Unbalance Protection - ABB REM 610 Technical Reference Manual

REM 610
4.1.4.7.
32
Motor Protection Relay
Technical Reference Manual
When the ground-fault current exceeds the set pickup value of element 51N, the
element will generate a pickup signal after a ~ 50 ms' pickup time. When the set
operate time at definite-time characteristic elapses, the element will generate a trip
signal. The element can be given an instantaneous characteristic by setting the
operate time to the minimum, i.e. 0.05 s. The ground-fault element will be reset in
50 ms after the ground-fault current has fallen below the set pickup value of the
element.
It is possible to block the tripping of the ground-fault element by applying a digital
input signal to the relay.
Element 51N can be set out of operation in SGF3. This state will be indicated by
dashes on the LCD and by "999" when the set pickup value is read via serial
communication.
To prevent the contactor in a contactor controlled drive from operating at too high
phase currents, the ground-fault element can be set to be disabled when one or
several phase currents exceed the FLA of the motor four, six or eightfold. The
selection is made in SGF4.
Note!
When element 51N picks up during motor start up, no pickup signal will be
generated.
Note!
The FLA secondary does not affect the ground fault current,

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 and I
a b
unbalance in a network feeding the motor will cause overheating of the rotor.
When the calculated NPS current value exceeds the set pickup value of element 46,
the element will generate a pickup signal after a ~ 100 ms' pickup time. When the
calculated operate time elapses, the element 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 element will be reset in 200 ms after the NPS current
has fallen below the set pickup value of the element.
The unbalance protection will be disabled when all phase currents fall below twelve
per cent of the FLA of the motor or one or several phase currents exceed the FLA of
the motor fourfold.
It is possible to block the tripping of the unbalance element by applying a digital
input signal to the relay.
Element 46 can be set out of operation in SGF3. This state will be indicated by
dashes on the LCD and by "999" when the set pickup value is read via serial
communication.
The operate time is calculated as below:
46TDIAL
t s [ ]
------------------------------------------------------------ -
=
2
( ) (
I 46 PICKUP
–
2
, caused by a broken conductor, for instance. Phase
c
2
)
1MRS 755537
.
I
n