Ground-Fault Protection - ABB REF610 Technical Reference Manual

1MRS755535
5.1.4.3.
Feeder Protection Relay
Technical Reference Manual - ANSI Version
Element 50P-2 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.
Elements 50P-1 and 50P-2 will be reset in 50 ms after all three phase currents have
fallen below the set pickup value of the element.
Elements 51P and50P-1 can be set to be blocked by the auto-reclose
function.

Ground-fault protection

The non-directional ground-fault current protection detects phase-to-ground
currents, caused by insulation failure due to ageing and thermal cycling, for
instance.
When the ground-fault current exceeds the set pickup value of the low-set element,
51N, the element will generate a pickup signal after a ~ 60 ms' pickup time. When
the set operate time at definite-time characteristic or the calculated operate time at
IDMT characteristic elapses, the element will generate a trip signal. The low-set
element can be given an instantaneous characteristic by setting the operate time to
the minimum, i.e. 0.05 s.
Element 51N has a settable resetting time (both at definite-time and IDMT
characteristics),RSET, for reset coordination with existing electromechanical relays
or for reducing fault clearance times of recurring, transient faults. If element 51N
has started and the ground-fault current falls below the set pickup value of the
element, the pickup of the element will remain active for the set resetting time. If the
ground-fault current exceeds 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 starts because of current spikes, it will not be
immediately reset. However, if element 51N has already tripped, the element will be
reset in 50 ms after the ground-fault current has fallen below 0.5 times the set pickup
value of the element.
The inverse-time function of element 51N can be set to be disabled when element
50N starts. In this case, the operate time will be determined by element 50N. The
selection is made in SGF4.
When the ground-fault current exceeds the set pickup value of the high-set element,
50N, the element will generate a pickup signal after a ~ 40 ms' pickup time. When
the set operate time at definite-time characteristic elapses, the element will generate
a trip signal. The high-set 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 the ground-fault current has fallen below the set pickup value of the
element.
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