Motor Protection - Ground Fault - GE MM3 Instruction Manual

4 SETPOINTS
PATH: SETPOINTS MM S2: PROTECTION MM MOTOR PROTECTION GROUND FAULT
Care must be taken when turning ON the GROUND FAULT TRIP feature. If the interrupting device
(contactor or circuit breaker) is not rated to break ground fault current (low resistance or sol-
idly grounded systems), the feature should be disabled. Alternately, the feature may be
NOTE
assigned to an auxiliary relay and connected such that it trips an upstream device that is
capable of breaking the fault current. Be aware that the MM3 will energize the auxiliary relay
and de-energize contactor A at the same time when the ground fault trip occurs. Unless a con-
tactor trip delay setting has been chosen (see AUX RELAY 1 CONFIG for details).
GROUND FAULT ALARM
LEVEL: OFF %FLC
MESSAGE
OR
GROUND FAULT ALARM
MESSAGE
LEVEL: OFF A
GROUND FAULT ALARM
MESSAGE
DELAY ON RUN: 10 s
GROUND FAULT ALARM:
MESSAGE
DELAY ON START: 10 s
GE Power Management
4.3.3 MOTOR PROTECTION – GROUND FAULT
Range: 10 to 100% FLC or OFF; Step: 1% FLC
This message will appear if the GROUND FAULT CT INPUT is set to RESIDUAL.
Set the GROUND FAULT ALARM LEVEL to some arbitrary amount below the
GROUND FAULT TRIP LEVEL to get an early warning of insulation
breakdown. For maximum sensitivity, the value selected should be just
high enough to prevent nuisance alarms. If the RESIDUAL value is
selected, the level is calculated as a percentage of the FULL LOAD
CURRENT setting.
Range: 0.1 to 15.0 A or OFF; Step: 0.1 A
This message will appear if the Ground Fault CT Input is set to 50:0.025
CBCT. See GROUND FAULT ALARM LEVEL (%FLC) above for details.
Range: 1 to 60 seconds; Step: 1 second
This delay is used when the motor is in a RUNNING condition. If the
ground current is equal to or above the GROUND PRIMARY ALARM PICKUP
setpoint value and remains this way for the time delay programmed in
this setpoint while the motor is running, the alarm relay will activate and
the GROUND ALARM message will be displayed.
When the phase current increases from 0, the GROUND
ALARM DELAY ON START setpoint described below is used
until the MM3 determines whether the motor is RUNNING
NOTE
or STARTING.
Refer to the ACCELERATION TIME setpoint in Section 4.3.5: LOAD
PROTECTION for details on how the MM3 detects a start condition.
Range: 1 to 60 seconds; Step: 1 second
This delay is used when the motor is in a STARTING condition. If the
ground current is equal to or above the GROUND PRIMARY ALARM PICKUP
setpoint value and remains this way for the time delay programmed in
this setpoint while the motor is starting, the alarm relay will activate and
the GROUND ALARM message will be displayed.
When the phase current increases from 0, this delay is
used until the MM3 determines whether the motor is RUN-
NING or STARTING.
NOTE
Refer to the ACCELERATION TIME setpoint in Section 4.3.5: LOAD
PROTECTION for details on how the MM3 detects a start condition.
MM3 Motor Manager 3
4.3 S2 PROTECTION
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