Transformer Winding Resistance

[changeabilities]

Hi everyone, I hope you all doing okay. I wonder something and you are the best crew i can ask :)
When we test winding resistance test for transformer we saw discrepancy in results when compare with the Factory Test results. Is there any way to calculate the result and see the true values? I research it but i couldnt find a good way.
Thank already...

[cunin21]

Hi everyone, I hope you all doing okay. I wonder something and you are the best crew i can ask :)
When we test winding resistance test for transformer we saw discrepancy in results when compare with the Factory Test results. Is there any way to calculate the result and see the true values? I research it but i couldnt find a good way.
Thank already...
We need more information to help you with your problem.
1. Did you convert your results for temperature conversion from the reference temperature from the factory test report?
2. Did you measure the Delta winding from L1 to L2 ?
3. Did you measure the Wye winding from X1 to X2 or from X1 to X0?

[changeabilities]

We need more information to help you with your problem.
1. Did you convert your results for temperature conversion from the reference temperature from the factory test report?
2. Did you measure the Delta winding from L1 to L2 ?
3. Did you measure the Wye winding from X1 to X2 or from X1 to X0?

Thank you for your response.
1- The results are very different so even if i correct according to reference temperature i dont think it affect a lot.
2- I have Vanguard WRM-10p 3 phase so i have results for 3 phase.

The difference between the factory results and my results is more than 20%.

[cunin21]

Thank you for your response.
1- The results are very different so even if i correct according to reference temperature i dont think it affect a lot.
2- I have Vanguard WRM-10p 3 phase so i have results for 3 phase.

The difference between the factory results and my results is more than 20%.

The Vanguard is a good test set. We use it all the time with very few issues. Most troubles are the test leads. What kind of transformer is this? Is it dry or liquid and does it have a LTC? How about posting your winding resistance results.

[changeabilities]

The Vanguard is a good test set. We use it all the time with very few issues. Most troubles are the test leads. What kind of transformer is this? Is it dry or liquid and does it have a LTC? How about posting your winding resistance results.

It is oil filled transformers. It has a LTC. There is no problem on primary windings results but secondary results are very different.

Factory results is like 3 milliohm but my values are around 270 microohm.

[cunin21]

It is oil filled transformers. It has a LTC. There is no problem on primary windings results but secondary results are very different.

Factory results is like 3 milliohm but my values are around 270 microohm.

Is this a new transformer or are you doing maintenance testing? Are the primary windings all within 1% of one another? On a winding with a tap changer do your testing with the tap off N. Use tap 1R or 1L. We run a winding resistance test from 16R to 16L with the test set on. If the test set kicks out we know that a set of contacts are breaking before making.Your results are very high. Are the phases within equal results?

[changeabilities]

Is this a new transformer or are you doing maintenance testing? Are the primary windings all within 1% of one another? On a winding with a tap changer do your testing with the tap off N. Use tap 1R or 1L. We run a winding resistance test from 16R to 16L with the test set on. If the test set kicks out we know that a set of contacts are breaking before making.Your results are very high. Are the phases within equal results?

This is a new transformer and primary windings results all within 1% of one another. i made the test in all taps actually. Secondary results are same for sure in all taps. What should be the results for 2500 kVa 15000/400-230 v transformer? Maybe there is a mistake on factory reports.

[cunin21]

This is a new transformer and primary windings results all within 1% of one another. i made the test in all taps actually. Secondary results are same for sure in all taps. What should be the results for 2500 kVa 15000/400-230 v transformer? Maybe there is a mistake on factory reports.

Some factory results are measured x1 to X2, X2 to X3, X3 to X1. Your test may include bus bars that there test did not include. I would say the results should be around 230 Microhms.

[rmr660]

Hi everyone, I hope you all doing okay. I wonder something and you are the best crew i can ask :)
When we test winding resistance test for transformer we saw discrepancy in results when compare with the Factory Test results. Is there any way to calculate the result and see the true values? I research it but i couldnt find a good way.
Thank already...

Are you asking for temperature corrected value or to try and calculate the values based off the voltage and current of the transformer?

[changeabilities]

Are you asking for temperature corrected value or to try and calculate the values based off the voltage and current of the transformer?

Hi
I want to try and calculate the values based off the voltage, current and power if its possible.

[SecondGen]

Hi everyone, I hope you all doing okay. I wonder something and you are the best crew i can ask :)
When we test winding resistance test for transformer we saw discrepancy in results when compare with the Factory Test results. Is there any way to calculate the result and see the true values? I research it but i couldnt find a good way.
Thank already...

As other have stated, I'd make sure you are using the exact same connections and test current as the factory test results. Also be mindful of additional bus you may be including, the readings you have wouldn't' raise alarm to me if I didn't see the factory results and my readings were within tolerance between each phase.

[rmr660]

Hi
I want to try and calculate the values based off the voltage, current and power if its possible.

So your winding resistance test set, what ever brand you use, should inject the winding(s) with a voltage and current. You usually can change the current you inject into the transformer. The results you got were the "true values" at the time. As windings heats up and if there are faults or contamination in the oil the resistance will go up; this is what changes your results from the factory. if you wanted to calculate the resistance you would just use ohms law. But that doesn't mean you will get a "true value" because no conductor is a perfect conductor and there is always capacitance and reactance.

I hope that helps

[SecondGen]

So your winding resistance test set, what ever brand you use, should inject the winding(s) with a voltage and current. You usually can change the current you inject into the transformer. The results you got were the "true values" at the time. As windings heats up and if there are faults or contamination in the oil the resistance will go up; this is what changes your results from the factory. if you wanted to calculate the resistance you would just use ohms law. But that doesn't mean you will get a "true value" because no conductor is a perfect conductor and there is always capacitance and reactance.

I hope that helps

Good point, I totally forgot to mention temperature is important as well. If you had just de-energized the transformer the winding temp will most likely be elevated and this should be corrected same as the factory results for true comparison.