Contactors are mainly used to control motors, electric heating equipment, welding machines, capacitor banks, etc. They can frequently connect or disconnect AC/DC main circuits, achieving remote automatic control. It has a low voltage release protection function and is widely used in electric drive automatic control circuits.
There are two types of contactors: AC contactors and DC contactors. Below is an introduction to the communication contactor.
Figure 2 shows the schematic diagram and graphical symbols of the structure of the AC contactor.
Figure 2 Schematic diagram and graphic symbols of the structure of the AC contactor
Components of AC contactors
(1) Electromagnetic mechanism: The electromagnetic mechanism consists of a coil, a moving iron core (armature), and a stationary iron core.
(2) Contact system: The contact system of an AC contactor includes a main contact and an auxiliary contact. The main contact is used to connect and disconnect the main circuit, with 3 or 4 pairs of normally open contacts; Auxiliary contacts are used to control circuits, perform electrical interlocking or control functions, and usually have two pairs of normally open and two pairs of normally closed contacts.
(3) Arc extinguishing device: Contactors with a capacity of 10A or more are equipped with arc extinguishing devices. For small capacity contactors, double break bridge contacts are often used to facilitate arc extinguishing; For large capacity contactors, longitudinal slot arc extinguishing enclosures and grid arc extinguishing structures are commonly used.
(4) Other components: including reaction springs, buffer springs, contact pressure springs, transmission mechanisms, and casings.
The contactor is labeled with terminal numbers, and the coils are A1 and A2. The main contacts 1, 3, and 5 are connected to the power side, and 2, 4, and 6 are connected to the load side. Auxiliary contacts are represented by two digits, with the first digit being the sequence number of the auxiliary contacts, followed by 3 and 4 indicating normally open contacts, and 1 and 2 indicating normally closed contacts.
The control principle of a contactor is simple. When the coil is connected to the rated voltage, electromagnetic force is generated to overcome the spring reaction force and attract the moving iron core to move downward. The moving iron core drives the insulating connecting rod and the moving contact to move downward, causing the normally open contact to close and the normally closed contact to open. When the coil loses power or the voltage is lower than the release voltage, the electromagnetic force is less than the spring reaction force, and the normally open contact opens and the normally closed contact closes.
