Grid Code Requirements for Diesel and Gas Gensets Solutions for Compliance with New Guidelines

White Paper — GRID CODE

Grid Code Requirements for Diesel and Gas Gensets Solutions for compliance with new Guidelines

The top priority in power production is keeping the grid stable. Power production plants feeding electricity into the grid must therefore follow clearly defined guidelines.

Renewable sources of energy with fluctuating output, such as wind and solar power, are becoming increasingly competitive compared with conventional energy producers. As a result, these sources will be supplying a greater share to the world‘s power grids. Against this backdrop, the challenge facing operators is to keep the grid stable and secure the supply of utility power. To deal with this, grid operators define standards in the form of so-called “Grid Codes” which all energy producers intending to supply the grid are obliged to follow. MTU Onsite Energy gas cogeneration systems and diesel gensets are playing a perceptibly more significant role in the global energy mix. They form a key component in driving the energy transition being highly efficient and, in marked contrast to renewable sources, available at any time to deliver controlled power pre- cisely when it is needed most. What’s more, they already meet existing requirements for by generating plants, such as the German BDEW guideline for medium-voltage networks, to Marcus Mücke supply power grids in normal operation and in case of disruption. Team Lead Automation Development MTU Onsite Energy GmbH Augsburg Michael Kreißl Manager Grid Compliance MTU Onsite Energy GmbH Augsburg Change of energy production Gross electrical energy production in Germany from 1990 - 20151

The power sector has been undergoing one of 100% Other the biggest transformations since its early days. The world is moving from high carbon-footprint Renewable: Waste energy production centered strongly on fos- Renewable: sil fuels such as coal, lignite and oil towards 80% Solar PV renewables such as solar power, wind power Renewable: Bio Mass and hydro power. However, this transforma- Renewable: Hydro Power tion features more than just the rapid increase 60% in the use of renewables: some countries are Renewable: Wind Offshore seeing growth in distributed power produc- Renewable: tion featuring smaller combustion engines to Wind Onshore 40% boost the overall efficiency of energy use. Oil

Both changes may be observed strongly in Natural Gas Germany, not simply because investment in 20% Coal renewable energies is becoming a cheaper, more competitive proposition, but primarily because Nuclear of the German Renewable Energies Act (“EEG”) Lignite which, in the year 2000, began to promote the 0% growth of renewable energy sources by offering 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 subsidies for this kind of power generation.

Until 2000, the main renewable energy power in 2010-2012, growth has been a mere of renewables of grid and distributed power source was hydro power. By 1996, wind 1.9 GW and 1.5 GW in the last two years. producers was quite low, the main rule speci- power was making itself felt, and has been fied for these power generators was that, in increasing steadily since 2000. The balance The growth of the renewables is set to con- the event of any malfunction, they had to trip of import and export of electrical energy was tinue. Improved competitiveness due to cost their systems within a very short time (e.g. stable up to 2004. Since then, the amount reductions will be one reason, but another is VDEW, “Generators in the low voltage grid”). of electrical energy exported by Germany political effort to achieve greener power genera- But tripping these renewables in response has been growing and, in 2015, reached tion. Germany is targeting 35% renewables by to a grid failure when most generation is 50 TWh of a total production of 652 TWh. 2020. Given the 30% seen in 2015, this goal being powered by renewables will produce is capable of being reached even earlier than a complete system blackout, as the UCTE Renewable energies constituted 30% of planned. The subsequent steps are at least network can only absorb a power drop of 3 German electrical power generation in 2015. 40% by 2030, 55% by 2040 and 80% by 2050. GW. Therefore, it is necessary for renewable At 13.3%, the largest proportion of renewa- However, Germany is not alone on this journey. and distributed power producers to deliver bles is wind, followed by biomass (7.7%) and In March 2007, the Council of Ministers of the system services to the grid in the same man- solar power (5.9%). Hydro power amounted European Union decided to achieve a 20% share ner as the large conventional power plants. to just 3%. In view of the current “EEG” of renewables (20% of total energy consumption: Since 2009, this requirement has been added Renewable Energies Act and the growth power, heating and transportation) by 2020. to the German BDEW MV Directive (German in renewables over the last two years, the European directive 2009/28/EC has distributed medium voltage grid technical directive enti- share of wind power is set to rise strongly. this European target down to national targets. tled “Generating Plants Connected to the Medium-Voltage Network”, further abbrevi- New wind power installations totalled Seen historically, big conventional power ated as BDEW Directive). Other countries also 4.3 GW in 2014 and approx. 3.6 GW in plants have delivered all system services nec- already have national directives to keep their 2015. The best years for solar power are essary to ensure the stability of the system at grids stable, e.g. CEI 016 in Italy and G59 in now behind us. From 7-8 GW of additional a very high level. In the past, when the share the UK. To harmonize local requirements at European level, Network Code Requirements for Generators (NC RfG) has been introduced. NC RfG sets a frame of requirements for Germany‘s electricity generation mix 2015 the implementation of national directives. Share of Germany’s gross electric power generation - Renewables reach 30%2 Grid Codes Natural gas The main purpose of grid codes is to specify the rules for delivery of system services by Nuclear Others Renewables all power generators, including renewable 30% = 194 billion kWh 8,8% and decentralized power generation units. 4,9% The requirements of these grid codes can Fossile 14,1% 13,3% Wind roughly be broken down into four groups: 453 billion kWh • Power quality — Harmonics / Interharmonics /Flicker — Switching operations 24% 647 30% • Static grid support Lignite billion kWh 7,7% — Frequency and active power control Bio Mass — Voltage and reactive power control • Dynamic grid support 5,9% • Grid code compliance 18,2% Solar PV 3% Power quality With the increase of numerous types of Coal Hydro Power power electronics, it was necessary to specify Data: German Association of Energy and Water (as of December 21, 2015) boundaries to keep grid repercussions of renewable and distributed power within an accept-

european power system Schematic map of UCTE area split into three areas as a result of a major grid failure3

Area 1 under-frequency

Area 2 over-frequency

Area 3 under-frequency

able range. Power quality is not a system ing in reactive power, decentralized power north of Germany and a power flow of 10 service. This part of regulation originates generation units have the ability to adjust GW from north to south. The split produced mainly from the power electronics of con- voltage at the point of common coupling. one area with too much power production verters of wind turbines and solar parks. and over-frequency, and two areas with less The demands of the grid codes include regu- // FREQUENCY AND ACTIVE POWER power production and under-frequency. lations for harmonics, flickers and switch- In the past, gensets have been allowed to In the absence of adjusted frequency require- ing operations. These topics are not critical disconnect from the grid in Germany and in ments for renewable and distributed power for gensets as these are typically equipped many other countries where frequency devi- producers, a situation as described above with a directly coupled synchronous gen- ated outside very tight limits (e.g. 49.00Hz would be even more dangerous today and erator. NC RfG does not specify power quality and 51.00Hz). This is no problem during nor- would not be manageable. By virtue of the requirements. But these requirements are mal operation. The UCTE network frequency formerly fixed frequency thresholds, all usually built into the national directives. is adjusted by primary control in a region of renewable and distributed power producers +/- 200mHz. The critical issue is maintaining in one area would disconnect at the same STATIC GRID SUPPOPRT the network during a malfunction scenario. time. If a huge amount of power generation This part describes behavior during normal Such a situation occurred in November were to trip out all at once, a power out- grid operation for purposes of stabilizing the 2006 when the European power system was age in these areas would be the result. grid. Key factors for normal grid operation divided into three different frequency areas. are frequency and voltage stability. Another To avoid such a sudden drop, grid code rules requirement is reactive power, which has a At this point, prior to the incident, there have been developed for the distributed major impact on voltage stability. When feed- was huge production of wind energy in the power producers. Firstly, the frequency

P-Q diagram of a synchronous Generator

PF -0,8 PF -0,9 kWe / rated kVA PF -0,7 0,95 0,8 PF 0,7 U max

Un U min 0,8 PF -0,6 PF 0,6

0,6 PF -0,5 PF 0,5

PF -0,4 PF 0,4 0,4

PF -0,3 PF 0,3

PF -0,2 0,2 PF 0,2

PF -0,1 PF 0,1

-1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8 1 kVAr / rated kVA

ranges have been widened, typically to and above the threshold. The droop setting voltage and reactive power. Nowadays, a range of 47.5 Hz to 51.5 Hz. Secondly, must be adjustable between 2% and 12%. many conventional power plants are being special features have been designed LFSM-U in NC RfG is only required for closed down, and a substantial amount of to deal with over-frequency (LFSM-O) bigger power modules (type C and D). In production takes place within distribu- and under- frequency (LFSM-U). this case, the power generating unit has to tion and on the low voltage network. In increase power if the frequency is below a this case, the voltage gradient will no General requirements in NC RfG demand threshold, and if it is technically feasible for longer be specified, and a distributed different frequency ranges between 47.0 Hz the power generating unit to increase power. power plant can lift the voltage at its point and 51.5 Hz for different areas of Europe of common coupling. If there are no rules (Continental Europe, Nordic, Great Britain, // VOLTAGE AND REACTIVE POWER for controlling the voltage or to feed in Ireland and Northern Ireland and the Baltics). With the rise of renewable and distrib- reactive power, it could result in unaccep- uted power generation, the direction of table figures in some parts of the grid. Another requirement is the LFSM-O mode. the power flow has changed. Formerly, Where a specific frequency threshold the power flow went from the transmis- In the past, conventional power plants were (between 50.2Hz and 50.5Hz) has been sion network to the distribution network also responsible for delivering reactive reached, the power producer has to reduce its and thence to the consumer. The systems’ power. Nowadays, renewable and distributed actual active power under a droop function voltage gradient was specified, and con- power generation has to deliver the reactive to avoid a further increase in frequency over ventional power plants were able to control power previously supplied by the large power

plants which have since been shut down. with reactive current to maintain voltage. protection systems. Another reason for the Reactive power is a very powerful tool for The dynamic grid support for a voltage dip is necessity of reactive power during malfunc- adjusting voltage. If a synchronous machine called “Low-Voltage Ride-Through” (LVRT). tions is to maintain grid voltage in order to is in under-excited mode, it decreases voltage avoid disconnection of further power plants. In at the point of common coupling. If a synchro- In most cases, the reasons for such voltage Germany, the goal is to protect the transmis- nous machine is over-excited, it is possible to dips are the fault rectification events on the sion system and, as a result, the European grid. increase voltage at the point of coupling. With transmission grid. In the case of a short-circuit A potential partial breakdown of the distribu- the development of intelligent rules regard- on the transmission grid, the affected area of tion system cannot be entirely prevented. ing voltage and reactive power control, it is the grid will be isolated within a few hundred also possible to avoid further investment in milliseconds. As long as the short-circuit is Dynamic grid support is very challenging for grids. With these rules, it is even possible connected to the grid, voltage within the trans- gensets with synchronous generators. In case

to connect more distributed power to a con- mission and distribution grid drops (falls). In of a small voltage dip (e.g. down to 70% Un), the nection point in existing networks without the past, all renewable and distributed power full mechanical power of the engine could be reactive power management. NC RfG does generators tripped and disconnected from the transferred to the grid. The result of the volt- not define the reactive power capability for grid when such an incident occurred. With age drop is an equivalent increase in current. Type B synchronous power generation mod- today’s energy mix, such action is no longer However, during a major voltage dip, the electri- ules. In this case, the system operator has acceptable because of the reduction in the cal power can no longer be transmitted to the

the right to specify the capability of a syn- number of conventional power plants. During grid. If voltage drops to 30% Un, the electrical chronous machine (NC RfG Article 17/1 b). a malfunction, the power plants have to feed power will also drop to approx. 30%. During in reactive power and deliver short-circuit the first moment of failure, the engine will The BDEW Directive outlines four different current. Without this short-circuit current, deliver the same torque as before the incident. methods for controlling reactive power: rapid isolation of the malfunction is not fea- The reaction time of the engine depends on the 1) A fixed active factor cosϕ or sible; reactive power is needed to trigger the gas volume between the throttle valve and the 2) An active factor cosϕ (P) or 3) A fixed reactive power in MVar or 4) A reactive power/voltage characteristic Q(U). 4,5 In the BDEW Directive, the demand for reac- lvrt curves tive power capability is currently specified as being in a range between 0.95 under-excited and 0.95 over-excited. However, system max LVRT profile power park modules max LVRT profile synchronous power generating modules operators want to widen this span to between U 0.90 under-excited and 0.90 over-excited. In n current LVRT profile synchronous power generating modules Germany 1 particular, 0.90 under- excited at undervolt- age is very challenging and usually implies oversizing of generators, resulting in higher 0,85 installation costs and lower efficiency. 0,7 In the BDEW Directive, the normal voltage operating range for a genset is specified

as being between 0.9 Un and 1.10 Un. In NC RfG, there is no specification for the voltage operating range of Type B units. 0,3 Dynamic Grid Support The requirement for dynamic grid support is 0,05 the ability to withstand sudden voltage dips. The gensets must ride through grid failures in 0 0,2 0,5 1 1,5 2 3 t in s a controlled manner and support the network

cylinder inlet, and on the responsiveness of the is also the case with the BDEW Directive. engine controller. Depending on engine size, With NC RfG, the separation in FRT requirements time spans greater than 100ms are realistic. between synchronous power generating mod- If the torque is constant and the active power ules and power park modules will also become decreases, engine speed will rise. The moment standard in other national European regulations. the voltage is recovering, the generator is under- excited, the load angle rises and can reach the GRID CODE COMPLIANCE transient stability limit for the synchronous OF MTU SOLUTIONS machine. In this case, the outcome would be Where a grid code is in force, proof of compli- a pole slip which could result in mechani- ance is required by the grid operator. This cal damage to the synchronous machine. procedure differs from country to country. Possible requirements of the procedure are: The situation is more critical, the weaker the manufacturer declarations, plant owner dec- electrical connection, the faster the speed larations, manufacturer unit test, plant test, increases, the deeper the duration and the models for static and/or dynamic behavior longer the malfunction. The most critical situ- and studies of static and/or dynamic behavior.

ation is a voltage dip down to 0% Un. In such It is also possible that only parts of compli- a scenario, no coupling to the network is left ance or full compliance must be proven via and the speed would increase very quickly. certificates issued by an authorized certifier.

A common presentation for an LVRT require- The proof of compliance to NC RfG requires ment is the visualization of the lower an operational notification by the power gen- required limit of a voltage-against-time pro- erating facility owner to the relevant grid file of the voltage at the connection point. operator. For Type B and C generating modules, a power generating module document NC RfG defines this requirement as non- (PGMD) has been issued which includes the exhaustive. Each member state may deter- proof of compliance. The format of the PGMD mine its own shape regarding this limit and the information to be given therein shall profile in order to complete the require- be specified by the relevant system opera- ments. The current German regulation for tor. The system operator is allowed to request gensets with synchronous machines is less the following information in the PGMD: strict than the NC RfG’s basic framework. • Evidence of an agreement regarding For converter technologies, it is easier to ride the protection and control settings through sudden voltage dips because they • Itemized proof of compliance are not directly coupled to the grid and there • Detailed technical data is no risk of a pole slip. For that reason, in • Equipment certificates issued many countries the LVRT curves for con- by an authorized certifier verters are deeper and wider than those for • Compliance test reports demonstrating synchronous machines. The big advantage steady-state and dynamic performance of synchronous machines over converters is • Studies demonstrating steady-state the deleveraging of a huge amount of reac- and dynamic performance tive current during malfunction. Converters • Simulation models (Type C only) are not able to deliver that much short-circuit current. By contrast with other directives, NC In Germany, under the BDEW Directive, a RfG takes this into account. There are differ- multi-step approach has been established ent limit curves for both technologies which during recent years. In the first step, the

manufacturer of power generating modules Future and outlook For the further development of solutions has to undergo a certification process. For Renewable, albeit fluctuating energy sources based on reciprocating engines, grid code this reason, a power generating module such as wind and solar are becoming more compliance will be as important a devel- is measured by an independent measure- and more competitive when compared to opment target as increasing efficiency ment institute under Technical Rule 3 from conventional power producers. This is set and meeting emission requirements. FGW. Based on these measurements, and to result in such energy sources penetrat- But it is definitely worth the effort! Gensets on a simulation model provided by the ing grids more strongly, worldwide. As a using reciprocating engines are a key suc- manufacturer, an independent certification result, all grids that are penetrated by a cess factor in moving our power infrastruc- company verifies that the power generat- higher share of renewable energies will have ture system towards being a system with ing module complies with the requirements to continue developing and will have to apply lower CO2 emissions but continuing to offer of the BDEW Directive. If this is the case, a regulations to keep the system stable and high-reliability power supplies. The solu- unit certificate based on certification rule ensure security of supply at a high level. tions offer inertia to the grid, provide short- Technical Rule 8 from FGW12 will be issued. These new regulations can already be found circuits, are flexible and controllable, boost in several countries. The need for action has efficiency in the use of heat and power and For every power plant, a second certificate also been recognized by the European Union. also harmonize with upcoming new technolo- — the plant certificate – is required during The European regulation known as NC RfG gies like power-to-heat and power- to-gas. the planning stage. On the basis of the unit (Network Code Requirements for Generators) certificate of the chosen power generation was published in the Official Journal of the modules and on the data of the additional scope European Communities on April 27, 2016. like transformers, medium voltage cables and This regulation specifies not only rules for additional protection devices, a certification renewable energies, but also for other kinds company assesses whether the plant is meet- of power generation such as combined heat ing the requirements as a whole. After con- and power (CHP) and diesel genset appli- struction and commissioning, a declaration of cations using reciprocating engines. conformity has to be provided to the relevant system operator, confirming that the power Unfortunately, the European regulation NC RfG plant will be operated as defined by the plant only specifies principles for new regulations. certificate. It is quite interesting how the topic However, it is necessary for all unexhausted of compliance is handled under NC RfG across issues to be specified in detail at national level. Europe, especially because of the wide range This will result in national regulations which of Type B power generating modules from 1 will differ from country to country. Therefore, to 50 MW. What is economically feasible for a manufacturers of gensets using reciprocating 50 MW power generating module might not be engines will have to keep careful track of these feasible for a 1 MW power generating module. national processes as they progress, in order to be able to adapt their products to the chang- With certified gas CHP units 0.1 to 2.5 MW ing requirements. Of special interest will be and diesel gensets from 0.6 to 3.2 MW as per the specified way of demonstrating compliance the BDEW Directive, MTU Onsite Energy with national regulations. In Germany, there is has demonstrated that the company is able a quite complex — but established — certifica- to supply products that comply with the tion process: firstly, the genset is measured new requirements. MTU, as one of the lead- by an independent measurement company ing manufacturers, played an active part in and then, based on these measurements, an the process of developing the German grid independent certification company verifies code. With this knowledge, MTU will also be compliance. If similar procedures end up being able to assist customers in other European established in other European countries, the countries in fulfilling the requirements of effort of providing compliant products to dif- their national grid codes based on NC RfG. ferent national regulations will increase.

Sources 1 BMWi, Share of renewable energies in electrical energy production 2015 in Germany, http://www.erneuerbare-energien.de/EE/Redaktion/DE/ Downloads/zeitreihen-zur-entwicklung-der-erneuerbaren-energien-in-deutschland-1990-2015 [as of January 26, 2016] 2 Strom Report, http://strom-report.de/strom-vergleich/#stromerzeugung-2015 [as of June 15, 2016] 3 European Network of Transmission System Operators for Electricity, https://www.entsoe.eu/fileadmin/user_upload/_library/publications/ce/oth- erreports/Final-Report-20070130.pdf [as of June 15, 2016] 4 BDEW, German medium voltage grid technical directive “Generating Plants Connected to the Medium-Voltage Network” 5 NC RfG, Network code on requirements for grid connection of generators

Bibliography - BMWi, Renewable Energies Act (“EEG”) - European Network of Transmission System Operators for Electricity, Final Report System Disturbance, 4 November 2006 - European Network of Transmission System Operators for Electricity, http://networkcodes.entsoe.eu/ - FNN, EU Grid Codes - Fördergesellschaft Wind und andere erneuerbare Energien, “Technische Regel 3 ‘Bestimmung der Elektrischen Eigenschaften von Erzeugung- seinheiten am Mittel-, Hoch- und Höchstspannungsnetz’” - Fördergesellschaft Wind und andere erneuerbare Energien, “Technische Regel 8 ‘Zertifizierung der Elektrischen Eigenschaften von Erzeugung- seinheiten und -anlagen am Mittel-, Hoch- und Höchstspannungsnetz’” - Roadmap dena, Study, System Services 2030 - VDEW, “Generators in the low voltage grid”

MTU Onsite Energy A Rolls-Royce Power Systems Company www.mtuonsiteenergy.com

MTU Onsite Energy is a brand of Rolls-Royce Power Systems. It provides diesel and gas-based power system solutions: from mission-critical to standby power to continuous power, heating and cooling. MTU Onsite Energy power systems are based on diesel engines with up to 3,250 kilowatts (kWe) power output and gas engines up to 2,530 kW.