The basic principle of single-phase motor
Single phase motor generally refers to the use of single-phase AC power supply(AC220V) small power single-phase asynchronous motor power supply. The motor is usually a two-phase winding on the stator, the rotor is common squirrel cage type.Distribution of single-phase motor phase windings in the stator is generally refers to the use of single-phase AC power supply (AC220V) small power single-phase asynchronous motor power supply. The motor is usually a two-phase winding on the stator, the rotor is common squirrel cage type. Two phase winding distribution on the stator and the supply situation is different, can produce the starting characteristics and operation characteristics of different.
Usually based on the motor starting and running modes, the single-phase asynchronous motor is divided into single-phase resistance starting single-phase capacitor start asynchronous motor, single phase capacitor motor, operation of single phase capacitor motor, induction motor starting and running, Dan Xiangzhao pole motor five.
When the single-phase sinusoidal current through the stator winding, the motor cangenerate an alternating magnetic field, the magnetic field intensity and directionchanges sinusoidally with time, but in the spatial position is fixed, so it is also calledthe magnetic field is alternating pulsating magnetic field. This alternating pulsed magnetic field can be decomposed into two at the same speed, the rotation direction of the mutual rotation is opposite to the magnetic field, when the rotor is at rest, the two rotating magnetic field generating torque two equal, in the opposite direction in the rotor, the synthesis of zero torque, so the motor can not spin. When we use a force so that the rotation of the motor to a certain direction (such as rotating in clockwise direction), then the rotor and the clockwise rotation direction of the rotating magnetic field between the motion of cutting magnetic lines become smaller; the rotor and the counterclockwise rotation direction of the rotating magnetic field between themotion of cutting magnetic lines become big. This equilibrium is broken, the totalelectromagnetic torque generated by the rotor will no longer be zero, the rotor willpush up along the direction of rotation.
To make the single-phase motor can automatically rotate together, we can add astarting winding in the stator, the starting winding and the main winding is 90 degreesin the space, must be connected in series with a suitable capacitor start winding, such that the current with the main winding in phase difference approximation
90 degrees, the so-called phase separation principle. This two time difference of 90 degrees in the current access between the two winding of 90 degrees in space, will be generated in the space (two-phase) rotating magnetic field,
In the rotating magnetic field, the rotor will start automatically after starting, to speedup to a certain time, with the aid of a mounted on the rotor of the centrifugal switch or other device for automatic control of the starting winding is disconnected, the normal work when only the main windings. Therefore, can make short work of startingwinding. But there are many times, starting winding and constantly open, we call this kind of motor is a single-phase motor, steering motor to change this, as long as theauxiliary winding terminal end change can be.
In the single-phase motor, another way to produce a rotating magnetic field is called the shaded pole method, also called the shaded pole motor. The motor stator is madesalient pole type, there are two poles and four poles two. Each pole in 1/3--1/4 fullpole provided with small grooves, the magnetic pole is divided into two parts, in thesmall part is sheathed on a short circuit copper ring, if this part of the pole cover up,so called shaded pole motor. Single phase winding is sheathed on the whole pole,each pole coil is connected in series, polarity connection must produce a followed by N, S, N, S arrangement. When the stator winding is energized, the generation of the main magnetic flux in the magnetic pole, according to Lenz's law, in which the main flux through the circuit copper loop in a copper ring is generated in a lag of inductioncurrent 90 degrees in phase, the current flux generated in phase lag in the main flux,starting role and capacitor motor it the winding equivalent, so as to produce a rotating magnetic field to make the motor rotate.
Single phase motor operation has two kinds, the first kind, centrifugal switch in thestarting circuit, connection method generally used in air compressor, this cutting machine, woodworking machine tool load without a stable place; second, in thestarting circuit is not connected with a centrifugal switch, starting winding andcapacitor starting not only plays a role in the runtime also play a role, it can improve the power factor and efficiency of the motor, so the performance is better than that ofthe motor running capacitor start motor. The capacitance of capacitor run motor startwinding series capacitor, is mainly based on operational performance requirementsand determined, this ratio according to the performance requirements to determine the starting capacitance is small, and the motor starting performance is not as good as the capacitor start motor is good. Capacitor run motors do not start the switch, so the structure is simple, the price is cheaper, mainly used in electric fans, air-conditioning fan motor, washing machine motor.
