What is Transformer Oil?
Transformer oil is mineral insulating oil derived from crude petroleum. It is a mixture of various hydrocarbons. It consist partly aliphatic compounds (open chain compounds) with the general formula CnH2n+2 and CnH2n.
Many oils also contain certain aromatic compounds (closed chain or ring compounds) related to benzene, naphthalene and derivatives of these with aliphatic chains. Good transformer oil must insulate and prevent flash over of the exposed parts within the equipment and it must effectively transform the heat from the core to the radiating surface.
The characteristics of new transformer oil is given in IS 335/1983.
If the dielectric strength is low, the oil is unfit for use regardless of any other condition.
Transformer Oil Tests
- Dielectric Strength
- Water Content
- Neutralisation Value
- Interfacial Tension
- Dielectric Dissipation Factor Test for Corrosive Sulphur in Oil
- Test for Oxidation Stability
- Specific Resistance (Resistivity)
- Flash Point
- Pour Point
- Sludge Test
- Dissolved Gas Analysis (DGA)
Dielectric Strength Test
The electrodes must be Copper, Brass, Bronze or Stainless steel and well polished having spherical shape with dip 12.5 mm to 13 mm. It shall have a spherical front as shown in the figure. The electrodes shall be mounted horizontally in the cell and the axis shall be immersed at a depth of approximately 40 mm, The electrode gap shall be 2.5 ± 0.1 mm.
Before carrying out the test the cell shall be cleaned by rinsing with the test oil. The sampling vessel containing the test oil shall be gently agitated to have homogeneous distribution of impurities and air bubbles to escape. The oil temperature at the time of testing shall be around 27°C (15°C to 35°C preferable).
Transformer Oil Treatment
Ditertiary butyl para cresol
Azo-bis- ISO-but ronitrate
lonex 220, AN 2246