How do you increase the starting torque of a squirrel cage induction motor?

The starting torque of squirrel cage induction motor can be increased by using double squirrel cage rotor. In this case, rotor has two sets of independent cages. Upper cage has high resistance and low reactance while lower cage has low resistance and high reactance.

How does induction motor increase torque?

An induction motor develops torque by inducing current to the rotor, which is proportional to the differential speed of the rotor and the rotating magnetic field in the stator. Due to the torque variation at each revolution the instantaneous speed will vary.

Why is the starting torque of the squirrel cage induction motor low?

It suffers from the disadvantage of a low starting torque. It is because the rotor bars are permanently short-circuited and it is not possible to add any external resistance to the rotor circuit to have a large starting torque.

Which of the following equipments would need high starting torque as compared to running torque?

Railway locomotives need high starting torque to move from a stationary position due to their heavy load. DC motors are well suited due to the locomotive’s high torque.

What is the starting torque of 3 phase squirrel cage induction motor?

Starting Torque of Squirrel Cage Motors – For the squirrel cage motors, the starting torque is very low about 1.5 to 2 times of the full-load value. Starting Torque of Wound Rotor Motors – In case of slip ring induction motors, the resistance of the rotor circuit can be increased by inserting external resistance.

Which of the following motor has high starting torque?

capacitor start motor
The capacitor start motor develops a much higher starting torque of about 3 to 4.5 times of the full load torque.

What is low starting torque?

As R2 is neglected, starting torque now depends upon X20 which is maximum at starting as slip is 1. So starting torque is low in induction motors. To get maximum starting torque, resistance is added to the rotor while starting slip ring motors, which is reduced gradually as motor picks up the speed.

How do you find the starting torque of an induction motor?

We know that at the start the rotor speed, N is zero. So, the equation of starting torque is easily obtained by simply putting the value of s = 1 in the equation of torque of the three phase induction motor, The starting torque is also known as standstill torque.

What is the starting torque of a squirrel cage induction motor?

⇒⇒ Squirrel cage induction motors have poor starting torque and high starting currents. Starting torque will be in the order of 1.5 to 2 times the full load torque and starting current is as high as 5 to 9 times the full load current.

What are the advantages and disadvantages of squirrel cage motor?

Squirrel cage motors operate at nearly constant speed, high overload capacity, and operates at better power factor. The main disadvantage of squirrel cage induction motor is poor speed control and low starting torque. However, with variable frequency drives, these disadvantages can be overcome.

How to get maximum torque at the start of a motor?

Thus to obtain maximum torque at the start, the value of rotor resistance must be equal to the rotor reactance at standstill. However, the normal rotor resistance is quite small as compared to the reactance, otherwise, the rotor losses will be high and the efficiency of the motor will be low.

What is the pull out torque of induction motor?

The maximum torque T m obtained at s m is also called pull out torque or break down torque. If the load torque increases beyond the pull-out torque then the induction motor will be pushed into the unstable region and will finally come to a standstill.