Transformer In-service testingThis refers to surveillance testing, which involves periodic checks and condition monitoring of in-service transformer. This offers a continuous check on transformer performance.Transformer Oil degassing, Filtration or other cleaning process are not the first point of call in transformer maintenance.Although the above may restore the insulating and other properties of the oil, but it does give the information on faults happening inside the transformer. Also, these do not prevent further occurrence of the same faults in the transformer.

Surveillance testing oil samplesWhen transformers are in operation, the simplest tests are carried out on oil samples taken on a regular basis. Measurement of oil properties, such as breakdown voltage, water content, acidity, dielectric loss angle, particle content and DGA, all give valuable information on the state of the transformer.Dissolved Gas Analysis (DGA) gives early warning of deterioration due to electrical or thermal causes, particularly sparking, arcing and service overheating.

Maintenance Testing on De-energized TransformerElectrical testing such as Winding resistance, Tan-delta test, Turns ratio per tap etc can give valuable information on the condition and the performance of a transformer. These tests are carried out while the transformer is de-energized.

These tests coupled with the transformer Oil tests above can help to determine the faults occurring in the transformer. With the accurate knowledge of the transformer condition, one can now takes steps towards removing the causes of faults, thereby recovering the transformer from imminent damage.