Thermal inspection shows internal heating in 133mVA PWT. No problem found in test.

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11bgrunt

Pragmatist
Location
TEXAS
Occupation
Electric Utility Reliability Coordinator
A thermal inspection of an industrial substation reveals an area under the X3 bushing with a Delta T of 10-12C when compared to X1. This 80/105/133mVA transformer serves an arc furnace at 3000 amps, 13.8kV Delta.
Original thermal pictures showed heating under the X3 bushing above the oil line. Winding and oil temp info has not changed and gauges show OK.
Moved load to nearby 60/80/100mVA and the hot spot moved with the load. X3/A phase on second transformer began showing similar temp rise under X3 bushing.
All transformer testing showed 133 transformer to be good. Oil was perfect.
There is a SVC+ connected at plant.
Since hot spot seems to move with load, we now look at load issues. We have no meters in place suggesting a problem.
We now think about harmonics or some other issue. Phase loads are balanced.
Has anyone seen this before?
We will be looking at oil circulation this week and monitoring the transformer.
Thia is a big deal for us. IMO.
I started this with the inspection and thought we would find a conection between winding lead and X3 bushing. Doesn't appear so....:happysad:
Thanks.
 
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