# Transformer Winding DC Resistance



## Zog (Apr 15, 2009)

zia said:


> What will be the effect on transformer if Winding DC Resistance Delta R% becomes high. what is maximum limit for Delta R%?


Never seen the term deltaR% but I think you are asking the maximum difference between phase winding resistances. If that is the case there is no spec I am aware of, but ANSI/NETA has this:

Temperature corrected winding-resistance values shall compare within one percent of previously obtained results.​ 
Now the phase resitances should be pretty close but hard to put a spec on it, too many factors including manufacturing to have something set in stone. Anything more than 5% though would make me investigate it more.


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## Electric_Light (Apr 6, 2010)

zia said:


> What will be the effect on transformer if Winding DC Resistance Delta R% becomes high. what is maximum limit for Delta R%?


The thermal properties on copper are well understood, so, change in DC resistance can precisely measure winding temperature.

If the change is too high, it means the windings are getting too hot.


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## Zog (Apr 15, 2009)

Electric_Light said:


> The thermal properties on copper are well understood, so, change in DC resistance can precisely measure winding temperature.
> 
> If the change is too high, it means the windings are getting too hot.


Winding resistance measurements are tempature corrected to have any meaningful purpose.


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## RIVETER (Sep 26, 2009)

Zog said:


> Winding resistance measurements are tempature corrected to have any meaningful purpose.


Would you be able to explain how a winding temperature could be compensated for? Also, if the winding is ok at manufacturing, is it the connections that go bad?


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## Zog (Apr 15, 2009)

RIVETER said:


> Would you be able to explain how a winding temperature could be compensated for? Also, if the winding is ok at manufacturing, is it the connections that go bad?


Yes, it is the connections that you are concerned about. 

Attached is the table for tempature correction, in this case 40C is used.


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