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Join Date: Mar 2019
Posts: 26

Overvoltage Protection

06/27/2021 9:55 AM

Dear all

please what is the standard magnitude and time for over voltage protection for power

transformer,in other word what is the maximum value of over voltage can the power

transformer stand it without insulation failure and for how much time.

thanks

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#1

Re: overvoltage protection

06/27/2021 2:23 PM
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Power-User

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#2

Re: overvoltage protection

06/28/2021 2:26 AM

I suppose you are meaning temporary overvoltage and not transient one like lightning/switching surge.

Overvoltage causes overfluxing in transformers and hence overfluxing protection will take care of overvoltages as well.

No separate overvoltage protection is provided.

Transformers, especially generator step-up transformers and grid transformers are expected to withstand

$ 110% overfluxing continuously,

$ 125% for 1minute and

$ 140% for 5sec.

Above is from IEC 60076.

Transformer data from manufacturer includes overfluxing withstand curve as well and should be referred for allowable limits and duration for protection setting.

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#5
In reply to #2

Re: overvoltage protection

06/30/2021 7:21 PM

thank you very much

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Guru
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#6
In reply to #2

Re: overvoltage protection

07/01/2021 5:06 AM

<...are expected...>

By whom?

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Power-User

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#3

Re: Overvoltage Protection

06/28/2021 7:28 AM

One should not talk about over voltage in isolation. As stated in some reply, it is over fluxing that should be talked about. But over voltage is not the only cause of over fluxing. Under frequency also causes over fluxing. So the ratio V/F (Volts per Hertz) is more important which takes care of over voltage as well as under frequency individually as well as in combination. Each transformer manufacturer supplies data of permissible over fluxing stating individual voltage variation, with rated frequency, permissible frequency variation with rated voltage and combination of the permissible variation of the voltage and the frequency together. So please look into the data sheet of the transformer supplied by the supplier or ask for the same if not given. Relevant National / International standard must also be referred.

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#4

Re: Overvoltage Protection

06/28/2021 7:32 AM

The <...standard magnitude and time for over voltage protection for power transformer...> can be obtained by contacting the relevant manufacturer(s) directly and discussing the transformer(s) in question. It may even be in a <...standard...> schedule of testing the manufacturer(s) carries/carry out and provide(s) as a test report upon purchase. Telephone?

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#7

Re: Overvoltage Protection

07/03/2021 2:32 AM

I believe you are asking for the Overvoltage Protection not overfluxing and I would draw your attention to the following link.

https://www.researchgate.net/publication/3276390_Overvoltage_Protection_of_Large_Power_Transformers-A_Real-Life_Study_Case

From this you may find information that is of use to you. I worked for many years in testing of overvoltage protection devices for supply authority power transformers consisting of spark gaps and surge diverters and the testing of those devices.

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