How high is too high for incoming voltage 3phase 4 wire high leg delta

S

Smash

Senior Member
Location
Philadelphia suburbs, PA USA
I have an old building with a supposed to be 240V high leg delta with a neutral. This company makes all their own 480V via transformers through out the plant. The utility supply comes off the pole and into an outdoor transformer on the property just for this building. The incoming voltage is roughly 133V per leg 270 between phases and 296 high leg to ground. On the load side of the transformers I get 485 phase to phase and 510 on the high leg roughly sometimes higher. Question is this high voltage a problem with 460V nameplate motors. Some even 440V Also there are motors from Japan operating at 270V when designed for Japans power grid of 200V Just really want to know is this harming the equipment or even the transformers one is 115KVA reverse wound that appears to be running hot and loud. Not my speciality so I respect the peoples opinion. Building owner seems to dismiss any idea of lowering the incoming saying it’s been that way for years. Is he right ?
 
Utility service voltage is supposed to be +-5%, so 270V P-P is too high. Generally the P-G voltage is irrelevant, but the 296 on the high leg to ground might mean that they have lost their ground reference for the neutral on the split phase, which is possibly why everything is reading high, because it’s all floating and what you are reading is based on the capacitance. Measuring under load may show different results as well.

NEMA specs for utilization voltages (what the motors would be designed to) is +-10%, but based on the lower voltage. So 460V motors would be able to handle 506V no problem. 440V listed motors though would be 484 max, so you are a little high there. But the Japanese 200V motors on 270V is a serious issue. As a gross general rule, each 1% voltage increase over the max. range can cut the motor life by 10%. But other effects can be more serious, especially the imbalance. I suggest you read this and maybe pass it on to those who say they are fine.
 
Smash said:
I have an old building with a supposed to be 240V high leg delta with a neutral. This company makes all their own 480V via transformers through out the plant. The utility supply comes off the pole and into an outdoor transformer on the property just for this building. The incoming voltage is roughly 133V per leg 270 between phases and 296 high leg to ground. On the load side of the transformers I get 485 phase to phase and 510 on the high leg roughly sometimes higher. Question is this high voltage a problem with 460V nameplate motors. Some even 440V Also there are motors from Japan operating at 270V when designed for Japans power grid of 200V Just really want to know is this harming the equipment or even the transformers one is 115KVA reverse wound that appears to be running hot and loud. Not my speciality so I respect the peoples opinion. Building owner seems to dismiss any idea of lowering the incoming saying it’s been that way for years. Is he right ?
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The load side of the 480 volt transformers should roughly be the same, the high leg has no effect on non-neutral loads. Is this an open delta? (Two transformers) Or a closed delta? (Three transformers)
 
Another question, are these backfed transformers that are step down, not step up? If step down, the voltage change taps will be on the new secondary, and may have been adjusted on two taps instead of all three? Is the secondary a corner grounded delta? If the secondary is a wye, the installers may have changed only two of the delta primary taps. Pictures would go a long way on solving the problem.
 
Sounds like a loose or missing neutral.
Look around outside for anything strange with the wires.
Call the poco
 
Two other things that could have happened:

1) I would also add that you check voltage with equipment running. Voltage comes down when circuits are highly loaded.

2) The Utility might have the taps set higher because someone complained about low voltage at a motor in the plant. A maintenance supervisor might have asked for it without even evaluating if it was a voltage drop issue on the feeder / branch circuits.

I have seen some utility HV circuits fluxuate more than 5% voltage when they use a switched capacitor in the middle of the afternoon or when a customer is running full production in a particular season. Like food production goes up in August - November for the holidays, but voltage is high the rest of the year.
 
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