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Thread: CT reversed in bus differential zone

  1. #31
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    Quote Originally Posted by mbrooke View Post
    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".
    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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  2. #32
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    Quote Originally Posted by rian0201 View Post
    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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    But the catch is the disconnects do not have any position switches. However, I guess my best bet is a 487B?
    What is esoteric knowledge today will be common knowledge tomorrow.

  3. #33
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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.

  4. #34
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    Quote Originally Posted by Bugman1400 View Post
    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.
    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.
    What is esoteric knowledge today will be common knowledge tomorrow.

  5. #35
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    Quote Originally Posted by mbrooke View Post
    But the catch is the disconnects do not have any position switches. However, I guess my best bet is a 487B?
    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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  6. #36
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    Quote Originally Posted by Bugman1400 View Post
    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.
    agreed, for me, i will do simulations to recheck this.. just to make sure..


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  7. #37
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    Quote Originally Posted by rian0201 View Post
    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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    The relaying is in the planning stage. Yes position switches could be added, but ultimately I'd like to keep costs low down.
    What is esoteric knowledge today will be common knowledge tomorrow.

  8. #38
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    Quote Originally Posted by mbrooke View Post
    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.
    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?

  9. #39
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    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



  10. #40
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    Quote Originally Posted by Ingenieur View Post
    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


    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.
    What is esoteric knowledge today will be common knowledge tomorrow.

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