Unbalance Protection - ABB REM 610 Technical Reference Manual

REM 610 REM 610
5.1.4.7.
40
Motor Protection Relay
Technical Reference Manual - ANSI Version

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:
46 TDIAL
[ ]
=
t s
( ) (
2
−
I 46 PICKUP
2
t = operate time
I = NPS current
2
46 PICKUP = set pickup value
46 TDIAL = set time constant equals the motor constant, I
manufacturer)
When element 46 picks up during motor start up, no pickup signal will
be generated.
Element 46 will be blocked during the tripping of the phase reversal
element.
The figure below illustrates the inverse-time curves of element 46.
, caused by a broken conductor, for instance. Phase
c
)
2
1MRS755537
(2)
2
x t (provided by the motor
2