Short-Circuit Protection - ABB REM 610 Technical Reference Manual

REM 610
4.1.4.4.
30
Motor Protection Relay
Technical Reference Manual
~ 100 ms' pickup time and calculate the thermal stress value, I
phase currents have fallen below the set pickup value. When the calculated value
exceeds the reference value, (48/14 PICKUP)
generate a trip signal. The element will be reset in 240 ms after all three phase
currents have fallen below the set pickup value of the element.
The operate time is calculated as below. However, the shortest possible operate time
of element (48/14 PICKUP)
is ~300 ms.
(48/14 PICKUP)
t[s] =
where
t = operate time
48/14 PICKUP = set start-up current of motor
48/14 TDLY= set start-up time of motor
I = phase current value
An advantage of start-up supervision based on thermal stress calculation is that the
operate time will be automatically extended during low-voltage conditions as it
depends on the start current of the motor.
Note!
Element (48/14 PICKUP)
cannot be used concurrently with element 48/14 based on definite time.
Start-up supervision with speed switch
In case the safe stall time is shorter than the start-up time of the motor stated by the
motor manufacturer, as with motors of ExE-type, for instance, a speed switch on the
motor shaft is required to give information on whether the motor is accelerating
during motor start up. The speed switch should be open at standstill and closed
during acceleration.
Elements 48/14 based on definite time and
thermal stress calculation will be blocked on activation of the speed switch input.

Short-circuit protection

The non-directional short-circuit protection detects overcurrent caused by
interwinding, phase-to-phase and phase-to-ground short circuits.
When one or several phase currents exceed the set pickup value of element 50P, 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 high-set overcurrent element can be given an instantaneous
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.
2
x (48/14 TDLY) , the element will
2
x (48/14 TDLY) based on thermal stress calculation
2
x (48/14 TDLY)
2
I
2
x (48/14 TDLY) based on thermal stress calculation
(48/14 PICKUP)
1MRS 755537
2
x t, until all three
2
based on
x (48/14 TDLY)