Oil Type Transformers

Oil-type transformers are a very common type of electrical transformer used in power distribution and transmission. Instead of being air-cooled, they use special insulating oil for both cooling and insulation.

Here’s a breakdown:
  • An oil-type transformer is a transformer where the core and windings are completely immersed in insulating oil, usually mineral oil or synthetic ester.
  • The oil serves a dual purpose:
    • Electrical insulation – it prevents short circuits by insulating live parts.
    • Heat dissipation – it absorbs heat from the windings/core and transfers it to the transformer tank walls, which then release it into the air.
Types of oil-type transformers:
  1. Distribution transformers (up to ~33 kV) – found on poles, in substations, near residential areas
  2. Power transformers (above ~33 kV) – used in high-voltage networks and substations
  3. Hermetically sealed (no air exchange, less oil degradation)
  4. Conservator type (oil level changes with temperature, requires a breather)
Key components:
  • Core and windings (like any transformer)
  • Insulating oil
  • Tank – sealed or conservator type (with an expansion chamber for oil volume changes)
  • Radiators or fins – to increase surface area for cooling
  • Bushings – insulated connections for incoming and outgoing conductors
  • Breather / silica gel unit (on conservator type) – keeps moisture out
Advantages:
  • High efficiency and long lifespan
  • Excellent cooling capacity → can handle higher loads than dry-type equivalents
  • Cost-effective for medium to very large power ratings
Disadvantages:
  • Fire risk (since mineral oil is flammable)
  • Heavier and less environmentally friendly than dry-type transformers
  • Requires regular maintenance (oil testing, leakage checks)

In short: Oil-type transformers are the backbone of power distribution grids worldwide, chosen for their reliability and cooling efficiency, but they come with fire and environmental considerations.