What is the Flash Point of Transformer Oil?
Flash Point of Transformer Oil is defined as the temperature at which light hydrocarbon present in the transformer oil starts evaporating causing a flash on introduction of source under specified condition. It is an important parameter which must be maintained above 140 degree Celsius.
Light hydrocarbons are already present in the transformer oil and gets evaporated under the influence of heat due to electrical stress. Light hydrocarbons are also generated by the degradation of the oil due to aging / heat / electrical stress.
Minimum Value of Flash Point Value of Transformer Oil
Flash Point of new Transformer Oil should be more than 140˚C. In any case, this temperature should not be allowed to be less than 130˚C for transformer oil in service.
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.
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.
Lighter hydrocarbons are also generated due to degradation of oil due to heat generated in the winding. Therefore, the flash point of transformer oil may slightly decrease during service condition.
Above all, if the varnish of the transformer winding is mixed in the oil then it may reduce the flash point by around 5˚C.
If larger amount of light hydrocarbon is present in the oil then it represents the incipient fault in the transformer. A flash point below 130 degree Celsius may indicate unsatisfactory working condition viz. electrical discharge, excessive internal temperature, core fault etc. In such case, the transformer should be taken out to investigate and subsequent repair.
Thus, the periodic flash point and other subjects 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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