From Mercury Arc to Hybrid Breaker 100 Years in Power Electronics

From mercury arc to hybrid breaker 100 years in power electronics

Andreas moglestue – 2013 marks the centenary of the by the desire to convert electricity from one frequency or involvement of ABB (and its forerunner companies) in power voltage level to another, without having to resort to moving electronics. Power electronics have become ubiquitous in a (and hence maintenance-intensive) mechanical parts. In the vast range of applications ranging from large HVDC (high early days, converters used mercury-arc rectifiers. These voltage direct current) installations – transmitting gigawatts were replaced by semiconductors from the 1950s and over thousands of kilometers – to everyday household 1960s. ABB has, throughout this 100 year timespan, been a devices. The development of power electronics was driven pioneer both of the technology itself and of its applications.

70 ABB review 2|13 1 A BBC contact converter from the 1950s (rated output 5,000 kW at 200 – 500 V)

be reversed (for DC to AC conversion), or Switching indeed used to convert between two dif- Whereas motor-generators feature a ferent frequencies of AC (several Euro- complete galvanic separation of the in- pean countries electrified their railways put and output, power electronics 2 at 16 ⁄3 Hz because this figure is pre achieve conversion by changing the cur- cisely one third of he early years of the commer- 50 Hz). The motor- cial use of electricity were generator setup Converters relying on me- marked by competition be- could even be ex- chanical switches remained a T tween different distribution panded for variable technologies. Edison’s DC vied with output applica- Tesla’s AC in a battle that the latter ulti- tions: For example maintenance liability. Power mately won. Whereas many applications the Ward-Leonard electronics set out to achieve are well suited to AC, there are also uses control uses the for which DC remains indispensable, excitation of the similar results but without thus requiring a means of converting AC DC generator to to DC. These applications include elec- vary its output volt- moving parts. trolysis (such as for the manufacture of age (permitting, for aluminum), battery charging, wireless example, a variable-speed drive). The rent path at discrete moments through communications and the electrification Scherbius machine permits the connec- externally-triggered switching actions. In of tramways, metros and some railways. tion of non-fully synchronized AC grids its simplest form, the principle of path These applications are still an important by allowing some phase slippage. switching can be observed in the DC part of ABB’s business today. The list motor, where a commutator reverses the has since been extended by the inclu- One valuable property of motor-genera- flow of current in the rotor winding in sion of newer applications such as data- tors is their ride-through resilience. Short function of its position (a simple DC to centers and HVDC transmission. power interruptions are bridged by the AC conversion). Another approach to a kinetic energy of the rotating mass. It is more general-purpose AC-conversion is From an early stage in the development of interesting to note that this energy-buff- the contact converter ➔ 1. This converter electrical systems, inventors were seek- ering functionality is mirrored by DC-link features fast-moving mechanical con- ing to convert AC to DC (rectification) and capacitors in today’s power-electronic tacts (effectively an H-bridge, but with DC to AC (inversion), as well as creating converters. mechanical switches rather than valves). variable output from fixed input (eg for One notable weakness was that, in con- variable-speed drives). Most power elec- The drawbacks of mechanical convert- trast to motor-generators, the waveform tronic applications today can still be ers include maintenance to moving parts, of the AC output was not a sine wave but placed in one of these three categories. such as lubrication and changing of car- a rectangle. This drawback was shared bon brushes, and the significant me- with many power-electronic circuits. As A precursor technology for AC to DC chanical forces affecting construction will be discussed later in this article, conversion was the motor-generator (a and anchoring. motor and generator fixed to a common Title picture drive shaft). The principle could equally A diode for traction applications (circa 1980)

From mercury arc to hybrid breaker 71 2 Power ranges of different switchable BBC mutator types (and contact converters) 3 An early mercury-arc valve enclosed in glass

Source: T. Wasserrab, Mutator Meeting at Baden in 1955, Introductory Lecture (proceedings published by BBC)

Mercury-arc valves the mercury cathode generated sufficient ASEA built the In the early years of the 19th century, the heat to sustain its continued emission of British chemist and inventor, Humphry electrons. The mercury-arc valve was world’s first perma- Davy, showed that an electric arc could born, and with it, power electronics. nent and commer- be created by passing current through two touching rods and then drawing In the following years, numerous inven- cial HVDC link, them apart. A plasma (gas of ionized par- tors and companies sought to improve ticles) forms in the gap between the elec- and commercialize this rectification prin- connecting the trodes and conducts current. The recom- ciple. Swedish island of bination of ionized particles in the plasma causes the emission of light, whereas the Manufacture of mercury-arc rectifiers Gotland to the heat generated by the current creates In 1908, the Hungarian engineer, Béla B. new ions (excitation) and sustains the Schäfer commenced research on mercu- mainland in 1954. arc. It is interesting to observe that the ry-arc valves for the Frankfurt based underlying physics of today’s semicon- company H&B (Hartmann & Braun). He ductor switches is equally concerned registered the first of many patents in overcoming this was to be one of the with the excitation, movement and re- 1909 (his first patent was a solution to major points of progress in the domain of combination of charge carriers. the challenge of embedding metal wires modern power electronics. to cross the glass wall without compro- In 1902, the American inventor, Peter mising air-tightness). H&B was the first Like motor-generators, converters rely- Cooper Hewitt, demonstrated a setup German company to supply a rectifier ing on mechanical switches remained a with one electrode made of mercury and (delivered to a Frankfurt foundry in 1911). maintenance liability. Power electronics the other of steel (carbon in later ver- As H&B’s main business lay in the manu- set out to achieve similar results but sions), enclosed in a glass bulb contain- facturing of scientific instruments and the without mechanical switches. ing mercury vapor. An interesting prop- company had little experience with in- erty was that current would conduct dustrial high-current applications, a joint Despite their apparent drawbacks, con- from the carbon to the mercury electrode venture was created with Swiss-based tact converters were able to fulfill current but not vice versa. Whereas the pool of BBC (Brown, Boveri & Cie) in 1913. The ratings beyond the scope of mercury-arc mercury readily emitted electrons once new company was called GELAG valves ➔ 2, and their production contin- the arc was ignited, the carbon anode (Gleichrichter AG) and based in Glarus, ued until the rise of silicon-based con- did not to any appreciable extent (in the Switzerland. GELAG was mainly converters. operating temperature range). The mer- cerned with research and development, cury vapor was ionized by the arc, and with BBC manufacturing the valves in the bombardment of mercury ions onto Baden, Switzerland. In 1916, BBC also

72 ABB review 2|13 4 Steel tank mercury-arc valves from BBC Semiconductivity was first recognized in silver sulfide by Michael Faraday in 1833, but the phenomenon was not fully understood until the early 1930s.

commenced production in Mannheim, Germany. German production was transferred to a larger factory at Lampertheim, Germany, in 1921 and joined by a second site that same year when BBC acquired the Berlin-based Gleichrichter 4a Type HG 5/6 valve (1923) (420 A, 650 kW, 4b A large mercury-arc valve in steel tank. GmbH (founded in 1919). 1,550 V and weighing 1,700 kg) as used for This 2,500 A, 2,000 kW example from the the Zweilütschinen electrification ➔ 5. 1950s weighed 1,235 kg and was more than BBC took over H&B’s stake in GELAG in 3 m tall. the 1920s, and finally dissolved the latter in 1939, absorbing its activities into the 5 Electrification of Bernese Oberland railway parent company. Later, H&B also became part of ABB’s heritage: The company was acquired by Elsag Bailey in 1995, which itself became part of ABB in 1999.

Schäfer left GELAG in 1921 and started his own consultancy. In 1927 he sold valve designs to ASEA (Allmänna Svens- ka Elektriska Aktiebolaget) for production in Ludvika, Sweden. Schäfer’s ex- pertise thus flowed into products of three of ABB’s predecessor companies.

Valve design and applications Due to the low thermal conductivity of glass, the power capability of a valve is restricted by its surface area ➔ 3. As power ratings increased, steel tanks The Bernese Oberland railway, in the Jungfrau The photograph shows the converter station in (with isolated electrodes) were adopted region of the Swiss Alps, was electrified by 1924 with in the foreground the two main instead ➔ 4. The market for mercury-arc BBC using 1,550 V DC in 1913. Rectification 220 kW motor-generators behind them the two valves boomed, and with it BBC’s pro- was performed by motor-generators, with the auxiliary 48 kW generators with controllable DC supply being supported by a battery. In excitation, and in the background the single duction ➔ 5 – 6. The company assumed a order to demonstrate its mercury-arc rectifier 650 kW mercury-arc rectifier, showing their leading position in the development of technology, BBC added such an installation in much reduced spatial requirements. the technology. 1920, with the rectifier working in parallel to the motor-generators. The demonstration Source: The mercury arc rectifier plant of the impressed the railway with its high efficiency Zweilütschinen substation of the Bernese Oberland A simple rectifier circuit is shown in ➔ 7. and reliability, remaining in service for 2¼ years. Railway. Brown Boveri Review, October 1925, page 214. It is equivalent to an H-bridge in which It was replaced by a permanent installation in a single enclosure with six anodes 1923. performs the function of six discrete diodes.

From mercury arc to hybrid breaker 73 6 The production of mutators was a rapidly 7 Mutator for rectification of three-phase AC growing business for BBC.

R S T AC

Anode

Cathode

DC + –

Whereas operation of such a valve could It was ASEA, however, that built the that an atom of the substrate material be sustained if the operating tempera- world’s first permanent and commercial would otherwise occupy. If the inserted ture was maintained within the limits and HVDC link, connecting the Swedish atoms have more electrons in their outer the arc was not permitted to fully extin- island of Gotland to the mainland in band than the host material (n-type), the guish, it could not start-up unaided when 1954. “spare” electrons are free to move no plasma was present. A starting elec- through the crystal and so increase its trode (to which a high voltage pulse was The manufacture of mercury-arc rectifi- conductivity. If the inserted atoms have applied) was thus provided to create the ers continued until the mid 1960s ➔ 9. fewer electrons in their outer band initial arc. The ability to trigger conduc- Mercury valves were finally replaced by (p-type), this creates so-called holes. tion at an arbitrary point in time had obvi- another revolution in power electronics: Electrons from neighboring atoms are ous potential for selective switching (the semiconductors. Advantages of semi- able to occupy these positions, which in valves described in this article so far conductors included greater power den- effect leads to the holes themselves hav- were all diodes). Development of such sity and speeds, lower weight and losses ing mobility. Holes thus behave like posi- switchable valves commenced in 1930, as well as avoiding the toxic aspects of tive charge carriers and also increase enabling phase-fired controls (these handling mercury. conductivity. valves fulfilled the same functionality that is today performed by thyristors – they Semiconductors A simple example of a semiconductor can be switched on arbitrarily but must The elements of the periodic table are device is a diode. A p-zone adjoins an wait for the current to reach zero generally divided into metals and non- n-zone on the same crystal. Current can to extinguish). By connecting them in an metals. In their pure form, metals con- flow from the p- to the n-zone (ie, in the H-bridge, a line-commutated inverter duct electricity, whereas nonmetals p-zone holes flow towards the p-n junc- can be made. As the term “rectifier” be- (mostly) do not. There is however an in- tion, in the n-zone electrons flow towards came increasingly incorrect in view of teresting group of nonmetals that display the junction, with the two types of carrier such new applications, in 1934 BBC be- intermediate levels of conductivity. These recombining at the junction). If a reverse gan referring to its valves collectively as are the semiconductor materials, most voltage is applied, charge carriers are “mutators”. notably germanium and silicon. Some depleted from the junction area and con- hybrid crystals such as gallium arsenide duction ceases. With both rectifier and converter func- and silicon carbide also have semicon- tionality now feasible, BBC built a tem- ductor properties. In order to create switchable valves, a porary demonstration line for the 1939 method was required to externally trigger Swiss National Exhibition and Trade Semiconductivity was first recognized in conductivity. The first transistor was cre- Show. The 500 kW, 50 kV DC link had a silver sulfide by Michael Faraday in 1833, ated by Bell Laboratories in 1947. It used converter station at either end and trans- but the phenomenon was not fully under- an electric field to control the availability mitted electricity 25 km from Wettingen stood until the early 1930s when the of charge carriers in a germanium crys- to the company’s exhibition pavilion in band theory of conduction emerged. tal, meaning that the current through it Zürich using a single pole cable ➔ 8 (the was determined by a control voltage. return path being by earth conduction). To raise the conductivity of semiconduc- This link was a precursor of today’s tor materials, impurities are selectively The invention of the transistor kicked off HVDC technology. inserted into the crystal. These atoms a rapid and highly visible development occupy positions in the crystal lattice culminating in the remarkable revolution

74 ABB review 2|13 8 At the 1939 Swiss National Exhibition in Zürich, BBC demonstrated DC transmission using 9 Milsestones of ABB’s 100 years in power mercury-arc converters. electronics

1913 BBC commences production of mercury-arc rectifiers in Baden 1915 BBC supplies stationary rectifiers to Limmattal Strassenbahn (tramway in Zürich area) 1921 Production commences in Lampertheim, Germany (BBC) 1924 Switching theory by Dällenbach and Gerecke published (BBC) 1928 ASEA commences production of mercury-arc rectifiers in Ludvika, Sweden 1938 BBC (Mannheim) equips locomotive with rectifier (experimental 50 Hz electrification in Germany) 1939 BBC demonstrates experimental DC transmission Wettingen – Zürich ➔ 8 1954 First BBC germanium diode 1954 First commercial HVDC, Gotland link (ASEA) 1960 BBC’s first thyristor 1961 HVDC link between Britain and France under English Channel (ASEA) in communications and data processing, blocking voltage and temperature. It was 1964 First BBC locomotive with silicon whose fruits (and ongoing develop- soon displaced by silicon. diode rectifier (Re 4/4 for BLS), ments) are highly visible today. Maybe Switzerland less obvious but equally spectacular is Thyristor 1967 First ASEA thyristor rectifier locomotive another semiconductor revolution that Transistor applications in analog amplifi- (Rc for Swedish Railways) occurred in parallel in the domain of ers (such as in radios and telecommuni- 1970 Pacific Intertie, HVDC linking Celilo power electronics: Today electricity can cations) are well known. However, the (Oregon) to Sylmar (Southern California) be transformed, controlled and convert- demands of power electronics are differ- – the last major project to use mercury-arc valves ed in ways which only some decades ent: Switches should ideally either be on ago would not have been considered or off, with the transition period being 1971 Semiconductor manufacturing at Lampertheim commences (BBC) possible. For example today’s ubiqui- kept as short as possible. This is be- tous data and communications devices cause the losses in the device, and 1973 BBC opens research center at Dättwil, Switzerland and their highly integrated microproces- hence the heat generated, are the prod- sor chips would be of little use without uct of the current and the voltage, and 1979 HVDC link Cabora Bassa – Johannesburg (BBC in collaboration power-electronic circuits delivering their so either one or the other must be kept with AEG and Siemens) power, charging their batteries and as close to zero as possible – both in the 1981 Semiconductor manufacturing at keeping the datacenters and communi- interests of energy efficiency and to pre- Lenzburg, Switzerland, commences (BBC) cations links running without which so- vent thermal damage to the device. 1984 HVDC link Itaipu – Sao Paolo (ASEA) cial networks and other online services could not function. Similarly, today’s An early switchable power semiconduc- 1987 First BBC locomotives to use GTO converters (for BT and SZU, Switzerland) boom in renewable energy and the re- tor was the thyristor, whose principle sultant reduction of emissions would not was proposed by William Shockley in 1988 Merger of BBC and ASEA to form ABB be possible without power-electronic 1950. A thyristor is similar to the p-n 1993 Development work for BiMOS commences converters assuring reliable and afford- diode described previously, but with ad- 1996 IGCT production commences able grid connectivity. ditional layers inserted between the out- 1998 BiMOS line opens in Lenzburg er p- and n-zones. These layers normally 2004 Three-gorges HVDC, China It took many decades of development to prevent conduction, but the injection of 2010 Acquisition of Polovodicˇe, make this feasible. Both BBC and ASEA current at a third contact (called the gate) Czech Republic commenced semiconductor develop- floods this area with charge carriers, en- 2010 New semiconductor factory in Lenzburg ment in circa 1954, with BBC’s first recti- abling current to flow if a forward voltage 2012 BIGT platform fier diodes (rated 100 V, 100 A) coming exists between anode and cathode. 2012 ABB announces hybrid breaker onto the market in 1956. These and Once triggered, the replenishment of 2013 Work begins on new semiconductor other early semiconductors were made charge carriers is self-sustaining, mean- reasearch facility in Dättwil of germanium 1, but the material was 2013 ABB celebrates 100 years in found to be unsuitable for power appli- Footnote power electronics cations due to constraints in terms of 1 Some manufacturers used selenium.

From mercury arc to hybrid breaker 75 10 Development of switching power of the three major power 11 Lenzburg is the heart of ABB’s semiconductor activities. semiconductor device types The new BiMOS plant is the building on the right.

1,E+08

150 mm 125 mm 100 mm

Press pack IGCT 1,E+07 Insulated

GTO

Switching power (VA) 1,E+06 Thyristor

GTO/IGCT

IGBT

1,E+05 1960 1970 1980 1990 2000 2010 2020

Year

12 Semiconductor manufacturing in 13 Cross-section of a pressure Lenzburg contact device

In pressure contact modules, the load current enters through one surface d and leaves through the opposing surface. Low electrical and thermal resitances of the contacts are assured through high mechanical pressure on those surfaces.

d b e c

a Heat sink d Copper b CTE compensation (Mo) e Semiconductor c Housing (ceramic)

ing the trigger current can be removed. it on. The ability to produce devices that ment activities and pilot production, but Conduction does not cease until the cur- were able to switch off without an artifi- also modest levels of production) was rent drops below a critical value. The de- cial zero crossing helped expand the transferred to Birr, Switzerland. These vice can thus be used for line-commutat- scope of application of power semicon- activities were moved to a new factory at ed inversion, but not for self-commutation ductors, enabling for example DC-DC Lenzburg , Switzerland, in 1981. (unless external components are used to converters and self-commutated invert- artificially create a zero-crossing of the ers. Furthermore, multiple switching Following the merger of ASEA and BBC voltage). cycles during an AC half-wave can make to form ABB in 1988, the Lampertheim the AC output less rectangular in shape. site was sold to IXYS, and ASEA’s factory Between 1960 and 1980, the maximum The width of current pulses is varied to at Västerås, Sweden, was closed, with blocking voltage and power handling per modulate the desired waveform, hence all production being concentrated at device increased in a roughly linear fash- reducing harmonics. Lenzburg. ASEA’s strength lay in thyris- ion, from about zero in 1960 to 6,000 V tors and rectifier components with nega- and 600 kW in 1980 ➔ 10. Semiconductor production tive bevel design, whereas BBC’s BBC’s early semiconductor production strength lay in diodes, GTOs and thyris- GTO was at Ennetbaden, Switzerland. BBC tors. Although there was some overlap, Production of GTOs commenced in the established a modern semiconductor the different ranges were largely comple- mid 1980s. A GTO (gate turn-off thyris- factory at Lampertheim in the late 1960s, mentary. tor) is a thyristor that can be turned off and sought to concentrate all manufac- by applying a current to the gate in the turing there. However, some of the pro- reverse direction to that required to turn duction at Ennetbaden (mostly develop-

76 ABB review 2|13 14 GTOs of different diameters 15 GTOs mounted in a stack with gate units and cooling elements

16 Cross-section of a Hi-Pak IGBT module 17 Soldering of contacts to IGBT chips

In insulated housing modules, the semiconductor f is galvanically isolated from the heat sink c . Electrical contacts within the module are provided by bonding wires.

b g f d e

a Power and control d Ceramic (usually AlN) connections e Base plate (usually AlSiC) b Bonding wire f Semiconductor c Heat sink g Housing

At the time, semiconductor manufacturing IGBT of faster operation, permitting higher was not recognized as a business in its Nilarp’s greatest achievement was the switching frequencies. own right within ABB, but was perceived new BiMOS factory that opened in Lenz- as an activity for the support of other burg in 1998, specifically tailored for the IGCT product areas, such as drives or HVDC. manufacture of IGBTs (insulated gate To also make hard-switching capability Product development and investment was bipolar transistor). The introduction of available for higher power classes, ABB thus largely driven by the needs of ABB’s IGBTs represented a fresh leap in terms pioneered the IGCT (integrated gate- other businesses. All this changed rapidly of manufacturing complexity and the commutated thyristor) in the mid 1990s. when Anders Nilarp was appointed to lead technologies involved, but at the same Developed on the basis of GTO technol- ABB’s semiconductor activities. He trans- time also represented a step change in ogy, the new device was capable of much formed the business into a standalone en- device performance and capability. An faster switching than conventional GTOs. terprise, directly competing with other IGBT is a power semiconductor con- In this it was supported by an integrated semiconductor manufacturers on the out- trolled by voltage rather than current – low-inductance gate unit. This develop- side market. His charismatic style also thus also reducing the power and space ment was remarkable as it occurred at a transformed the workings of the Lenzburg requirements of the gate units (the exter- time that other manufacturers were with- factory as he continuously sought to moti- nal drive units that turn the switch on or drawing from GTO development, assum- vate and empower employees. In 1995, off via the gate), permitting more coming the technology had no future. the Lenzburg factory was a finalist in the pact and lightweight converters. IGBTs European Quality Award, and in 1996 it are also more inherently stable than ABB further strengthened its market was awarded the “Supplier of the Year GTOs, reducing the need for protective presence with the acquisition of the Award” by General Electric. circuitry, and are furthermore capable Czech semiconductor company, Polo

From mercury arc to hybrid breaker 77 18 Hi-Pak IGBT modules 19 StakPak IGBT modules

vodicˇe, in 2010. This gave ABB a second Contact wires are soldered directly onto manufacturing site (in Prague). At the the chips ➔ 16 – 18, eliminating the need same time, capacity at Lenzburg was for pressure-mounting in stacks and thus again increased with the construction of simplifying converter assembly while re- a further factory ➔ 11. ducing weight and space requirements and making it easier to exchange indi- Manufacturing and design vidual modules during maintenance. The manufacture of semiconductors is a However, IGBTs are also provided in highly sensitive process. The silicon base press-pack housing for applications re- material must be of a very high quality quiring such assemblies (StakPaks) such with extremely low levels of contamina- as for HVDC ➔ 19. tion. The insertion of the necessary p- or n-materials (doping) is a very precise BIGT process requiring the correct duration The latest development of the IGBT fam- and temperature. Manufacturing thus ily is the BIGT (bimode insulated-gate occurs in so-called clean-rooms charac- transistor), an IGBT that integrates the terized by a carefully controlled atmo- reverse-conducting diode in a highly sphere to keep contamination levels as space saving manner (the BIGT is dis- low as possible ➔ 12. cussed more fully on pages 19 – 23 of this issue of ABB Review). The BIGT is an Most larger semiconductors (including important component of one of ABB’s thyristor, GTO and IGCT) feature a so- most significant announcements of re- called free-floating housing. The silicon cent decades: the hybrid circuit breaker Andreas Moglestue wafer is sealed inside a ceramic shell (discussed on pages 6 – 13). ABB Review with copper contacts ➔ 13 – 14. The con- Zurich, Switzerland tacts must be pressed against the silicon The hybrid circuit breaker is a further [email protected] by a specified external force to assure example of semiconductors finding their optimal electric and thermal conductivity. way into entirely new uses. The range Further reading To assure this force, devices are mount- of applications of power electronics is H. R. Zeller, The winning chips: History of power ed in stacks ➔ 15, with cooling units usu- growing in ways that only some years semiconductors at ABB, ABB Review 3/2008, ally interspersed in the same stack. ago would have seemed unimaginable. pages 72–78 Devices are designed to short-circuit S. Linder, Power semiconductors: Part one, Basics and applications, ABB Review 4/2006, pages 34–39 Contributions to this article by Björn Backlund, when they fail. A typical stack with series- S. Linder, Power semiconductors: Part two, Jürgen Bernauer, Christoph Holtmann, Norbert connected devices will thus have some Housing technology and future developments, Lang, Munaf Rahimo, Marco Rossinelli and Adriaan ABB Review 1/2007, pages 62–66 redundancy, permitting normal operation Welleman are gratefully acknowledged. to continue until the next scheduled E. Anwand, A. Kloss, 75 Jahre BBC-Leistungs elektronik, Elektroniker Nr. 11/1988 maintenance intervention. R. Wetzel, Die Geschichte des Quecksilberdampf gleichrichters bei BBC Deutschland 1913–1963, The introduction of the IGBT marked a PhD thesis University of Stuttgart, 2001 departure from this practice. Rather than L. Haglöf, P. Danfors, HVDC Veterans Presentation, Visby Gotland, 2004. using large area-wafers, IGBT modules Schiesser, 25 Jahre Brown Boveri Mutator, feature larger numbers of small chips. Brown Boveri Mitteilungen 5/6 1938

78 ABB review 2|13