Two-phase AC power generation principle There are only two kinds of AC power sources, one is three-phase AC power source, and the other is single-phase AC power source composed of three-phase AC power source. There is no two-phase AC power supply in the power supply circuit. So how do you get a two-phase AC power supply?
According to the characteristics of components in AC circuit, in capacitive reactance circuit, the phase of current is ahead of voltage. In an inductive circuit, the current phase lags behind the voltage. The amount of lead or lag depends on the size of resistance and capacitive reactance or resistance and inductive reactance. Accordingly, if two circuits with different inductances and resistances are connected in parallel, or the circuit with inductance is connected to a single-phase AC power supply, the phases of currents in the two circuits are different, and two-phase AC power can be obtained from the single-phase AC power supply. According to the difference of resistance and inductance of two-phase winding, single-phase alternating current is divided into two-phase alternating current, which is called split-phase motor. Using capacitive reactance of capacitor to obtain two-phase alternating current is called capacitive split-phase motor. There are two types: capacitor start-up type and capacitor operation type. A covered pole motor that uses a covered pole coil to obtain two-phase alternating current is called a covered pole motor. Single-phase asynchronous motor has only main and auxiliary two-phase windings, and their relative positions are 90 degrees apart. The secondary winding is used to start the rotor, which is called starting winding. The main winding is to make the rotor run continuously, which is called running winding.
Operation principle of capacitor split-phase starting motor Now, take capacitor split-phase starting motor as an example to illustrate its rotation principle, as shown in the figure. In the figure, AC is the main winding and B-D is the secondary winding. Two windings are connected in parallel on the same single-phase AC power supply. If the capacitor capacity is properly selected, the starting winding current can be 90 degrees ahead of the running winding in time phase. Let the running winding current be iA, the starting winding current be iB, and iB is 90 degrees ahead of IA. In order to determine the direction of the magnetic field generated by the two-phase current flowing into the two-phase winding, it is specified that the current flows in from the head end (A or B) of the coil, denoted by the symbol X, and flows out from the end end (C or D) of the coil, denoted by the symbol 0. According to the right-hand spiral rule, ωt=O, (ωt=90 degrees, ωt= 180 degrees, ωt=270 degrees. It can be seen that the two-phase windings are 90 degrees apart in space, and the two-phase composite magnetic field generated by currents with a 90-degree difference is a rotating magnetic field. The direction of the rotating magnetic field is related to the order in which the current in each phase winding reaches the maximum. The direction of the synthetic magnetic field is from the B-D phase of the current leading starting winding to the AC phase of the current lagging running winding. Under the action of this rotating magnetic field, the motor can start to rotate. The starting and rotating direction of single-phase asynchronous motor can change the power supply by adjusting any phase head-tail pair in two-phase winding.