Dry type transformer abnormal heating 2

[capuchi]

hi guys, i hope you can help me on this one. We have a 175 KVA, 480/240v, 3phase, 60 Hz. 65 degrees C rise, delta/wye neutral ungrounded dry type transformer with 15 % load and 40% unbalance. The unit is showing abnormal heating of 45 degrees C as shown by IR scan. Megger readings is 200 Megs average between high and low side to ground. Likewise, there is abnormal vibration.
Is the unbalance causing the abnormal heating considering that the load is only 15%? How much unbalance can a transformer take without overheating?

would appreciate your help.

capuchi

 

[DanDel]

45°C is not abnormal for a transformer, especially if it's on the core. The rating is for 65°C above ambient, so it's well within the rating.

 

[dpc]

Agree with DanDel - seems within normal limits to me. Fully-loaded dry-type transformer can be so hot you cannot keep your hand on it.

 

[capuchi]

to dpc and dandel

thanks for your response. just for general guidance, how much load unbalance can a transformer take or is tolerable without causing damage to the unit itself.

again your help will be appreciated.

capuchi

 

[DanDel]

This would vary for each transformer. The manufacturer would be the best resource.
In any case, if the transformer temperature is within limits, there shouldn't be any significant damage which would change the normal lifespan of the unit.

 

[dpc]

As long as individual windings are not overloaded so much that high temperature results, unbalanced loads are generally not a problem for transformers. They cause problems for your motors because they create unequal phase voltages.