When "Cooling Fan Manufacturer" single-phase sinusoidal current through the star winding, the motor will produce an alternating magnetic field, the strength and direction of the magnetic field at any time inter cropping sine law change, but in the spatial orientation is fixed, so called this magnetic field is alternating pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two at the same rotational speed, the rotational direction of the rotating magnetic field opposite to each other, when the "Cooling Fan Manufacturer" rotor is stationary, both two equal-sized rotary magnetic field generated in the rotor in the opposite direction torque, so that the net torque is zero, the motor can not turn. When we use the force of the motor to rotate in one direction (e.g., clockwise rotation), and the cutting lines of magnetic force and the movement of the rotating magnetic field of the rotor in the clockwise direction of rotation becomes smaller; "Cooling Fan Manufacturer" and the counterclockwise direction of rotation of the rotor movement of the cutting lines of magnetic force between the rotating magnetic field becomes large. Such a balance is broken, the total electromagnetic torque generated by the rotor will no longer be zero, the rotor will spin up along the push direction