Breaker Fail Philosophy
Breaker Fail Philosophy
(OP)
I am fresh out of college and entered a Substation/Transmission Engineering position, where currently there is a debate on Breaker Fail philosophy.
The question is:
On a radial 115kv substation (designed to expand to breaker and a half scheme) is it best to:
1. Use a separate 50BF relay initiated by the primary and secondary line protection relays, or
2. Program in a breaker fail scheme into both the primary and secondary line protection relays eliminating the need for another relay, knowing that the breaker fail scheme is a Breaker Fail, not a Relay Fail scheme.
The argument seems to be between saving money by reducing relays (since programming into the relays does the same thing as having a separate 50BF relay), and making it easier to test the breaker fail by having a separate relay with separate test switches, etc.
Any suggestions or comments on the best breaker fail philosophy, or what is used in your communities/companies?
The question is:
On a radial 115kv substation (designed to expand to breaker and a half scheme) is it best to:
1. Use a separate 50BF relay initiated by the primary and secondary line protection relays, or
2. Program in a breaker fail scheme into both the primary and secondary line protection relays eliminating the need for another relay, knowing that the breaker fail scheme is a Breaker Fail, not a Relay Fail scheme.
The argument seems to be between saving money by reducing relays (since programming into the relays does the same thing as having a separate 50BF relay), and making it easier to test the breaker fail by having a separate relay with separate test switches, etc.
Any suggestions or comments on the best breaker fail philosophy, or what is used in your communities/companies?






RE: Breaker Fail Philosophy
RE: Breaker Fail Philosophy
Keeping the BF inside the A & B relays keeps the systems isolated.
RE: Breaker Fail Philosophy
I prefer to use two separate breaker fail relays - one
on the A protection, and one on the B protection.
The breaker fail "initiate" input is energised by
the main protection. The trip output of the BF relay
takes its positive from the same point as the
"initiate" input.
The arrangement is designed to ensure that a busbar
trip can be issued only if both of the following occur:
(a) The main protection has operated.
(b) The BF sees current after the CB should have opened.
The scheme is more secure than one programmed into the
main protection relay, because two separate relays
must "vote" together before a bus trip occurs.
If, due to a programming error or malfunction, the
main protection relay operates incorrectly, the worst
that can result is the tripping of the protected object.
No bus trip can result because the BF relay will
perform its own current check.
If the BF relay operates incorrectly, the bus cannot
be tripped because the main protection has not provided
a positive for the BF relay to trip the bus with.
An added advantage is that the wiring and settings for
the BF relay are simple, standard, and well understood
by the field staff.
Bear in mind that testing a BF scheme for security is
very difficult. Typical relay tests involve providing
some input and checking that the right response occurs.
Proving that a scheme will NOT trip in all circumstances
when it shouldn't is practically impossible.
Some will argue that my approach is too costly. This cost
should be weighed against the cost of an incorrect busbar
trip. In a radially-fed substation, a bus trip may not
be a big deal.
If two separate BF relays cannot be provided, I would
prefer to program an internal BF into each main relay
rather than crossing A/B wiring.
Thanks,
Submonkey
RE: Breaker Fail Philosophy
RE: Breaker Fail Philosophy
RE: Breaker Fail Philosophy
RE: Breaker Fail Philosophy
If we had dual batteries, I would be more likely to want truely independant and redundant protection. With only a single battery, the remote backup requirements for battery failure seems comparable to a breaker failure with a primary relay failure.
RE: Breaker Fail Philosophy
I am told that SEL is about to release SEL411L relay which has dual CT input and will replace SEL 311L relay
RE: Breaker Fail Philosophy
http://www
RE: Breaker Fail Philosophy
Thank you bacon4life for that document.
RE: Breaker Fail Philosophy
RE: Breaker Fail Philosophy