Control Trfr Impedances

[veritas]

Hi

I have a 1kVA, singlephase, 3 winding trfr, pri = 1000V, sec 1 = 240V and sec 2 = 12V.

Can anyone tell me what the typical impedances of such a trfr will be please?

Thanks.

 

[engbknr1976]

S=1kVA
Z=U*U/S

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[waross]

Hi veritas;
If the information is not on the nameplate or the spec sheet, you may have to measure it.
A heads up, the impedance is measured/rated at operating temperature. Your measured value on a cold transformer will be a little on the low side.
I once sent a group of students into the lab to check the impedance of some small transformers without checking myself ahead of time. All the test results were low. Some hurried research under pressure and I found the information that impedance tests are done with the transformers "hot".

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

 

[ScottyUK]

Does resistance change with temperature make that much difference to the impedance Bill? Bigger transformers are predominantly reactive, dominated by the leakage reactance. I've never had cause to look at small ones. Interesting.


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If we learn from our mistakes I'm getting a great education!

 

[veritas]

Gents

The customer does not have the nameplate data available. He asked me to use "typical" values. Having never worked with this kind of trfr before, I'm at a bit of a loss as to what typical values are.

Any rules of thumb? suggestions?

Thanks.

 

[waross]

Hi Scotty. I don't remember the numbers, it was a long time ago. The transformers were single phase dry types, about 2 or 3 KVA. If I run across any literature on X:R ratios for small transformers I'll try to let you know.
I do remember that my whole class was upset that the numbers did not match up. That much error for some reason. I put it down to temperature, but I may have been mistaken. These little units do run quite hot.

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

 

[ScottyUK]

Impedance and regulation are not directly equivalent to each other, impedance being the vector sum of winding resistance and reactance, and regulation being dependant on the character of the load and how it interacts with the transformer impedance, but if you can find regulation values for your transformer or one similar it should give you a ballpark value.


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If we learn from our mistakes I'm getting a great education!