SEL-352
SEL-352
(OP)
When can a substation get away without having breaker failure relays?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: SEL-352
RE: SEL-352
FWIW, as a side, if you have two breakers in series my understanding is you can skip breaker failure protection?
RE: SEL-352
In the newer relays with built in breaker failure logic we use that, but in the 311 family, when connected to a single breaker, it's real easy to implement breaker failure in logic.
Tripping two breakers in series should drastically reduce the chances of breaker failure but I'd still be prepared for it. The fault could be between them so a single breaker failure still needs additional tripping. Simultaneous failure of multiple breakers can, and has, happened. One large company discovered that the hard way. Eventually they determined that the wrong grease had been used during breaker maintenance and a whole bunch of breakers had frozen up.
RE: SEL-352
https://cdn.selinc.com//assets/Literature/Product%...
But personally for my applications it would be a significant over investment that is unlikely to pay back at first glance. Currently all breakers I deal with are single 3 phase units commanded by two sets of relays (primary and secondary backup). If both have BF equipped and enabled, I am already covered with a stand alone unit having no merit. I did find this paper on the subject, very helpful:
https://cdn.selinc.com//assets/Literature/Publicat...
Good point regarding fault in between the breaker, although Id imagine multiple breaker failures in a substation would require something far more complex like remote tripping than simply opening all the breakers on the buss as current BF relays do in my setup.
The station that had the seized breakers, was this the double breaker double buss station you mentioned a while back lol?
RE: SEL-352
I am a bit confused by what they mean in regards to main and transfer buss as my understanding has always been that main and transfer buss substations are always designed and relayed as a single simple buss having no dynamic zones of protection. Unless they are referencing a concern regarding the transfer buss breaker (I treat the transfer buss as a transmission line)?
RE: SEL-352
In a number of our older bulk power stations there's a 230kV M&T high side with a single main bus that includes two 230/115kV transformers. On the low side there's a single aux (transfer) bus but three segments to the main bus. Each transformer is on an end and the tie (substitution) breaker is on the middle section by itself. The two sectionalizing switches are interlocked so that they can't both be closed at the same time. This way one tie breaker can serve two otherwise independent buses. BF for the tie needs to know which bus lockout to trip.
RE: SEL-352
In any case I want to give you a big Thank you. :) Your knowledge on the subject is worth its weight in gold.
RE: SEL-352
To those who went from separate stand alone relays to an integrated approach, what pros and cons have you witnessed? Any misoperations? Or simply stop worrying enjoy the benefits?
RE: SEL-352
I have also seen SEl-421/411L/311L 321/311C schemes where 50BF & 79 is implemented into the relays to trip the 86B/86BF. The advantage I see from this scheme is that an entire protection system (Primary or backup) can be taken out of service for maintenance / modifications, without the loss of BF protection. It makes things a bit easier to explain to system operations that only the primary, or back up protection will be out of service, when starting work. Generally with the Transco this is straightforward, but if dealing with other entities such as Genco (Nuclear especially), having all parties aware that all functionality is in place is a statement most like to hear.
As far as reducing testing errors, yes it can occur, but if a BF trip from an IED that does it internally, or one that just initiates a dedicated relay, in either case the schematic was not analyzed and all trips or initiates were not pulled.
RE: SEL-352
Over the years we've seen more examples of inputs picking up falsely than we have of outputs closing falsely. Based on that, I'd say that internal BF is more secure than a separate BF relay.
Different utilities look at identical problems and come up with very different solutions; there's no single right answer.
RE: SEL-352
Where inputs have failed to pickup correctly, was this via incorrect settings or a defect within the relay itself?
RE: SEL-352
In my system breaker failure energizes the same master trip circuit that buss differential energizes, unless of course its dynamic zones, which BF simply tells the buss diff relay to trip the buss in question by its own logic. FWIW I do not employ lockout relays since buss faults have the option of being reset by SCADA (yes I know that may turn heads lol). But in any case what matters is having the BF mechanism close its contacts only when a breaker has actually failed.
Same here, my thinking precisely. Having all functions in service without any portion being taken out during maintenance gives the biggest appeal for me ditching separate relays. IF security can be met, its a no brainier.
I run my trip circuit through the test switches, and plan on doing the same for the breaker failure circuit coming out of the relay.
RE: SEL-352
My thinking: program SEL411L and SEL 311L (and the like) so that internal BF is automatically initiated when a dedicated input is energized (by the buss trip relay). This way each line relay will try and re-trip its breaker along with initiating the BF timer. IF CTs do now drop below 100amps after a 8 cycles a DTT signal will be sent to the remote station via fiber optic path (OPGW) supporting normal current differential.
For transformer relays the same input will take place, however instead the relay will trip the low side breaker (as will probably happen even for a normal breaker response).
I've checked the SEL manuals and nothing stands out regarding this.
The other option is simply clearing via zone2/zone3 which is intend only as an absolute last resort.
How easily doable/common is this?