No-Load Operation

The no-load power and no-load current of a transformer refer to its behavior at rated input voltage and frequency when no load is connected. The no-load power is the absorbed active power, while the no-load current is the apparent input current in this state. Due to core sheet tolerances, these values can vary significantly.

The losses of a transformer mainly consist of iron losses and copper losses. To a first approximation, no-load current and no-load power are a measure of iron losses. The copper losses in turn can be estimated by a short circuit test.

If a transformer is expected to be operated mainly at no-load or under small partial load, it is possible and sensible to optimise it with regard to no-load losses.

Note:
The standards for core materials allow for considerable tolerances. The quality of the core materials and thus the idle currents can vary accordingly. Transformer manufacturers and suppliers unfortunately have limited influence on this and limited alternatives on the global market.