GE 469 Manual

GE Power Management 469 Motor Management Relay 4-49
4 SETPOINT PROGRAMMING 4.7 S6 CURRENT ELEMENTS
4
4.7.5 CURRENT UNBALANCE
a) FUNCTION
469 unbalance is defined as the ratio of negative-sequence to positive-sequence current,
I
2
/ I
1
, if the motor is
operating at a load (
I
avg
) greater than FLA. If the motor I
avg
is less than FLA, unbalance is defined as I
2
/ I
1
×
I
avg
/ FLA. This derating is necessary to prevent nuisance alarms when a motor is lightly loaded. If enabled, a
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
avg
> 25% FLA and current in any one phase is zero, the motor is considered single phasing
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.
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.
y
CURRENT UNBALANCE
y
[ENTER] for more
CURRENT UNBALANCE
ALARM: Off
Range: Off, Latched, Unlatched
ASSIGN ALARM RELAYS:
Alarm
Range: Alarm, Alarm & Auxiliary2, Alarm & Aux2 & Aux3,
Auxiliary2, Aux2 & Aux3, Auxiliary3
CURRENT UNBALANCE
ALARM PICKUP: 15%
Range: 4 to 40%, step: 1
CURRENT UNBALANCE
ALARM DELAY: 1 s
Range: 1 to 60 sec., step: 1
CURRENT UNBALANCE
ALARM EVENTS: Off
Range: On, Off
CURRENT UNBALANCE
TRIP: Off
Range: Off, Latched, Unlatched
ASSIGN TRIP RELAYS:
Trip
Range: Trip, Trip & Auxiliary2, Trip & Aux2 & Aux3,
Trip & Auxiliary3
CURRENT UNBALANCE
TRIP PICKUP: 20%
Range:4 to 40%, step: 1
CURRENT UNBALANCE
TRIP DELAY: 1 s
Range: 1 to 60 sec., step: 1
ENTER
ESCAPE
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NOTE

GE 469 Specifications

General

Brand	GE
Model	469
Category	Relays
Language	English