Contactor is an automatic switching device used to frequently switch on or off high-current circuits such as AC and DC main circuits and large-capacity control circuits. In terms of function, in addition to automatic switching, the contactor also has the remote operation function and the loss of voltage (or undervoltage) protection function that the manual switch lacks, but it does not have the overload and short circuit protection functions of the low-voltage circuit breaker.
Advantages and classification of contactors
The contactor has the advantages of high operating frequency, long service life, reliable work, stable performance, low cost, and easy maintenance. It is mainly used to control motors, electric heating equipment, electric welding machines, capacitor banks, etc., and is the most applied in electric drive control circuit One of a wide range of control appliances.
According to the form of the main contact connection circuit, it is divided into: DC contactor and AC contactor.
According to the operating mechanism, it is divided into: electromagnetic contactor and permanent magnet contactor.
The structure and working principle of low voltage AC contactor
Structure: AC contactor includes electromagnetic mechanism (coil, iron core and armature), main contact and arc extinguishing system, auxiliary contact and spring. The main contacts are divided into bridge contacts and finger contacts according to their capacity. AC contactors with a current of more than 20A are equipped with arc extinguishing covers, and some also have grid plates or magnetic blowing arc extinguishing devices; auxiliary contacts The points are divided into normally open (moving close) contacts and normally closed (moving open) contacts, all of which are bridge-type double-break structures. The auxiliary contact has a small capacity and is mainly used for interlocking in the control circuit, and there is no arc extinguishing device, so it cannot be used to switch the main circuit. The structure is shown in the figure below:
Principle: After the coil of the electromagnetic mechanism is energized, magnetic flux is generated in the iron core, and electromagnetic attraction is generated at the armature air gap, which makes the armature close. The main contact is also closed under the drive of the armature, so the circuit is connected. At the same time, the armature also drives the auxiliary contacts to close the normally open contacts and open the normally closed contacts. When the coil is de-energized or the voltage is significantly reduced, the suction force disappears or weakens, the armature opens under the action of the release spring, and the main and auxiliary contacts return to their original state. The symbols of each part of the AC contactor are shown in the figure below:
Models and technical indicators of low-voltage AC contactors
1. Model of low-voltage AC contactor
The commonly used AC contactors produced in my country are CJ0, CJ1, CJ10, CJ12, CJ20 and other series of products. In the CJ10 and CJ12 series of products, all impacted parts adopt a buffer device, which reasonably reduces the contact distance and stroke. The movement system has a reasonable layout, a compact structure, and a structural connection without screws, which is convenient for maintenance. CJ30 can be used for remote connection and breaking of circuits, and is suitable for frequently starting and controlling AC motors.
2. Technical indicators of low-voltage AC contactors
⑴Rated voltage: refers to the rated voltage on the main contact. Commonly used grades are: 220V, 380 V, and 500 V.
⑵Rated current: refers to the rated current of the main contact. Commonly used grades are: 5A, 10A, 20A, 40A, 60A, 100A, 150A, 250A, 400A, 600A.
⑶The commonly used grades of the rated voltage of the coil are: 36V, 127V, 220V, 380V.
⑷Rated operating frequency: refers to the number of connections per hour.
Selection principle of low voltage AC contactor
1. Select the type of contactor according to the type of load current in the circuit;
2. The rated voltage of the contactor should be greater than or equal to the rated voltage of the load circuit;
3. The rated voltage of the attracting coil should be consistent with the rated voltage of the connected control circuit;
4. The rated current should be greater than or equal to the rated current of the controlled main circuit.
Post time: Nov-11-2021