Losses are the source of inefficiency in motors, i. e. energy that goes into a motor but does not produce useful work. Losses in induction motors are classified into two types:
1. No-load Losses: These losses are independent of load and incurred even when the motor is idling.
2. Load dependent Losses: Vary as function of motor loading
The losses in a motor are of two types such as fixed i.e. independent of load on the motor and the other variable i.e. dependent on the load.
Fixed losses consist of Iron loss and mechanical loss (friction and windage loss). The iron loss vary with the material and geometry and with input voltage whereas friction and windage losses are caused by friction in the bearings of the motor and aerodynamic losses associated with the ventilation fan and other rotating parts.
Variable losses consist of resistance losses in the stator and in the rotor and other stray losses. Resistance to current flow in the stator and rotor result in heat generation that is proportional to the resistance of the material and square of the current. Stray losses arise from a variety of sources and are difficult to measure directly or to calculate and are generally considered proportional to the square of the rotor current.
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