ABB REM 610 Technical Reference Manual page 36

REM 610 REM 610
36
Motor Protection Relay
Technical Reference Manual - ANSI Version
Start-up supervision based on definite-time overcurrent
protection
The non-directional low-set element, 48/14, detects overcurrent, caused by an
overload or a short circuit, for instance. When one or several phase currents exceed
the set pickup value of element 48/14, the element will generate a pickup signal after
a ~ 55 ms' pickup time. When the set operate time elapses, the element will generate
a trip signal.
The overcurrent element will be reset when all three phase currents have fallen
below the set pickup value of the element. The resetting time depends on how sharp
the drop is: if the phase currents fall below 0.5 x 48/14, the element will be reset in
10 ms; if the phase currents fall below 48/14 but not below 0.5 x 48/14 PICKUP, the
element will be reset in 50 ms.
It is possible to block the tripping of the low-set overcurrent element by applying a
digital input signal to the relay.
A disadvantage of start-up supervision based on definite-time overcurrent protection
is that the operate time is fixed and cannot be extended during low-voltage
conditions.
Element 48/14 cannot be used concurrently with element (48/14
2
PICKUP)
When element 48/14 picks up during motor start up, no pickup signal
will be generated.
Start-up supervision based on thermal stress calculation
Element (48/14 PICKUP)
locked rotor during motor start up, for instance. The element can be set to pickup
either when the conditions for motor start up are met or when one or several phase
currents exceed the set pickup value. The selection is made in SGF3.
When element (48/14 PICKUP)
conditions for motor start up are met, the element will calculate the thermal stress
2
value, I x t, for as long as the conditions for motor start up are met and compare it
to a reference value, (48/14 PICKUP)
to equal the amount of thermal stress built up during a normal start up of the motor.
The element will not generate a separate pickup signal. When the reference value is
exceeded, the element will generate a trip signal. The element will be reset in 240
ms after the motor start up has ended and the motor is running.
When element (48/14 PICKUP)
or several phase currents exceed the set pickup value (Ip>48/14 PICKUP), the
element will generate a pickup signal after a ~ 100 ms' pickup time and calculate the
x 48/14 TDLY.
2
x (48/14 TDLY) detects thermal stress, caused by a
2
x (48/14 TDLY) has been set to pickup when the
2
x (48/14 TDLY). The reference value is set
2
x (48/14 TDLY) has been set to pickup when one
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