GE 750, Инструкция по эксплуатации

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GE Power Management 750/760 Feeder Management Relay 14-
11
14 S7 CONTROL 14.4 COLD LOAD PICKUP BLOCKING
14
14.4 COLD LOAD PICKUP BLOCKING 14.4.1 DESCRIPTION
The 750/760 can be programmed to block instantaneous overcurrent elements and to raise the pickup level of
time overcurrent elements when a cold load condition is detected. Under normal operating conditions, the
actual load on a feeder is less than the maximum connected load, since not all consumers require maximum
load at the same time. When such a feeder is closed after a prolonged outage, the feeder inrush and motor
accelerating current may be above some protection settings. Without historical data on a particular feeder,
some utilities assume an initial cold load current of about 500% of normal load, decaying to 300% after one
second, 200% after 2 seconds, and 150% after 4 seconds. See the figure below.
Figure 14–6: COLD LOAD PICKUP
A cold load condition is initiated and overcurrent settings are altered when all phase currents drop below 5% of
the nominal current for an amount of time greater than the
OUTAGE TIME BEFORE COLD LOAD
. The cold load con-
dition can also be immediately initiated by asserting the logic input function ‘Cold Load Pickup’. Overcurrent
settings are returned to normal after any phase current is restored to greater than 10% of nominal and then a
timer of duration equal to
COLD LOAD PICKUP BLOCK TIME
expires.
14.4.2 SETPOINTS
■
COLD LOAD PICKUP
■
[ENTER] for more
The Cold Load Pickup Blocking setpoints path is:
\ SETPOINTS \ S7 CONTROL \ COLD LOAD PICKUP
COLD LOAD PICKUP
FUNCTION: Disabled
Range: Disabled, Alarm, Latched Alarm, Control
Select the required function.
COLD LOAD PICKUP
RELAYS (3-7):
Range: Any Combination of the 3-7 AUXILIARY Relays
Select the output relays required.
OUTAGE TIME BEFORE
COLD LOAD: 100 min
Range: 1 to 1000 in steps of 1 min.
Enter the minimum outage time required for a load to be considered cold.
COLD LOAD PICKUP
BLOCK TIME: 5 s
Range: 1 to 1000 s in steps of 1 s.
Enter the period of time following restoration of source to a feeder whose load
has become cold for which overcurrent elements will be blocked or will have
their pickup levels raised.
Time (seconds)
C
urrent
(%
o
f norma
l)
0
100
200
300
400
500
-1 0 1 2 3 4 5 6
OUTAGE
PICKUP
PICKUP
LOAD ENERGIZED
X
NORMAL TRIP SETTING