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What is the difference between single-phase and three-phase motors?

Update:08 Sep 2018

Since the single-phase motor has only a pulsation cycle […]

Since the single-phase motor has only a pulsation cycle and no rotating magnetic field, it needs to be rotated by an external force (starting the winding capacitor centrifugal switch, etc.), the efficiency is low, the current is large, the starting torque is small, and the power is limited to 3 kw or less.
The three-phase motor has a phase difference of 120 degrees, and the motor winding is also 120 degrees. The starting torque is large, and the power is easily maintained from several watts to several hundred kW.
1. Single-phase motor generally refers to a low-power single-phase asynchronous motor powered by a single-phase AC power supply (AC220V). It is a device that converts electrical energy into mechanical energy. Usually, the single-phase asynchronous motor has a small capacity, requires only a single-phase power supply, and is convenient to use, and is widely used in the fields of industry, agriculture, and household appliances. Typical applications are: washing machines, electric fans, refrigerators, air conditioners, water pumps, blowers, juicers, soya-bean milk machines, etc.
2. Three-phase motor refers to the three-phase stator winding of the motor (each phase difference is 120 degrees electrical angle). After three-phase alternating current is applied, a rotating magnetic field is generated, which rotates the rotor winding to generate induction in the rotor winding. The current (the rotor winding is a closed path), the current-carrying rotor conductor generates an electromagnetic force under the rotating magnetic field of the stator, thereby forming an electromagnetic torque on the motor shaft, driving the motor to rotate, and the motor rotating direction is the same as the rotating magnetic field.