Which of the following is NOT a type of three-phase motor?

A capacitor-start motor is typically a type of single-phase motor, which incorporates a capacitor in its design to provide an initial phase shift that helps start the motor. While it is tailored for efficient operation in single-phase applications, it does not function in three-phase systems as the other options do.

In contrast, squirrel-cage induction motors, synchronous motors, and wound-rotor induction motors are all well recognized as types of three-phase motors. Squirrel-cage induction motors are commonly used due to their robustness and simplicity. Synchronous motors operate at synchronous speed, maintaining a constant speed regardless of load, utilizing a rotating magnetic field. Wound-rotor induction motors feature a rotor with windings, providing varying resistance that enhances starting torque and performance.

Understanding the characteristic differences between these motor types is crucial for diagnosing issues and applying the correct operational principles in various electrical engineering scenarios.