Why does speed of three phase induction motor reduces as load on its shaft is increased?

Why the speed of three phase induction motor does fall slightly when the load on the motor is increased?

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.

Why does the speed of an induction motor fall as the load torque is increased?

If the load torque is further increased, the speed falls (because the load torque is more than the motor torque), and as it does so the shortfall between motor torque and load torque becomes greater and greater.

When the load of a three phase induction motor increases its slip?

Slip increases with increasing load – providing a greater torque. It is common to express the slip as the ratio between the shaft rotation speed and the synchronous magnetic field speed. When the rotor is not turning the slip is 100 %.

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What is effect of load on 3 phase induction motor?

As the load is increased the rotor speed is slightly reduced. The emf induced in the rotor causes the current increased to produce higher torque, untill the torque developed is equal to torque required by load on motor. CIRCUIT DIAGRAM : The circuit diagram of load test on 3 phase squirrel cage induction motor.

What happens if load increases in induction motor?

When the load on an induction motor is increased from no load to full load, both slip and power factor increase. In the low slip region torque is directly proportional to slip. The torque slip characteristics of the induction motor is a straight line. So as load increases, speed decreases, increasing the slip.

What happens when motor load increases?

Assuming it is not being controlled at a constant speed, then really the same thing happens in all three cases. As the load is increased, the motor will slow down, and the torque will increase. Current into the motor will also increase. If the load is increased above the maximum, the motor may overheat after a while.

What are the types of load torque?

3 Types of Loads (Constant Torque/Constant Power/Variable Torque)


Which induction motor has maximum speed?

Synchronous and full load speed of amplitude current (AC) induction motors

Speed (rpm)
Number of Poles Frequency (Hz, cycles/sec)
Synchronous Full Load
2 3600 2900
4 1800 1450

What decreases torque increases?

As output speed increases, the available output torque decreases proportionately. As the output torque increases, the output speed decreases proportionately.

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What is full load slip?

The slip corresponding to full load speed of th motor is called full load slip. Example 1 : A 4 pole, 3 phase induction motor is supplied from Hz supply. Determine its synchronous speed. On full load, its speed is observed to be 1410 r.p.m. calculate its full load slip.

What is the formula for rotor turns per phase?

8. What is the formula for rotor turns per phase? Explanation: Firstly, the winding factor for stator is obtained along with the winding factor for stator. Next the ratio of the rotor voltage per phase to the stator voltage per phase.