2 multi-source ground-fault relay – GE Industrial Solutions Entellisys 5.0 User Manual User Manual
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Multi-Source Ground-Fault Relay
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7.2 Multi-Source Ground-Fault Relay
Entellisys offers optional Multi-Source Ground-Fault Relay Protection. Multi-source Ground Fault
is needed in systems where there is a parallel path for the neutral current, for example, in a
double-ended substation with two mains and a tie circuit breaker. In that case, the neutral
current from either side can return through both the neutral bus at the tie and the ground bus.
Therefore, a ground fault algorithm cannot just look at the currents in one main circuit breaker
or just the tie circuit breaker. MSGF is implemented on a per-zone basis (see
for more information on this topic). The zone functions measure the
total ground fault current into the zone, not the ground fault current from the source. The zone
function trips all circuit breakers that feed that zone.
MSGF also has a summation function that measures the total ground current from all sources.
The summation function and the zone functions interact. If a zone function is in pickup, the
summation function is suspended until the zone drops out of pickup. If no zone is in pickup, the
summation function trips the ties when it times out. The summation function can also be set to
open the mains. This allows the zone to clear the fault without unnecessarily tripping tie circuit
breakers in systems with three or four main circuit breakers.
Multi-Source Ground-Fault Relay has two types of relays to select from: an alarm-only relay and
a trip relay. The trip relay has a built-in backup function. MSGF also includes an optional backup
function. If the backup function is enabled, the MSGF function will open additional circuit
breakers in the event that opening the circuit breakers that feed the zone does not clear the
fault. This can happen, for example, when the fault is in a tie circuit breaker that only has one set
of CTs. The backup function can be configured to operate with no additional delay, or after 100
msec of operation of the primary relay.
Each relay comes with a set of pickup and delay settings. Each relay can have either a constant
time or an inverse time. The alarm-only relay activates an alarm if the fault is above the
specified limit for the specified duration of time. The trip relay opens/trips the trip and/or
backup targets and also activates an alarm if the fault is above the specified limit for the
specified duration of time.
7.2.0.1 Interoperation with Zone Selective Interlock function
Each MSGF zone can be configured as a member of a ZSI Ground Fault zone. See
for more information.