced speed and voltage, but generate high series-connected insulated-gate bipolar – to less than 0.01 percent of transmit- transfer losses. transistor (IGBT) DC breakers. Due to ted power. Parallel connection of IGBT the large di/dt stress during current modules increases the rated current of ABB’s hybrid HVDC breaker system [2] breaking, a mechanical design with low the hybrid HVDC breaker; series-con- overcomes these hurdles with a com-­ stray inductance has been adopted. nected, redundant IGBT positions bination of mechanical and semicon- Application of ABB StakPak IGBTs improve the LCS reliability. A three-by- ductor devices. It has an opening enables a compact stack design and three matrix of IGBT positions for each time of less than 5 ms, a few tens of ensures a stable short-circuit failure current direction was, therefore, chosen

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­64 ABB review special report The hybrid HVDC 4 Hybrid HVDC breaker test results showing fault current and voltage versus time breaker melds

reliable power Main breaker electronics opens

Main breaker ­already used in Voltage across current breaker

HVDC converter Load commutation stations and fast- switch (LCS) opens disconnecting gas-insulated 2 switchgear tech- 1 Start of fault 250 µs delay for 2 ms delay for Time nology. current LCS opening UFD opening (2 ms/div) for the base design. A minor cooling The purpose of the tests was to verify breaker will be premiered. The hybrid system is required due to the switch’s the switching performance of the power DC breaker will finally allow the long- continuous exposure to the line current. electronic parts and the opening speed held visions of HVDC grids spanning of the mechanical UFD. The test object Europe and other regions to become a The UFD opens at zero current with consisted of one 80 kV unidirectional reality. low-voltage stress and can, thus, be main breaker cell. The higher voltage realized as a disconnector with a rating is accomplished by the series lightweight and segmented contact connection of several main breaker cells. system ➔ 3. A similar series connection approach is also used to test HVDC Light and System validation and key compo- Classic valves. To verify reliable and nent testing safe operation, tests have also been Successful verification testing at device carried out with IGBTs that have deliber- and component level has proven that ately been made defective [4]. the system performs as required. The complete hybrid HVDC breaker has Benefits, markets and applications Jürgen Häfner been verified in a demonstrator setup at Fast, reliable and nearly zero-loss HVDC Reza Derakhshanfar ABB facilities. The diagram in ➔ 4 shows breakers and current limiters based on Peter Lundberg a breaking event with peak current of the hybrid HVDC breaker concept have ABB Power Systems, Grid Systems 8.5 kA and a 2 ms delay time for opening been verified at component and system Ludvika, Sweden the UFD in the branch parallel to the levels for HVDC voltages up to 320 kV [email protected] main breaker. Switching performance and rated currents of 2 kA. The next [email protected] of the UFD has been verified for 2,000 step is to test such breakers in a real [email protected] consecutive open and close operations, HVDC transmission line. An increase of including subsequent dielectric integrity voltage rating to accommodate 500 kV References tests. Other synthetic tests typical for HVDC systems by improving UFD [1] C.M. Franck, “HVDC Circuit Breakers: high-voltage circuit breakers have been insulation extends the range of possible A Review Identifying Future Research Needs,” IEEE Transactions on Power Delivery, vol. 26, performed, verifying the required per- applications of the hybrid HVDC breaker pp. 998–1007, April 2011. formance at full ratings. The maximum from cable-based DC grids to embed- [2] J. Häfner, B. Jacobson, “Proactive hybrid rated fault current of 8.5 kA is the limit ded HVDC links utilizing overhead lines. HVDC Breakers – A key innovation for reliable for the generation of semiconductors HVDC grids,” Cigré, Bologna, Paper 0264, 2011. used during initial testing. Application of The hybrid DC breaker is the key [3] M. Rahimo, et al., “The Bimode Insulated Gate bimode insulated-gate transistor (BiGT) technical element that finally makes a Transistor (BIGT), an ideal power semiconduc- devices allows for breaking currents true multiterminal DC grid with multiple tor for power electronics based DC Breaker exceeding 16 kA [3]. protection zones possible. In the applications,” Cigré, Paris, Paper B4-PS3, 2014. extension of existing point-to-point [4] R. Derakhshanfar, et al., “Hybrid HVDC systems and in the construction of new Breaker – A solution for future HVDC system,” HVDC grids will be where the hybrid DC Cigré, Paris, Paper B4-304, 2014.

Trend lines 65­ tubes were replaced by transistors as 1 Original Gotland converter firing control system based on vacuum tubes Fast and soon as they became available in the late 1950s, which greatly increased reliable reliability. The need for ever faster and higher- precision control systems for HVDC The MACH™ meant that ABB always adopted the latest and most advanced electronic control and pro- technologies as soon as they became tection system available. Microprocessors for HVDC In the 1970s, the microprocessor was introduced and ABB immediately (in 1973) adopted the Intel 8008 in thyristor monitoring systems. In 1975, HANS BJORKLUND – High-voltage the brand-new Intel 8080 was used direct current (HVDC) transmissions in ABB’s emergency power control have always differed from alternating system. current (AC) transmissions in that the conduction pattern of an HVDC The advent of microprocessors finally An HVDC control system can benefit converter is fully controllable. made it possible to build single board from a calculation capacity higher Indeed, this property is what pro- computer (SBC) systems that had than an SBC can provide, so from the vides many of the outstanding everything needed for one function early 1980s, solutions that employed features of HVDC transmission. (inputs, A/D converters, microproces- parallel-bus backplanes hosting To make sure that the HVDC valve sor and output circuitry) on one board. multiple processing boards began to conduction sequence is tightly HVDC protection is very different from appear. It was fully digital-converter adhered to and that the system is AC protection in that it has to be firing control running on multiproces- run within the foreseen operating much faster (sub-millisecond re- sors that made the world’s first fully envelope, a fast and reliable control sponse) and has to mix DC and AC redundant control system possible in and protection system is required. current and voltage measurements. Gotland 2 in 1983. And the better this system is, the better the HVDC transmission will DSP and operate. For this reason, ABB’s The need for ever faster and FPGA HVDC control and protection prod- In the 1990s, ucts have always been very quick higher-precision control sys- two new to exploit the very latest and best technologies technology. In fact, the story of tems for HVDC meant that appeared: HVDC control and protection sys- ABB always adopted the latest the digital tems over the past 60 years mirrors signal that of the main trends in computing and most advanced electronic processor technology. (DSP), with technologies as soon as they an instruction The modern era of HVDC transmission became available. set tailored began in 1954 when the island of for very fast Gotland was linked to the Swedish calculations mainland by an HVDC connector. SBCs are ideal for this. A 16-bit SBC (allowing control system cycle times At that time, AC systems still relied on that could implement all HVDC station below 100 µs) and the field program- electromechanical relays for protec- protection functions by just using mable gate array (FPGA), which tion and control, but the nature of different software, was introduced in opened up the possibility of imple- HVDC demanded that the Gotland 1983 for the Gotland 2 transmission menting larger-scale programmable HVDC link have a very different and link. A few years later, the SBC found logic in HVDC applications. much faster system. The best technol- large-scale use in the Itaipu project in ogy available was used: amplifiers Brazil, where several hundred were Combining circuit boards using these based on vacuum tubes – technology used to implement all protection technologies with the latest 32-bit unheard of in other areas of power functions in the HVDC converters. micro-processors on a fast parallel systems at that time ➔ 1. The vacuum multiprocessor backplane resulted in

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­66 ABB review special report 2 PS700, the latest main computer for MACH 3 Distributed I/O unit

the first-generation ABB MACH™ PCI Express bus Computer processing power will (modular advanced control for HVDC) The use of parallel backplane buses continue to increase in the years to control system, which was introduced involves many signals and complex come and this will bring further in 1991. The first installation using the connector arrangements. This can improvements in the capabilities of MACH system, a cable between introduce unreliability when data control and protection systems, and Norway and Denmark, was put into transfer speeds increase. Therefore, deliver many new and fascinating commercial operation in late 1993. the industry is moving to multiple applications. serial buses and the PCI bus has now PCI bus been replaced by the software-com- The interfaces used in the MACH When the high-speed PCI (peripheral patible PCI Express bus. ABB has system have been chosen very component interconnect) bus was used this opportunity to upgrade the carefully so that MACH can continue introduced, it allowed even faster MACH system, after 20 years, with a to evolve and remain the base for microprocessors to be used, thus new 64-bit multicore microprocessor ABB’s HVDC control and protection further improving the performance of unit and new multicore DSP units, all systems at least for the next 30 years. the control and protection system. connected by the PCI Express bus. Maybe it will even live to see the The PCI bus also allowed ABB to take This latest advance means that a Gotland HVDC link celebrate its advantage of DSP computing muscle control system can be built much centenary in 2054. and introduce, for the first time in the smaller, yet with 10 to 100 times the industry, floating-point DSP clusters. calculation capacity ➔ 2. Further, less When ABB introduced the second power is used, so fans are not generation of the MACH system in necessary – thus increasing reliability. 1999, these powerful control and There is backwards software compat- protection computers were combined ibility so that applications developed Hans Björklund with a revolutionary input/output (I/O) for earlier systems using ABB’s ABB Power Systems, Grid Systems system that was connected only by function block programming language, Ludvika, Sweden serial buses, even for the highest HiDraw, can be recompiled and run in [email protected] speed measurement signals. This was the newest systems. the first time a control and protection References system for a power system application I/O units [1] C.M. Franck, “HVDC Circuit Breakers: A had been built using solely serial The full assortment of well-proven Review Identifying Future Research Needs,” IEEE Transactions on Power Delivery, vol. 26, buses for all I/O needs (voltage and modular MACH I/O units is still pp. 998–1007, April 2011. current measurement, breaker trip and available, but, with the latest MACH [2] J. Häfner, B. Jacobson, “Proactive hybrid close operations, etc.). This resulted generation, ABB is also introducing a HVDC Breakers – A key innovation for reliable in an extremely flexible control and series of environmentally hardened I/O HVDC grids,” Cigré, Bologna, Paper 0264, 2011. protection architecture in which the units ➔ 3. These can be distributed [3] M. Rahimo, et al., “The Bimode Insulated location of the different components further afield and placed, for example, Gate Transistor (BIGT), an ideal power could be chosen much more freely in breaker junction boxes or trans- semiconductor for power electronics based than in a conventional system where formers. In this way, the traditional DC Breaker applications,” Cigré, Paris, Paper B4-PS3, 2014. all signals have to be brought to the copper cabling connecting the [4] R. Derakhshanfar, et al., “Hybrid HVDC various controllers and protection devices back to the control system is Breaker – A solution for future HVDC devices by discrete wiring. replaced by optical fibers. system,” Cigré, Paris, Paper B4-304, 2014.

Trend lines 67­ control and protection of converters, 1 Working with hardware in the HVDC grid simulation center lines and DC/AC grid interconnectivity HVDC must be understood in a fundamental way. To advance this understanding, grid ABB has constructed a real-time HVDC grid simulator with control and protec- tion hardware- and software-in-the- simulation loop [2] ➔ 1. ABB HVDC grid simulation center The HVDC grid simulation center is a state-of-the-art installation where ABB’s A new HVDC grid ability to meet market requirements and simulation center handle the challenges thrown down by DC grids are demonstrated. It forms brings deeper part of ABB’s HVDC response to the growing number of renewable energy understanding of sources coming onto the grid, to multiterminal integration of electric power markets and to the growing problem of power HVDC control system bottlenecks becoming more frequent as power systems are run and protection centers. HVDC, being the superior tech- closer to their thermal and electrical nology for transportation of bulk power stability limits. over long distances, is becoming a TOMAS LARSSON, MAGNUS CALLAVIK – major player in this new transmission Further, since the versatility, reliability It is predicted that the coming years infrastructure. In the long term, a super- and availability of a DC grid will help a will see an increase in the use of grid or overlay grid based on HVDC is customer to create a business case, electricity generated by sources considered to be a very feasible propo- the simulation center provides a forum remote from load centers and in- sition [1]. It makes sense to integrate where practical demonstrations that creased integration of electricity individual HVDC lines on the DC side of underline these advantages can take markets. High-voltage direct current a converter into a grid when the HVDC place – for example, by showing the (HVDC) technology is emerging from capabilities of being a relatively specialized technol- a hybrid DC ogy to becoming a central element of Since the versatility, reliability breaker. the future transmission assets neces- sary to make this happen in a timely and availability of a DC grid will A visitor to and efficient way. A supergrid or the ABB overlay grid based on HVDC is help a customer to create a HVDC grid considered to be feasible and also business case, the simulation simulation to be the most efficient technology center will to use for a future extended high-volt- center provides a forum where initially age electric network. However, the encounter the development will come in steps. As practical demonstrations that simulated the first building blocks of an HVDC underline these advantages environment grid are being planned now, there is of an operator already a demand for systems for can take place. that repre- control and protection of converters, sents ABB’s lines and DC/AC grid interconnectivity. proposal as To advance understanding in this field, density in the transmission network to what an operator would face in his ABB has constructed a real-time increases. Recent developments in daily work ➔ 2. The operator’s comput- HVDC grid simulator with control and voltage source converters (VSCs), cable ers collate and display information from protection hardware- and software-in- technologies and DC breakers mean the simulated power system and the-loop. that the time has arrived to plan for transmit orders from the operator to a such scenarios. real HVDC MACHTM control system. All New transmission assets are being parts of the control system in the HVDC planned and constructed to connect In order to master HVDC grids and to grid simulation center are identical to power markets and to bring power from ensure everything is handled in a safe their counterparts in real-life installa- remote renewable generators into load and efficient manner, the behavior, tions, so everything is operated in real

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­68 ABB review special report pensation. The rest of the system will 2 HVDC grid simulation center: a visitor’s view be intact after the fault clearance but for a short while, given that the DC voltage controlling station tripped, be without a common DC voltage control. In the interim, every converter has its own local functionality to control the DC voltage until the master controller has assigned a new DC voltage controlling station and calculated new optimal set points for the remaining stations.

Apart from demonstrating ABB’s performance and ideas in the context of a DC grid, another task of the ABB HVDC grid simulation center is to deliver results to ongoing ABB-internal research and development projects – for example, applications of the DC breaker in a power system. time and the operator experiences DC grid is combined with requirements As the spread of HVDC grids widens exactly the same as he would in a real for robust selective tripping involving in future years, the ABB HVDC grid control room. fast-rising fault currents. By having the simulation center will continue to real control system in the loop, confi- increase in sophistication and scope, Responses from the process – ie, the dence is gained that the protection in and continue to provide insight into HVDC converters and the AC and DC real life will secure the DC grid by HVDC protection and control for ABB power systems – are also obtained fast-tripping only parts that belong to and customers alike. in real time, but with one significant the faulty zone while keeping the difference to a field installation: In the healthy circuitry on line.

For an HVDC To advance this understanding, grid, ABB’s philosophy ABB has constructed a real- involves overlaying a time HVDC grid simulator master with control and protection controller in order to hardware- and software-in-the- optimize system loop. disposition. This function- simulation center they are simulated by ality too has been implemented in the a model running in a real-time digital HVDC grid simulation center. Besides simulator (RTDS). For the MACH control assisting the operator in finding an Tomas Larsson system, then, it is a real-world experi- optimal operation point of the DC grid, Magnus Callavik ence, but with one major advantage: the master controller also helps to ABB Power Systems, Grid Systems Because the high-voltage equipment restore the DC grid after a fault. A Västerås, Sweden is simulated, it can be stressed with typical case would be a DC fault in a [email protected] contingencies, faults and other excep- cable attached to a converter that is [email protected] tions that, in some cases, would be acting as a DC voltage controller. The totally impossible to perform in a real protection system would, after the fault, field installation. This allows verification first clear the fault by disconnecting the References of responses from troublesome cases cable. The isolated converter could then [1] CIGRE Technical Brochure 533, Paris, 2013. [2] P. Mitra, T. Larsson, “ABB’s HVDC Grid that are run in offline simulations. This stay connected on the AC side and, if Simulation Center – a powerful tool for is of great interest for time-critical required, work as a Statcom, eg, SVC real-time research of DC grids,” EWEA, processes, such as when a fault in the Light, providing reactive power com- Barcelona, Spain, March 2014.

Trend lines 69­ Gas- 1 Examples of DC GIS components insulated HVDC switch- gear Flexible and compact power routing 1a DC GIS surge arrester 1b Gas-insulated disconnector and earthing switch

PER SKARBY – Gas-insulated As in AC power systems, DC GIS switchgear (GIS) is much more technology spans a number of It is anticipated compact and requires far less switchgear components, eg, bus clearance than air-insulated switch- ducts, disconnect switches, earthing that DC GIS com- gear (AIS). Another advantage is the switches, and current and voltage ponents with rat- routing flexibility of the ducts measurement sensors ➔ 1. DC GIS compared with cables. GIS is now has two principal advantages: ings up to 500 kV replicating its AC success in the Installations can be made far more world of HVDC. compact than the AIS equivalent and DC will be devel- they have a significantly lower sensitivity to ambient factors. oped and offered to the market in The most obvious cost-saving potential can be found on offshore the near future. converter platforms where the air DC GIS has two clearance required for AIS would lead connection with the facility of cross- principal advan- to a large and heavy offshore struc- border trading ➔ 2. This increases the ture. By using DC GIS, where the live utilization of the cables and the tages: Installa- parts are encapsulated in a pressur- security of supply, and can provide ized and grounded enclosure, the redundancy of the wind park transfer tions can be need for air clearance around the capacity in case of capacity reduction made far more components is completely eliminated at one of the receiving ends. and the volumetric space of the compact than the switchgear component can be HVDC installations on shore may also drastically reduced, typically by 70 to be drastically reduced in footprint and air-insulated 90 percent. Furthermore, the space building height by applying DC GIS to switchgear (AIS) savings obtained can accommodate selected components of the converter new functionality. An example of this station. equivalent and functionality is a multiterminal DC system (MTDC) – ie, a set of onshore Due to the combination of solid and they have a sig- or offshore marshalling points for gaseous insulation in GIS and the nificantly lower multiple cable connections. Using composite dielectric stress of both these, an offshore wind park with a direct and impulse voltages, special sensitivity to am- converter platform can be connected care needs to be taken in the design to different grids in different countries, of the insulating components. The bient factors. combining the utility of wind park grid support insulators inside the enclo-

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­70 ABB review special report ABB Review Special Report 2 DC GIS can provide compact grid 60 years of HVDC interconnections in multiterminal HVDC The most obvious July 2014 systems. cost-saving po- Editorial Council Claes Rytoft tential can be Chief Technology Officer Group R&D and Technology and Grid A Head of Technology Grid B found on offshore Power Systems division

Magnus Callavik Offshore converter plat- Technology Manager wind Grid Systems business unit farm forms where the Hans Johansson Head of HVDC Marketing and Sales air clearance Grid Systems business unit

HVDC converter Peter Lundberg and DC hub required for AIS Product Manager HVDC Light would lead to a Grid Systems business unit Erik Jansson Grid C Project Manager large and heavy Grid Systems business unit

Harmeet Bawa offshore structure. Head of Communications Power Products and Power Systems divisions

Sara Funke Head of Communications Grid Systems business unit sure, also known as GIS spacers, Sarah Stoeter Editor, ABB Review must be able to withstand not only the direct rated voltage but also transient Andreas Moglestue Chief Editor, ABB Review switching and lightning overvoltages of different polarities. All these factors Publisher ABB Review is published by ABB Group R&D and need to be considered in the design Technology. of the insulators. ABB Technology Ltd. ABB Review Affolternstrasse 44 A direct application of existing AC GIS CH-8050 Zurich components is typically not possible Switzerland [email protected] but these have been shown to be an excellent starting point in developing ABB Review is published four times a year in English, French, German, Spanish and Chinese. DC GIS components [1]. ABB Review is free of charge to those with an interest in ABB’s technology and objectives. For a ­sub­scription, please contact your nearest Based on the fact that well-estab- ABB representative or subscribe online at www.abb.com/abbreview lished AC GIS technology with voltage ratings up to 1.1 GV is available, it can Partial reprints or reproductions are permitted­ subject to full acknowledgement. ­Complete be anticipated that DC GIS compo- reprints require the publisher’s written consent. nents with ratings up to 500 kV DC will Publisher and copyright ©2014 be developed and offered to the ABB Technology Ltd. market in the near future. Zurich/Switzerland Printer Vorarlberger Verlagsanstalt GmbH AT-6850 Dornbirn/Austria

Layout DAVILLA AG Zurich/Switzerland

Per Skarby Disclaimer ABB Power Products, High Voltage Products The information contained herein reflects the views of the authors and is for informational purposes Zurich, Switzerland only. Readers should not act upon the information contained herein without seeking professional [email protected] advice. We make publications available with the understanding that the authors are not rendering technical or other professional advice or opinions Reference on specific facts or matters and assume no ­ [1] M. Mendik, et al., ”Long term performance liability whatsoever in connection with their use. verification of high-voltage DC GIS,” IEEE The companies of the ABB Group do not make any warranty or guarantee, or promise, expressed Transmission and Distribution Conference, or implied, concerning the content or accuracy of New Orleans, LA., April, 1999, vol. 2, the views expressed herein. pp. 484–488. ISSN: 1013-3119

www.abb.com/abbreview

Trend lines 71­ The corporate ABB technical journal

Electricity across borders? Certainly.

Demand for reliable power continues to rise and so does the quest to integrate clean renewable energies. These trends are encouraging countries to install cross- border power links to improve power security and balance demand and supply. ABB is leading the way with HVDC and HVDC Light® systems, enabling grid interconnec- tions and facilitating the transmission of electricity beyond borders through overhead lines, underground and underwater cables with minimal environmental impact. ABB’s HVDC Light technology is also being used for offshore links to wind farms and oil and gas platforms. www.abb.com/hvdc