Three autotransformers used for stepdown from 24.9/14.4kV to 14.4/8.3kV. One autotransformer failed, A phase. No spare available.
Used a convention transformer 12.4/7.2kV with a voltage regulator to get the correct voltage as the temporary replacement. That conventional transformer was tapped to 95% and the regulator was taken to 16 raise, or +10%, to match existing phase voltage of the other phases. In my network there are some very smart people with years of experience that I lean on for advice.
The consensus was there could be a voltage phase shift due to the mixed transformation type. I explored that using a wireless MV voltage angle tool.
I consider the testing inconclusive, but the result from that test was A-B=111 degrees, A-C= 246 degrees. There was talk about limits and overheating and what could happen if we were too far out.
Yesterday I had a chance to visit with a meter tech. He said that in the thousands of test he has done over the years on Y-Y systems, all come back at 0 -120-240. His understanding is that the voltage phase angles are fixed by the wire lead connection on the generator and cannot vary from the way those phases leave the generator.
How did the water get muddy on this? Why is there more than one opinion? I don't know the answer.
We all are aware of Delta-Wye transformation and the accompanying phase angle shift. We have dealt with that in the past when paralleling two different sources.
Used a convention transformer 12.4/7.2kV with a voltage regulator to get the correct voltage as the temporary replacement. That conventional transformer was tapped to 95% and the regulator was taken to 16 raise, or +10%, to match existing phase voltage of the other phases. In my network there are some very smart people with years of experience that I lean on for advice.
The consensus was there could be a voltage phase shift due to the mixed transformation type. I explored that using a wireless MV voltage angle tool.
I consider the testing inconclusive, but the result from that test was A-B=111 degrees, A-C= 246 degrees. There was talk about limits and overheating and what could happen if we were too far out.
Yesterday I had a chance to visit with a meter tech. He said that in the thousands of test he has done over the years on Y-Y systems, all come back at 0 -120-240. His understanding is that the voltage phase angles are fixed by the wire lead connection on the generator and cannot vary from the way those phases leave the generator.
How did the water get muddy on this? Why is there more than one opinion? I don't know the answer.
We all are aware of Delta-Wye transformation and the accompanying phase angle shift. We have dealt with that in the past when paralleling two different sources.
