What are the normal service condition requirements for power distribution transformers?

Normal service condition requirements as defined by IEC 60076 Part 1 are as follows :-

A height above sea-level not exceeding 1 000 m (3 300 ft).

A temperature of ambient air not below –25 °C and not above +40 °C. For water-cooled transformers, a temperature of cooling water at the inlet not exceeding +25 °C.

Further limitations, with regard to cooling are given for:

– oil-immersed transformers in IEC 60076-2

– dry-type transformers in IEC 60076-11

A supply voltage of which the wave shape is approximately sinusoidal.

For three-phase transformers, a set of three-phase supply voltages which are approximately symmetrical.

An environment with a pollution rate that does not require special consideration regarding the external insulation of transformer bushings or of the transformer itself.

An environment not exposed to seismic disturbance which would otherwise require special consideration in the design. (This is assumed to be the case when the ground acceleration level ag is below 2 m/s.)