Views: 3 Author: Site Editor Publish Time: 2023-01-18 Origin: Site
As an electrician, we all know the difference between three-phase ac motors and single-phase ac motors. If you pay a little attention, you will find that single-phase ac motors have one more equipment than three-phase ac motors, that is, starting capacitors.The common ones are household appliances, and the starting capacitors of household appliances with motors are almost required.
What is the principle of starting capacitor?
The single-phase current flowing through the single-phase motor cannot generate a rotating magnetic field. Capacitors are needed to separate the phases. The purpose is to make the currents in the two windings produce a phase difference close to 90° to generate a rotating magnetic field.
Capacitive induction motors have two windings, a start winding and a run winding. The two windings are spaced 90 degrees apart.A capacitor with a large capacity is connected in series on the starting winding. When the running winding and starting winding pass through single-phase alternating current,due to the effect of the capacitor, the current in the starting winding is 90 degrees ahead of the current in the running winding in time, and reaches the maximum value first.
Two identical pulsed magnetic fields are formed in time and space, so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, an induced current is generated in the motor rotor, and the current interacts with the rotating magnetic field to generate The electromagnetic field torque makes the motor spin up.
The principle of starting capacitor
Because the single-phase power supply is different from the three-phase power supply, a three-phase rotating magnetic field will be generated in the motor.
The principle of single-phase motor capacitor starting is to use the principle that the current of the capacitor is 90 degrees ahead in the circuit, so that a magnetic field that is 90 degrees ahead of the main winding is generated in the starting winding.In this way, there will be an alternating magnetic field at an angle of 90 degrees to each other in the motor. To put it bluntly, the phase-shifting principle of the capacitor is used to change the single-phase power supply into a two-phase power supply at 90 degrees to each other, and an alternating magnetic field at 90 degrees to each other is generated in the motor. Degree of rotating magnetic field, there is a rotating magnetic field, the motor can rotate.
Personal understanding, the starting capacitor is to give the motor a thrust when the motor is started, so that the motor can change from moving to rotating. Without him, when the single-phase ac motor starts, it will vibrate at the origin instead of rotating.The starting capacitor is the "leading angle" of the two-phase ac motor. Without it, the magnetic field cannot exert force on the rotor, and the rotation is of course impossible. From this aspect, it is easy to understand.
When encountering some two-phase ac motors that "hum" but do not rotate, it is natural to think of checking whether the starting capacitor is damaged.
But the starting capacitor is also divided into different sizes. It is not enough to install a random capacitor to make the motor run. If it is too large, the motor will run too fast and will generate heat. It will burn out the motor easily if it runs for a long time;If it is too small, it will not be able to give enough force to the rotor. If the thrust is too weak, the motor will not start. Therefore, when changing the starting capacitor, do not change the size of the original capacitor without authorization.