AC contactor selection tips and precautions

1. The selection of AC contactor should be determined whether it is DC or AC. AC is generally expressed by AC. DC represents DC. According to China's standards, the rated voltage should be selected in the following standard system:

DC: 12, 24, 36, 48, 60, 72, 110, 125, 220, 250, 440V;

Communication: 24, 36, 42, 48, 127, 220, 380, 660, 1140V.

2, contact parameters

The main contacts of the contactor are in the form of double breakpoint bridge contacts and single breakpoint finger contacts. The former has the advantage of having two effective arc extinguishing regions and good arc extinguishing effect. Generally, a small-capacity AC contactor with a rated voltage of 380 V or less and a rated current of 20 A or less can extinguish the arc by the near-cathode effect of the two fractures when the current naturally crosses zero. The AC contactor with rated current of 20-80A can effectively extinguish the arc under the condition of adding the arc-lead piece or using the circuit electric power to blow the arc, and then double-breaking to cooperate, but for the sake of reliability, sometimes it is necessary Install a grid or spacer. If the rated current is greater than 80A, the main contact of the AC contactor is double-broken, and the arc-extinguishing must be installed with an arc-extinguishing grid or other arc-extinguishing chamber. Generally, the double-fault contact has a small opening distance, a compact structure, a small volume, and no soft connection, so it is beneficial to improve the mechanical life of the contact. However, the parameters of the double-fault contact are inconvenient to adjust, and there is generally no rolling motion when closing, and the oxide on the surface of the contact cannot be removed, so the contact needs to be made of silver or silver-based alloy material, and the cost is high. The single-fault finger contact has a rolling motion during the closing process, which is easy to remove the oxide of the surface and ensure reliable contact, so the contact can be made of copper or copper-based alloy material, and the cost is low. However, the rolling motion of the contacts increases the mechanical wear of the contacts. Since there is only one fracture, the opening distance of the contact is larger than that of the double fracture, so the volume is also large, and the movable contact needs to be externally connected through the soft connection, so that the mechanical life is limited.

3, the choice of auxiliary contacts, according to your equipment, you can choose 1a1b, which is a common open 2a2b, 3a1b, 5a1b and so on.

4, protection, can be equipped with the type of thermal relay, such as GMC-22 contactor can be equipped with GTH-22 thermal relay.

5, the size of the complete set of installation, the general selection of AC contactor is a small size, beautiful contactor, generally use GMC series of contactors, stable performance, beautiful and generous.

6. When selecting a contactor, the current level of the contactor should be selected according to whether the work of the load controlled by it is a light task, a general task or a heavy task, the power and operation of the motor or other load. According to the control loop power supply condition, the coil parameters of the contactor are selected, and the general or special specification products, such as the CJX2 series AC contactor, are selected according to the use environment, and the performance is better.

7, the contactor common faults are:

1 Can not be closed after power-on or can not be completely closed, because the coil voltage level is wrong or the voltage is insufficient, the moving parts are stuck, the contact over-travel is too large, and the contact spring and the release spring reaction force are too large;

2 The suction process is too slow, because the air gap of the moving and static iron core is too large, the reaction is too large, and the coil voltage is insufficient;

3 The noise is too large or vibrates. The reason is that the magnetic ring is broken, the coil voltage is insufficient, and the surface of the core is dirty and rust.

4 The coil is damaged or burnt because of internal disconnection or inter-turn short circuit of the coil, over-voltage or under-voltage operation of the coil;

5 After the coil is de-energized, the core is not released. The reason is that the residual magnetism is too large, the reaction force is too small, the board surface has viscous grease, and the moving parts are stuck;

6 The temperature rise of the contact is too high and fusion welding occurs. The reason is that the load current is too large, the overtravel is too small, the contact pressure is too small and the breaking capacity is insufficient. The contact surface of the contact has metal particles or foreign matter, during the closing process. The vibration is too intense or multiple vibrations occur.

8. The contactor is an important low-voltage electrical component. The length of its life is one of the quality evaluation and main indicators, so it is very important to take some measures to improve the life. A reasonable fit between the suction and reaction characteristics can increase the life of the contactor.

9. The operating voltage of the contactor is 85%~110%Un. The primary and secondary bounce of the contacts when the contacts are closed and the core is pulled may cause the contacts to be welded and increase their electrical erosion. In order to reduce the contact jump time, the quality and speed of the contact should be appropriately reduced, and the initial contact force of the contact should be appropriately increased. In order to reduce and prevent the second bounce of the contact (at this time, due to the large starting current, the hazard is more serious), in addition to the good cooperation of the suction force characteristic and the reaction force characteristic to reduce the collision energy, the electromagnetic system needs to be added. A buffer device is installed to absorb the kinetic energy of the armature or the like.

10. When using the contactor at the end, pay attention to the use environment of the contactor. Do not use it in a place that is too humid, and it is easy to oxidize the contacts of the contactor.