TRANSELECTRICA - DEN

1. TRANSELECTRICA - DEN RES-E Impact on Transmission Grid and Power System Reserves Florin Balasiu Director of Operational Planning Division Update Romanian Renewable Market 02 apr 2012

2. Content 1. Benefits and Challenges to Integrate RES 2. Technical Topics Regarding RES Integration • Connection schemes. Network development • Power system stability topics • Shortcircuit withstand • Protective schemes • Power quality 3. Conclusions

3. 1. Benefits and Challenges to Integrate RES-E • Developing and integration of RES (wind and photovoltaic) contribute to: • Actions to mitigate climate changes • Secure energy requirements • Increase competitiveness and wealth • New challenges arise from: • Variable nature of the RES • Distributed nature • Different electrical technologies • Larger forecast errors

4. Fluctuating Nature of RES Peak - 926 MW Increase 340 MW; 2 h Decrease 390 MW; 1 h

5. Distributed Nature of RES

6. 2. Technical Topics on RES Integration • Connection scheme depends on: region, installed capacity, existing lines, active power generation-load balance of the region • Power System Stability – rotor angle, frequency and voltage stability • Frequency stability – balance between total active power generation and load at Romanian power grid level, including load, export and storage • Voltage stability – balance between reactive power generation and absorption capability • Shortcircuit withstand – symmetrical and asymmetrical (SLG) faults • Protective schemes of the generating units and of the network • Power quality – voltage drops, swings, flicker, operational performance indexes • Total investment costs • 4

7. Network development • S/s modernization; • Transmission lines reinforcement vs new lines • increase transmission capacity by use of high temperature conductors • optimal power flow management • New lines: 400 kV Cernavoda-Gura Ialomitei-Stalpu • 400 kV Suceava-Gadalin • 400 kV Gutinas-Smardan • 400 kV Portile de Fier-Resita-(Pancevo)-Timisoara-Arad • Typical 110 kV connection diagrams • 4

8. Typical 110 kV Connection Layouts for Renewable Medium Size (1) • Visible for system operators • Operational security => N-1 fulfilled • Reliable protective system: • Dependability • Security • Critical clearing time

9. Typical 110 kV Connection Layouts for Renewable Medium Size (2) • Visible for system operators • Operational security => N-1 not fulfilled • Islanding issues • The protective system: • Difficulties to avoid unwanted trips or delayed ones • Difficulties to provide remote back-up thus not recommended

10. Power System Stability Topics Frequency control – balance between load and generation • Aim – to maintain the balance between load and generation within a synchronous area • Based on three control actions: • Primary frequency control is a local control to maintain load-generation balance and stabilise frequency after large disturbances • Secondary frequency control – centralised automatic generation control (AGC) to bring back the frequency to its reference value. It restores the interchanges with surrounding power systems • Tertiary frequency control – to restore primary and secondary reserves Secure system operation is only possible by close cooperation between owners of Power Generating Facilities and the Network Operators. In particular, the system behavior in disturbed operating conditions depends upon the response of Power Generating Facilities to deviations from nominal values of voltage and frequency.

11. Effects – frequency range of operation

12. Effects – active power frequency response • P = the change in MW output from the generator • f = the frequency deviation in the network • Pmax = the max capacity to which P is related Active Power frequency response of Generating Units in Frequency Sensitive Mode

13. Effects – tertiary reserves • Tertiary frequency control is performed manually in order to restore primary and secondary • reserves. • Tertiary control may be achieved by: • connection of generating units – fast startup, enough generating units • changes in the dispatching of units • changes in the interchanges program • load control – energy storage • Actual limit for RES in the grid – about 3000 MW installed capacity

14. Power System Stability Topics Voltage stability – reactive power control Voltage stability refers to the ability of the power system to maintain voltages at all busbars within the operational ranges during normal operation as well as after being subjected to disturbances in the network. Sufficient reactive power support is the most important part for voltage control and voltage stability in a transmission and distribution network. As reactive power can not be transported over long distances, the reactive power has to be supplied where required. Consequently, increasing amount of wind generation reduces reactive power reserves in the transmission system, which is defined by available reactive power of the synchronous generators, SVCs and shunt capacitors minus reactive power consumption in the network including reactive power of the switchable inductors.

15. Effects – voltage range of operation

16. Effects – fault ride through (FRT) Ability of non-conventional generators to stay connected in the case of network faults It is of particular importance to transmission system operators, that wind farms and photo-voltaic generators stay connected, in case of faults at transmission or distribution levels that lead to a voltage dips in a wide area. It is mandatory for RES to be equipped with FRT-capability FRT profile of a RES connected at 110 kV or above voltage levels. Boundaries for a voltage-against-time profile at the Connection Point

17. Power System Stability Topics Transient stability – critical fault clearing time • The main aspects having a possible impact on transient stability issues are: • RES are usually connected at different locations than conventional power stations. Hence, power flows are considerable different in the presence of a high amount of renewable power and actual power systems are typically not optimized for renewable power transport. This aspect is relevant for Dobrogea area • Renewable generating units are usually based on different technologies than conventional synchronous generators and new tools for modeling and calculations are needed • Based on these differences two phenomena can be distinguished, which can be affected by RES generation: • Global effects which can result in loss of synchronism of generators: • Transient stability (large-disturbance effect) • Local effects • Trip of RES generators after subjected to a disturbance (w/o FLTR)

18. Transient stability – critical fault clearing time Transient stability = the ability of the power system to maintain synchronism during and after severe disturbances, for example short circuits or generator trips The behaviour of the system is highly dependent on the type and duration of disturbance, thus to ensure transient stability in a system often a number of critical contingencies have to be simulated at different locations For transient stability, the Critical Clearing Time is of utmost importance and represents an useful measure for characterizing the transient stability performance of a given dispatch scenario To counteract against transient stability problems: Fast protection tripping time + fast CB opening time => teleprotection schemes Fast bus-bar faults clearing time => BBP and BFP

19. 3. Conclusions Large scale renewable power integration in the Romanian Power System is possible by taking plenty technical measures The installed RES (wind and photovoltaic) integration capability depends on transmission and distribution lines and S/s development as well as balancing capabilities and available reserves Secure system operation is only possible by close cooperation among owners of Power Generating Facilities, Network Operators and ANRE

20. Thank You ! Florin Balasiu Update Romanian Renewable Market 02 apr 2012