mbrooke
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Explain. The OC is so a fault on the spare bus gets detected.
CT reversed in bus differential zone
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Explain. The OC is so a fault on the spare bus gets detected.
cant the partial differential detect the fault at the spare bus?
there will be two 87 protecting half of the bus.. one for bus a and one for bus b, they overlap via bus coupler ct.. so whatever the configuration, it is okay..
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there will be two 87 protecting half of the bus.. one for bus a and one for bus b, they overlap via bus coupler ct.. so whatever the configuration, it is okay..
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Agreed. But he needs an additional set of CTs on the other side of the coupler breaker.
Bugman1400
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Agreed, a single bus diff that is connected to all the shown CTs except the coupler CT could potentially work without having to short anything. Shorting CTs via the test switch with an enabled bus diff is bad practice. The more common practice is to temporarily disable the bus diff scheme during switching. Bus faults can be covered during a disabled diff scheme by remote-end relaying. However, the clearing times have to be verified.
mbrooke
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What happens when the bus differential is enabled while a CT is switched out?
I am hesitant on complete disable as the clearing times crawl into Zone 2.
mbrooke
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The coupler CT. This will take the coupler out of the normal bus zone, effectively making both bars one single zone which will allow switching to take place unimpeded.
This is all on the drawing board for now, hence all the "what ifs".
Looking back at your single line diagram; since you have the ABS's of your feeder breakers selectable to either bus, methinks that coupler CT of yours will not register any current when those switches will be actuated.
mbrooke
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Thats the whole point, when the coupler CTs are opened, the idea is to have it out of the differential zone so bays can be transferred from bus 1 to bus 2.
i still dont understand the what ifs..
just like ive said, partial 87 will take care of it, whatever the configuration on either bus coupler or feeders.
the coupler will only be indicated whether it is one bus or two bus zones for 87b.. if bus coupler is open, then two 87bs.. if close one 87b configured as partial 87b with check zone..
thats it..
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mbrooke
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But the catch is the disconnects do not have any position switches. However, I guess my best bet is a 487B?
Bugman1400
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As far as I can tell, since the load/source CTs are on the line and not on the disconnect legs, the CTs would not care which bus and disconnect the flow is from/to. The coupler CT would not be used.
mbrooke
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But the coupler CT will need to be included in order to clear a fault on the aux bus when the station is in "normal" mode. Otherwise the zone of protection will reach into the aux bus.
for me, it is not a catch, since this discussion is in its planning stage, why purchase disconnects that dont have position switches? this is a must requirement if you are planning to use 87b, that is, for me..
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agreed, for me, i will do simulations to recheck this.. just to make sure..
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mbrooke
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The relaying is in the planning stage. Yes position switches could be added, but ultimately I'd like to keep costs low down.
Bugman1400
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So what? With your way, what will clear for a fault in the bus coupler? Are you worried about tripping both buses for a fault on the aux bus. I think you'll have far more nuisance tripping during this crazy switching scheme and trying to follow unclear switching procedures. Just how many aux bus faults do you expect? Is the aux bus above or below the main bus?
This is a standard configuration
posters far more knowledgable than the op (or myself) have given practical and sound advice
I would be more concerned about switching sequences and transients
you will DEFINITELY want position feedback
yet the op always comes up with an outlandish or remote scenario to make it more complicated
'what if', or 'cost considerations', or other remote hypotheticals
imo you have been given good solutions
stop trying to reinvent the wheel
SEL most likely has good guidance docs on this
posters far more knowledgable than the op (or myself) have given practical and sound advice
I would be more concerned about switching sequences and transients
you will DEFINITELY want position feedback
yet the op always comes up with an outlandish or remote scenario to make it more complicated
'what if', or 'cost considerations', or other remote hypotheticals
imo you have been given good solutions
stop trying to reinvent the wheel
SEL most likely has good guidance docs on this
mbrooke
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Not sure why you need to criticize asking intelligent questions based in reality as outlandish when judging by your posts most of your experience appears to be limited in regards to private sector MV/HV... Only dumb question is that which is never asked. Even in your line of work you can not tell me you have never worked within a budget. Sometimes you have to re-invent the wheel and consider all options on the table in order to be respected or stay employed. I have an imagination, and I am willing to use it before hand rather than after the fact.
FWIW, many older substations did not even have bus bar protection and rely on zone 2 or reverse zones to clear a bus fault. Adding position switches to existing installations is more $$$$, and they can and do fail. Some POCOs are going as far as getting rid of MODs and position switches in disconnects due to a variety of failures observed over the years. Looking at SEL's papers they talk about SBDB in a "classical" format rather than main and reserve as observed here.
But, I am open to all view points. If someone believes or knows one practice to be better over the other I will take it. I'd like to know the good, bad and the ugly before hand so to speak. :thumbsup:
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