What is the role of starting capacitors_The role of starting capacitors_The role of single-phase motor starting capacitors

一、 Introduction of the starting capacitor

Starting capacitor, ac electrolytic capacitor or polypropylene or polyester capacitor used to start single-phase asynchronous motor. A capacitive induction motor has 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 the 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 MAX value first.

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.

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 interaction between the current and the rotating magnetic field generates an electromagnetic field torque, which makes the motor rotate.

To make the single-phase motor rotate automatically, we can add a starting winding to the stator, and the starting winding and the main winding are 90 degrees apart in space.The starting winding should be connected in series with a suitable capacitor so that the phase difference with the current of the main winding is approximately 90 degrees, which is the so-called phase-splitting 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, and a (two-phase) rotating magnetic field will be generated in space.Under the action of this rotating magnetic field, the rotor can start automatically. After starting, when the speed rises to a certain level, the starting winding is disconnected by means of a centrifugal switch installed on the rotor or other automatic control devices. During normal operation, only the main winding works.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 kind of motor a capacitive single-phase motor. To change the direction of this kind of motor, it can be realized by changing the position of the capacitor connected in series.

Calculation formula for starting capacitor

Calculation formula for running capacitance of single-phase motor: C=1950I/ucos∮

formula:

I: motor current, U: power supply voltage; cos∮: power factor, take 0.75, 1950: constant

The starting capacitor is generally calculated according to 1-4 times the running capacitor capacity

二、What is the function of the starting capacitor_The role of the 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. 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.

A capacitive induction motor has 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 the 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 MAX 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 interaction between the current and the rotating magnetic field generates an electromagnetic field torque, which makes the motor rotate.

To make the single-phase motor rotate automatically, we can add a starting winding to the stator. The starting winding and the main winding have a space difference of 90 degrees. 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, and a (two-phase) rotating magnetic field will be generated in space.Under the action of this rotating magnetic field, the rotor can start automatically. After starting, when the speed rises to a certain level, the starting winding is disconnected by means of a centrifugal switch installed on the rotor or other automatic control devices. During normal operation, only the main winding works.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 kind of motor a capacitive single-phase motor. To change the direction of this kind of motor, it can be realized by changing the position of the capacitor connected in series.

三、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, this is the case: after the motor is powered on, it will generate 2 rotating magnetic fields with the same speed and opposite directions.The torque resultant force generated by these two magnetic fields is 0, so the rotor cannot rotate, but if an external force is applied to it, it 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 switch and 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, and when the rotational speed reaches a certain speed, the switch of the starting winding is disconnected by centrifugal force, and then the main winding works 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 depends on the rotating magnetic field generated by the current. The three-phase motor flows a three-phase current with a phase difference of 120 degrees, which can generate a rotating magnetic field.However, the single-phase current flowing through a single-phase motor cannot generate a rotating magnetic field, and certain methods need to be adopted to make it generate a rotating magnetic field. Using capacitors is one of the methods, and it is also a very common method. Capacitors are used to separate phases.The purpose is to make the currents in the two groups produce a phase difference close to 90° to generate a rotating magnetic field. In three-phase electricity, the current itself between each two phases has a phase difference, and there is no need to separate the phases.

A capacitive induction motor has 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 the starting winding pass through a single 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 MAX 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 interaction between the current and the rotating magnetic field generates an electromagnetic field torque, which makes the motor rotate.