Current Unbalance - GE 469 Instruction Manual

469
Motor Management Relay

Current Unbalance

CURRENT
UNBALANCE
NOTE
5–52
PATH: SETPOINTS S6 CURRENT ELEM.
[ ] CURRENT UNBALANCE
ALARM: Off
ASSIGN ALARM RELAYS:
MESSAGE
Alarm
CURRENT UNBALANCE
MESSAGE
ALARM PICKUP: 15%
CURRENT UNBALANCE
MESSAGE
ALARM DELAY: 1 s
CURRENT UNBALANCE
MESSAGE
ALARM EVENTS: Off
CURRENT UNBALANCE
MESSAGE
TRIP: Off
ASSIGN TRIP RELAYS:
MESSAGE
Trip
CURRENT UNBALANCE
MESSAGE
TRIP PICKUP: 20%
CURRENT UNBALANCE
MESSAGE
TRIP DELAY: 1 s
For the 469 relay, unbalance is defined as the ratio of negative-sequence to
positive-sequence current, I
than FLA. If the motor 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 equals
or exceeds the
CURRENT UNBALANCE ALARM(TRIP) PICKUP
by the
CURRENT UNBALANCE ALARM(TRIP) DELAY
exceeds 40%, or when I
avg
motor is considered single phasing and a trip occurs within 2 seconds. Single
phasing protection is disabled if the unbalance trip feature is turned "Off".
When setting the
CURRENT UNBALANCE ALARM(TRIP) PICKUP
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 page
5–45 for details).
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
to "15" and the
PICKUP CURRENT UNBALANCE TRIP PICKUP
tripping; 5 or 10 seconds is a reasonable delay.
http://www.GEindustrial.com/multilin
CURRENT UNBALANCE
Range: Off, Latched, Unlatched
Range: Alarm, Alarm & Auxiliary2,
Range: 4 to 40% in steps of 1
Range: 1 to 60 s in steps of 1
Range: On, Off
Range: Off, Latched, Unlatched
Range: Trip, Trip & Auxiliary2, Trip &
Range: 4 to 40% in steps of 1
Range: 1 to 60 s in steps of 1
/ I , if the motor is operating at a load (I
2 1
is less than FLA, unbalance is defined as I
. If the unbalance level equals or
≥ 25% FLA and current in any one phase is zero, the
S6 Current Elements
Alarm & Aux2 & Aux3,
Auxiliary2, Aux2 & Aux3,
Auxiliary3
Aux2 & Aux3, Trip & Auxiliary3
) greater
avg
/ I × I
2 1 avg
for a period of time specified
level, note that a 1%
CURRENT UNBALANCE ALARM
to "20" to prevent nuisance
GE Multilin
/