Losses of 3- phase Induction Motor
The power losses in an induction motor fall in the same general classification as in any dynamo.
There are electrical losses due to heat produced by the current in the stator and rotor winding, which is called copper loss, magnetic losses in the iron due to hysteresis and eddy currents, which is called the core losses, mechanical losses due to friction in the bearing and ventilation, which is called the friction and windage losses and stray load losses.
There are copper losses and core losses in the stator, and copper losses and mechanical losses in the rotor. Actually, there is some core loss in the core in the rotor but under normal operating conditions, the rotor frequency is so low that rotor core loss may be neglected.
The iron and mechanical losses are considered to be constant are based on no-load condition.
Friction losses actually very slightly with load as wall as with the speed.
The core losses are due to both the main and leakage fluxes. The magnitude and distribution of such losses very with the load. With the increase in load, the leakage fluxes increase due to increase in current and the mutual flux decrease.
Thus, the loss due to mutual flux is reduced and that due to leakage fluxes is increased with the increase in load.
Except for the rotor tooth losses, practically all the core losses occur in the stator, owing to the low frequency of the rotor flux.
The copper losses vary with the load and the stator and rotor copper loss vary with the square of their respective current.
The stray load losses include rotor iron loss, additional fundamental frequency and high frequency losses in the iron, strand and circulating current losses in the stator winding. These losses are 0.5% of power supplied to the motor.
The standard definition of efficiency (output/input) applied to the induction motors.
Also Read- Operation of a 3 phase induction motor
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