Principle of single phase motor
When a single-phase sinusoidal current through the stator windings, the motor generates an alternating magnetic field, the
The intensity and direction of the magnetic field vary with the time, but it is fixed in the spatial direction, so the magnetic field is called alternating pulsating magnetic field. The alternating pulsating magnetic field can be divided into two with the same speed, the rotation direction of the rotating magnetic field are on the contrary, when the rotor is at rest, the two rotating magnetic field generating torque of two equal and opposite in the rotor, the synthetic torque is zero, so the motor can not rotate. When we use a force of the motor rotation to one direction (e.g., clockwise), the rotor and the clockwise rotation direction of the rotating magnetic field between the motion of cutting magnetic lines becomes smaller; the rotor and the counterclockwise rotation direction of the rotating magnetic field between the motion of cutting magnetic lines becomes large. So the balance is broken, and the total electromagnetic torque produced by the rotor will no longer be zero, and the rotor will rotate in the direction of the push.
To make the single-phase motor can automatically rotate together, we can add a starting winding in the stator, the starting winding and the main winding is 90 degrees in space, is connected in series with a suitable capacitor start winding, the main winding current and in phase difference approximation
90 degrees, that is, the so-called phase separation principle. In this way, two currents with a difference of 90 degrees in time are passed into two windings with a difference of 90 degrees in space, which will produce (two phase) rotating magnetic field in space,
In the rotating magnetic field, the rotor will start automatically after starting to rise to a certain speed, with the aid of a mounted on the rotor of the centrifugal switch or other control device will automatically disconnect the starting winding, when working normally only the main winding. Therefore, can make short work starting winding. But in many cases, the starting winding continues to open, we call this motor as a single-phase motor, to change the steering of the motor, as long as the auxiliary winding end of the switch can be.
In the single-phase motor, another method of producing rotating magnetic field is called the shaded pole method, also known as the single phase shaded pole motor. The motor stator made of salient pole type, there are two kinds of poles and quadrupole. Each pole in the 1/3--1/4 side at a small groove is arranged, the magnetic pole is divided into two parts, in the small part is sheathed on a short-circuit copper ring, if this part of the pole cover, so called shaded pole motor. The single phase winding is sheathed on the whole pole, and the coils of each pole are connected in series. The polarity of the pole must be arranged according to N, S, N and S in turn. When the stator winding is energized, the main magnetic flux in the magnetic pole, according to Lenz's law, in which the main flux through the circuit copper ring in copper ring generates a lag induced current 90 degrees in phase, the current flux generated in phase also lags behind the main magnetic flux, and it starting capacitor motor the winding, resulting in a rotating magnetic field of the motor to rotate.