Hot transformer

[joshgarcia]

We have a transformer that is getting very hot to the touch with no load, 240 degrees F on the top. Other transformers in the area are cool to the touch. The transformer is dedicated to the welding receptacles in the plant. I have never seen this before and I was wondering what possible causes may be? Thanks,

Josh

 

[zog]

We have a transformer that is getting very hot to the touch with no load, 240 degrees F on the top. Other transformers in the area are cool to the touch. The transformer is dedicated to the welding receptacles in the plant. I have never seen this before and I was wondering what possible causes may be? Thanks,

Josh

Could be many things, what testing has been done?

 

[broadgage]

There are indeed may possible causes, including a defective transformer, wrong input voltage, lack of ventilation, or failed fans, if fan cooled.

By far the most common cause though is electrical overload.
Transformers will take short term overloads as might be caused by intermitant or cyclic loads such as welders, but sufficient cooling time must be allowed.

A very common misconception is that a transformer may loaded to 200%, if this is only for 50% of the time.
In fact the heat produced is roughly proportional to the SQAURE of the load, therefore twice the load=four times the heat=duty cycle of 25%

 

[poeboy]

240 F is about 115 C..... that is not extremely unusual for most transformers, however it is quite warm. I think most transformers I install are rated at 150 C, which is about 302 F.

Exactly what is your transformer rated at?
what size and type of transformer is it?
How many amps flow through each phase and for how long?
All of this information can be found on the nameplate of the transformer. (a picture of the nameplate would be very useful here).
Is it well ventilated (at least according to manufacturer's specs)?
does it create a neutral? if so, is that neutral properly bonded??

If the transformer has been in place for YEARS, a shop vac and with a brush attachment on the end of it will remove all of the cobwebs blocking the vents on the bottom, if that is the cause of the warm.....

I'd also suggest you remove the cover and use an IR thermometer to check the terminations and the temperature of the conductors themselves. Most wire has a maximum temp of 90 C , and if the wire or terminations exceed that rating, then you are looking for a lot more trouble down the road.... not just a warm transformer.

If the terminations have loosened over the years of heating/ cooling, that in itself could be the cause of the warming.

 

[LarryFine]

. . . I was wondering what possible causes may be?

Improperly terminated, maybe? Have you actually disconnected the secondaries inside the cabinet?

It's not easy to overheat an unloaded transformer.

 

[gar]

100709-1231 EST

joshgarcia:

Check that the transformer is truely unloaded, meaning for a number of hours. Measure the output voltage on all phases, and the output currents. If unloaded the output currents will be zero. Measure the input voltage on all phases, and input currents on all input lines.

On a small single phase 120 V input 175 VA transformer I read about 0.29 A with an average reading meter. This is about 20% of the VA rating of the transformer. I do not believe you would be too far off scaling this to many transformers.

For a truely unloaded transformer either the transformer is supplied with voltage that is too high, or there are internal shorted turns.

.

 

[zog]

Improperly terminated, maybe? Have you actually disconnected the secondaries inside the cabinet?

It's not easy to overheat an unloaded transformer.

Harmonics can do it. Major core heating from the additional hysterisis losses if harmonics are an issue.

 

[LarryFine]

Harmonics can do it. Major core heating from the additional hysterisis losses if harmonics are an issue.

That requires a load (under normal conditions), doesn't it?

I was thinking of mis-matched voltage taps, or something like that.

How about measuring individual winding currents inside the unit?

Added:[/] We're talking about Delta, right? Y wouldn't have circulating currents.

 

[zog]

That requires a load (under normal conditions), doesn't it?

I was thinking of mis-matched voltage taps, or something like that.

How about measuring individual winding currents inside the unit?

Added:[/] We're talking about Delta, right? Y wouldn't have circulating currents.

Yes it would require a load but the OP said it was feeding welders, did I miss something?

 

[iwire]

Yes it would require a load but the OP said it was feeding welders, did I miss something?

A little

We have a transformer that is getting very hot to the touch with no load,

 

[mcclary's electrical]

Yes it would require a load but the OP said it was feeding welders, did I miss something?

QUOTE=joshgarcia;1216659]We have a transformer that is getting very hot to the touch with no load,

 

[480sparky]

I went through the same thing several years ago. Transformer was almost hot enough to cook on. I shot an IR thermometer on it, and I had temps to 190?F.

This was a 112.5 kva, and the ambient temp was around 70. It was only running about 40 amps on the secondary side for temp lights and construction outlets. I contacted the manufacturer and they said that was normal.

 

[gar]

100710-0745 EST

Post #1 used the word transformer not ---ers. It also stated the transformer was unloaded. The implication is that it is a single phase transformer or a true three phase transformer.

A 240 deg F surface temperature for an unloaded transformer in an ambient of maybe 70 deg F and likely indoors seems to be quite high. Additionally the internal temperature will be higher than the surface temperature.

Also stated was a comparison with other probably similar transformers that were much cooler. Therefore, this particular transformer stands out as a "red flag".

Unloaded transformers may and most likely run hot to your hand, but 240 deg F is extremely hot to the hand.

There needs to be clarification as to whether this is a single phase transformer or a three phase transformer, how large is the transformer, and other items brought up in various posts.

.

 

[zog]

QUOTE=joshgarcia;1216659]We have a transformer that is getting very hot to the touch with no load,

Opps, my bad.

 

[Besoeker]

We have a transformer that is getting very hot to the touch with no load, 240 degrees F on the top. Other transformers in the area are cool to the touch. The transformer is dedicated to the welding receptacles in the plant. I have never seen this before and I was wondering what possible causes may be? Thanks,

Josh

If it really is 240F (115C) touching it would probably cause a burn.
If it is really no load, I can think of two possibilities.
The first is overvoltage on the primary. This could be caused either by supply overvoltage or an incorrect connection.
If the transformer has been in service and other similar units are connected to the same supply that would rule out a supply voltage problem. And, if it has run in the past without getting as hot, that would rule out an incorrect connection unless it might have been disconnected at some point and reconnected incorrectly.
The second is a transformer fault. Shorted turns, insulation failure, bridged laminations...or something else.

 

[brian john]

With the power off have you opened the transformer and vacuumed it? Dirt and dust in an industrial application will ad to heat retention.

From a laundry facility we did an IR in.

 

[kwired]

With the power off have you opened the transformer and vacuumed it? Dirt and dust in an industrial application will ad to heat retention.

From a laundry facility we did an IR in.

Isn't gray conductor covering reserved for grounded circuit conductors?

 

[cadpoint]

Nice picture wheres the IR of that visible photo ?

 

[vinod]

Correct me If am wrong, may the heat up can be caused by wrong connection of Neutral (X1) point? May be it is not grounded properly.

 

[e57]

With the power off have you opened the transformer and vacuumed it? Dirt and dust in an industrial application will ad to heat retention.

From a laundry facility we did an IR in.

Them darned dust bunnies just crawled in there and died....