Overcurrent Alarm; Offline Overcurrent - GE 489 Instruction Manual

4.6 S5 CURRENT ELEMENTS
PATH: SETPOINTS S5 CURRENT ELEMENTS

OVERCURRENT ALARM

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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-
4
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:
PATH: SETPOINTS S5 CURRENT ELEMENTS
OFFLINE O/C
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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.
NOTE
4-24
OVERCURRENT ALARM
ð
OVERCURRENT
ENTER
ð
ESCAPE ALARM: Off
ASSIGN ALARM
ESCAPE
RELAYS (2-5): ---5
MESSAGE
OVERCURRENT ALARM
ESCAPE
LEVEL: 1.01 x FLA
MESSAGE
OVERCURRENT ALARM
ESCAPE
DELAY: 0.1 s
MESSAGE
OVERCURRENT ALARM
ESCAPE
EVENTS: Off
MESSAGE
Generator FLA 3 × rated generator phase-phase voltage
=
OFFLINE O/C
ð

OFFLINE OVERCURRENT

ENTER
ð
TRIP: Off
ESCAPE
ASSIGN TRIP
ESCAPE
RELAYS (1-4): 1---
MESSAGE
OFFLINE OVERCURRENT
ESCAPE
PICKUP: 0.05 x CT
MESSAGE
OFFLINE OVERCURRENT
ESCAPE
TRIP DELAY: 5 cycles
MESSAGE
489 Generator Management Relay
4.6.2 OVERCURRENT ALARM
Range: Off, Latched, Unlatched
Range: Any combination of Relays 2 to 5
Range: 0.10 to 1.50 × FLA in steps of 0.01
Range: 0.1 to 250.0 s in steps of 0.1
Range: On, Off
4.6.3 OFFLINE OVERCURRENT
Range: Off, Latched, Unlatched
Range: Any combination of Relays 1 to 4
Range: 0.05 to 1.00 × CT in steps of 0.01
Range: 3 to 99 cycles in steps of 1
4 SETPOINTS
(EQ 4.8)
GE Multilin