IMPACT OF WIND POWER GENERATION ON DISTRIBUTION SYSTEMS

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IMPACT OF WIND POWER GENERATION ON DISTRIBUTION
SYSTEMS
Chuck Mozina Consultant Beckwith Electric Co.,
Inc.
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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 1980s when tax
  incentive terminated
• Late 1990s 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 2000s when
  natural gas prices increased
• Late 2000s 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

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Types of Wind Power Generators

• Induction
• Asynchronous
• Four Types of Wind Generator Design

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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

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DG Interconnection Protection
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DG Interconnection Protection
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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.
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Induction Generator Short Circuit Current
Decay 3-phase fault on MV bus
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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

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FERRORESONANCENEW YORK FIELD TESTS 1989FIELD
TEST CIRCUIT
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FERRORESONANCENEW YORK FIELD TESTS -198950KW
Induction DG, 9KW load, 100KVAR Capacitance and
Wye-Delta Interconnection TransformerA2.74 pu
B2.34 pu C2.92 pu
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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

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FERRORESONANCENEW YORK FIELD TESTS -198950KW
Induction DG, 9KW load, 100KVAR Capacitance and
Wye-Delta Interconnection TransformerA2.74 pu
B2.34 pu C2.92 puPROTECTION SOLUTION MEASURE
PEAK OVERVOLTAGE NOT RMS (59I)
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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 SPCs

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Asynchronous GeneratorStatic 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

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DG Interconnection Protection
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DG Interconnection Protection
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DG Interconnection Protection
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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

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

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THE END
IMPACT OF WIND POWER GENERATION ON DISTRIBUTION
SYSTEMS QUESTIONS