Cooling type

Due to power losses in the form of heat that a transformer generates during operation, it must always be subject to some form of cooling in order not to overheat. The operating temperature has a significant influence on the service life of the transformer. The cooling types for transformers are always differentiated according to the type of internal cooling system and the type of external cooling. The internal cooling system comes into contact with the winding. External cooling removes the heat from the transformer. Dry-type transformers, which are operated by convection of the ambient air, have only one cooling system. The cooling types are differentiated according to cooling media and type of coolant and are subdivided as follows.

A – Air
G – Gas (SF6)
O – OIL
K – Liquid with a focal point above 300°C

A – Air
W – Water

N – Natural convection due to heating
F – Forced flow. With forced flow in an oil circuit, the pump is installed in such a way that the entire flow also runs through the cooler, as the back pressure is a critical point in the circuit.
D – Forced flow directed specifically at the windings. E.g. high-current transformer.