Synchronous Motor Torques: Understanding Breakaway Torque

Synchronous motors, like other types of electric motors, are associated with various types of torques that describe their operational characteristics under different conditions. Understanding these torques is crucial for analyzing motor performance and selecting the right motor for a specific application.

The question asks about a specific torque known as breakaway torque. Let's examine the different torques mentioned in the options and their definitions:

• Starting torque: This is the torque developed by the motor at the instant of starting, i.e., at zero speed. It must be sufficient to overcome the static friction and initial load torque to start the motor.
• Pull in torque: In a synchronous motor, this is the maximum torque under which the motor will pull into synchronism when the field winding is energized. It is measured at synchronous speed.
• Running torque: This refers to the torque developed by the motor while it is operating at its rated speed and under normal load conditions. It is also sometimes called the shaft torque or load torque.
• Pull out torque: This is the maximum torque a synchronous motor can develop without losing synchronism (falling out of step). If the load torque exceeds the pull-out torque, the motor will stop rotating synchronously.

The term breakaway torque is used to describe the torque required to initiate movement from a standstill. This is essentially the torque needed to overcome the initial inertia and static friction to get the motor shaft rotating. By definition, this corresponds directly to the starting torque of the motor.

Therefore, the torque that is also known as breakaway torque in the context of synchronous motors (or any motor) is the starting torque.