1、 The basic structure of AC contactors.

Contactors are generally composed of electromagnetic mechanisms, contact systems, arc extinguishing devices, spring mechanisms, brackets, bases, and other components. For power operators, the most commonly used components are the coil of AC contactors and the contact system of contactors.

The contacts of AC contactors can be divided into main contacts and auxiliary contacts. The main contact is a normally open point applied in the main circuit, and the auxiliary contact is used in the control circuit in conjunction with the contactor coil, indirectly controlling the operation of the circuit by controlling the contactor coil.

2、 AC contactor function.

The basic function of an AC contactor: After the AC contactor is powered on, the main contact closes, the circuit is connected, the normally open point in the auxiliary contact closes, and the normally closed point opens, in order to generate certain dynamic changes in the circuit and control the normal operation of the circuit.

3、 The function and purpose of the main and auxiliary contacts.

1. Main contact function.

The main contact is connected in series in the main circuit (mostly for motors) to connect or disconnect the circuit, achieving the purpose of controlling the circuit (for motor operation). The main contact function is relatively simple.

2. Auxiliary contact function. Auxiliary contacts generally have three functions:

(1) Form a self-locking circuit. The self-locking circuit is an essential and widely used basic circuit in power control, as shown in the figure:

When the start button SB2 is pressed, the coil of the AC contactor KM is energized and closed, and the corresponding main contact KM of the AC contactor in the main circuit is closed to connect the circuit. The auxiliary normally open contact is closed to form a self-locking, ensuring that the circuit still maintains its operation after the start button SB2 is released.

In practical applications, the self-locking circuit uses the normally open contact of the contactor, which is connected in parallel with the start button.

(2) Form an interlocking loop.

The contactor interlocking circuit is also a widely used basic circuit, and the interlocking principle is shown in the figure:

The normally closed contacts of AC contactor KM1 are connected in series in the coil circuit of AC contactor KM2. Correspondingly, the normally closed contacts of AC contactor KM2 are also connected in series in the coil circuit of AC contactor KM1. In other words, these two AC contactors cannot work simultaneously.

In practical applications: In the interlocking circuit of contactors, the normally closed point of the contactor is used, which is connected in series with the interlocking contactor coil.

(3) Perform signal transmission in the circuit.

In general, the signal transmission of the switching value can be achieved through the auxiliary normally open or normally closed points of the contactor. Take the simplest example: a contactor controls the operation of an electric motor, and the stop and running signals of the motor!

In general, we use the normally open point of the contactor as the motor operation signal action indicator, and the normally closed point as the motor stop signal indicator. Under normal circumstances, the motor is in standby mode, and the normally closed point of the contactor is used to connect the stop indicator light signal, telling us that the motor is in the stop position. When the motor is running, the contactor closes, the normally open point closes, and the normally closed point opens. The corresponding "stop" indicator circuit is powered off, and the "run" indicator circuit is conductive. At this time, the signal transmitted is: the stop indicator light is off, and the run indicator light is on.

4、 Precautions for using contactors:

1. Distinguish the power supply voltage of the contactor and connect it correctly to the power supply. The most commonly used contactor power supplies are AC220V, DC220V, AC380V, and other voltage levels. The wiring process should be clearly observed, otherwise it is easy to burn out the contactor.

2. When crimping the wire of the contactor, it should be tightly pressed and firmly contacted, and should not be pressed onto the wire skin or appear to be non connected. This is a common fault point in work.

3. During the use of AC contactors, it is important to distinguish between self-locking points, interlocking points, and signal transmission points, and avoid mixing or reversing them!