Basler Electric BE1-851 - Manual (Page 202)

This function block has an independent fast drop out phase and ground current detector that detects a
breaker opening and stops timing. An open breaker is detected when the current drops below 10% of
nominal.
Setting the time delay at zero disables the BF function block. This permits the traditional radial system
backup scheme of coordinated relays tripping different breakers.
Contingency Operation - Backup Protection for BUS Relay Out-of-Service
When the BUS relay is out of service, backup protection is provided by the BACKUP main bus relay. The
BACKUP main bus relay provides permanent backup protection for the BUS relay regardless of other
feeder contingencies. Under this contingency, protection for bus faults will be delayed by an 18-20 cycle
coordination interval.
Contingency Operation - Backup Protection for BACKUP Relay Out-of-Service
When the BACKUP relay is out of service, full high-speed bus fault protection and overload protection are
provided by the BUS relay. Under this contingency, bus breaker failure protection is not provided, as this
is a double contingency situation.
Contingency Operation - Backup Protection for Feeder Relay Out-of-Service
OUT3 of each of the feeder relays should be wired to an auxiliary transfer relay (83/Fn) with one normally
open and one normally closed contact. Under normal conditions, OUT3 of the feeder relay is closed and
the 83 aux. Relay is picked up. When the feeder relay is out of service due to failure, being in test mode,
or if it is drawn out from its case, the 83 auxiliary relay will drop out.
The normally open contact (NO in shelf state) of the 83/Fn aux. relay is wired to Input 2 of the BACKUP
relay to signal the BUS and BACKUP relays to change to setting group 1. When the BUS relay is in
setting group 1, the 50T and 51 overcurrent function blocks trip an auxiliary tripping relay (94/BU) via
OUT5.
In setting group 1, the BACKUP relay 51 time settings must coordinate with the BUS relay 51 time dial
settings. Since the feeder relays provide a blocking signal to the BUS relay upon pickup of the 51 function
blocks, it is not necessary for the 51 time dial settings on the BUS relay to coordinate with the feeder
relays in setting group 1. Therefore, the 51 time dial settings of the BUS relay can be reduced in setting
group 1 to provide the necessary coordination interval between the BUS relay and the BACKUP relay for
this contingency. This minimizes the time delay that needs to be added to the 51 time dial settings for the
BACKUP relay and provides a greater opportunity to keep the setting below the transformer damage
curve.
The tripping output of the 94/BU auxiliary relay and the normally closed contacts (form B) of the 83/Fn
auxiliary relay are wired in series with the feeder breaker trip coil. This allows the 94/BU relay to trip the
feeder breaker when the feeder relay is out of service.
When the BUS and BACKUP relays are in feeder relay backup mode, operation for the various faults is
as follows:
• A fault on a feeder with its relay still in service will send a blocking signal to the BUS relay
preventing it from tripping high-speed. The 51 functions of the BUS and BACKUP relays are set
to coordinate with each other and the feeder relays.
• A fault on the feeder with the relay out of service will not send a blocking signal to the BUS relay
so it will trip the feeder breaker via the 94 and 83 relay contacts. Fault clearing will be after the 2
to 4 cycle coordination interval set on the BUS relay 50T functions or in BUS relay 51 time if the
fault is farther out. For this reason, the BACKUP relay 51 functions must be set to coordinate with
the BUS relay in this setting group.
• A fault on the bus will cause the BUS relay to trip the feeder breaker with the relay out of service
because no blocking signal will be sent by any of the feeder relays. Since this will not clear the
fault, the BACKUP relay will clear the fault with its 18-20 cycle coordination interval.
8-46 BE1-851 Application 9289900990 Rev R