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5.7.5
Current Unbalance
CURRENT
5–62
For example, if a pump is cooled by the liquid it pumps, loss of load may mean that the
pump overheats. In this case, enable the undercurrent feature. If the motor loading should
never fall below 0.75 × FLA, even for short durations, the
could be set to "0.70" and the
always started loaded, the
(programmed as "0").
The
UNDERCURRENT ALARM DELAY
as possible, i.e. 1 second.
PATH: SETTINGS
S6 CURRENT ELEM.
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MESSAGE
MESSAGE
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For the 469 relay, unbalance is defined as the ratio of negative-sequence to positive-
sequence current, I
/ I
, if the motor is operating at a load (I
2
1
motor I
is less than FLA, unbalance is defined as I
avg
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
UNBALANCE ALARM(TRIP) PICKUP
UNBALANCE ALARM(TRIP) DELAY
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
trip feature is turned "Off".
When setting the
CURRENT UNBALANCE ALARM(TRIP) PICKUP
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
UNDERCURRENT ALARM PICKUP
BLOCK UNDERCURRENT FROM START
or
UNDERCURRENT TRIP DELAY
CURRENT UNBALANCE
CURRENT UNBALANCE
ALARM: Off
ASSIGN ALARM
RELAYS:
CURRENT UNBALANCE
ALARM PICKUP: 15%
CURRENT UNBALANCE
ALARM DELAY: 1 s
CURRENT UNBALANCE
ALARM EVENTS: Off
CURRENT UNBALANCE
TRIP: Off
ASSIGN TRIP
RELAYS:
CURRENT UNBALANCE
TRIP PICKUP: 20%
CURRENT UNBALANCE
TRIP DELAY: 1 s
2
for a period of time specified by the
. If the unbalance level equals or exceeds 40%, or when
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
UNDERCURRENT TRIP PICKUP
to "0.75". If the pump is
settings should be disabled
is typically set as quick
Range: Off, Latched, Unlatched
Range: Alarm, Alarm & Auxiliary2,
Alarm & Aux2 & Aux3,
Auxiliary2, Aux2 & Aux3,
Auxiliary3
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 &
Aux2 & Aux3, Trip & Auxiliary3
Range: 4 to 40% in steps of 1
Range: 1 to 60 s in steps of 1
) greater than FLA. If the
avg
/ I
× I
/ FLA. This derating is
1
avg
CURRENT
CURRENT
level, note that a 1% voltage
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