AC motors generally use a three-phase system because compared to single-phase motors, three-phase AC motors have significant advantages in performance indicators, raw material utilization, and price. A three-phase motor of the same power is smaller in size, lighter in weight, and cheaper than a single-phase motor. Three phase motors have self starting capability. Single phase motors do not have starting torque, and special measures need to be taken to solve the starting problem. The torque of a single-phase motor is pulsating and the noise is relatively high, but the required power supply is relatively simple, especially convenient for use in households. Therefore, small household motors and instrument motors often use single-phase motors.
