Pull torque, also known as "pull-out torque" or "breakdown torque," refers to the maximum torque that a synchronous motor can develop while maintaining synchronization with the supply frequency. In other words, it's the maximum load torque that a synchronous motor can withstand before it loses synchronization and comes to a stop.
In a synchronous motor, the rotor rotates at the same speed as the rotating magnetic field generated by the stator. This synchronization is maintained as long as the motor is able to overcome the load torque applied to its shaft. The pull torque is the point at which the motor's torque output is just enough to overcome the load torque and maintain synchronous rotation. Beyond the pull torque, the motor will lose synchronization and stop.
Synchronous motors are commonly used in applications where constant speed and precise control are required, such as industrial processes, power generation, and electric propulsion systems. Pull torque is an important parameter to consider in these applications, as it defines the motor's ability to handle sudden increases in load or momentary overloads without losing synchronization.
It's worth noting that the pull torque of a synchronous motor is influenced by factors such as the motor's design, magnetic characteristics, and the supply frequency. In some cases, if the load torque exceeds the pull torque, the motor will stall and lose synchronization. To prevent this, additional measures like using an external starting mechanism or reducing the load momentarily might be necessary.
Overall, pull torque is a critical parameter to consider when selecting and operating synchronous motors to ensure reliable and stable operation under various load conditions.