1 Overview A single-phase asynchronous motor is a rotating resistor powered by a single-phase AC power supply, and its stator windings are single-phase. When a single-phase AC power source is connected, it generates an alternating pulsating magnetic field in the air gap between the stator and the rotor. This magnetic field does not rotate in space, but the magnitude of the magnetic flux and the magnetic induction intensity changes sinusoidally with time. A fluctuating magnetic field with a fixed spatial axis and a sinusoidal regularity can be decomposed into two rotating magnetic fields with the same rotational speed and opposite directions. When the rotor is stationary, the resultant electromagnetic torque generated by the two rotating magnetic fields is zero, so the single-phase asynchronous motor cannot start automatically. In order to make the single-phase asynchronous motor self-starting, a rotating magnetic field is generated at the start-up. For this reason, capacitor phase separation can be used to achieve self-starting of a single-phase asynchronous motor.
It is the wiring schematic diagram of the capacitive phase splitting asynchronous motor.
Chen Yongli (1970-), male, Shenzhou, Hebei Province, lecturer, engaged in electrical and electronic teaching and research work, research direction: PLC control and information processing; Chen Peng (1968-), male, Shijiazhuang, Hebei Province, associate professor, Engaged in electrical and electronic teaching and research work, scientific research direction: PLC control and pattern recognition; the stator has two windings, AX is the working winding, BY is the starting winding, BY winding and the capacitor in series, the axis of the two windings in the space perpendicular to each other. By appropriately selecting the circuit parameters, the current iB in the winding BY is advanced by 90° in phase than the current iA in the AX winding. In this way, a rotating magnetic field is generated in the air gap between the stator and the rotor after energization, so that the single-phase asynchronous motor starts on its own. As shown in the two-phase currents iA, B, the direction of the generated rotating magnetic field is from BY to AX, that is, the winding (AX) whose current is delayed by the current leading winding (BY) rotates clockwise. Under the effect of the rotating magnetic field, the rotor will rotate clockwise together.
2 The reversal of the motor to reverse the single-phase asynchronous motor, the key is to change the direction of rotation of the rotating magnetic field, but it can not be replaced by two power cords like three-phase asynchronous motor to achieve. Through analysis, it can be seen that the key to inverting the rotating magnetic field of a single-phase asynchronous motor is to change the relationship between lead and hysteresis between iA and iB. If it is assumed that iB is ahead of iA 90* and the single-phase asynchronous motor rotates clockwise in the forward direction, then the single-phase asynchronous motor must be reversed, so long as iA is advanced to iB90*. after.
Capacitor split-phase asynchronous two-phase current waveform motor reversal wiring diagram Change the connection mode between the working winding and the power supply As shown in the figure, connect the head end of the winding AX to the power supply line 2, and connect the terminal X to the power supply line 1. The change of the connection mode causes the phase of the current iA in the winding AX to change, that is, the iA is inverted. Then at this time, iA changes from lag iB90* to lead iB90*. Therefore, the rotating magnetic field will also be reversed, and the single-phase asynchronous motor will reverse. The two-phase current is as shown.
Capacitor split-phase asynchronous two-phase current waveform motor reversing wiring Conclusion To sum up, if a single-phase asynchronous motor is started by a capacitive split-phase method, the serial connection position of the capacitor c may be changed, and the connection between the start branch and the power supply may be changed. Ways to achieve and change the connection of working windings and power supply. The above method has been experimentally verified and is indeed feasible.
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