characteristic by setting the operate time to the minimum, i.e. 0.05 s. The element
will be reset in 50 ms after all three phase currents have fallen below the set pickup
value of the element.
The set pickup value of element 50P can be set to be automatically doubled in a
motor start-up situation, i.e. when the object to be protected is being connected to a
network. Consequently, a set pickup value below the connection inrush current level
can be selected for the element. In this case, the short-circuit protection will still
detect overcurrent caused by a locked rotor when the motor is running, which in turn
may be caused by bearing failure, for instance. The selection is made in SGF3.
When automatic doubling is in use and the FLA secondary has been set
to be very low, it must be assured that the doubled set pickup value of
element 50P does not exceed the maximum measured current.
If the FLA secondary is set to 0.5, the maximum measured current is
25 x full load current of the motor.
It is possible to block the tripping of the high-set overcurrent element
by applying a digital input signal to the relay.
The high-set overcurrent element can be set out of operation in SGF3
to prevent the contactor in a contactor controlled drive from operating
at too high phase currents. This state will be indicated by dashes on the
LCD and by
“
999
”
when the set pickup value is read via serial
communication.
When element 50P pickups during motor start up, no pickup signal will
be generated.
5.1.4.5.
Undercurrent protection
The non-directional undercurrent protection detects loss of load, caused by a
damaged pump or a broken conveyor, for instance, and can be used in applications
where undercurrent is considered a fault condition.
When all three phase currents fall below the set pickup value of element 37, the
element will generate a pickup signal after a ~ 300 ms
’
pickup time. When the set
operate time elapses, the element will generate a trip signal. To avoid tripping a de-
energized motor, element 37 will be set out of operation when all phase currents fall
below twelve per cent of the FLA of the motor.
The undercurrent element will be reset in 350 ms after one or several phase currents
have exceeded the set pickup value of the element.
38
REM 610
REM 610
Motor Protection Relay
Technical Reference Manual - ANSI Version
1MRS755537
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