1. Introduction of starting capacitor
Starting capacitors are AC electrolytic capacitors or polypropylene and polyester capacitors used to start single-phase asynchronous motors. Capacitive induction motors have two windings, the start winding and the run winding. The two windings are 90 degrees apart in space. A capacitor with a large capacity is connected in series on the starting winding. When the running winding and the starting winding pass single-phase alternating current, the current in the starting winding is 90 degrees ahead of the current in the running winding due to the action of the capacitor, and reaches the maximum value.
Second, the working principle of the starting capacitor
The single-phase current flowing through the single-phase motor cannot generate a rotating magnetic field, and a capacitor is needed to separate the phases. The purpose is to make the current in the two windings generate a phase difference of nearly 90゜ to generate a rotating magnetic field.
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 rotor of the motor, and the current interacts with the rotating magnetic field to generate an electromagnetic field. torque to make the motor spin.
To make the single-phase motor rotate automatically, we can add a starting winding to the stator. The starting winding is 90 degrees apart from the main winding in space. The phase difference is approximately 90 degrees, which is the so-called phase separation principle. In this way, two currents with a difference of 90 degrees in time pass into two windings with a difference of 90 degrees 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. After starting, when the speed reaches a certain level, the starting winding is disconnected by means of a centrifugal switch or other automatic control device installed on the rotor. In normal operation, only the main winding is used. Work. Therefore, the starting winding can be made into a short-time working mode. But in many cases, the starting winding is not disconnected. We call this motor a capacitive single-phase motor. To change the steering of this motor, it can be achieved by changing the position of the capacitor in series.
1. Calculation formula of starting capacitor
Calculation formula of single-phase motor running capacitance: C=1950I/ucos∮ Among them:
I: motor current, U: power supply voltage; cos∮: power factor, take 0.75, 1950: constant
The starting capacitor is generally calculated as 1-4 times the capacity of the running capacitor.
3. The role of starting capacitor
AC electrolytic capacitors or polypropylene and polyester capacitors used to start single-phase asynchronous motors.
The single-phase current flowing through the single-phase motor cannot generate a rotating magnetic field, and a capacitor is needed to separate the phases. The purpose is to make the current in the two windings generate a phase difference of nearly 90゜ to generate a rotating magnetic field. Capacitive induction motors have two windings, the start winding and the run winding. The two windings are 90 degrees apart in space. A capacitor with a large capacity is connected in series on the starting winding. When the running winding and the starting winding pass single-phase alternating current, the current in the starting winding is 90 degrees ahead of the current in the running winding due to the action of the capacitor, and reaches the maximum value. 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 rotor of the motor, and the interaction between the current and the rotating magnetic field produces The electromagnetic field torque makes the motor spin.
To make the single-phase motor rotate automatically, we can add a starting winding to the stator. The starting winding is 90 degrees apart from the main winding in space. The phase difference is approximately 90 degrees, which is the so-called phase separation principle. In this way, two currents with a difference of 90 degrees in time pass into two windings with a difference of 90 degrees 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. After starting, when the speed reaches a certain level, the starting winding is disconnected by means of a centrifugal switch or other automatic control device installed on the rotor. In normal operation, only the main winding is used. Work. Therefore, the starting winding can be made into a short-time working mode. But in many cases, the starting winding is not disconnected. We call this motor a capacitive single-phase motor. To change the steering of this motor, it can be achieved by changing the position of the capacitor in series.
Fourth, the role of single-phase motor starting capacitor
Capacitors are used to generate rotating magnetic fields in single-phase electricity. If there is no capacitor, it is like this: after the motor is powered on, it will generate two rotating magnetic fields with the same speed and opposite directions. The combined torque generated by these two magnetic fields is 0, so the rotor cannot rotate, but this is if an external force is added to it. , you can rotate, if the external force is clockwise, it will rotate clockwise, and if the external force is counterclockwise, it will rotate counterclockwise.
So if you want to automatically add a capacitor, the capacitor is added to the starting winding, and the difference in space is 90 degrees, and an additional rotating magnetic field will be generated, which is equivalent to an external force. At this time, it will rotate. When the speed reaches a certain speed, the start winding switch is disconnected by centrifugal force, and then the main winding is working to make it rotate.
Strictly speaking, the motor cannot be distinguished by the voltage level. The so-called 220V and 380V are just our daily abbreviations. Here we should say single-phase and three-phase.
The rotation of an AC motor relies on a rotating magnetic field created by an electric current. The three-phase motor flows through three-phase currents with a phase difference of 120 degrees, which can generate a rotating magnetic field. The single-phase current flowing through a single-phase motor cannot generate a rotating magnetic field, and a certain method needs to be taken to make it generate a rotating magnetic field. One of the methods is to use a capacitor, and it is also the most common method. The capacitor is used for phase separation, the purpose is to make the two The currents in the Rao group produce a phase difference of approximately 90° to generate a rotating magnetic field. In three-phase electricity, there is a phase difference between the currents between each two phases, and there is no need for phase separation.
Capacitive induction motors have two windings, the start winding and the run winding. The two windings are 90 degrees apart in space. A capacitor with a large capacity is connected in series on the starting winding. When the running winding and the starting winding pass through a single AC current, the current in the starting winding is 90 degrees ahead of the current in the running winding due to the action of the capacitor, and reaches the maximum first. value. 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 rotor of the motor, and the interaction between the current and the rotating magnetic field produces The electromagnetic field torque makes the motor spin.
