IMPACT OF WIND POWER GENERATION ON DISTRIBUTION SYSTEMS

1. IMPACT OF WIND POWER GENERATION ON DISTRIBUTION SYSTEMS Chuck Mozina Consultant Beckwith Electric Co., Inc.

2. Brief DG History • Until Public Utility Regulatory Policies Act (PURPA) in 1978, U.S. utilities were not required to interconnect with small generators. - Started DG - Beckwith gets into the interconnection protection business - Hot until late 1980’s when tax incentive terminated • Late 1990’s DG again hot - Driven by high utility rates and de-regulation - DGs can generator cheaper at source of consumption + Peak Shaving and Load Following - Hot until early 2000’s when natural gas prices increased • Late 2000’s Green Power drives resurgence of DGs - Regulates require utilities to generator a portion of their power from green sources. - Set high buy back rate – key driver for Distribution Wind Installations

3. Types of Wind Power Generators • Induction • Asynchronous • Four Types of Wind Generator Design

4. VAr Source Induction Wind Generator • Induction • Excitation provided externally • Start up like a motor(no sync. equipment needed) • Less costly than synchronous machines • Limited in size to 500 KVA

5. DG Interconnection Protection

6. DG Interconnection Protection

7. Induction Generator Short Circuit Calculations --- Voltage source in series with the direct axis sub-transient inductance That means for a 3-phase fault at the LV terminals, it contributes approximately a maximum symmetrical short-circuit current with a magnitude equals to the induction generator locked rotor current during the first cycle after the fault.

8. Induction Generator Short Circuit Current Decay 3-phase fault on MV bus

9. Induction Generator: Ferroresonance • Ferroresonance can take place between an induction machine and pole top capacitors after utility disconnection from feeder. Ferroresonance can also occur on Synchronous Generators! • Generator is excited by pole top capacitors if the reactive components of the generator and aggregate capacitors are close. • This interplay produces non-sinusoidal waveforms with high voltage peaks. This causes transformers to saturate, the non-linearities exacerbate the detection problem

10. FERRORESONANCENEW YORK FIELD TESTS –1989FIELD TEST CIRCUIT

11. FERRORESONANCENEW YORK FIELD TESTS -198950KW Induction DG, 9KW load, 100KVAR Capacitance and Wye-Delta Interconnection TransformerA=2.74 pu B=2.34 pu C=2.92 pu

12. CONDITIONS FOR FERRORESONANCE • DG Must be Separated From the Utility System (islanded condition) • KW Load in the Island Must be Less than 3 Times DG Rating • Capacitance Must be Greater Than 25 and Less Than 500 Percent of DG Rating • There Must be a Transformer in the Circuit to Provide Nonlinearity

13. FERRORESONANCENEW YORK FIELD TESTS -198950KW Induction DG, 9KW load, 100KVAR Capacitance and Wye-Delta Interconnection TransformerA=2.74 pu B=2.34 pu C=2.92 puPROTECTION SOLUTION: MEASURE PEAK OVERVOLTAGE NOT RMS (59I)

14. Asynchronous Generator VARS • Asynchronous • Static Power Converter (SPC) converts generator frequency to system frequency • Generator asynchronously connected to power system • IEEE P 929 and UL 1741 Provide Guidance on SPC’s

15. Asynchronous Generator:Static Power Converter (SPC) • Some have Built-In Anti-Islanding Protection • SPC tries to periodically change frequency • If grid is hot, SPC cannot change the frequency • If grid has tripped, the frequency moves and the controller trips the machine • Difficult to test; some utilities do not trust and require other protection

16. DG Interconnection Protection

17. DG Interconnection Protection

18. DG Interconnection Protection

19. DG Interconnection Protection Impact of Interconnection Transformer • Ungrounded Primary Transformer Winding • Overvoltage may be caused by Wind Generator when ungrounded primary transformer windings are applied (no ground source) and the Wind Generator backfeeds once utility disconnects • Grounded Primary Transformer Winding • Ground fault current contribution caused by Wind Generator grounded primary transformer windings during utility faults • Source feeder relaying and reclosers responding to secondary ground faults within the Wind Generator facility

20. Ungrounded Interconnection Transformers Advantages Provide no ground fault backfeed for fault at F1 & F2. No ground current from breaker A for a fault at F3. Problems Can supply the feeder circuit from an underground source after substation breaker A trips causing overvoltage Low Voltage (SEC.) High Voltage (PRI.) Wind Generator

21. Grounded Primary Interconnection Transformers Advantages No ground current from breaker A for faults at F3(). No overvoltage for ground fault at F1. No overvoltage for ground fault at F1. 2 Problems Provides an unwanted ground current for supply circuit faults at F1 and F2. Allows source feeder relaying at A to respond to a secondary ground fault at F3( ). Low Voltage (SEC.) High Voltage (PRI.) Wind Generator 3

22. Interconnection Protection Placement Key Protection Element – 59I

23. Interconnection Protection Placement –Key Protection Element – 59I

24. Interconnection Protection Placement – Key Protection Element 59I

25. CONCLUSIONS 1. Wind Power Generation Interconnected on Distributions Systems Present Significant Technical Problems and Potential Harzards 2. There are No “Standard” Solutions Only Choices with Undersirable Drawbacks. 3. Over-Voltage 59I is Key Element to Detect Ferroresonance 4. When Developing Wind Interconnection Protection the Technical Issues Raised in this Paper Need to be Addresses

26. THE END IMPACT OF WIND POWER GENERATION ON DISTRIBUTION SYSTEMS QUESTIONS