Induction Motor Efficiency, Power Factor and Mechanical Load

1. Explain why the efficiency of the induction motor increases when the mechanical load increases.
2. Explain why the input power factor of the induction motor increases when the mechanical load increases.

Explain:
1. The efficiency of the induction increases when the mechanical load increases because as the motors load increases, its slip increases, and the rotor speed falls. Since the rotor speed is slower, there is more relative motion between the rotor and the stator magnetic fields in the machine. Greater relative motion produces a stronger rotor voltage which in turn produces a larger rotor current. With a larger rotor current, the rotor magnetic field also increases. The increase in the rotor magnetic field tends to increase the overall torque induced in the motor. Ultimately induction motors are more efficient when they are running closer to synchronous speed i.e. the pullout torque is near synchronous speed.

2. The input power factor of the induction increases when the mechanical load increases because in general, the higher the resistance (a load), the higher the power factor. A higher power factor means that there is a tapping of electrical energy in terms of active power. And more active power means higher mechanical output to compensate for the increasing rotor resistance.