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CHAPTER 5: SETPOINTS
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
5–33
5.6.2
Overcurrent Alarm
PATH: SETPOINTS
ZV
S5 CURRENT ELEM.
Z
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 programmed 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 calculated as:
(EQ 0.8)
5.6.3
Offline Overcurrent
PATH: SETPOINTS
ZV
S5 CURRENT ELEM.
ZV
OFFLINE OVERCURRENT
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.
1 OVERCURRENT
[
Z
]
ALARM
OVERCURRENT
ALARM: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN ALARM
RELAYS (2-5): ---5
Range: Any combination of Relays 2 to
5
MESSAGE
OVERCURRENT ALARM
LEVEL: 1.01 x FLA
Range: 0.10 to 1.50
×
FLA in steps of
0.01
MESSAGE
OVERCURRENT ALARM
DELAY: 0.1 s
Range: 0.1 to 250.0 s in steps of 0.1
MESSAGE
OVERCURRENT ALARM
EVENTS: Off
Range: On, Off
Generator FLA
Generator Rated MVA
3 Generator Rated Phase-Phase Voltage
×
--------------------------------------------------------------------------------------------------------------
=
1 OFFLINE
[
Z
]
OVERCURRENT
OFFLINE OVERCURRENT
TRIP: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to
4
MESSAGE
OFFLINE OVERCURRENT
PICKUP: 0.05 x CT
Range: 0.05 to 1.00
×
CT in steps of
0.01
MESSAGE
OFFLINE OVERCURRENT
TRIP DELAY: 5 cycles
Range: 3 to 99 cycles in steps of 1
Содержание Multilin 489
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