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Thread: Transformer Issue

  1. #31
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    Quote Originally Posted by brian john View Post
    Understand but a Turn Ratio Test should ascertain if a turns to turns short existed?
    Well, yes, theoretically, as long as your measuring technique can tell the difference between a 500:250 ratio and a 499:250 ratio.

    Sent from my XT1585 using Tapatalk

  2. #32
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    We own several TTR meters manufactured by Megger.

    http://www.mitchellinstrument.com/me...YaAl4rEALw_wcB
    Brian John
    Leesburg, VA

  3. #33
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    Quote Originally Posted by brian john View Post
    It appears the shield ground is internal and not accessible.
    Is the core strap accessible? if so for the sake of process of elimination, temporarily unground it with no load and confirm this is the problem area. it sounds to me like the source feeding this xfmr is corner grounded secondary, is this correct? whether low impedance or not. i am questioning the insulation resistance test results, it just sounds exactly like a primary winding is shorted and your source is impedance grounded. textbook. i hate asking you because i know you are light-years ahead of me in the testing realm but what voltage did you use primary to core/ground(if core is grounded)?
    Last edited by Wire-Smith; 12-19-18 at 07:05 PM.

  4. #34
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    Quote Originally Posted by Wire-Smith View Post
    Is the core strap accessible?
    No

    if so for the sake of process of elimination, temporarily unground it with no load and confirm this is the problem area. it sounds to me like the source feeding this xfmr is corner grounded secondary, is this correct?
    Supply is from a solidly grounded wye



    whether low impedance or not. i am questioning the insulation resistance test results, it just sounds exactly like a primary winding is shorted and your source is impedance grounded. textbook. i hate asking you because i know you are light-years ahead of me in the testing realm but what voltage did you use primary to core/ground(if core is grounded)?
    [/QUOTE]

    We insulation resistance tested at 1000 VDC

    The manufacturer is pulling an identical transformer out of stock and performing some test at the factory. If the electrical contractor can get approval from his customer I would like to perform another load test monitoring primary and secondary voltage and current (phase, neutral and ground current)
    Brian John
    Leesburg, VA

  5. #35
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    Quote Originally Posted by brian john View Post



    Supply is from a solidly grounded wye



    We insulation resistance tested at 1000 VDC

    The manufacturer is pulling an identical transformer out of stock and performing some test at the factory. If the electrical contractor can get approval from his customer I would like to perform another load test monitoring primary and secondary voltage and current (phase, neutral and ground current)
    Gotcha,

    Now i am thinking the laminations are unintentionally grounded at two points and allowing circulating current in the surrounding connected metal material. I'm not familiar with shields but it could be something like that with the shield as well. by my understanding of the description given with no accessible ground strap i have no idea how to check this without some dissection.
    Last edited by Wire-Smith; 12-20-18 at 06:36 PM.

  6. #36
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    Quote Originally Posted by brian john View Post
    The manufacturer is pulling an identical transformer out of stock and performing some test at the factory. If the electrical contractor can get approval from his customer I would like to perform another load test monitoring primary and secondary voltage and current (phase, neutral and ground current)
    I am certainly interested to hear about the findings when finished.
    BB+/BB=?

  7. #37
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    As a subcontractor, I am not on the job to do any further testing but the electrician on site is filling me in. The manufacturer set up an identical transformer in the same setup, they had current on the frame ground conductor, they rerouted this conductor and the ground current dropped.

    The electrical contractor rerouted the conductor and the current dropped from 15.9 amps to 11.7 amps. At the factory, they were able to lower the amperage to 10.0 amps. The manufacturer feels this level of current is acceptable but not say why it is acceptable.

    I asked the electrician to extend the ground conductor which would allow him to move the conductor in different directions and see if how the current changes.

    The end user wants a letter from the manufacturer stating this is an acceptable level of current.


    I would like to get back on site to load test the UPS and transformer and watch this current at different load levels as well as move the conductor as load levels are stepped up and see how that affects the current compared to the primary current..
    Brian John
    Leesburg, VA

  8. #38
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    It may also be clarified from the manufacturer whether the transformer shield is grounded at more than one point in which case objectionable induced current would exist.

  9. #39
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    Thanks for the update. Please share additional info if you get any.

    Got any pics that might show how the ground wire is being moved around and how it might be interacting with the fields? Must be cutting field lines somewhere to get the induced current but why would the design have it in the way to start with?
    BB+/BB=?

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