The current drawn by the induction motor when it is not coupled to the driven equipment is called no-load current of the motor. The equivalent circuit of an induction motor at no load is as given below.
- Magnetizing component of the current(Im)
- Loss components( Hysteresis and eddy current loss)-Ic
The magnetising current(Im) is drawn by an induction motor to set up the magnetic flux in the air gap. The magnetizing current is responsible for setting up air gap power in induction motor. The loss component current(Iw) is drawn by the motor to meet out the eddy current loss and hysteresis loss. The loss component current is independent of the load current and thus the loss component current(Iw) is constant for a particular motor. The no load current(Io) is fairly constant current and does not change with increased loading on the motor.
If the magnetizing current of the induction motor is 5 amperes and the core loss current is 2 amperes, then no load current of the motor is ;
The higher magnetizing current leads to poor power factor of an induction motor.
However, the higher magnetizing current leads to better overloading capacity of the motor. The magnetizing current of the motor increases with an increase in the number of poles of the motor. The no load current has prominent effect on the performance of the induction motor. The energy efficient motors have lower no load current compared to the conventional motor. The no load current of induction motor varies fro 30 to 60 % of its full load current.
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