Unbalance Protection - ABB REM 610 Technical Reference Manual

REM 610
4.1.4.7.
32
Motor Protection Relay
Technical Reference Manual
To prevent the contactor in a contactor controlled drive from operating at too high
phase currents, the earth-fault stage can be set to be inhibited when one or several
phase currents exceed the FLC of the motor four, six or eightfold. The selection is
made in SGF4.
Note!
When stage I > starts during motor start up, no start signal will be generated.
0
Note!
The PU scale does not affect the earth fault current, I

Unbalance protection

The inverse-definite-minimum-time (IDMT) unbalance protection is based on the
calculated negative-phase-sequence (NPS) current and detects phase unbalance
between phases I , I
L1 L2
unbalance in a network feeding the motor will cause overheating of the rotor.
When the calculated NPS current value exceeds the set start value of stage I
stage will generate a start signal after a ~ 100 ms' start time. When the calculated
operate time elapses, the stage will generate a trip signal. The operate time depends
on the current value: the higher the current value, the shorter the operate time. The
unbalance stage will be reset in 200 ms after the NPS current has fallen below the
set start value of the stage.
The unbalance protection will be inhibited when all phase currents fall below twelve
per cent of the FLC of the motor or one or several phase currents exceed the FLC of
the motor fourfold.
It is possible to block the tripping of the unbalance stage by applying a digital input
signal to the relay.
Stage I > can be set out of operation in SGF3. This state will be indicated by dashes
2
on the LCD and by "999" when the set start value is read via serial communication.
The operate time is calculated as below:
K
2
t s [ ] ------------------------------------------
=
2
( ) I ( >
I –
2 2
where
t = operate time
I = NPS current
2
I > = set start value
2
K = set time constant equals the motor constant, I
2
manufacturer)
Note!
When stage I > starts during motor start up, no start signal will be generated.
2
Note!
Stage I > will be blocked during the tripping of the phase reversal stage.
2
and I , caused by a broken conductor, for instance. Phase
L3
2
)
1MRS 752263-MUM
.
0
2
x t (provided by the motor
2
>, the
2