Overcurrent Protection - ABB REF 610 Technical Reference Manual

1MRS 755535
4.1.4.2.
Feeder Protection Relay
Technical Reference Manual - ANSI Version

Overcurrent protection

The non-directional overcurrent protection detects overcurrent caused by phase-to-
phase and phase-to-ground short circuits.
When one or several phase currents exceed the set pickup value of the low-set
element, 51P, the element will generate a pickup signal after a ~ 55 ms. When the
set operate time at definite-time characteristic or the calculated operate time at
IDMT (mode) characteristic elapses, the element will generate a trip signal. Element
51P has a settable resetting time (both at definite-time and IDMT (mode)
characteristics), RSET, for reset coordination with existing electromechanical relays
or for reducing fault clearance times of recurring, transient faults. If element 51P has
picked up and the phase currents fall below the set pickup value of the element, the
pickup of the element will remain active for the set resetting time. If the phase
currents exceed the set pickup value again, while the timer is being reset, the pickup
of the element will remain active. Consequently, the set resetting time ensures that
when the element picks up because of current spikes, it will not be immediately
reset. However, if element 51P has already tripped, the element will be reset in 50
ms after all three phase currents have fallen below 0.5 times the set pickup value of
the element.
The inverse-time function of element 51P can be set to be disabled when element
50P-1 and/or 50P-2 picks up. In this case, the operate time will be determined by
element 50P-1 and/or 50P-2. The selection is made in SGF4. It is possible to block
the tripping of the low-set overcurrent element by applying a digital input signal to
the relay.
When one or several phase currents exceed the set pickup value of the high-set
element, 50P-1, the element will generate a pickup signal after a ~ 30 ms' pickup
time. When the set operate time at definite-time characteristic elapses, the element
will generate a trip signal. Element 50P-1 can be given an instantaneous
characteristic by setting the operate time to the minimum, i.e. 0.04 s.The set pickup
value of element 50P-1 can be set to be automatically doubled in a pickup 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
element 50P-1. A pickup situation is defined as a situation where the maximum
phase current rises from a value below 0.12 x 51P to a value above 1.5 x 51P within
less than 60 ms. The pickup situation ends when all phase currents fall below 1.25 x
51P and remain below for at least 200 ms. The selection is made in SGF4.
It is possible to block the tripping of the high-set overcurrent element by applying a
digital input signal to the relay.
Element 50P-1 can be set out of operation in SGF3. This state will be indicated by
dashes on the LCD and by "999" when the set pickup value is read via serial
communication.
When one or several phase currents exceed the set pickup value of the instantaneous
element, 50P-2, the element will generate a pickup signal after a ~ 30 ms' pickup
time. When the set operate time at definite-time characteristic elapses, the element
will generate a trip signal. Element 50P-2 can be given an instantaneous
characteristic by setting the operate time to the minimum, i.e. 0.04 s.
REF 610
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