GE 489 - Manual (Page 74)

4-24 489 Generator Management Relay GE Multilin
4.6 S5 CURRENT ELEMENTS 4 SETPOINTS
4
4.6.2 OVERCURRENT ALARM
PATH: SETPOINTS ÖØ S5 CURRENT ELEMENTS Ö OVERCURRENT ALARM
If enabled as Latched or Unlatched, the Overcurrent Alarm will function as follows: If the average generator current (RMS)
measured at the output CTs exceeds the level programmed for the period of time specified, an alarm will occur. If pro-
grammed as unlatched, the alarm will reset itself when the overcurrent condition is no longer present. If programmed as
latched, once the overcurrent condition is gone, the reset key must be pressed to reset the alarm. The generator FLA is cal-
culated as:
(EQ 4.8)
4.6.3 OFFLINE OVERCURRENT
PATH: SETPOINTS ÖØ S5 CURRENT ELEMENTS ÖØ OFFLINE O/C
When a synchronous generator is offline, there should be no measurable current flow in any of the three phases unless the
unit is supplying its own station load. Also, since the generator is not yet online, differentiation between system faults and
machine faults is easier. The offline overcurrent feature is active only when the generator is offline and uses the neutral end
CT measurements (Ia, Ib, Ic). It may be set much more sensitive than the differential element to detect high impedance
phase faults. Since the breaker auxiliary contacts wired to the 489 Breaker Status input may not operate at exactly the
same time as the main breaker contacts, the time delay should be coordinated with the difference of the operation times. In
the event of a low impedance fault, the differential element will still shutdown the generator quickly.
If the unit auxiliary transformer is on the generator side of the breaker, the pickup level must be set greater
than the unit auxiliary load.
„ OVERCURRENT ALARM
„ [ENTER] for more
OVERCURRENT
ALARM: Off
Range: Off, Latched, Unlatched
ASSIGN ALARM
RELAYS (2-5): ---5
Range: Any combination of Relays 2 to 5
OVERCURRENT ALARM
LEVEL: 1.01 x FLA
Range: 0.10 to 1.50 × FLA in steps of 0.01
OVERCURRENT ALARM
DELAY: 0.1 s
Range: 0.1 to 250.0 s in steps of 0.1
OVERCURRENT ALARM
EVENTS: Off
Range: On, Off
„ OFFLINE O/C
„ [ENTER] for more
OFFLINE OVERCURRENT
TRIP: Off
Range: Off, Latched, Unlatched
ASSIGN TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to 4
OFFLINE OVERCURRENT
PICKUP: 0.05 x CT
Range: 0.05 to 1.00 × CT in steps of 0.01
OFFLINE OVERCURRENT
TRIP DELAY: 5 cycles
Range: 3 to 99 cycles in steps of 1
ENTER
ESCAPE
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MESSAGE
ESCAPE
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ESCAPE
MESSAGE
ESCAPE
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ESCAPE
Generator FLA 3 rated generator phase-phase voltage × =
ENTER
ESCAPE
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MESSAGE
ESCAPE
MESSAGE
ESCAPE
MESSAGE
ESCAPE
NOTE