111R
Electrical
- May 4, 2012
- 114
I am currently using a winding resistance meter with a demag function to demagnetize 3Ø power transformers (25MVA ONAN Dy and 50MVA ONAN autos are the largest). It is capable of providing 15A output. Despite showing that the demagnetization is complete on multiple attempts, excitation tests are showing irregular patterns between the three legs. Based on the short period of time it takes to run the demag process with only 15A, it is not surprising that it's not actually demagnetizing the core.
Doble recommends using a battery for successively lower time periods while swapping polarity on the leads at the transformer terminals. We have some safety concerns due to the inrush current and possible arcing due to the inductive load.
Is this something we should avoid? Doble seems to be a trustworthy source and we've seen contractors demag with a battery, but if there are safety concerns, we would prefer to get a device purpose-built for this task.
Thanks
Doble recommends using a battery for successively lower time periods while swapping polarity on the leads at the transformer terminals. We have some safety concerns due to the inrush current and possible arcing due to the inductive load.
Is this something we should avoid? Doble seems to be a trustworthy source and we've seen contractors demag with a battery, but if there are safety concerns, we would prefer to get a device purpose-built for this task.
Thanks