Which of the following are important characteristics of good transformer oil?

Which of the following are important characteristics of good transformer oil?

Right Answer is:

All the above

SOLUTION

Properties of transformer oil:

  • High dielectric strength
  • High impulse strength
  • High volume resistivity
  • Low dielectric dissipation factor
  • High specific heat and thermal conductivity
  • Good chemical stability
  • Low viscosity
  • Low volatility and high flash point
  • Good arc quenching properties
  • Non-flammable and non-toxic
  • Cheap and easily available.

Electrical properties:

  • Very high dielectric strength. The minimum breakdown voltage of transformer oil or dielectric strength of transformer oil at which this oil can safely be used in the transformer is considered as 30 kV.
  • High specific resistance or resistivity. The minimum standard specific resistance of transformer oil at 90°C is 35 × 1012 ohm-cm and at 27°C it is 1500 × 1012 ohm-cm.
  • Low dielectric dissipation factor.

Chemical properties:

  • Moisture or water content in transformer oil is highly undesirable as it affects the dielectric properties of the oil adversely. The water content in an oil is allowed up to 50 ppm as recommended by IS–335(1993).
  • Acidic transformer oil is a harmful property. If oil becomes acidic, the water content in the oil becomes more soluble in the oil. The acidity of oil deteriorates the insulation property of paper insulation of winding. Acidity accelerates the oxidation process in the oil.

Physical Properties:

  • Good Transformer oil generally exhibits high interfacial tension. Inter facial tension between the water and oil interface is the way to measure the attractive molecular force between water and oil in Dyne/cm or milli-Newton/meter.
  • It is desirable to have a very high flash point of transformer oil. The Flash-point of transformer oil is the temperature at which oil gives enough vapors to produce a flammable mixture with air. In general, it is more than 140°C.
  • Lower pour point. If the oil temperature falls below the pour point, the transformer oil stops convection from flowing and obstructs cooling in a transformer.
  • Transformer oil has a low viscosity and low volatility with good gas absorbing properties, while It resists oxidation, slugging, and emulsification with water.
  • Viscosity is the resistance of flow, in normal conditions. Resistance to flow of transformer oil means obstruction of convection circulation of oil inside the transformer. Good oil should have a low viscosity so that it offers less resistance to the conventional flow of oil thereby not affecting the cooling of a transformer
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