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4 SETPOINT PROGRAMMING
S CURRENT UNBALANCE
S [ENTER] for more
a) FUNCTION
469 unbalance is defined as the ratio of negative-sequence to positive-sequence current, I
operating at a load ( I
) greater than FLA. If the motor I
avg
I
/ FLA. This derating is necessary to prevent nuisance alarms when a motor is lightly loaded. If enabled, a
avg
trip and/or alarm occurs once the unbalance magnitude exceeds the CURRENT UNBALANCE ALARM/TRIP PICKUP
for a period of time specified by the CURRENT UNBALANCE ALARM/TRIP DELAY. If the unbalance level exceeds
40%, or when I
> 25% FLA and current in any one phase is zero, the motor is considered single phasing
avg
and a trip occurs within 2 seconds. Single phasing protection is disabled if the unbalance feature is turned "Off".
When setting the CURRENT UNBALANCE ALARM/TRIP PICKUP level, note that a 1% voltage unbalance typically
translates into a 6% current unbalance. Therefore, to prevent nuisance trips or alarms, the pickup level should
not be set too low. Also, since short term 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 Section 4.6.4: UNBALANCE BIAS on page 4–42).
Unusually high unbalance levels may be caused by incorrect phase CT wiring.
NOTE
b) 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.
GE Power Management
ð
CURRENT UNBALANCE
ENTER
ALARM: Off
ESCAPE
ASSIGN ALARM RELAYS:
ESCAPE
Alarm
MESSAGE
CURRENT UNBALANCE
ESCAPE
ALARM PICKUP: 15%
MESSAGE
CURRENT UNBALANCE
ESCAPE
ALARM DELAY: 1 s
MESSAGE
CURRENT UNBALANCE
ESCAPE
ALARM EVENTS: Off
MESSAGE
CURRENT UNBALANCE
ESCAPE
TRIP: Off
MESSAGE
ASSIGN TRIP RELAYS:
ESCAPE
Trip
MESSAGE
CURRENT UNBALANCE
ESCAPE
TRIP PICKUP: 20%
MESSAGE
CURRENT UNBALANCE
ESCAPE
TRIP DELAY: 1 s
MESSAGE
469 Motor Management Relay
4.7 S6 CURRENT ELEMENTS
4.7.5 CURRENT UNBALANCE
Range: Off, Latched, Unlatched
Range: Alarm, Alarm & Auxiliary2, Alarm & Aux2 & Aux3,
Auxiliary2, Aux2 & Aux3, Auxiliary3
Range: 4 to 40%, step: 1
Range: 1 to 60 sec., step: 1
Range: On, Off
Range: Off, Latched, Unlatched
Range: Trip, Trip & Auxiliary2, Trip & Aux2 & Aux3,
Trip & Auxiliary3
Range:4 to 40%, step: 1
Range: 1 to 60 sec., step: 1
is less than FLA, unbalance is defined as I
avg
4
/ I
, if the motor is
2
1
/ I
×
2
1
4-49
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