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Came across this one on a Linked In power quality board.

Skiers blowing up UV light bulbs

I am looking for a small three phase voltage regulator/ power conditioner to fix utility voltage fluctuation problem that is blowing expensive UV lamps in the water purification system in a small town. You see, the water filtration facility ( or shack ) is connected to the grid at the end of a long utility line; and it’s closest neighbor is a ski hill. When the sky lifts; or the pumps for the snow making machines start/ stop, the 600V gets high voltage spikes of up to 640V. This is blowing up the UV bulbs.

I need to replace the existing auto transformer with a 600V – 3 wire input, and a 277V – 3 wire output power conditioner/ voltage regulator. Probably will need something in the 10-15kVA range.

Open Delta Autotransformer

Any ideas for good quality US or Canadian manufacturer?


Spoiler Alert: odds are pretty good that this site does not need a “power conditioner/ voltage regulator”. The culprit here is almost certainly the transformer used to convert 600 VAC (ph-ph) to 277 VAC (ph-n) for the lighting circuits. They are using autotransformers hooked up in an Open Delta configuration – no doubt something like this:

Open Delta Wiring


  1. The voltages from X1 / X2 / X3 to neutral are not going to be balanced or particularly stable – they will definitely change with load. X3-N will in fact be 347 VAC. The other phases will be all over the place, and will fluctuate with load.
  2. The voltages from X1-X3 and X2-X3 will be fairly stable (direct magnetic coupling) but X1-X2 (the open delta phase) will fluctuate.

I’d probably recommend measuring the X1 / X2 / X3 voltages (Ph-Ph, Ph-N, and Ph-G) and when they come up unbalanced, I’d know where the problem was.

Now a dozen or so power quality experts (with a product to sell and a commission to accrue) had lots of suggestions for power conditioning or voltage regulation solutions. These might fix the problem, but at a much higher cost / complexity.

The best solution is mostly likely a simple Delta-Wye isolation transformer, 600 VAC primary, 480Y/277 VAC secondary.

Delta Wye Wiring

The problem is – nobody gets much of a commission on a 15 KVA isolation transformer (maybe a $1500 box plus installation, breakers, etc.) so who wants to recommend THAT?

Your friendly neighborhood independent power quality consultant, that’s who . . .