what is the name of transformer oil ? Can transformer oil be used for cooking?

properties of transformer oil, electrical, physical and chemical property of transformer oil


  • Insulating oil/ mineral insulating oil.
  • obtained by fractional distillation and subsequent treatment of crude petroleum
  • Transformer oil dissipates heat of the transformer e.i. acts as a coolant and prevents direct contact of atmospheric oxygen with cellulose made paper insulation of windings, which is susceptible to oxidation.


Types of Transformer Oil



1. Paraffin based transformer oil 2. Naphtha based transformer oil

Paraffin based transformer oil


  • lower oxidation rate than that of Naphtha oil.
  • insoluble oxidation product or sludge
  • obstruct the transformer cooling system.
  • easy availability
  • high pour point due to the wax content
  • use due to warm climate condition of India.


Naphtha based transformer oil


  • easily oxidized than Paraffin oil.
  • soluble oxidation product, i.e. sludge
  • does not disturb the transformer cooling system


Parameters of Transformer Oil

Electrical parameters :– Dielectric strength, specific resistance, dielectric dissipation factor. Chemical parameter :- Water content, acidity, sludge content. Physical parameters :- Inter facial tension, viscosity, flash point, pour point.

1. Dielectric Strength/ breakdown voltage of Transformer Oil


  • Break down voltage is measured by observing at what voltage, sparking strants between two electrodes immerged in the oil, separated by specific gap,
  • low value of BDV indicates presence of moisture content and conducting substances in the oil
  • For measuring BDV of transformer oil, portable BDV measuring kit is generally available at site.
  • Distance between electrode 2.5 to 4 mm
  • The rate of rising voltage is controlled at 2 KV/s
  • measurement is taken 3 to 6 times in the same sample of oil, and we take the average value of these readings.
  • Minimum breakdown voltage / dielectric strength of transformer oil at which this oil can safely be used in transformer, is considered as 30 KV.


Specific Resistance of Transformer Oil


  • measure of DC resistance between two opposite sides of one cm3 block of oil.
  • unit - ohm-cm at a specific temperature.
  • With increase in temperature the resistivity of oil decreases rapidly.
  • Temp of oil very ambient to 90 degree C at overload
  • Minimum standard specific resistance of transformer oil at 90oC is 35 × 1012 ohm–cm and at 27oC it is 1500 × 1012 ohm–cm.


Dielectric Dissipation Factor OR Tan Delta of Transformer Oil


Tangent of the angle by which it is short of 90o is called dielectric dissipation factor or simply tan delta of transformer oil.


  • The loss angle is small, means resistive component of the current IR is small which indicates a high resistive property of the insulating material.
  • High resistive insulation is a good insulator.
  • High value of this tanĪ“ is an indication of the presence of contaminants in transformer oil.
  • If the resistivity of the insulating oil gets decreased, the value of tan-delta increases and vice verse.
  • both resistivity test and tan delta test of transformer oil are generally not required for the same piece of the insulator or insulating oil.

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