The speed of an induction motor falls slightly with the increase of:

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ALP CBT 2 Electrician Previous Paper: Held on 22 Jan 2019 Shift 1

Answer 1

When the load on the motor shaft increases, the load torque becomes higher than the motor torque. So that there is deceleration of rotor, due to which rotor speed is reduced, which increases the slip of rotor w.r.t RMF.
Due to increased slip induces more emf in the rotor and hence more current in the rotor circuit.
The air gap power being transferred to the rotor is now higher than before and hence more current is drawn in from supply at stator terminals. Hence, the motor torque is increased.
So, this increase in slip, rotor induced emf, rotor current, air gap power, motor torque goes on until the motor torque becomes equal to the required load torque. The increased load is now being driven at a lower speed.
At no load, slip is quite small because the only amount of motor torque required is to overcome friction and windage.