12.47kV Tap on a 14.4kV Transformer?

[Eleceng01]

I am new at this and still learning so I thought I would ask for the commmunities help here. Field data was given to me for a 14.4kV-480/277V, 1000kVA, Balteau Standards transformer using tap D (12.47kV). It has always been my understanding that the standard taps are +/- 2.5% and +/-5%. I figure 12.47kV/14.4kV = -15% tap?

I researched the transformer and found that they are no longer in business. It throws me that the tap setting is D, I would think it would be E (an extreme) instead.

Any thoughts on this are greatly appreciated and I will keep looking at it myself. Man, you never quite learning in this field (smile - yeah!)

Thanks again for feedback.

 

[dpc]

It's A-B-C-D.

ANSI standard is two 2.5% taps above and below nominal, but anything can be specified and built. Only way to know for sure is to look at the transformer nameplate and THEN, look at the tap indicator and verify.

I would advise that you check it yourself, or at least ask that it be verified. It's possible there's a 12.47 kV tap, but it would be non-standard. It's also possible that since it is probably connected to a 12.47 kV system, whoever sent you the data just assumed that the D tap corresponded to 12.47 kV.

 

[tinfoil]

Be V-E-R-Y careful with this transformer in your intended use.

Common 3 phase utility voltages are:
7.2kV L-G (12.47kV L-L)
14.4kV L-G (24.94kV L-L)

I have seen a single phase (one primary bushing) xmfr nameplated at 7200/12470V Y because it was intended for use as part of a 3ph bank

I have seen a 1 ph unit labelled 14400/24940Y : 277/480Y because it was intended for use in a 3ph bank. I have also seen functionally identical xmfrs nameplated to be simply 14.4kV : 277V

Look at the nameplate to be sure, but you may be mixing L-L and L-G voltages here. The HV/LV ratio should be a good indicator.

 

[rcw retired EE]

Eleceng01- welcome to the forum and the business.

You mentioned tap "E" for extreme. Taps are usually numbered A,B,C,D,E or 1,2,3,4,5. No "B" for bad "C" for correct or "D" for darn good.

Check the nameplate. I have tested transformers that were designed for use on a 13.8 kV or a 12.0 kV system. They were custom designed with an internal tap to switch ranges and had the usual +/-5% taps externally operable.

I beleive Balteau was bought by Areva, if that's any help.

 

[Eleceng01]

rcwilson,

Thanks for the welcome and the advice. To clarify, I didn't think that E=extreme. I have seen transformers with A,B,C,D,E taps and I have always thought of C as the center tap and A & E being the "extreme" taps. Thanks again.

I agree I will have to make a site visit this transformer - our technician swears by what he saw, but I think I need to look at the nameplate for my own peace of mind.