ABB REM 610 Technical Reference Manual page 31

1MRS755537
Motor Protection Relay
Technical Reference Manual - ANSI Version
stress and long-time thermal history. After a short period of thermal stress, e.g. a
motor start up, the thermal level will start to decrease quite sharply, simulating the
levelling out of the hot spots. As a consequence, the probability that successive start
ups will be allowed increases.
If p is set to 100 per cent, the thermal level will decrease slowly after a heavy load
condition. This makes the protection suitable for applications where no hot spots are
expected.
The reduced ability of the motor to cool down during standstill is taken into account
by setting the cooling time constant to be longer than the heating time constant. The
time constant dial, K , is the ratio of the cooling time and the heating time constant
c
and determines the cooling rate of the motor at standstill.
At power up, the thermal level will be set to approximately 70 per cent of the
thermal capacity of the motor. This will ensure that the element will trip within a
safe time span. Under a low-load condition, the calculated thermal level will slowly
approach the thermal level of the motor.
At a low prior alarm level, connecting the auxiliary supply to the relay
will cause a thermal alarm due to the initialization of the thermal level
to 70 per cent. The thermal level can be reset via the HMI during
power up.
The thermal level can be reset or changed via serial communication,
which will generate an event code.
On the rising edge of the emergency start signal the thermal level will
be set below the thermal restart disable level. This will allow at least
one motor start up even though the thermal level has exceeded the
restart disable level.
When element 49 picks up during motor start up, neither a picks up
signal nor an event code will be generated.
REM 610 REM 610
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