Context: significant penetration of DG = increased risks for system security

Transcription

1 Distributed Generation: towards an effective contribution to power system security IEEE Tampa GM 2007: Panel on Impact of Dispersed Generation on Power System structure & security Bruno Meyer

2 Outline Context: significant penetration of DG = increased risks for system security DG penetration UCTE rules and frequency control Decoupling protections: comparison of rules across Europe Solution: contribution of DG to ancillary services New harmonized settings for decoupling protections New grid code requirements Advanced control systems for wind farms Conclusion

3 1 Context: penetration of DG

4 Context : a significant penetration of DG What is DG? Not centrally planned Less than MW Usually connected to distribution grid (20kV-110kV) Cogeneration Wind PV Presently wind energy is the fastest growing DG

5 Fast increasing installed wind power Source: EWEA

6 Limitations in DG penetration ew risks induced by DG: Changes in power flow in distribution networks Poor harmonization of connection rules in Europe IMPACT ON POWER SYSTEM SECURITY requency behaviour is discussed in this presentation: Risks of unexpected tripping of generation in case of frequency deviation (disturbances of 4 November 2006) No contribution to frequency support Improvements to keep DG connected? Possible active support of DG to frequency control?

7 UCTE rules on frequency behaviour rimary frequency control reserve: production capacity automatically activated and fully deployed within 30 seconds after a sudden change in frequency 3000 MW for the whole UCTE f the security of the system cannot be maintain with the sole eserves: Harmonized automatic load shedding Load shedding starts at 49 Hz Source UCTE

8 Decoupling protections In European countries: islanded operation of DG in distribution networks is forbidden for safety reason: to prevent DG units from supplying power to customers under abnormal voltage and/or abnormal frequency conditions to avoid false couplings when isolated networks are reconnected to ensure that the protection and automatic control systems of DSO operate properly Need of decoupling protection systems mainly based on over and under voltage, over and under frequency criteria

9 Comparison of decoupling protections for DG across some European countries RANCE ~ 7000 MW of decentralized production installed at the end of For a significant part : threshold is set to 49.5 Hz Hz. New wind farms connected to the distribution grid (20 kv): ERMANY often connected through underground cables to dedicated feeders threshold is set to 47.5 Hz-51 Hz. The DSO determines the threshold values in the Hz range, in regards to the nominal voltage / frequency of the network. The producer are free to set stricter values inside these limits.

10 Comparison of decoupling protections for DG across some European countries lack of harmonization SPAIN Ministerial Order of September, 5 th 1985 for the connection of small hydraulic power plant (< 5000 kva): DG connected to the distribution network should be equipped with frequency relays to detect frequency outside 49 to 51 Hz. Lack of harmonization in the settings of decoupling protections A concerted modification of connection rules could be discussed to lower this risk 0

11 1 Conclusion : Risks of decoupling protections tripping during severe grid disturbances The DSO of each country specifies the settings of the decoupling protections according to the network protection scheme. In case of a major frequency deviation, the decoupling protections will react differently across European countries leading to possible unwanted disconnections Not optimal since DG has the ability to remain connected during such grid disturbances if not disconnected by decoupling protections DG could be used to provide some frequency support without compromising the islanding detection

12 2 2 Contribution of DG to frequency control

13 3 Wind farms production management by control systems For DG that has the ability to remain connected to the grid during major system frequency disturbances advanced control functions should be considered ensuring an effective contribution to frequency support Many grid codes define new requirements on wind farms control (ex: Ireland, Denmark) these power plants may be asked to contribute to frequency control, as required for other technologies

14 4 New grid codes requirements on frequency control Exemple: in Ireland and Denmark, wind power plants are expected to change their active power output in case of frequency variations Active power vs. frequency curve for wind farms, according to the Irish distribution code (source: ESB)

15 New grid codes requirements on frequency control he Danish grid code defines sophisticated control strategies or wind farms connected on transmission grid: different regulation mode may be required ex: balance regulation : implementation of a rapid power regulation ensuring upward/downward regulation of the farm production when required Balance regulation (source: Energinet.dk) 5

16 Contribution of wind farms control systems to frequency support 6 Control systems are currently being implemented for wind farms: New features for wind turbines regulation Advanced requirements related to grid integration More advanced security assessment by TSO: EON: generation management Aim: relieve grid constraints Reduction signal sent to RES power plants all over a region 1100 MW of installed capacity concerned in E.ON control zone Spain: power output reductions may be required to preserve system s security

17 7 3 Conclusion

18 Conclusion requency behaviour of DG must be improved: Common set of rules for load shedding in Europe (UCTE) But lack of harmonization in decoupling strategies Decoupling protections settings are not the same Protections will react differently Risk of massive loss of generation due to protections tripping n active frequency support by DG should be considered: Constructive capacities of DG enable advanced control functions Grid codes are defining new requirements for system stability Active contribution of DG to power system must be considered nd a compromise has to be found between safe islanding etection and frequency support 8