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Dry-Type Transformer Testing

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    Dry-Type Transformer Testing

    Hi guys,
    I need some help. I am testing a Dry Type 1500 kVA tranformer. Insulation tests are okay but in Ratio test my device giving an "High Execuation Current" error. There is 2 of this transformer and giving same error. What cause this problem ? How can i solve this? thanks.

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    Quote Originally Posted by changeabilities View Post
    Hi guys,
    I need some help. I am testing a Dry Type 1500 kVA tranformer. Insulation tests are okay but in Ratio test my device giving an "High Execuation Current" error. There is 2 of this transformer and giving same error. What cause this problem ? How can i solve this? thanks.
    What model ratio set are you using and what voltage are you testing at?

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    Quote Originally Posted by SecondGen View Post
    What model ratio set are you using and what voltage are you testing at?
    I am using AEMC-DTR 8510. It is 50Vrms and using 32Vrms for execuation current test. Voltage is not adjustable.

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    Quote Originally Posted by changeabilities View Post
    I am using AEMC-DTR 8510. It is 50Vrms and using 32Vrms for execuation current test. Voltage is not adjustable.
    High excitation current usually indicates a short in the test circuit. Verify that your leads are connected properly. If you are getting the same thing on both transformers the issue is probably related to the test procedure.

    It's also possible the test voltage is low and causing excess current. 1500kVA dry type doesnt sound that big, what's the voltage and expected ratio? Do you have a way to field test the TTR to verify its working properly?

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    Quote Originally Posted by SecondGen View Post
    High excitation current usually indicates a short in the test circuit. Verify that your leads are connected properly. If you are getting the same thing on both transformers the issue is probably related to the test procedure.

    It's also possible the test voltage is low and causing excess current. 1500kVA dry type doesnt sound that big, what's the voltage and expected ratio? Do you have a way to field test the TTR to verify its working properly?
    Also verify that you have the correct transformer type/vectors setup in the test set. Be sure to reconnect any neutrals (X0) if they were lifted for megger testing.

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    Quote Originally Posted by SecondGen View Post
    High excitation current usually indicates a short in the test circuit. Verify that your leads are connected properly. If you are getting the same thing on both transformers the issue is probably related to the test procedure.

    It's also possible the test voltage is low and causing excess current. 1500kVA dry type doesnt sound that big, what's the voltage and expected ratio? Do you have a way to field test the TTR to verify its working properly?
    Any TTR should be able to field test by connecting the High side leads directly to the low side leads and obtaining a ratio of 1:1.
    H1 to X1, H2 to X2, H3 to X3, H0 to X0

    It would be helpful if you showed the vector diagram, sounds like you have a special transformer. Could be a zigzag, or maybe a delta to wye with no accessible neutral or etc. which would require a special connection (i.e. install jumper or program the ttr).

    Also, it could have an electrostatic shield which could cause problems (haven't seen one cause ttr problems only insulation resistance but possible).

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    I already try my device in a another transformer and it is working properly. There is no problem on the device. And transformer connected delta-delta 480/450. There is 2 of them and i am taking same error on 2 transformer.

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    Quote Originally Posted by changeabilities View Post
    I already try my device in a another transformer and it is working properly. There is no problem on the device. And transformer connected delta-delta 480/450. There is 2 of them and i am taking same error on 2 transformer.
    If it is a delta delta configuration then make sure you are hooking the high side leads and the low side leads exactly the same (H1 red and H2 black)then(X1 red to X2 black) etc if you are hooking them up like a delta wye you will get a high excitation fault. On the equipment diagram you should have the relationship labeled for high and low. Hope that may help. Good luck.

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    Quote Originally Posted by changeabilities View Post
    I already try my device in a another transformer and it is working properly. There is no problem on the device. And transformer connected delta-delta 480/450. There is 2 of them and i am taking same error on 2 transformer.
    There are still variant configurations for Delta to Delta:
    Dd0, Dd2, Dd4, Dd6, Dd8, and Dd10.
    Sometimes this can be read on the nameplate, but most of the time you just have to use the back of the manual associated with the ttr.

    Also, if this is a Dry-type transformer, take a look at the actual tap changer. On some, they have nice screw holes which allow for easy transition between taps. Others have small loops pulled out of the winding which the high side connection makes contact. On these, the manufacturer usually sets the tap prior to baking the epoxy around it, but if they baked it prior to making the connection, the epoxy can prevent good connection to the winding and you might have to use a file to ground off the epoxy to make a proper connection. I would think this would only create an open circuit which would cause a voltage overload vice excitation current overload. The other question is the
    checking that the connections are made properly coming out of the transformer.

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