OK, I have two prints showing the same transformer. It's a three phase oil filled transformer. It's 5000 KVA, 34.4 KV to 4160 V. One print says it has 1.9% impedance. And the other says it has 5.7 % impedance. The transformer exists in a remote location and someone else is attempting to locate the actual nameplate information. In the mean time I would like to continue my analysis and assume which is more likely correct. I have never seen a transformer with Z as low as 1.9%. However, there is other circumstantial type evidence that the 1.9% may be correct. Any words of wisdom on this.
transformer impedance guesstimate
- Thread starter billyzee
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drbond24
Senior Member
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- Barboursville, West Virginia
I agree. Given those two choices, the higher one is definitely the way I'd go.
zog
Senior Member
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- Charlotte, NC
Agreed also, a never seen a transformer that small with 1.9%Z, I think 5% sounds about right.
ANSI C57.12.10, reproduced in the IEEE Red Book, gives the standard impedance for oil-filled three-phase transformers 750/860 kVA and above. With a high-voltage BIL of 60-110 kV and low voltage 2400 V and above without OLTC, the standard impedance is 5.5%. For 150 kV BIL (probably your case), standard impedance is 6.5%.
1.9% impedance is common for smaller 7200-120/240 volt distribution transformers where there is no standard impedance.
1.9% impedance is common for smaller 7200-120/240 volt distribution transformers where there is no standard impedance.
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