solutions to common distribution protection challenges · recloser. pitting and beading due to...
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Copyright © SEL 2016
Solutions to Common Distribution Protection Challenges
Jeremy Blair, Greg Hataway, and Trevor MattsonSchweitzer Engineering Laboratories, Inc.
• Unnecessary operations on fast curve due to inrush• Long protection times as multiple devices coordinate• Operation of feeder relay caused by conductor slap• Closure into faults in loop schemes from lack of
communication
Common Distribution Protection Problems
• Zones of protection are large and diverse• Selectivity is classically established using time• Topology is dynamic• Maximum load conditions can be close to minimum
fault conditions
Distribution System ProtectionChallenges
• Multiple shots of reclosing
• Measurements distributed across the protected system
• Advanced feeder relays and recloser controls Event records
Historical data
Multiple protection elements
Custom logic
Distribution System ProtectionAdvantages
• High speed• High sensitivity• Low security during inrush Magnetizing inrush
Load inrush
• Frequent exposure to inrush due to reclosing
Eliminate Unnecessary Fast-Curve OperationsProblem
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)1,000100 10,000
Fuse
Recloser Slow
Recloser Fast
Eliminate Unnecessary Fast-Curve OperationsExample – R2 Trips on Inrush When R1 Recloses
52.3851.88 52.88 53.38 53.88 54.38Time (seconds)
Feeder 1 Feeder 2
1 Fast Curve2 Slow Curves
4000
2000
0
–2000
–4000400
200
0
–200
–400
Cur
rent
(A)
Cur
rent
(A)
1 Fast Curve2 Slow Curves
R2
R1
Eliminate Unnecessary Fast-Curve OperationsSolution 1 – Use Slower Fast CurveTi
me
(sec
onds
)
10
1
0.1
1,000
0.01
100
Current (A)1,000100 10,000
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)1,000100 10,000
Fuse
Recloser Slow
Recloser Fast
Fuse
Recloser Slow
Recloser Fast
Eliminate Unnecessary Fast-Curve OperationsSolution 2 – Predict Inrush and Block Fast Curve
27A227B227C2
50P4
EnableFast Curve
Cycles
0.25
10
Eliminate Unnecessary Fast-Curve OperationsSolution 3 – Detect Inrush With Second Harmonic
Cur
rent
(A)
300200100
–300
Cycles
0–100–200
0.0 2.5 5.0 7.5 10.0 12.5 15.0
TRIPHBL2T51P2T51P251P1T51P1
• Typical coordination interval is ~ 0.2 second
• Fuse size (100T) may be limited by downstream load
• Feeder curve may be limited by upstream overcurrent protection or damage curves
Reduce Time-Overcurrent Protection TimesProblem
T = 0.237 s @ 6,000 A
T = 0.038 s @ 6,000 A
100T
Feeder
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)
1,000100 10,000
• Recloser installed between feeder and 100T fuse is meant to improve feeder sectionalization
• Coordination interval does not allow for it
Reduce Time-Overcurrent Protection TimesExample
T = 0.237 s @ 6,000 A
T = 0.038 s @ 6,000 A
Recloser
100T
Feeder
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)
1,000100 10,000
• Allow feeder and recloserto miscoordinate on first time-overcurrent trip
Reduce Time-Overcurrent Protection TimesSolution 1 – Faster Curve on Reclose
T = 0.217 s @ 6,000 A
T = 0.038 s @ 6,000 A
Recloser
Feeder
100T
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)1,000100 10,000
• Allow feeder and recloserto miscoordinate on first time-overcurrent trip
• Use faster curve on recloser for subsequent time-overcurrent trips
Reduce Time-Overcurrent Protection TimesSolution 1 – Faster Curve on Reclose
Recloser
Feeder
100T
T = 0.237 s @ 6,000 A
T = 0.028 s @ 6,000 A
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)1,000100 10,000
• Allow feeder and recloserto miscoordinate on first time-overcurrent trip
Reduce Time-Overcurrent Protection TimesSolution 2 – Even Faster Curve on Reclose
Recloser
100T
Feeder
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)1,000100 10,000
• Allow feeder and recloserto miscoordinate on first time-overcurrent trip
• Use instantaneous or short time-delay overcurrent to reduce through-fault energy
Reduce Time-Overcurrent Protection TimesSolution 2 – Even Faster Curve on Reclose
Recloser
100T
Feeder
Tim
e (s
econ
ds)
10
1
0.1
1,000
0.01
100
Current (A)1,000100 10,000
Prevent Feeder Lockout Due to Conductor SlapProblem
Magnetic field from fault current causes upstream conductors to contact
FDR
FDR RCL
RCL
Prevent Feeder Lockout Due to Conductor SlapProblem
Feeder trips, butrecloser may not trip
FDR
FDR RCL
RCL
RCLFDR
Prevent Feeder Lockout Due to Conductor SlapExample – Multiple Conductor Slaps After Fault Clears
Cur
rent
(A)
Cur
rent
(A)
31.94 32.44 32.94 33.44 33.94 34.44 34.94 35.44 35.94
–4000
40002000
0–2000
1:51P1T1:TRIP2:51P1
–4000
40002000
0–2000
–6000
4:51P1T4:TRIP6:51P1
Time (seconds)
Feeder
Recloser
Prevent Feeder Lockout Due to Conductor SlapSolution
0
10
60
0
Overcurrent
Three-Phase Undervoltage Source Side
Good Voltage
CountUp
Reset
=
Alarm
Trip and Lockout
Preset Value
Recloser Cycling
Seconds
Cycles
Prevent Restoration of Faulted Lines in Noncommunicating Loop Schemes
Problem
vs.
FDR RCL
RCLFDR
FDR RCL
RCLFDR
RCL
RCL
N
FDR RCL
FDR RCL
FDR RCL
FDR RCL
RCL
RCL
N
Prevent Restoration of Faulted Lines in Noncommunicating Loop Schemes
Solution
Feeder 2nd Open Interval3 seconds
Recloser 2nd Open Interval5 seconds
60
03.5
0
Three-Phase Undervoltage Source Side
Good Voltage Source Side
CountUp
Reset
=
2 Three-Phase Undervoltage Source Side
Seconds
Disarm Automatic
RestorationSeconds
Enable Evaluation on Second Open Interval
• Data from modern relays help explain complex distribution protection problems
• Multiple protection elements and custom logic can improve Security of fuse-saving schemes
Selectivity of tightly coordinated feeders
Speed of overcurrent protection during reclose cycle
Security of feeders at risk of conductor slap
Selectivity of noncommunicating loop schemes
Conclusion