CHAPTER 5: SETTINGS
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL 5–63
unbalances are common, a reasonable delay should be set to avoid nuisance trips or
alarms. The unbalance bias feature is recommended to bias the thermal model for motor
heating caused by cyclic short term unbalances (see page –54 for details).
Note
Unusually high unbalance levels may be caused by incorrect phase CT wiring.
For example, fluctuations of current unbalance levels are typically caused by the supply
voltage. It may be desirable to have a latched alarm to capture any such fluctuations that
go beyond the Unbalance Alarm parameters. Also, a trip is recommended.
If the supply voltage is normally unbalanced up to 2%, the current unbalance seen by a
typical motor is 2 × 6 = 12%. In this case, set the
CURRENT UNBALANCE ALARM PICKUP to
“15” and the
CURRENT UNBALANCE TRIP PICKUP to “20” to prevent nuisance tripping; 5 or
10 seconds is a reasonable delay.
5.7.6 Ground Fault
PATH: SETTINGS ZV S6 CURRENT ELEM. ZV GROUND FAULT
GROUND
FAULT [Z]
GROUND FAULT
OVERREACH FIL-
Range: On, Off
MESSAGE
GROUND FAULT
ALARM: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN ALARM
RELAYS:
Range: Alarm, Alarm & Auxiliary2,
Alarm & Aux2 & Aux3,
Auxiliary2, Aux2 & Aux3,
Auxiliary3
MESSAGE
GROUND FAULT
ALARM
Range: 0.1 to 1.00 x CT in steps of 0.01
or 0.25 to 25 A in steps of 0.01
MESSAGE
INTENTIONAL GF
ALARM
Range: 0 to 1000 ms in steps of 1
MESSAGE
GROUND FAULT
ALARM
Range: On, Off
MESSAGE
GROUND FAULT
TRIP: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN TRIP
RELAYS:
Range: Trip, Trip & Auxiliary2, Trip &
Aux2 & Aux3, Trip & Auxiliary3,
Auxiliary2, Aux2 & Aux3,
Auxiliary3
MESSAGE
GROUND FAULT TRIP
PICKUP: 0.20 x CT
Range: 0.1 to 1.00 x CT in steps of 0.01
or 0.25 to 25 A in steps of 0.01
MESSAGE
INTENTIONAL GF
TRIP
Range: 0 to 1000 ms in steps of 1
MESSAGE
GROUND FAULT TRIP
BACKUP: Off
Range: On, Off
MESSAGE
ASSIGN BACKUP
RELAYS:
Range: Auxiliary2, Aux2 & Aux3,
Auxiliary3
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