# NCEES #126 Power



## threatta (Apr 5, 2010)

So, I want to double check myself here. The reason that you can't parallel a wye-wye and a wye-delta transformer is because the secondary voltages would be 30 degrees out of phase. That is due to the wye-delta transformer shifting the phase 30 degrees while the wye-wye doesn't, correct? You can parallel like transformers (i.e. 2 wye-deltas, 2 delta-wyes, 2 delta-deltas or 2 wye-wyes)?


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## Flyer_PE (Apr 5, 2010)

^Correct.


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## MSEE_PE (Apr 6, 2010)

threatta said:


> So, I want to double check myself here. The reason that you can't parallel a wye-wye and a wye-delta transformer is because the secondary voltages would be 30 degrees out of phase. That is due to the wye-delta transformer shifting the phase 30 degrees while the wye-wye doesn't, correct? You can parallel like transformers (i.e. 2 wye-deltas, 2 delta-wyes, 2 delta-deltas or 2 wye-wyes)?


The main problem with connecting 2 transformers with the same rating but different configuration the phase shift which can cause circulating currents.


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## kris7o2 (Jun 22, 2021)

Is this for NCEES 125. The question for NCEES 126 asks about a grounded industrial power system and what would be least likely to improve


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