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Transmission Line Fault Question

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  1. Jtmc78 is offline Junior Member
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    Transmission Line Fault Question

    Hey guys- just putting this out there- has anyone seen a question like this on the new test?

    Two 138 KV lines are separated by a separate line source breaker and incoming line breaker. A
    fault occurred at one of the transmission lines tripping the source breaker and corresponding
    station breaker the source breaker on the un-faulted line also tripped what is the most likely
    cause for tripping the un-faulted line?
    A. Breaker coordination too slow
    B. Uneven loading
    C. ferro Resonance thru xfmr to trip other OCB
    D. broken piolet relays
    E. Load sheading

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    Quote Originally Posted by Jtmc78 View Post
    Hey guys- just putting this out there- has anyone seen a question like this on the new test?

    Two 138 KV lines are separated by a separate line source breaker and incoming line breaker. A
    fault occurred at one of the transmission lines tripping the source breaker and corresponding
    station breaker the source breaker on the un-faulted line also tripped what is the most likely
    cause for tripping the un-faulted line?
    A. Breaker coordination too slow
    B. Uneven loading
    C. ferro Resonance thru xfmr to trip other OCB
    D. broken piolet relays
    E. Load sheading
    Just taking a guess, ferro resonance makes the most sense to me. Pilot relays are working if source and station tripped on the faulted line, so option C is out. A, B, and E seem like distractors. What are your thoughts?

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  5. Jtmc78 is offline Junior Member
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    Quote Originally Posted by SecondGen View Post
    Just taking a guess, ferro resonance makes the most sense to me. Pilot relays are working if source and station tripped on the faulted line, so option C is out. A, B, and E seem like distractors. What are your thoughts?
    I really don't know that's why I asked- lol.

    If I was thinking about real world problems instead of how to answer questions on a test. It could be that source breaker relay coordination and breaker operating cycles incorrect, say the two source breakers that tripped was on the same bus, could push into breaker failure and clear that bus. The question does not really specify transformers at each end although probable.
    In my hypothetical - relays are set for 50BFT=2cy and breaker takes 5cy to clear fault.

    If I was thinking as a relay tech because relay techs always check for coordination by comparing name plate of breaker and settings which operate it. . It would be uneven loading caused by sagging voltage on the adjacent line breaker due to the fault on the other line, coupled with incorrect time delay on voltage elements. Also, its never the relay guys fault.

    If I was thinking all fancy and on a test my answer would be Ferro resonance through transformer. As that is pretty much the definition, but the question should say it has transformers- wouldn't the transformer relay see this as well?

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