A condition where a transformer is energized on its primary side with the secondary open-circuited, or a motor is spinning at full voltage without driving a mechanical load. In this state, the device only draws enough current to magnetize its core and overcome internal mechanical or iron losses. It is a baseline condition used in testing to determine core losses and efficiency.
The transformer is running hot even at no-load, which points to an issue with the core lamination.
Related terms
Core loss
The electrical energy dissipated as heat within the magnetic core of an AC device.
Transformer
A static electromagnetic device that transfers electrical energy between circuits at changed voltage levels.
Induction motor
An alternating current motor where the rotor current is induced by the magnetic field of the stator.