Speed Torque Curve of an induction motor

The speed torque curve of an induction motor is a plot of speed on the x-axis and torque on the y-axis.  When the motor is started, the initial torque is about 250% of the rated torque.  This is the torque required by the motor to overcome the inertial of the standstill.  As the motor picks up speed the torque drops to the pull-up torque.  If the pull-up torque of a motor is less than the torque requirement of the load coupled to it, the motor will stall and over heat.

The breakdown torque is the maximum torque which can be developed by the rotor before it overheats.  The breakdown torque needs to be high for loads with high inertia and which are susceptible to overloads such as conveyor belts.

The full load torque is the torque produced by a motor operating at the rated speed and load.  Exceeding the full load torque causes reduction in the life of the motor.

When the motor is run on no load, the rotor speed reaches the synchronous speed.  The slip becomes zero and the motor runs at zero torque

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