5-2
Applications
Date Code 20010515
SEL-2BFR, -2/BFR Instruction Manual
a short safety margin should be added. The amount of time available for a safety margin is
limited by the operating time of the line protective relays and the local and remote breakers.
When the failed breaker is isolated by disconnect switches or removed from service for
maintenance and testing, the breaker failure scheme should be disabled. This prevents
inadvertent tripping of other breakers in service.
Figure 5.2: Basic Breaker Failure Scheme Timing
The breaker failure scheme discussed above protects the breaker and line equipment when the
breaker fails to clear a fault. Other breaker failure modes include:
Failure of breaker to trip load current
Failure of breaker to open completely, leaving trip resistors in service
Failure of breaker to close completely, leaving close resistors in service
Failure of a breaker pole to close
Pole flashover failure while breaker is open
You can enable the SEL-2BFR Relay to protect a breaker independently for each of these failure
types, as shown below.
In ring-bus and breaker-and-a-half installations, two circuit breakers must operate to interrupt line
current. Current distribution between the two breakers is unknown until the first breaker opens.
The bulk of fault current initially may be carried by a single breaker. Both breakers receive the
trip signal at the same time, but the 50FT element associated with the low current breaker may
not assert until the other breaker opens. This causes an uncertainty with respect to the timing of
50FT element assertion. This uncertainty is not present in a single breaker arrangement. Timing
uncertainty is accounted for in the SEL-2BFR Relay breaker protection schemes intended for
these complex bus/breaker arrangements. The SEL-2BFR Relay is intended to protect a single
breaker, regardless of the bus/breaker arrangement. In breaker-and-a-half and ring-bus
arrangements, you must use an independent breaker failure relay for each breaker.
The SEL-2BFR Relay simplifies breaker failure protection schemes by combining the relay
elements, timer, and logic in one small package. Panel space, wiring, and maintenance
Содержание SEL-2BFR
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Страница 234: ...C 8 Appendix C Date Code 990714 SEL 2BFR 2 BFR Instruction Manual Figure C 2 Horizontal Front and Real Panel Drawings ...
Страница 235: ...Date Code 990714 Appendix C C 9 SEL 2BFR 2 BFR Instruction Manual Figure C 3 Vertical Front and Rear Panel Drawings ...
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