COOLING METHODS OF A TRANSFORMER
- Air cooling:
AN – Ambient air as coolant with natural circulation by convection [ up to 1.5MVA] and special conditions such as mines
AF – Forced air circulation
- OIL IMMERSED, OIL COOLING:
ONMAN- Natural oil circulation and natural air flow over the tank (tubes) up to 5MVA
ONAF – Natural oil circulation with air blown (forced) on to the tank surface.
OFAN – Oil is pumped round the system while natural air blows over tank. With this, high current densities can be used in the windings.
OFAF – Forced oil – an air – circulation method used for transformer up to 300MVA and upward.
- OIL – IMMERSED, WATER COOLING
ONWF – Natural oil cooling of windings and water is forced through copper cooling coils mounted in the tank above the level of the transformer core, but below the oil surface.
OFWF – Oil/water heat exchangers are external to the transformer and are pumped into it. Thus, the tank does not need to contain cooling oils and the tank is smaller.