Thanks Engineering Simple for interesting videos. Can you tell me what is the reason of using DC instead of AC current for winding resistance testing? Thank you in advance
Load losses are composed of I^2*R+stray losses. Stray losses are due to leakage flux that causes extra losses in the structural components such as core clamps… Losses are measured at the factory at room temperature say 25 degrees C. The load losses are guaranteed at 85 degrees C for IEEE designs. Resistance needs to be corrected for temperature to recalculate losses at reference temperature. If you apply AC power to measure resistance, you will need to measure power (watts) and calculate resistance. However, AC resistance will typically be higher than DC resistance due to skin effect. The skin effect is already accounted for in the stray losses so DC power is used to measure winding resistance.
Load losses are calculated and quoted at the reference temperature. For IEEE, the reference temperature is 85 degree C. The resistance and load losses (I2R+stray losses) will be measured at ambient temperature, typically 20-30 degree C so they need to be converted to the reference temperature. I made other videos on load losses.
Thank you for the question. The resistance that this video is covering is the DC resistance. No skin effect is taken into account. The DC resistance calculation is the resistivity of the material (copper or aluminum) times the total length of the conductor divided by the conductor total cross section area. If you are referring to the to turn to turn, then there is no effect on DC resistance. The same applies if you are referring to strand to strand for conductors that use multiple strands. I hope this answers your question. If it does not answer your question, please elaborate on “inter turn” and I will be happy to respond. Thank you.
@@engineeringsimple Thank you am answered. I am new in the transformer manufacturing circle where i work as a tester,so i have been curious about how would i interpret winding resistance results to detect inter turn fault. i will continue to ask question in future where i need explanation.Thank you
You are in the right channel. I will be posting more videos on other tests such as induced, impulse, etc. Depending on the size of transformers, resistance is typically small. A small change in resistance, shorting or adding extra turns may make resistance still appear within tolerance. In general, shorting turns will exclude them from resistance measurement. Resistance will be smaller than design value. If by mistake, there are extra turns, resistance will be bigger than design value. However as I stated earlier, if the number of turns shorted or added is small, it may be hard to tell by resistance measurement. However, if there is an issue with number of turns, core loss test and induced voltage test will definitely catch the issue. Hope this helps. What transformer size? Distribution or power class? Thanks.
Testing units from 10KVA to 1MVA, distribution transformer. The comapnay rarely manufacture anything greater than 1 MVA, it only does on special requests.. ill keep my eyes wide open for your next videos on other transformer related tests
Thanks for watching! Let me know if you have any questions or would like a certain topic covered in the future.
Thanks it was great 👍
Thanks Engineering Simple for interesting videos. Can you tell me what is the reason of using DC instead of AC current for winding resistance testing? Thank you in advance
Load losses are composed of I^2*R+stray losses. Stray losses are due to leakage flux that causes extra losses in the structural components such as core clamps… Losses are measured at the factory at room temperature say 25 degrees C. The load losses are guaranteed at 85 degrees C for IEEE designs. Resistance needs to be corrected for temperature to recalculate losses at reference temperature. If you apply AC power to measure resistance, you will need to measure power (watts) and calculate resistance. However, AC resistance will typically be higher than DC resistance due to skin effect. The skin effect is already accounted for in the stray losses so DC power is used to measure winding resistance.
Subramani
I would like to work in field of repair power Transformer could you add all of test that we need to repair transformer.
Thanks again 🙏🏼🙏🏼🙏🏼
If temperature increases resistance should decrease right??
But in problem that doesn't seem to be!
As temperature increases, conductor (Ex. Copper, Aluminum, etc.) resistance increases.
Why we need to convert the measured value to some other temperature?
Load losses are calculated and quoted at the reference temperature. For IEEE, the reference temperature is 85 degree C. The resistance and load losses (I2R+stray losses) will be measured at ambient temperature, typically 20-30 degree C so they need to be converted to the reference temperature. I made other videos on load losses.
@@engineeringsimple Thanks
WHAT IS THE EFFECT OF INTER TURN ON WINDIND RESISTANCE
Thank you for the question. The resistance that this video is covering is the DC resistance. No skin effect is taken into account. The DC resistance calculation is the resistivity of the material (copper or aluminum) times the total length of the conductor divided by the conductor total cross section area. If you are referring to the to turn to turn, then there is no effect on DC resistance. The same applies if you are referring to strand to strand for conductors that use multiple strands. I hope this answers your question. If it does not answer your question, please elaborate on “inter turn” and I will be happy to respond. Thank you.
@@engineeringsimple Thank you am answered. I am new in the transformer manufacturing circle where i work as a tester,so i have been curious about how would i interpret winding resistance results to detect inter turn fault. i will continue to ask question in future where i need explanation.Thank you
You are in the right channel. I will be posting more videos on other tests such as induced, impulse, etc.
Depending on the size of transformers, resistance is typically small. A small change in resistance, shorting or adding extra turns may make resistance still appear within tolerance. In general, shorting turns will exclude them from resistance measurement. Resistance will be smaller than design value. If by mistake, there are extra turns, resistance will be bigger than design value. However as I stated earlier, if the number of turns shorted or added is small, it may be hard to tell by resistance measurement. However, if there is an issue with number of turns, core loss test and induced voltage test will definitely catch the issue. Hope this helps. What transformer size? Distribution or power class? Thanks.
Testing units from 10KVA to 1MVA, distribution transformer. The comapnay rarely manufacture anything greater than 1 MVA, it only does on special requests.. ill keep my eyes wide open for your next videos on other transformer related tests