Motor Protection - Ground Fault - GE MOTOR MANAGER 2 Instruction Manual

4 SETPOINTS
Therefore:
Thermal Capacity Used
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 solidly grounded systems), the feature should be disabled. Alternately,
NOTE
the feature may be 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 MM2
will energize the auxiliary relay and de-energize contactor A at the same time when
the ground fault trip occurs. Unless a contactor trip delay setting has been chosen
(see AUX RELAY 1 CONFIG for details).
A change has been made in the way the MM2 calculates the 5A G/F alarm and trip lev-
els. On all software revisions prior to 3.30, the levels are based upon a percentage of
FULL LOAD CURRENT. From software revisions 3.30 and up, the levels are based on a
NOTE
percentage of CT PRIMARY.
GROUND FAULT ALARM
LEVEL: OFF %CT
OR
GROUND FAULT ALARM
LEVEL: OFF A
GROUND FAULT ALARM
DELAY ON RUN: 10 s
GE Power Management
actual motor current
× (
= ---------------------------------------------------- -
FULL LOAD CURRENT
80 A
× ( )
100% 70%
= --------------- - –
100 A
4.3.5 MOTOR PROTECTION – GROUND FAULT
Range: 3 to 100% CT or OFF; Step: 1%
This message will appear if the GROUND FAULT CT INPUT is set to 5A SEC
CBCT or 5A RESIDUAL. Set the GROUND FAULT ALARM LEVEL to some arbi-
trary 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 5A SEC
CBCT value is selected, the level is calculated as a percentage of the G/F
CT PRIMARY setting; if the 5A RESIDUAL value is selected, the level is cal-
culated as a percentage of the PHASE CT PRIMARY setting.
Range: 0.5 to 15.0 A or OFF; Step: 0.5 A
This message will appear if the Ground Fault CT Input is set to 50:0.025
CBCT. See GROUND FAULT ALARM LEVEL (%CT) 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 below is used until the MM2
determines whether the motor is RUNNING or STARTING.
NOTE
Refer to the ACCELERATION TIME setpoint in Section 4.3.7: LOAD PRO-
TECTION for details on how the MM2 detects a start condition.
MM2 Motor Manager 2
100% HOT/COLD CURVE RATIO
–
24%
=
4.3 S2 PROTECTION
)
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