Typical Torque-Speed Curve of a Cage Induction Motor

Typical Torque-Speed Curve of a Cage Induction Motor

Torque-Speed Curve of a Cage Induction Motor

Types of Torques

Locked Rotor or Starting or Breakaway Torque

    The Locked Rotor Torque or Starting Torque is the torque the electrical motor develops when it starts at rest or zero speed.

    A high Starting Torque is more important for applications or machines that are hard to start, such as positive displacement pumps, cranes etc. A lower Starting Torque can be accepted in applications as centrifugal fans or pumps where the start load is low or close to zero.

Pull-up Torque

    The Pull-up Torque is the minimum torque developed by the electrical motor when it runs from zero to full-load speed (before it reaches the break-down torque point)

    When the motor starts and begins to accelerate, the torque in general decreases until it reaches a low point at a certain speed – the pull-up torque – before the torque increases until it reaches the highest torque at a higher speed – the break-down torque – point.

    The pull-up torque may be critical for applications that need power to go through some temporary barriers achieving the working conditions.

Break-down Torque

    The Break-down Torque is the highest torque available before the torque decreases when the machine continues to accelerate to the working conditions.

Full-load Torque or Braking Torque

    The Full-load Torque is the torque required to produce the rated power of the electrical motor at full-load speed.