The capacitor in the motor separates the single-phase alternating current into another alternating current with a phase difference of 90 degrees through capacitive phase shifting. When the two-phase alternating current is fed into two or four groups of motor coil windings, a rotating magnetic field is formed in the motor. The rotating magnetic field generates an induced current in the motor rotor.
The magnetic field generated by the induced current is in the opposite direction to the rotating magnetic field and is affected by the rotating magnetic field. Push and pull to enter rotation. Single-phase electricity cannot produce a rotating magnetic field. To make a single-phase motor rotate automatically, a starting winding can be added to the stator. The starting winding and the main winding are 90 degrees apart in space. A suitable capacitor must be connected in series to the starting winding.
This makes the current in the main winding approximately 90 degrees different in phase, which is the so-called phase separation principle. In this way, two currents that are 90 degrees different in time are passed into two windings that are 90 degrees different in space, which will generate a (two-phase) rotating magnetic field in space. Under the action of this rotating magnetic field, the rotor can start automatically. The single-phase asynchronous motor has no starting torque and cannot start on its own. It needs to be started somehow, even if it can generate a rotating magnetic field.
According to different starting methods, common single-phase motors are divided into the following three categories. 1. Split-phase start motor Split-phase start motor is divided into resistor split-phase start motor and capacitor split-phase start motor. at startup. In the auxiliary winding of the motor, a resistor (or the auxiliary winding itself has a greater resistance than the main winding) or a capacitor is connected in series.
When the motor speed reaches about 80% of the synchronous speed, the starting winding or capacitor is disconnected from the power supply through the starting device. The motor that disconnects the resistor from the power supply is called a resistor split-phase start motor, and the one that disconnects the capacitor from the power supply is called a capacitor split-phase start motor. 2. Capacitor-run motor A capacitor-run motor does not cut off the auxiliary winding and capacitor during operation. The auxiliary winding and capacitor should be calculated and selected according to the long-term operation of the motor. 3. Shaded pole motors use short-circuited copper rings or short-circuited coils to cover 1/4 to 1/3 of the magnetic poles to generate a rotating magnetic field to start the single-phase motor. This type of motor is called a shaded pole motor. Shaded pole motors do not require starting devices and capacitors.
Post time: Jan-10-2024
