Which of the following modifications increases the ratio of full load torque to maximum torque in an induction motor?

Concept:

In an induction motor, the ratio of full load torque to maximum torque (pull-out torque) is influenced by rotor resistance. The torque equation for an induction motor is given by:

\( T \propto \frac{R_2}{s} \)

where:

• \(R_2\) = Rotor resistance
• \(s\) = Slip of the motor

Increasing the rotor resistance shifts the maximum torque point to a higher slip, closer to the full load operating point. This increases the ratio of full load torque to maximum torque, making the motor more efficient at handling varying loads.

Calculation:

- Increasing rotor resistance shifts the maximum torque to a higher slip region.
- This helps to bring the maximum torque point closer to the operating point of the motor.
- As a result, the ratio of full load torque to maximum torque improves.

Final Answer: Increasing rotor resistance increases the ratio of full load torque to maximum torque in an induction motor.