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Thread: Introduction to TTR Testing

  1. #1
    Join Date
    Apr 2015
    Location
    IL
    Posts
    188

    Introduction to TTR Testing

    Forum,

    We have a TTR in our shop that I've never seen used, and we had an arrester blow on one of our power transformers, so I thought I'd get it out and mess with it. Got it hooked up to a 13,800 HV Delta to 480 LV Wye w/ Neutral transformer. For the V-Ratio I get 28.756, 28.757, and 28.759. For the T-Ratio I get 49.806, 49.809, and 49.812. Seems pretty good to me. Just a few questions I have are 1) is there a general rule of thumb in terms of TTR testing tolerances? I've heard 0.05 percent from theoretical but wondering if the forum has heard anything different, and 2) is it a requirement to unwire the transformer when doing TTR, or can the primary and secondary wires still be landed but obviously isolated from the source and load? Would this skew the testing results?

    Thanks as always

  2. #2
    Join Date
    Jun 2003
    Location
    NE (9.1 miles @5.07 Degrees from Winged Horses)
    Posts
    10,198
    Quote Originally Posted by adamscb View Post
    Forum,

    We have a TTR in our shop that I've never seen used, and we had an arrester blow on one of our power transformers, so I thought I'd get it out and mess with it. Got it hooked up to a 13,800 HV Delta to 480 LV Wye w/ Neutral transformer. For the V-Ratio I get 28.756, 28.757, and 28.759. For the T-Ratio I get 49.806, 49.809, and 49.812. Seems pretty good to me. Just a few questions I have are 1) is there a general rule of thumb in terms of TTR testing tolerances? I've heard 0.05 percent from theoretical but wondering if the forum has heard anything different, and 2) is it a requirement to unwire the transformer when doing TTR, or can the primary and secondary wires still be landed but obviously isolated from the source and load? Would this skew the testing results?

    Thanks as always
    What is a TTR?
    Obviously I won’t be answering your questions.
    Tom
    TBLO

  3. #3
    Join Date
    Nov 2014
    Location
    Miami, Florida, USA
    Posts
    185
    Transformer turns ratio.

  4. #4
    Join Date
    Jan 2014
    Location
    chicago, il, USA
    Posts
    410
    I don't know that it would skew the results, but in a typical test yes all cables are completely disconnected from the Transformer.
    The world is round, you will get there no matter what path you take.

  5. #5
    Join Date
    Feb 2005
    Location
    Charlotte, NC
    Posts
    6,801
    TTR results should not deviate by more than 0.5% from either adjacent coils or nameplate ratio per ANSI/NETA MTS

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