F-4
Setting Negative-Sequence Overcurrent Elements
Date Code 20001006
SEL-351 Instruction Manual
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”)
Traditional Phase Coordination
Figure F.3: Traditional Phase Coordination
51F: pickup = 600 A (above max. feeder load, I
F
)
51R: pickup = 200 A (above max. line recloser load, I
R
)
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.
Apply the Feeder Relay Negative-Sequence Overcurrent Element (Guidelines 1 to 3)
Applying negative-sequence overcurrent element coordination Guidelines 1 to 3 results in the
feeder relay “equivalent” phase overcurrent element (51EP) in Figure F.4. Curve for 51F is shown
for comparison only.
Содержание SEL-351
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