Transformer Oil

Which Transformer Oil is used in transformer ? Why it is used ?

What is transformer oil ?

Transformer is a special type oil having very good insulating and high stability of temperature. Transformer oil is used in oil filled transformer as a coolant and insulating material.

Type of Transformer oil !

  1. Parrafin based transformer oil
  2. Naphtha based transformer oil

Transformer oil properties

What are Electrical properties of Transformer Oil ?

Dielectric strength of Transformer oil (BDV):-

The Dielectric of strength of Transformer oil also known as BDV (Break down voltage). And what is Break down voltage, it means at a voltage level when the transfomer oil loss its insulating properties. If the Value of BDV is low it means its having moisture content. A transformer oil having 30 KV BDV say to be good and used as transformer oil.

As per IEC rules in electicals , the minimum BDV value of Transformer should not be less than 30 KV. And that why BDV should be used periodically to keep transformer healthy.

BDV Testing How to test BDV of Transformer oil ?

Specific resistanc:

Transformer oil sholud have value Specific Resistance at high temperaure. As with increase in temperature the resistivity of oil decreases rapidly. Becuase during full load of transformer, the temperature will be very high and may go up to 90oC at an overload condition so resistivity of the insulating oil must be high at room temperature and also it should have good value at high temperature.

What are Chemical properties of Transformer Oil ?

Water Content in Transformer oil

Transformer oil should be free from water content as it effects dielectric strenght of the oil. As in the transformer paper insulation is used in transformer winding as a insulator. And water content in oil also effect the Paper insulation as paper attract water molecules and will try to obserb water so in resultant life of insulation will reduce.

Transformer oil are packaged in closed container or drum to avoid direct contact with air. As air having moisturing content in it, may increase water content in the oil and reduce the insulating properties of oil.

How transformer oil transport

Acidity of transformer oil 

it is also a harmful factor for transformer oil. Due to Acidity in oil water content will become more soluble and redeuce the insulating properties of paper insulation. Also due to acidity transformer wil get oxidized and start rusting in the core of the transformer.

How acidity in the transformer oil forms ? The interaction of Oxyzen and heat with the insulating oil forms the acid in the oil .The acidity of healthy transformer oil is o.3Mg KOH/gram. in simple words we can say 0.3 miligram of KOH (Potassium hydroxide -which having high -PH factor(Negative)) required to neutralize 1 gram of insulating oil.

The PH Value of transformer oil must be below 7.

Property of Transformer oil


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