Oil-immersed transformers are marked with four alphabetical codes for their cooling mode

Oil-immersed transformers are marked with four alphabetical codes for their cooling mode.

(1) The first letter indicates the internal cooling medium in contact with the winding:

O — mineral oil or synthetic insulating liquid with ignition point not greater than 300℃;

K — insulating liquid with ignition point greater than 300℃;

L — insulating liquid with undetectable ignition point.

(2) The second letter indicates the circulation mode of the internal cooling medium:

N — The oil flow flowing through the cooling equipment and inside the winding is a natural thermal convection circulation;

F — The oil flow in the cooling equipment is a forced circulation, and the oil flow flowing through the inside of the winding is a thermal convection circulation;

D – The oil flow in the cooling equipment is a forced cycle, and (at least) the oil flow in the main winding is a forced guided cycle.

(3) The third letter indicates the external cooling medium:

A — air;

W — water.

(4) The fourth letter indicates the circulation mode of the external cooling medium:

N — natural convection;

F — forced circulation (fan, pump, etc.).

Such as

Oil immersed self-cooling (ONAN)

Oil immersed Air Cooling (ONAF)

Forced Oil Circulation Air Cooling (OFAF)

Forced Oil Circulation Water Cooling (OFWF)

Forced Guided Oil Circulation Air Cooling (ODAF)

Forced guided oil circulation Water cooling ODWF)