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Thread: Voltage phase shift through a transformer

  1. #1
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    Voltage phase shift through a transformer

    Is there a voltage phase shift through every transformer? If that is the case then in the case of a potential transformer, how does a relay know exactly where on the primary voltage waveform it is, if there is a voltage phase shift between the primary and secondary side of a potential transformer providing an input to an feeder protection relay?

    An example I am referencing is a 4160V to 120V potential transformer providing an voltage input/reference to a multilin feeder protection relay.

  2. #2
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    Typically there will not be a phase shift because you would not use a delta/wye transformer. Most relays today have a setting that allows you tell the relay what the primary and secondary transformer configuration is, and the relay will adjust itself. The beauty of processor based relaying.
    "Just because you're paranoid, doesn't mean they're not out to get you"

  3. #3
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    Quote Originally Posted by kingpb
    Typically there will not be a phase shift because you would not use a delta/wye transformer.
    Does a phase shift only happen on a Delta/wye transformer? Is there any shift at all on a delta/delta?

  4. #4
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    The phase shift I believe you are talking about is the IEEE std 30 degree shift between delta/wye transformers. It says that when specifying a transformer, unless stated otherwise there will be a 30 deg shift beteen the HV and LV terminals. In a standard delta/wye it would be the HV side leads the low voltage side by 30 degrees, or LV side lags the HV side by 30. (equivalent statements)

    However, often not talked about are possible additional phase shifts as follows:

    Delta/delta - 0, 60, 120, 180, 240, 300
    Delta/wye or Wye/delta - 30, 150, 210, 330
    Wye/wye - 0, 180
    "Just because you're paranoid, doesn't mean they're not out to get you"

  5. #5
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    Detla-Wye transformers appear to have very large (30 degree) phase shifts simply because of the difference in connection between primary and secondary. Through suitable interconnection of different secondary coils from a three phase primary (you may need more than three secondaries, and they may have different numbers of turns) you could get any phase shift desired. For example, special transformers are sometimes used to generate 18 phases on the secondary, each with its own phase displacement, in order to feed rectifiers and get smoother DC.

    But the original question really speaks to phase shift in a single phase transformer. An ideal single phase transformer doesn't produce any phase shift; the output signal is a perfect in phase copy of the input signal. Real transformers have numerous non-idea features, and will produce a small phase shift. This can be minimized but not eliminated, by using more expensive construction techniques. It becomes an engineering problem to select a transformer with sufficiently small phase shift and distortion for any given application.

    I did a quick search on 'potential transformer phase shift' and pulled the following of interest:
    http://www.hipotronics.com/support/t...eknote9904.pdf
    http://focus.ti.com/lit/an/slaa122/slaa122.pdf

    -Jon

  6. #6
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    I might add that you can obtain 180 degrees of phase shift depending on the way you connect the secondary. But be warned that however obviously true this simple statement is, it is not accepted by some.
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