GE Industrial Solutions Entellisys 4.0 System User Manual - Manual (Page 105)

Bus Differential Relay 105
7
7 Multipoint functions
7.1 Bus Differential Relay
Entellisys offers optional Bus Differential Relay Protection. The bus differential relay monitors the
currents on each phase entering and leaving a zone (refer to section on zones and topologies
for more information). If a fault occurs within the zone, the bus differential relay will detect this.
Because Bus Differential can discriminate between in zone and out of zone faults, the pickup
settings of the Bus Differential relay can be set independent of the settings needed to serve the
load. For example, if the 3,200A main Short Time pickup is set at 6X to start all loads than the
minimum in zone fault the main will detect is 19,200A. Bus Differential can be set to levels
similar to ground fault (1200A or less), offering far more sensitivity to detect bus and circuit
breaker faults.
Bus Differential Protection has two types of relays to select from: an alarm-only relay and a trip
relay. The trip relay also has an optional backup function. If the backup function is enabled, the
Bus Differential 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.
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.
7.1.1 Setup
7.1.1.1 Configuring Bus Differential zones
The Bus Differential configuration, namely the member circuit breakers for each zone, the
current flow direction, and the circuit breakers to trip, is set up by GE.
7.1.1.2 User settings
Entellisys supports up to 16 topologies, from 0 to 15. Topology 0 is the Reduced Let-Thru Mode
topology and topology 1 is the default topology. If no topology circuit breakers are defined,
Entellisys supports only topologies 0 and 1. See
Zones, buses, and topologies on page 101 for
more information.
Each Bus Differential Relay (Alarm-Only and Trip) can be enabled or disabled in each zone for
each topology. Bus Differential has two pickup settings and two time delay settings for each
relay (i.e., Alarm-Only and Trip) in each zone and for each topology. The backup function of the
Trip relay can be enabled to operate along with the Trip relay or after a delay of 100 msec by
selecting Trip Immediately or Trip After 100msec from the Backup Time Delta drop-down
menu on the Topology Settings tab as shown in Figure 7-3. These two settings are also
topology-specific.