Torque speed characteristics of induction motor

The torque-speed characteristic of an induction motor is a fundamental curve that shows how the torque output of the motor varies with rotor

Torque-Speed Curve of an Induction MotorThe general shape of the curve can be divided into 4 main regions:

1. Starting Region (Zero Speed, s = 1):

• Motor is not rotating.
• High slip (s = 1).
• Torque is non-zero but limited—depends on rotor resistance.
• Often called starting torque.

1. Acceleration Region (High Slip):

• Speed increases from 0 towards synchronous speed.
• Torque increases initially and reaches a maximum at a certain slip (typically s ≈ 0.2).
• This peak is called the breakdown torque (or pull-out torque).

1. Stable Operating Region (Low Slip, near synchronous speed):

• Normal operation occurs here (slip ~ 0.01 to 0.05).
• Torque decreases as speed increases.
• Motor operates at a constant speed determined by the load torque.

1. Synchronous Speed (s = 0):

• Rotor speed equals stator field speed.
• No torque is produced since there's no relative motion between stator field and rotor.
• Motor cannot operate at synchronous speed under normal conditions.