Pad Mount Transformer ─ Real Life Stories
The best test to predict the reliable operating condition of an oil filled transformer is the combustible gas-in-oil analysis. Using a syringe, 40 cc of oil is taken from the transformer and analyzed. When threshold levels of specific gases in the oil are reached, protocol demands appropriate action be taken. This is an extreme oversimplification of a combustible gas-in-oil analysis.
One such case involved a 3000 kva, 25 kv primary, 600 volt secondary, foundry furnace transformer. The oil test results indicated the transformer began generating high levels of acetylene. Additional tests were performed and the transformer was shut down and taken out of service. A temporary transformer was put in its place to continue plant production. The defective transformer was sent out to be rebuilt.
Furnace transformers are special breeds of cats, designed to withstand the stresses of heavy shifting loads. Often times these transformers are pushed to the max in terms of load limits. Based on secondary ampere readings, this transformer was pushed to over 100% of rated load capacity, creating high thresholds of heat in the windings. Transformers don’t much like that too well. Heat puts all kinds of funny stresses on the internals of transformers.
In two months time the rebuilt transformer was put back in service and life continued on.