Transformer impedance 1

[7087]

Is there any difference between the usual Transformer impedence(primary/secondary or refferd value to either side)and the percentage impedence usually quoted on Transformer name plates (usually in percent)? Can they be used interchangebly?

 

[davidbeach]

What do you see as the difference? The question seems to read as "Is transformer impedance the same as transformer impedance?"

 

[7087]

I wish to correct the thread because I submitted before checking the wording. What I wanted to inquire whether I can use the Transformer NAME PLATE impedence to determine circulating currents in parallel Transformers of slightly different impedences ?(normally qouted in percent).

 

[dpc]

Yes. The transformer impedance on the nameplate is measured by test after the transformer is built. However, keep in mind that the impedance may vary slightly on different taps.

(Just for future reference, since posts cannot be edited, the best thing to do is to "red-flag" your own post and ask that it be corrected. )

 

[waross]

You may have to consider regulation as well.
With the same transformer ratios there should be no circulating current between parallel transformers. At normal loading levels different impedances will result in disproportionate load sharing.
The actual load sharing is more dependant on the regulation of the transformers than the impedance. The power factor of the load also has an effect. With a high power factor the resistive component of the impedance predominates. Under short circuit conditions the impedance of the transformer determines the power factor and current is dependant on the impedance.
If you parallel transformers of different ratios there will be circulating currents that will be limited by the transformer impedances.
You should also check the X/R ratio of the transformers. If the X/R ratio of the transformers is significantly different you should break the impedance of each transformer into its
resistive and inductive components and add them vectorily to determine the impedance of the parallel combination.
respectfully

 

[stevenal]

Beckwith says transformers within 7% of each other may be paralleled. The percentage applies on top of your impedance percentage, not a straight addition. Papers at their website have calculation examples.