Is Breaker Fail protection relevant!!
Is Breaker Fail protection relevant!!
(OP)
Present day breakers (both outdoor and indoor) have compact operating mechanisms with less moving components and made with better materials. Hence, breaker stuck conditions are extremely rare.
Hence, do you think the protection schemes can do away with breaker fail protection!!
Hence, do you think the protection schemes can do away with breaker fail protection!!






RE: Is Breaker Fail protection relevant!!
RE: Is Breaker Fail protection relevant!!
Three years ago we had a generator loose it's speed signal and went to trip on overspeed. The wires had not been hooked up due to an incomplete controls upgrade. Luckily our 86BF (Breaker fail) relay picked up and dropped the unit offline.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Is Breaker Fail protection relevant!!
When a BFP actuates incorrectly, the affected servcie area is much larger than a single breaker trip. That is why a lot of care must be taken in selecting the correct logic and settings for a BFP system.
An old IEEE survey identified maintenance work as a major cause of a breaker's failure to operate. A control power switch, manual interlock or lifted wire left in the wrong position after maintenance prevented correct breaker operation. Modern breakers require less maintenance so probability of failures due to the historical causes should be less. But the remianing failures can still be catastrophic.
RE: Is Breaker Fail protection relevant!!
It's a intresting Q.
We also thinks about it.
On this moment:
1. For the voltage level from 69kV, we use 50BF/BFP.
2. For the MV, where used reversed logic, we don't use 50BF/BFP, but if the a generator bus, we used 50BF/BFP
For the HV, we used BFP as part of BBP(87B).
So, is depend.
Best Regards.
Slava
RE: Is Breaker Fail protection relevant!!
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RE: Is Breaker Fail protection relevant!!
PHovnanian, TurbineGen, and rcwilson also offer valid reasons for failure to open (failure of CT's or relays, improper control upgrade, and improper maintenance procedures).
I would not do away with the failure to open protection since this is a good backup to all of the above conditions.
RE: Is Breaker Fail protection relevant!!
I think it is best to have layered/backup protection. With newer relay designs incorporating multi-functions, one could invest on a separate backup scheme (BFP, etc.). The key is to never rely on a single protection scheme or protection lumped in one physical space. However, it's the protection engineer's call! Extra relaying could be very prohibitive in some cases, IMHO.
RE: Is Breaker Fail protection relevant!!
May you grow up to be righteous, may you grow up to be true...
RE: Is Breaker Fail protection relevant!!
Most applications I have seen use over current as a requirment.
However if set to low it can be misoperated for a tech. mistake and normal load currents.
Also for generator protection, a trip can be issued for a very low current condition.
Would it be prudent to apply a more than one misoperation mode BFP?
RE: Is Breaker Fail protection relevant!!
The risks are false trips by technicians, and bigger outages as well.
Our solution is to include BF Trip isolations in the formal switching instructions, along with formal training and authorisation of staff to carry out these isolations.
We also use a different type of link for the BF Trip, just so it stands out from the others, and makes the technician think.
RE: Is Breaker Fail protection relevant!!
cranky108, you are right.
Newer relays have a few criterions for the BFP scheme.
High current criterion
Low current with CB position criterion
Mix of both of criterions, for example: if current less then 0.3In CB position criterion will operated, if more, CB postition dosen't taked in account.
Is a good practic for the transformer and generator protection, like to reverse power, frequency and voltage protection, mechanical protection of transfromer, etc.
Newer relays have also option of SF6 signal (CB fault) for the BFP accelaration.
Best Regards.
Slava
RE: Is Breaker Fail protection relevant!!
Also in BFP logic, do many of you use the manual trip switch as a BFP initiate command? Some of our clietns reason that the operator should be aware that the breaker failed to open, so their BFP logic is only initiated by fault protections. This is to avoid nuisance trips.
RE: Is Breaker Fail protection relevant!!
If generator loose it's speed signal how breaker failure protection was initiated?