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

Fault developsdownstream of recloser

Prevent Feeder Lockout Due to Conductor SlapProblem

FDR RCL

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

Pitting and Beading Due to Conductor Slap

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

Questions?