75kva transformer not putting the right voltage or is utility the problem.

[new-master]

I got a call from Customer who said that their transformers going bad and it’s not putting out the 208v as it should only 193v
But also the room temperature really warm about 95°F top of transformer enclosure

There are three water heaters & a furnace in this room.

Could the heat be the cost of the voltage drop.
I put a fan on the transformer and the voltage has risen 200volts and temperature above transformer enclosure 93.5°F

Utility voltage coming in each phase is 267-269v
A-B= 463v
B-C= 463v
A-C= 468v

Please help what should I do on this situation?

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[infinity]

You need to change the primary taps inside of the transformer because they're currently set to 480 volts.

 

[kwired]

Was utility voltage still same after output voltage went up?

95F is not hot enough to be concerned if loaded could easily be warmer than that.

And I agree with infinity, if connected to the 480 input taps then output is about in line with input voltage, so question is was the input temporarily low for some reason since it did go up coincidentally with your cooling attempt.

 

[electrofelon]

Is the electrical system supplying the transformer supposed to be 460 or 480?

 

[infinity]

The utility voltage is the problem. Has the voltage ever been 208 volts on the transformer secondary?

 

[new-master]

Is the electrical system supplying the transformer supposed to be 460 or 480?

I am not sure, there is a separate room in the shopping center that feeds the tenants electric with 277v to that transformer


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[new-master]

The utility voltage is the problem. Has the voltage ever been 208 volts on the transformer secondary?

I’ll be opening the transformer and checking the taps


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[kwired]

I’ll be opening the transformer and checking the taps


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The fact that voltage did come up some according to your OP, suggests either utility issues or voltage drop issues on the primary circuit due to loading changes maybe? Or maybe even undersized transformer for that system for the load it is supplying?

 

[infinity]

I’ll be opening the transformer and checking the taps

The nameplate rating is 480 volts so the taps from the factory are set for 480 volts.

 

[new-master]

The utility voltage is the problem. Has the voltage ever been 208 volts on the transformer secondary?

I’m not sure, first time, Customer


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[jaggedben]

@new-master
Is 193V the secondary voltage on all three phases or just one? You did not report if the secondary voltages are balanced like the primary. If they are not, it could be a bad connection instead of a transformer problem.

You need to change the primary taps inside of the transformer because they're currently set to 480 volts.

But the secondary voltage is about 93% of 208 and the primary voltage is about 96% of 480. So perhaps the taps were set for high voltage. Or there's an additional issue.

 

[new-master]

Was utility voltage still same after output voltage went up?

95F is not hot enough to be concerned if loaded could easily be warmer than that.

And I agree with infinity, if connected to the 480 input taps then output is about in line with input voltage, so question is was the input temporarily low for some reason since it did go up coincidentally with your cooling attempt.

Would i need to raise taps to get proper voltage on load side?
120/208v


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[new-master]

Is the electrical system supplying the transformer supposed to be 460 or 480?

Call the utility company, they take about four days to get an answer on what voltage should be coming in from the transformer?
But it did happen to me for 460v. Would I need to just raise the tabs? 492volts?


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[electrofelon]

Call the utility company, they take about four days to get an answer on what voltage should be coming in from the transformer?
But it did happen to me for 460v. Would I need to just raise the tabs? 492volts?


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Before changing taps I would do a little more investigation. 460 is an odd service voltage. Before changing tabs, I would see if the voltage is supposed to be 480, and if it is whether the utility voltage is low or there is excessive voltage drop on the way to that transformer.

 

[new-master]

Before changing taps I would do a little more investigation. 460 is an odd service voltage. Before changing tabs, I would see if the voltage is supposed to be 480, and if it is whether the utility voltage is low or there is excessive voltage drop on the way to that transformer.

Thank you so much all you guys input , I have made the call and yes, they told me it’s four days to get an answer


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[jim dungar]

Your transformer needs to be vacuumed out as standard maintenance.
Your transformer is rated to create a 115°C rise above a 30°C ambient. Your room temperature of roughly 35°C is likely not a real concern.

Your taps should be set based on your base, steady state, incoming voltage. The problem with adjusting taps due to temporary utility issues, like heavy AC loading during heat waves, is the resultant over voltage when things return to normal.

 

[electrofelon]

Thank you so much all you guys input , I have made the call and yes, they told me it’s four days to get an answer


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Can you look at the main service and take some voltage readings there and maybe look at what other equipment or transformers are labeled?

 

[jim dungar]

Can you look at the main service and take some voltage readings there and maybe look at what other equipment or transformers are labeled?

Please make all of the 10 possible voltage measurements.
L-L
L-N
L-G
And
N-G

 

[ptonsparky]

Include the secondary current for each phase as well.

 

[ptonsparky]

Take time for a bit of thought to your safety. Those working clearances appear to be lacking.