Transformer Demagnetization

[JLo1234]

Is there a practical and easy way to demagnetize a 10MVA 69kV/13.8kV 3-ph transformer without the use of a tester or after a transformer test. Someone has told me that I can use a car battery and swap the (+/-) leads back and forth to demagnetize it. The high winding will have to be shorted, as well as the low windings. Would this be a good procedure to follow?

Thanks,
JLo

[Kalbi_Rob]

Is there a practical and easy way to demagnetize a 10MVA 69kV/13.8kV 3-ph transformer without the use of a tester or after a transformer test. Someone has told me that I can use a car battery and swap the (+/-) leads back and forth to demagnetize it. The high winding will have to be shorted, as well as the low windings. Would this be a good procedure to follow?

Thanks,
JLo

I would highly recommend renting a transformer winding resistance tester that has a demag function. The key to de-magnetizing is the DC current. Here is a good explanation and video of the procedure. There is no shorting of the transformer, just test performed across each winding.

https://www.youtube.com/watch?v=GRQMRSWf7mU

https://www.dv-power.com/demagnetization-transformer/#:~:text=Transformer%20core%20demagnetization%20is %20performed,remanent%20magnetism%2C%20is%20also%2 0annulled.

[cnowak]

I would highly recommend renting a transformer winding resistance tester that has a demag function. The key to de-magnetizing is the DC current. Here is a good explanation and video of the procedure. There is no shorting of the transformer, just test performed across each winding.

https://www.youtube.com/watch?v=GRQMRSWf7mU

https://www.dv-power.com/demagnetization-transformer/#:~:text=Transformer%20core%20demagnetization%20is %20performed,remanent%20magnetism%2C%20is%20also%2 0annulled.

I was just asking a co-worker about this earlier. I saw this thread and asked about it and he said that he had heard about the battery trick but had never seen it. I was just curious myself if it was a thing. Thanks for the Video and link.

[JLo1234]

I would highly recommend renting a transformer winding resistance tester that has a demag function. The key to de-magnetizing is the DC current. Here is a good explanation and video of the procedure. There is no shorting of the transformer, just test performed across each winding.

https://www.youtube.com/watch?v=GRQMRSWf7mU

https://www.dv-power.com/demagnetization-transformer/#:~:text=Transformer%20core%20demagnetization%20is %20performed,remanent%20magnetism%2C%20is%20also%2 0annulled.

Thank you Kalbi, very instructive.

Jorge

[Kalbi_Rob]

I was just asking a co-worker about this earlier. I saw this thread and asked about it and he said that he had heard about the battery trick but had never seen it. I was just curious myself if it was a thing. Thanks for the Video and link.

I would be not try the battery trick, as your dealing with charging inductors and not controlling the current. Same advice as using Hand held Megger DLRO with winding resistance feature and prong test leads. Danger of flashover can occur.