The transformer oil must be periodically tested to ensure the trouble free operation of the transformer.The transformer oil is very important key factor for reliable operation of the transformer. There are various testing standards and procedure set by international standards, most of the standards are set by ASTM.  The following transformer oil parameters are tested using the ASTM( American Society for Testing and Materials) standard,

• Standard Specifications for Mineral Insulated Oil used in Electrical Apparatus (ASTM D3487)

• Dielectric Breakdown Voltage (ASTM D877)

• Interfacial Tension(IFT) (ASTM D971)

• Acid Number (ASTM D664)

• Specific Resistance (ASTM D1169)

• Liquid Power Factor (ASTM D924-08)

• Corrosive Sulphur (ASTM D1275)

• Visual Examination (ASTM D1524)

The above tests are carried out on transformer oil as per the procedure and standards specified by ASTM to ensure whether the transformer oil parameters are as per the specifications of the transformer oil. Any deviation in the oil parameter shows contamination of the transformer oil and oil must be replaced with new transformer in the transformer.

Apart from above tests, the Dissolved Gas Analysis(DGA) Test is also conducted to know the healthiness of the  transformer oil. The DGA test is useful for predictive maintenance of the transformer.