IMPACT OF GREEN POWER GENERATION ON DISTRIBUTION SYSTEMS

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

2. DG:GreenorNot Green • Not Green • Burn conventional fuel • Gas • Diesel, oil, gasoline • Green • Use renewable sources to reduce reliance of fossil fuels: • Solar • Methane (from decomposition) • Wind • Hydro • Biomass (burn it) • Tidal

3. To Utility System InterconnectionTransformer Interconnection Relay Utility System IPP System Local Loads Typical Interconnection Protection • Disconnects the generator when it is no longer operating in parallel with the utility. • Protects the utility system from damage caused by connection of the generator (fault current and overvoltage). • Protects the DG generator from damage from the utility system, especially through automatic reclosing. Point of common coupling

4. Local Loads Typical Generator Protection • Generator internal short circuits. • Abnormal operating conditions (loss of field, reverse power, overexcitation and unbalance currents).

5. Types of Green Power Generators • Induction • Synchronous • Asynchronous

6. VAr Source Induction 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 • Types of Generators • Wind Power

7. Synchronous Generator • Types of Generators • Internal Combustion Engines • Small Hydro • Synchronous • dc field provides excitation • Need to synchronize to utility system

8. Asynchronous Generator VARS • Types of Generators • Solar, PV • Fuel Cells • 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

9. IEEE 1547 SAYSA DG SHALL: • Not Cause Overvoltages or Loss of Utility Relay Coordination • Disconnect When No Longer Operating in Parallel With the Utility. + Only Discusses 81O/U and 27, 59 • Not Energize the Utility when it is De-energized • Not Create an Unintentional Islands • Use “Utility Grade” Relays • Not Cause Objectionable Harmonics • Not Cause Loss of Synchronism That Results in Objectionable Flicker

10. DG Interconnection Protection Islanded Operation of DG with Utility Loadis Generally Not Allowed • Greatly complicates restoration • Requires synchronizing at utility substation • Inhibits automatic reclosing • Power quality issue • DG may not be able to maintain voltage, frequency andharmonics within acceptable levels.

11. DG Interconnection Protection DG Facility Islanding to the Utility is Allowed • Feeder deenergizes when utility opens feeder • Restoration responsibility on the DG • Requires synchronizing to utility • Inhibits automatic reclosing

12. OVERVOLTAGE AND LOSS OF COORDINATION Two Sources of Overvoltage +Choice of Delta Interconnection Transformer Primary Winding + Ferroresonance Loss of Coordination +Choice of Grounded Interconnection Transformer Primary Winding.

13. DG Pole-top transformer rated for line-to-neutral voltagesexample:13.2 KV3  7.6 KV

14. 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.) DG

15. 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.) DG 3

16. FERRORESONANCENEW YORK FIELD TESTS –1989FIELD TEST CIRCUIT

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

18. FERRORESONANCENEW YORK FIELD TESTS -198950KW Synchronous 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)

19. 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

20. PROTECTION FUNCTION BEYOND 81O/U,27 AND 59 Total Interconnect Package Loss of Parallel Fault backfeed removal Damaging conditions Abnormal power flow Restoration

21. TYPICAL INTERCONNECTION PROTECTION FOR WYE-GROUNDED (PRI.) INTERCONNECTION TRANSFORMER

22. TYPICAL INTERCONNECTION PROTECTION FOR UNGROUNDED (PRI.) INTERCONNECTION TRANSFORMER

23. CONCLUSIONS 1. Green Power DGs Interconnected on Distributions Systems Present Significant Technical Problems and Potential Harzards 2. There are No “Standard” Solutions Only Choices with Undersirable Drawbacks 3. IEEE 1547 Provides Limited Real Guidance – Simply Cites Obvious Requirements 4. When Developing DG Interconnection Protection the Technical Issues Raised in this Paper Need to be Addresses

24. THE END IMPACT OF GREEN POWER GENERATION ON DISTRIBUTION SYSTEMS QUESTIONS