Date Code 20080213
Instruction Manual
SEL-351A Relay
Appendix F
Setting Negative-Sequence
Overcurrent Elements
Setting Negative-Sequence Definite-Time
Overcurrent Elements
Negative-sequence instantaneous overcurrent elements 50Q1–50Q6 and
67Q1–67Q4 should not be set to trip directly
.
This is because negative-
sequence current can transiently appear when a circuit breaker is closed and
balanced load current suddenly appears.
To avoid tripping for this transient condition, use negative-sequence definite-
time overcurrent elements 67Q1T–67Q4T with at least 1.5 cycles of time
delay (transient condition lasts less than 1.5 cycles). For example, make time
delay setting:
67Q1D =
1.50
for negative-sequence definite-time overcurrent element 67Q1T. Refer to
and
for more information on negative-sequence
instantaneous and definite-time overcurrent elements.
Negative-sequence instantaneous overcurrent elements 50Q5 and 50Q6 do not
have associated timers (compare
). If 50Q5 or 50Q6
need to be used for tripping, run them though SEL
OGIC®
control equation
variable timers (see
) and use the outputs of the
timers for tripping.
Continue reading in
Coordinating Negative-Sequence Overcurrent Elements
for guidelines on coordinating negative-sequence definite-time
overcurrent elements and for a coordination example. The coordination
example uses time-overcurrent elements, but the same principles can be
applied to definite-time overcurrent elements.
Содержание SEL-351A
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