AC motors generally use three-phase systems, because three-phase AC motors have obvious advantages compared with single-phase motors in terms of performance indicators, raw material utilization, and price.
A three-phase motor of the same power is smaller, lighter, and less expensive than a single-phase motor. The three-phase motor has self-starting capability. Single-phase motors have no starting torque. To solve the starting problem, some special measures need to be taken. The torque of a single-phase motor is pulsating and the noise is relatively large, but the required power supply is relatively simple, especially in the home is very convenient. Therefore, single-phase motors are mostly used in small household motors and instrument motors.