Oil Dielectric Testing Ensures Continuous Service of High Voltage Transformers

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Insulating oils in transformers serve as both an insulator and a coolant. Contamination by moisture and rust can affect its performance and can damage the transformer if not corrected immediately. Oil dielectric testing should be done periodically to ensure continuous operation and safety.


Oil filled transformers are prone to moisture formation especially for vented types. Other contaminants like rust and dissolved acids can affect the quality of the dielectric fluid. This can cause partial shorts, poor heat dissipation and winding problems. Periodic testing of the dielectric fluid should be done to check if it is still within its rating. A dielectric test is usually done to determine the amount of contaminants in the oil. A test voltage of several kiloVolts is applied and the breakdown voltage is measured. Low breakdown voltage indicates contaminated oil because of its increased conductivity. The acceptable breakdown voltage for transformers with a rating of 287.5 kiloVolts and above should be 30 kiloVolts and 25 kiloVolts for transformers with a rating below 287.5 kiloVolts.

If you need to rent electrical testing equipment, let Protec be your testing partner. We carry many testing instruments like oil dielectric test sets, AC hipots and power quality analyzers. You can choose from major brands like Doble, Megger and Metrel test equipment. Contact us for more details on equipment for rent.