noloadström

noloadström, or no-load current, is a term used in electrical engineering to describe the current drawn by an electrical device when its output is open and no load is connected. It is most commonly discussed in relation to transformers and electric motors. The no-load current comprises magnetizing current, which sustains the magnetic flux in the core, and core loss current, which accounts for hysteresis and eddy current losses in the core material. As a result, the no-load current has both reactive and active components and is typically small compared with the current drawn under full load.

In transformers, the no-load current is determined primarily by the inductive magnetizing reactance of the core and by the rate of energy losses in the core. It can be measured by applying the rated primary voltage with the secondary open and recording the primary current. The magnitude of noloadström affects voltage regulation and overall efficiency, particularly in unloaded or lightly loaded conditions, where it sets the minimum current the transformer draws from the supply.

Typical values for power transformers range from about 1% to several percent of the rated current, depending on core material, lamination, and design. Higher-quality cores with low losses tend to have smaller no-load currents.

See also magnetizing current, core losses, transformers, induction motors.