Transformer oil Specification


In this article, we are describing transformer oil specification. Let us focus on what are its key specification & properties.These are all which we must be aware of.

Transformer oil performs three main actions. These are:

  • It takes care of the transformer;
  • to be an effective electric insulation barrier,
  • and to become a heat transfer way and to prevent the transformer extra time.

To safeguard these basic actions there are particular items that have been advanced over time, based on trained and professional from isolated parties on the market.

Transformer Oil Specification


The condition case manufacture, testing, supply and delivery and the need of latest insulating oil of petroleum source satisfactory for use as insulating and warmness relocation medium and are demolishing medium in power/ distribution transformers and other equipment.

The oil which we are using should contain a minimal load of impurities inclusive moisture, grease and must have some stated physical and chemical traits as detailed in the specification.


The oil shall be without any infected item like hydrocarbon mineral oil, without any impurities, fresh and purified and free from moisture and other foreign waste materials. Mineral insulating oil is obtained from selected fraction of crude oil.

The crude oil is mainly composed of hydrocarbon, which may is likely seemed different in their content of the main types of hydrocarbon along with impurities like paraffin, naphthenic and aromatics. The transformer oil should be free from aromatics hydrocarbons as there is some unsaturated and hence least stable.

Service Quality

The transformer oil will be used in WBSEDCL’s power or distribution transformer and fuse established in outside sub-terminal of several varieties to all class of repeated weather alteration considering equatorial and moist weather and rain, thunderstorm along with the impact of dust particles of transformers.

Transformer oil must take care of the desired traits even though the performance under serious service condition with all types of above transformer manufactured in India consist of those fitted with on-load tap changing equipment.


The characteristics of the oil when it is sampled of smallest part of whole for analysis at the manufacturer’s works and / or at the point of dispatch and tested in accordance with ISS: 335-1993 should obey with the result given in the IS Specification (ISS: 335-1992 along with recent amendment will be applicable) excluding for certain characteristics for which the value is accessible.

Sampling and Testing

A sampling of the oil shall be done in comply with (IS: 6855-1973) and the exams will be carried out in complying with exams method referred to (IS: 335-1993) with recent amendments and updated list of moisture content only, in the manufacturer’s laboratory arranged by them. Their list of devices accessible in the manufacture’s laboratory for precise testing should be equipped along with the passage. Any test, which cannot be operated in the laboratory, should be clearly settled in the offer. Those who doesn’t require any major testing facilities in the laboratory need not refer it.

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