Practice and Testing of Transformer Oil

Transformer oil – the lifeline of equipments

Transformer oil is a mineral insulating oil. It serves as liquid insulation in electrical equipment and also dissipates heat of such equipment.  All winding and core fully immerse in the oil inside the equipment.  The Transformer oil also prevents direct contact of atmospheric oxygen to avoid any type of oxidation.

In words, The Transformer oil is a lifeline of equipments.

In view of the above, it is very essential to monitor the quality of Transformer oil. You should test it regularly as per standard laid down under various test methods.  You have to conduct all these test under various standards for each parameter.

Practice and testing of transformer oil

American Society of Testing and Materials (ASTM), Indian Standard (IS), British Standard (BS) and International Electro technical Committee (IEC) are popular standards in the world.  In India major test method are adopted as per IS-335 & IS-1866 for acceptance of new oil as per agreement with seller and purchaser and maintenance and supervision of Electrical equipment in Service.  A sampling of liquid oil for carrying out the various test is also very important and the bureau of Indian Standard recommend and publish a standard for sampling (IS-6855).  The sampling of Transformer oil for testing from container or equipment should be, as per this standard to get proper and correct results.

For new Transformer oil

For new Transformer oil,  carry out certain tests such as appearance, Flashpoint, Pour Point, Viscosity, Break Down Voltage, Acidity, Neutralization Value, Power Factor & Water contents etc which is called routine tests.  Other tests are long duration tests such as corrosive sulphur, oxidation and ageing tests. They are helpful to determine the oil life in equipments.  Keep all these tests within the acceptable limits as agreed upon under various standards.
In Service, you have to subject transformer oil to normal deterioration due to the equipment conditions.  The oil darkens in colour and its acidity begins to increase.  All these changes may have an effect on both solid and liquid insulating material.  There are different best ways to carry out the tests on Transformer oil in service.  Fields test cum on site testing are limits to visual inspection such as colour, appearance, break down voltage and neutralization value.  The complete examination is only possible to fix the appropriate action to ensure the reliable operation of equipments.  The laboratory tests merely seek to establish the quality of transformer oil for a long life of equipments. The tests include are Break down voltage, Flash Point, Power Factor, Resistivity, water contents and presence of sediments and sludge.

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