Current Differential Relay
GARD 8000 SYS RFL Electronics
June 20, 2014 13-57 973.334.3100
13.5.1.3 CLOSE INTO FAULT PROTECTION
The bias boost function described in section 13.5.1.2.7 allows the current differential protection
routines to provide the required CIF protection.
13.5.1.4 HIGH-SET TRIP PROTECTION
As described in section 13.5.1.2 the current differential routines work entirely upon half-cycle current
measurements which, by definition, cannot be completed until the half cycle is completed. In cases of
extremely high fault currents it is desirable to provide a mechanism that does not require the half-cycle
measurement. This is for two reasons; first, it provides faster tripping and, second, the fault may cause
an extended delay in the zero-crossing of the current (which is used to determine the bounds of the
half-cycle measurement). The relay includes a high set trip (HST) routine for this purpose.
The HST algorithm is a two stage process. First, if a relay measures inordinately high current it sends
a message to the remote relay. The remote relay then checks it’s measured current and blocks the trip
if it is an external fault. If the remote relay does not determine it to be an external fault it will trip and
send a trip signal back to the originating relay.
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