Schweitzer Engineering Laboratories SEL-351-5, Инструкция по эксплуатации, Страница: 626 / 706

F.4
SEL-351-5, -6, -7 Relay Instruction Manual
Date Code 20070117
Setting Negative-Sequence Overcurrent Elements
Coordinating Negative-Sequence Overcurrent Elements
Figure F.2 Distribution Feeder Protective Devices
Traditional Phase Coordination
Figure F.3 Traditional Phase Coordination
Figure F.3 shows traditional phase overcurrent element coordination between
the feeder relay and line recloser phase overcurrent elements. Phase
overcurrent elements must accommodate load and cold load pickup current.
The 450 A maximum feeder load current limits the sensitivity of the feeder
phase overcurrent element, 51F, to a pickup of 600 A. The feeder relay cannot
back up the line recloser for phase faults below 600 A.
where:
I
F
= Maximum load current through feeder relay = 450 A
I
R
= Maximum load current through line recloser = 150 A
51F = Feeder relay phase time-overcurrent element
51QF = Feeder relay negative-sequence time-overcurrent element
51R = Line recloser phase time-overcurrent element (phase
“slow curve”)
Feeder Relay
Feeder
I
R
Bus
I
F
51F, 51QF
R
Line Recloser
52
51R
where:
51F: pickup = 600 A (above max. feeder load, I
F
)
51R: pickup = 200 A (above max. line recloser load, I
R
)
Time (
Sec
onds
)
10.0
5.0
2.0
1.0
0.5
0.2
0.1
Phase Current (Amps)
125 250 500 1000 2000 4000
51R
51F
I
F
I
R