High temp on a xfmr

[KevinVost]

First, some info:
I have encountered a 50kva, single phase, 480v primary, 120/240 secondary, dry type, indoor transformer. All the voltages to/from the unit are correct. Currently, the unit is loaded to 29 amps, on the secondary.

The top, external casing of the unit is so hot to the touch, you can not keep your hand on it for more than a few seconds. With a IR temp gun, I read 162 F degrees on the top of the unit. The manufacturer has stated to me that the unit "skins" or casing can have a temp of up to 194 F degrees (90 C). I can not imagine that this is correct (and I have asked for this in writting), since a temp that high could burn someone on contact.

The unit was factory tested and came with a cert from the factory (saying it was tested by them, and all was OK) :-?

Now the questions:
What would cause the unit to run this hot, bad windings???? Contaminents in the core steel?????

I could not find anything in the code or white book. Any ideas????

 

[acrwc10]

There is no way at 29 amps on the secondarys, and a 50KVA that this is a safe transformer. Something is wrong.

 

[acrwc10]

Megger Time.:grin:

 

[A/A Fuel GTX]

Is there adequate ventilation?

 

[KevinVost]

Is there adequate ventilation?

Yes. Unit is spaced from away from wall and is in a conditioned space.

 

[Jim W in Tampa]

With a load that small i agree it sounds way to high. Perhaps take amp readings on both input and output and multiply times volts to see what your losses are in heat.

 

[don_resqcapt19]

While there may be a issue here because the load is small, many transformers are designed with a 150?C rise over a 40?C ambient. This design will result in very high surface temperatures on the exterior. I would not be surprised to see a transformer with this temperater rise and fully loaded to have a surface temperature that will produce burns on contact.

I wonder how these work with the OSHA rules? I think that there is a rule that requires some type of protection for people when the temperature exceeds 60?C (140?F)

 

[Dan coulstring]

Dry-type transformers are available in three standard temperature rises: 80C, 115C, or 150C. That means, for example, that an 80C rise dry transformer will operate at an average winding temperature of 120C when at full-rated load, in a 40C ambient environment. (So-called hot spots within the transformer may be at a higher temperature than average.) Since most dry transformers use the same insulation on their windings (typically rated at 220C), the 80C rise unit has more room for an occasional overload than a 150C rise unit, without damaging the insulation or affecting transformer life.


These temps are at the windings not on the outer skin, which can be much hotter.

 

[steve66]

Harmonics can cause overheating, but I doubt that's your problem at that light load. Also, I'm not sure harmonics affect single phase transformers that much??

I would suggest measuring the current on the primary. Use the current X voltage to see if the input power is about the same as the output power.

If the input power is much higher (it seems like it has to be to produce a temp. that high), there has to be something wrong with the xformer or wiring.

Steve

 

[WorkSafe]

I wonder how these work with the OSHA rules? I think that there is a rule that requires some type of protection for people when the temperature exceeds 60?C (140?F)

I'm almost certain OSHA does not have a specific standard dealing with hot surfaces, but they would just fall back on the good 'ole General Duty Clause of 5(a)(1).

 

[Dan coulstring]

You are correct.

OSHA does consider exposed heated surfaces, if there is a potential for injury, to be a hazard and will issue citations if employees can come into contact with such surfaces. While there are not any OSHA standards, except those that are applicable only to specific industries, which address exposed heated surfaces, there are several OSHA general standards which address such hazards. Those standards are:

1910.261(k)(11): Steam and hot water pipes
1910.262(c)(9): Steam and hot water pipes

And the ever present
Section 5(a)(1) of the OSHAct:
Each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees.