A synchronous motor with an amortisseur winding for starting is electrically similar to which type of motor?

A synchronous motor with an amortisseur winding is electrically similar to a squirrel-cage induction motor because both types utilize a rotor structure that allows for the generation of starting torque and responds similarly in terms of magnetic interaction in the air gap.

The amortisseur winding in a synchronous motor serves a crucial purpose during startup. It consists of short-circuited conductors embedded in the rotor, akin to the rotor of a squirrel-cage induction motor, which allows it to behave like an induction motor at startup. This characteristic is fundamental in providing the necessary starting torque while the rotor is still at standstill, preventing stalling and ensuring smooth acceleration to synchronous speed.

In contrast, other motor types listed, such as a capacitor-start motor, universally operate with additional features (like capacitors) specifically designed for phase shifting and improving starting torque, while a universal motor operates on both AC and DC with a different rotor construction and operating principle. Shaded-pole motors primarily focus on very low-torque applications with unique design characteristics that are quite different from both synchronous motors and squirrel-cage induction motors.

Thus, the similarity between the operation of the synchronous motor equipped with an amortisseur winding and a squirrel-cage induction motor makes the choice of the second option appropriate.