Transformer primary voltage drop cause increase in secondary current?

[housemoney]

Client maintenance guy called and said an existing 480: 120-/240V 10kVA single phase transformer (maybe 15A load) is hot enough to cook eggs on. It's fed from 850' feeder- 60A/480V breaker upstream (AWG unknown). Feeder has about 35A 480V load on it + the 15A of single phase.

My first thought was bad transformer but Is it possible voltage drop on the #6AWG primary feeder at this distance is causing higher secondary current on the the transformer to overheat it?

 

[LarryFine]

Only a motor load would draw more current at a lower voltage.

Can you see whether it cools with the secondary not loaded?

 

[infinity]

As Larry mentioned you need to know type of load on the transformer. A resistive load like a heater would just have a lower output and lower current draw.

 

[drcampbell]

The secondary current depends on the secondary voltage and the load impedance, not the primary voltage.
What are the voltages & currents at the transformer primary & secondary terminals?
Excessive heat could be the result of turn-to-turn shorts in either winding.

 

[Hv&Lv]

Maintenance guy…

Where is the transformer and how much crap is piled around or on top of it?
Dry packs need a good air flow

 

[housemoney]

The secondary current depends on the secondary voltage and the load impedance, not the primary voltage.
What are the voltages & currents at the transformer primary & secondary terminals?
Excessive heat could be the result of turn-to-turn shorts in either winding.

Not asking an unqualified guy to check voltages and currents, we couldn't get anyone out there until tomorrow, told him bad windings in the transformer most likely. He had another contractor install this side and I'm not sure what's going on, just wanted to rule out voltage drop on the primary but doesn't sound like that could be an issue based on comments above.

 

[jim dungar]

A small 10kVA transformer may be encapsulated, which runs extremely hot. I would not be surprised to find skin temperatures over 160F.

First thing is to get an actual infrared thermometer reading.

 

[synchro]

The temperature rise spec on the transformer would be important information to have. For example, if it's a dry transformer with a 150° temperature rise on the windings expect the external housing to also get quite hot under normal operation.

 

[housemoney]

A small 10kVA transformer may be encapsulated, which runs extremely hot. I would not be surprised to find skin temperatures over 160F.

First thing is to get an actual infrared thermometer reading.

Good guess, photo shows it is an encapsulated transformer in an unventilated pump shed around 100 degrees in there ambient. IR from our guy showed 150F+, he found no issues with it.