Transformer Rating

[haisa]

Given a Transformer without nameplate, how do I find the find the Rating of the transformer at site where there is 415V?

 

[rbulsara]

You need to collect more helpful info. Not possible with what you posted.

Is it in service or sitting idle?
Where did you find it?.
What do you know about its history?
Photos?
Size and type of transformer? dry/oil filled?
Physical condition?
Voltage ratio? Meggar readings?
Type and size of windings conductors?

If you have most of the above info, there may be a remote chance of estimating something.

Rafiq Bulsara

http://www.srengineersct.com

 

[edison123]

Love your optimism, Rafiq.

"If you have most of the above info, there may be a remote chance of estimating something."

Muthu

http://www.edison.co.in

 

[waross]

Find a variable voltage AC supply. Connect it to the smallest set of leads. Monitor the current and slowly increase the voltage. Check the voltage on the other leads for a higher voltage, as a safety precaution.
When the current starts to increase disproportionately to the voltage increase, you have reached magnetic saturation. The next lower reasonable standard voltage is probably the rated voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

Muthu:
Grin!!
Nothing is impossible, just takes longer and costs more money!


Rafiq Bulsara

http://www.srengineersct.com

 

[haisa]

Actually the Voltage rating of the transformer is 132/33KV and I know that the percent impedance is the ratio of the rated volage that will produce rated current at the output if short circuited.
But the volage I have at site is 415V. If I apply 415V the short circuit current obtain is small. How can I obtain the percent impedance with 415V?

 

[rbulsara]

haisa:

You can't use that transformer at 415 V so why do you need %Z at 415V?. %Z is only useful at rated voltage ranges.

What are you trying to test or achieve?

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

Study ratios in arithmetic. Test on the low (33kV) side with 415 volts. Use ratios. Not the best but fairly close. 415 volts should be enough to get you into a fairly linear part of the flux density curve and you don't have to worry about saturation on an impedance test.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[marks1080]

There is an easy way to find the rating of the transformer, as long as it doesn't matter if it blows up.

If you require the transformer to be in working condition than others here will have more useful suggestions.

 

[haisa]

What I am actually after is the KVA Rating. So How do I find the Rated output Current of the Transformer?

 

[davidbeach]

You can't. Depending on various other factors, the same size core and conductors may have different kVA ratings. Basically all kVA ratings are based on keeping the insulation below some fixed temperature and without a nameplate you don't even know what that temperature is. I'd say find the physical size and compare that to other transformers and then derate a size or two. Don't try for maximum output or you'll be sure to get minimal output.

 

[jghrist]

Rated current depends on rated kVA.
Amps = kVA/kV/sqrt(3)

You could assume a percent impedance and do a short circuit test per your previous post and Bill's post on ratios. Then you can calculate the kVA that will give you the assumed impedance.

The problem is, for a 132-33 kV transformer, impedances range from 8.5% to 13% (this is from an old Westinghouse T&D Manual and may not be current). This method can only get you into a range of kVA ratings.