Self-consumption of voltage transformer

[lz5pl]

One of site tests of voltage transformers required here is transformer ratio. For MV transformers it is not a problem, but starting with 110 kV and up it is hard to perform this test using 220 V for supply of primary winding. Transformed voltage on secondary side is too low to be measured with enough precision.

We are going to order step-up transformer 220 to 1500 V, but I wonder about the necessary power. Actually I have no idea how much would be self-consumption for example of a typical 110000/100 V voltage transformer. For capacitive VT's it is easy to calculate, because data of the capacitive voltage divider are available, but I have no idea about inductive ones.
Also typical data for 220 and 400 kV VT's will be helpful.


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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[DanDel]

There is a specific test instrument, called a Turns Ratiometer, which can be used, instead of voltage application and measurement. It is much more accurate, also.

 

[Zogzog]

Yep, TTR is the way to go, much safer too.

 

[lz5pl]

Thank you, but specialized test sets are too expensive for my application. If we have regular orders it is another story.

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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[Zogzog]

Cheaper than a transformer.

Have a testing company that does transformer testing for a living come test it for you, dosent cost much. You can find one near you at

http://www.netaworld.org

 

[dpmac]

You can rent a TTR and have it on site the next day for far less then the step up transformer you thinking of purchasing. Your test results would be much more accurate and take far less time to perform.

 

[scottf]

The same issue exists with TTR sets though, since their input voltage is normally less than 1kV. For VTs at this voltage class, checking the ratio with this low of a voltage will do little more than detecting a pure open circuit in one of the windings.

 

[lz5pl]

In my view these tests are not intended to check whether the TTR is within accuracy limits - there are factory test records for that. Important is to check for wrong reconnection in case of multi-ratio instrument transformers.

Actually I cannot see much sense in field checking of TTR of voltage transformers. The possibility for wrong ratio is very small if we have factory test sheets at hand. But it is required by the authorities in our country.

Site check of TTR for current transformers is necessary, specially for these with several primary taps. It helped me several times to find wrong primary re-connection before to energize the bay and find zero sequence current in secondary circuits.



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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[scottf]

lz5pl-

I agree. However, as a manufacturer of VTs, you wouldn't believe how many calls we field from people that think they have problems with high voltage VTs because the ratio measured with a TTR is slightly off from nameplate. I finally had to write a technical bulletin on the subject just so people would believe me. It's amazing...I can tell someone something over the phone and they won't believe me. I can write it on a piece of paper and they'll not question it

 

[slavag]

Scottf and Lz5pl.
Im fully agree with you!!!!!
Best Regards.
Slava

 

[lz5pl]

scottf, I have been in similar situation, but not in technical questions.

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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant