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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 Mozina
Consultant
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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To Utility System
Typical
Interconnection
Protection
Interconnection
Transformer
Interconnection
Relay
Utility System
IPP System
Point of common coupling
Local Loads
•
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.
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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
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What 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 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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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
DG
Pole-top transformer rated for line-to-neutral voltages
example: 13.2 KV 3  7.6 KV
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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
Low
Voltage
(SEC.)
DG
High
Voltage
(PRI.)
Can supply the feeder
circuit from an
underground source
after substation breaker A
trips causing overvoltage
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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.
2
Problems
Provides
an unwanted
ground current for supply
circuit faults
at F1 and F2.
Low
Voltage
(SEC.)
DG
3
High
Voltage
(PRI.)
Allows source feeder
relaying at A to respond to
a secondary
ground fault at F3(
).
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FERRORESONANCE
NEW YORK FIELD TESTS –1989
FIELD TEST CIRCUIT
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FERRORESONANCE
NEW 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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FERRORESONANCE
NEW 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 WYEGROUNDED (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 Angle Analysis of
Out-of-Synchronism Condition
Power
P = |Eg| |ES|
Max
X
STABLE
A2
120
UNSTABLE
Pm=Pe
If A1>A2 DG goes
unstable and slips a
pole, results in high
levels of transient shaft
torque
XFAULT
Line
Recloser
A1
Line
Recloser
Trips
PFAULT
Angle
Utility
Substation
180
Q -Q
g s
DG
Local
Load
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CONCLUSIONS
1. 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 END
UPDATE ON THE CURRENT STATUS OF DG
INTERCONNECTION PROTECTION
QUESTIONS