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Thread: CT reversed in bus differential zone

  1. #21
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    Quote Originally Posted by rian0201 View Post
    hihi.. is the OC backup in your scheme? it is always to do the backup.. for me, i would use partial 87 with check zone and finish..


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    Explain. The OC is so a fault on the spare bus gets detected.
    What is esoteric knowledge today will be common knowledge tomorrow.

  2. #22
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    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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  3. #23
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    Quote Originally Posted by rian0201 View Post
    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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    Agreed. But he needs an additional set of CTs on the other side of the coupler breaker.

  4. #24
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    yes i agree i think if the 87 is one unit, it could be done.


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  5. #25
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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.

  6. #26
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    Quote Originally Posted by Bugman1400 View Post
    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.
    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.
    What is esoteric knowledge today will be common knowledge tomorrow.

  7. #27
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    which ct is switched? is it that when a feeder is transferred?

    i thought that the 87b is dynamic? it automatically takes care for that as long as you programmed it to do so..


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  8. #28
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    Quote Originally Posted by rian0201 View Post
    which ct is switched? is it that when a feeder is transferred?

    i thought that the 87b is dynamic? it automatically takes care for that as long as you programmed it to do so..


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

  9. #29
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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".
    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.

  10. #30
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    Quote Originally Posted by topgone View Post
    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.
    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.
    What is esoteric knowledge today will be common knowledge tomorrow.

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