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1MRS751802-MUM
REX 521
239
Protection Relay
Technical Reference Manual, Standard Configurations
Example:
Motor start-up current is 5.2
x
FLC and thereby the estimated K-setting is
175/(5.2)
2
= 6.5%.
The most severe unbalance is caused by an broken phase. It should be checked that
in case of broken (open) phase the operation time of the unbalance protection is
shorter than the permissible locked-rotor jam time.
11.7.3.6.
Phase reversal protection
The separate phase-reversal protection (3I()) checks for phase reversal conditions
based on the phase order of currents. The protection operates within a set definite
time after detecting wrong phase sequence.
Alternatively, the phase-sequence voltage protection (U1<U1U2>) can be used for
phase-reversal protection if it is set to trip at high negative phase sequence voltage.
Because the protection is based on voltage instead of current, this protection can be
used to inhibit the starting of the motor on wrong phase sequence.
The phase-reversal protections should be taken out of use for a motor which is used
also with a reversed direction of rotation.
11.7.3.7.
Undercurrent protection
The undercurrent protection (3I<) operates upon a sudden loss of load. The
protection is used, for example, for submersible pumps where the cooling is based
on a constant flow of liquid. If this flow is interrupted, the cooling capacity of the
motor is reduced. This condition is detected by the undercurrent unit, which trips the
motor.
11.7.3.8.
Fuse fail protection
If an undervoltage or phase sequence voltage protection is used, the fuse failure
supervision (FUSEF) should be used to block these protections. This will prevent
disruptive tripping (for example fuse blow) in case of failure in the voltage
measuring circuits.
11.7.4.
Condition monitoring
11.7.4.1.
Operation time counter
Operation time counting (in hours) is necessary for some motors. The TIME1
function block uses the motor runs-indication for counting the operate time. Refer
to Section 11.7.5.3. Indication of motor status on how to enable motor status
indication. The cumulative counting value is recorded.
The ALARM output of the TIME1 function block can be connected to Alarm 1 or
Alarm 2 output signal (
Main menu\Configuration\Output SWGRP\
).
The operate time alarm can also be connected to the Alarm LED 8
(
Main menu\Configuration\Alarm LEDs\
).
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