B5 IASRuralElectricWind Power10

IMPACT OF WIND POWER GENERATION ON DISTRIBUTION SYSTEMS : 

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

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 Brief DG History

Types of Wind Power Generators : 

Types of Wind Power Generators Induction Asynchronous Four Types of Wind Generator Design

Induction Wind Generator : 

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

DG Interconnection Protection : 

DG Interconnection Protection

DG Interconnection Protection : 

DG Interconnection Protection

Slide 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.

Slide 8: 

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

Slide 9: 

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 Induction Generator: Ferroresonance

FERRORESONANCENEW YORK FIELD TESTS –1989FIELD TEST CIRCUIT : 

FERRORESONANCENEW YORK FIELD TESTS –1989FIELD TEST CIRCUIT

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 : 

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

CONDITIONS FOR FERRORESONANCE : 

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

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) : 

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)

Asynchronous Generator : 

Asynchronous Generator 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 VARS

Slide 15: 

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 Asynchronous Generator:Static Power Converter (SPC)

DG Interconnection Protection : 

DG Interconnection Protection

DG Interconnection Protection : 

DG Interconnection Protection

DG Interconnection Protection : 

DG Interconnection Protection

Slide 19: 

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 Impact of Interconnection Transformer DG Interconnection Protection

Ungrounded Interconnection Transformers : 

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

Grounded Primary Interconnection Transformers : 

Grounded Primary Interconnection Transformers Problems 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. Low Voltage (SEC.) High Voltage (PRI.) 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( ). Wind Generator 2 3

Slide 22: 

Interconnection Protection Placement Key Protection Element – 59I

Slide 23: 

Interconnection Protection Placement –Key Protection Element – 59I

Slide 24: 

Interconnection Protection Placement – Key Protection Element 59I

CONCLUSIONS : 

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

THE END : 

THE END IMPACT OF WIND POWER GENERATION ON DISTRIBUTION SYSTEMS QUESTIONS