Flash Point of Transformer Oil and its Importance

Flash point of the transformer oil is 140˚C. In this article, we will discuss the flash point of the transformer oil and what is its importance.

What is the Flash Point of Oil?

The transformer oil on heating hydrocarbon present in the oil releases enough vapors. The vapor so produced on heating may or may not produce a flash on the application of flame depending on the flash point of the oil. All types of oil have a different flash point. Thus, we can say the flash point of transformer oil is the temperature at which the oil catches fire if oil receives the flame.

Flash Point Value of Transformer oil

The transformer has the following tripping values of its oil and winding temperature.

Oil Temperature Trip = 90˚C
Winding temperature Trip = 95˚C

When current flows in the winding, it produces a heat loss(I2R) in the transformer. The transformer oil takes the heat from the winding and its temperature increase. Further, the oil transfers the heat to the radiator and in this way transformer, oil cooling process completes.

The tripping points of winding and oil temperature must be well below the oil flash point in order to prevent fire.

The flash point of the transformer oil is above 140˚C. The higher flash point temperature is a desirable feature because it minimizes the possibility of fire.

In the case of a fault in the transformer, there is a chance of an increase in oil temperature above 120 ˚C or more. We keep the temperature tripping much below the rated flash point, thus a safety margin in temperature 120-90 = 30˚C ensures tripping of the transformer well before the temperature reaches its flash point.

How does Flash Point affect the transformer life?

The transformer oil’s flash point depends on the number of light hydrocarbons present. The transformer oil is a Mineral Insulated oil, that we obtain through the refining of crude oil.

During the refining of crude oil, the products like kerosene, petrol, and diesel are separated to increase the flash oil of the oil. The flash point of the kerosene and petrol is 50˚C and 35˚C respectively.

If the light hydrocarbons in the transformer oil are less, its flash point will be higher. Do you think the hydrocarbon in transformer oil remains the same during the transformer is in service? Obviously -No

The reasons for the deterioration in the transformer flash point are as follows.

  • The varnish of the transformer if mingled with the oil may reduce the transformer oil flash point by 5˚C.
  • In the event of a fault, the many types of gases get evolved and get dissolved in the oil. The gases are detected through the dissolved gas analysis(DGA) test.

Thus, the periodic testing of the transformer oil is a must when the transformer is in in-service condition. This reduces the possibility of fire hazards and ensures a longer life of the transformer.

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