Integrated vs Seperate breaker faluire relays

[mbrooke]

What are the pros and cons of both?

 

[Bugman1400]

What are the pros and cons of both?

It depends on how the BF relay is set:
1.) If set above load and below min fault then, a separate BF relay will cover failure of primary relay. If connected to separate CT's then, separate BF relay covers failure of that too.
2.) The benefit for integrated BF relay is if number of CTs are limited. The lower cost is also a benefit.

 

[mbrooke]

It depends on how the BF relay is set:
1.) If set above load and below min fault then, a separate BF relay will cover failure of primary relay. If connected to separate CT's then, separate BF relay covers failure of that too.
2.) The benefit for integrated BF relay is if number of CTs are limited. The lower cost is also a benefit.

Integrated BF is simpler, however if the relays malfunctions its possible to clear the entire station. Hence my hesitation. BTW, do you really need a separate CT for BF? Whats wrong with feeding through the BF relay with the same CT as the line protection relay?

 

[Bugman1400]

Integrated BF is simpler, however if the relays malfunctions its possible to clear the entire station. Hence my hesitation. BTW, do you really need a separate CT for BF? Whats wrong with feeding through the BF relay with the same CT as the line protection relay?

As I mentioned, if your CT fails for the primary relay, it also will for the BF relay....what good is that? However, if you cannot set your BF relay above load and be able to detect its own fault (during same fault as the primary relay) then, there is no use in having a separate CT since the BF relay can only operate with a Breaker Failure Initiate (BFI) from the primary relay.

 

[mbrooke]

As I mentioned, if your CT fails for the primary relay, it also will for the BF relay....what good is that? However, if you cannot set your BF relay above load and be able to detect its own fault (during same fault as the primary relay) then, there is no use in having a separate CT since the BF relay can only operate with a Breaker Failure Initiate (BFI) from the primary relay.

Good point, I had not thought of that. So it looks like I should grab the buss differential CT, feed it through the BF relay and have both line protection relays send a signal to the BF relay when they operate?