clemson university dg conference update on the current status of dg interconnection protection what...
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CLEMSON UNIVERSITY DG CONFERENCE
UPDATE ON THE CURRENT STATUS OF DG
INTERCONNECTION PROTECTION
WHAT IEEE 1547 DOESN’T TELL YOU ABOUT INTERCONNECTION PROTECTION
Chuck MozinaConsultant
Beckwith Electric Co., Inc.
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OUTLINE
Update the Current Status of DG Interconnection Protection
Tell You What IEEE 1547 Doesn’t
Discuss New DG Method and Practices
+ Calf. Rule 21
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Types of DG Generators
• Induction
• Synchronous
• Asynchronous
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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.
Local Loads
Utility System
IPP System
InterconnectionRelay
InterconnectionTransformer
To Utility System
Point of common coupling
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Typical Generator Protection• Generator internal short circuits.
• Abnormal operating conditions (loss of field, reverse power, overexcitation and unbalance currents).
Local Loads
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IEEE 1547
Addresses Generators 10 MVA or Less
Started Work in 1997
Has Over 300 Participants
Met Every Other Month
Referred Most Issues of Substance to 3 New Standards Groups
CLEMSON UNIVERSITY DG CONFERENCEWhat 1547 SAYS
A 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
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What 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
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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.
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Typical 4-Wire Distribution Feeder Circuit
Pole-top transformer rated for line-to-neutral voltagesexample: 13.2 KV 3 7.6 KV
DG
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Ungrounded Interconnection Transformers
Problems
Advantages
Can supply the feeder circuit from an underground sourceafter substation breaker A trips causing overvoltage
Provide no ground faultbackfeed for fault at F1 &F2. No ground current from breaker A for a fault at F3.
LowVoltage(SEC.)
HighVoltage(PRI.)
DG
CLEMSON UNIVERSITY DG CONFERENCEGrounded Primary Interconnection
Transformers
Problems
AdvantagesNo ground current from breaker A for faults at F3(
). No overvoltagefor ground fault at F1.
No overvoltage for ground fault at F1.
LowVoltage(SEC.)
HighVoltage(PRI.)
Provides an unwanted ground current for supply circuit faultsat F1 and F2.
Allows source feeder relaying at A to respond to a secondary ground fault at F3( ).
DG
2
3
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FERRORESONANCENEW YORK FIELD TESTS –1989
FIELD TEST CIRCUIT
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FERRORESONANCENEW YORK FIELD TESTS -1989
50KW Synchronous DG, 9KW load, 100KVAR Capacitance and Wye-Delta Interconnection Transformer
A=2.74 pu B=2.34 pu C=2.92 pu
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FERRORESONANCENEW YORK FIELD TESTS -1989
50KW Synchronous DG, 9KW load, 100KVAR Capacitance and Wye-Delta Interconnection Transformer
A=2.74 pu B=2.34 pu C=2.92 pu
PROTECTION SOLUTION: MEASURE PEAK OVERVOLTAGE NOT RMS (59I)
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CONDITIONS FOR FERRORESONANCE
1. DG Must be Separated From the Utility System (islanded condition)
2. KW Load in the Island Must be Less than 3 Times DG Rating
3. Capacitance Must be Greater Than 25 and Less Than 500 Percent of DG Rating
4. There Must be a Transformer in the Circuit to Provide Nonlinearity
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PROTECTION FUNCTION BEYOND 81O/U,27 AND 59
Total Interconnect Package
Loss of Parallel
Fault backfeed removal
Damaging conditions Abnormal power flow Restoration
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TYPICAL INTERCONNECTION PROTECTION FOR WYE-GROUNDED (PRI.) INTERCONNECTION TRANSFORMER
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TYPICAL INTERCONNECTION PROTECTION FOR UNGROUNDED (PRI.) INTERCONNECTION TRANSFORMER
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RECIPROCATING ENGINE OUT OF SYNCHRONISM CONDITION
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Power
Pm=Pe
PFAULT
Angle
A2
180
PMax
= Eg ESX
120
UNSTABLE
A1
g-s
Line Recloser
Trips
STABLE
Power Angle Analysis of Out-of-Synchronism Condition
If A1>A2 DG goes unstable and slips a pole, results in high levels of transient shaft torque
LocalLoad
UtilitySubstation
DG
X
LineRecloser
FAULT
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CONCLUSIONS1. DGs Interconnected on Distributions Systems Present Significant Technical
Problems
2. There are No “Standard” Solutions Only Choices with Undersirable Drawbacks
3. IEEE 1547 Provides Limited Real Guidance – Simply Cites Obvious Requirements
4. Hopefully, the Three Newly Formed IEEE Standards Groups Will Address the Technical Issues Raised in this Paper
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THE ENDUPDATE ON THE CURRENT STATUS OF DG
INTERCONNECTION PROTECTION
QUESTIONS