AC contactor usage and working principle

AC contactor is the most commonly used low-voltage control appliance in electric drive and automatic control systems. As an actuator, it is used to connect and disconnect lines, or frequently control the operation of equipment such as motors. It consists of moving and static main contacts, arc extinguishing cover, moving and static iron cores, auxiliary contacts and bracket shell. After the electromagnetic coil is energized, the moving iron core is attracted under the action of electromagnetic force, and the moving contact contacts the static contact directly or through lever transmission to complete the circuit. After the electromagnetic coil is powered off, the moving iron core returns automatically under the action of the return spring, commonly known as release, the contacts separate, and the circuit is broken.

AC contactors are generally used to start equipment. Different control wiring methods can be used to control the forward and reverse rotation, start and stop of the motor, and the length of the control cable can be used to achieve remote control. Changing the connection method can also achieve multi-site control. In addition, it can keep the motor (machinery) in a stopped state during a power outage to prevent the motor (machinery) from running due to a power outage and causing unforeseen injuries to the operators. Of course, the motor (device) can be considered to be started after the call is received. There are also AC contactors used together with overheating relays or motor comprehensive protectors, which can protect the motor from burning due to overload and phase loss, thus achieving the purpose of protecting the motor.

The AC contactor carries a large current. Generally, the internal pull-in coil controls its action, and the control coil is composed of various types of contactors connected in series with it. The reason why the relay will trip after lightning is because the relay of the AC contactor has overcurrent or grounding protection function. When lightning falls on the line, it will control the action of the AC contactor and cut off the load power supply to protect the equipment from being damaged. High voltage, high current damage or grounding may cause safety hazards.

Working principle of AC contactor:

When the coil is energized, the static iron core generates electromagnetic attraction, which will move the The iron core pulls in. Since the contact system is linked to the moving iron core, the moving iron core drives the three moving contacts to move simultaneously. The main contact closes, and the auxiliary normally closed contact mechanically connected to the main contact opens, and the auxiliary normally closed contact opens. The normally open contact closes, turning on the power. When the coil is powered off, the suction force disappears, and the linkage part of the moving iron core is separated by the reaction force of the spring, causing the main contact to open, the auxiliary normally closed contact mechanically connected to the main contact closes, and the auxiliary normally open contact opens , thus cutting off the power supply.

1: Generally, a three-phase contactor has a total of 8 points, three inputs, three outputs, and two control points. The output and input correspond to each other and can be easily seen. If you want to add self-locking, you also need to connect a line from a terminal of the output point to the control point.

2: First of all, you should know the principle of AC contactor. It uses an external power source to apply to the coil to generate an electromagnetic field. When power is applied, the contact point is disconnected. After knowing the principle, you should figure out the contacts of the external power supply, which are the two contacts of the coil, usually at the bottom of the contactor, and on each side. The other inputs and outputs are generally on the upper part and can be identified at a glance. Also pay attention to the voltage of the external power supply (220V or 380V), which is usually marked. And pay attention to whether the contact point is normally closed or normally open. If there is self-locking control, just adjust the circuit according to the principle.

The role of AC contactor:

The AC contactor carries a large current, which is generally the internal absorption current. The coil is closed to control its action, and the control coil is operated by various types of relays connected in series with it. The reason why the AC contactor will trip after lightning is because the relay of the AC contactor has an overcurrent or grounding protection function. When If there is lightning on the line, it will control the action of the AC contactor and cut off the load power supply to protect the equipment from damage by high voltage, large current or safety hazard caused by grounding.

1 Classification of uses

Contactor is an automated control electrical appliance. Contactors are mainly used to frequently connect or break AC and DC circuits. They have large control capacity and can be operated at long distances. With relays, they can achieve timing operation, interlock control, various quantitative controls and voltage loss and undervoltage protection. They are widely used. For automatic control circuits, its main control object is the motor, but it can also be used to control other electrical loads, such as electric heaters, lighting, welding machines, capacitor banks, etc. Contactors can be divided into AC contactors and DC contactors according to the type of controlled current. Here we mainly introduce the commonly used AC contactors. AC contactors can be divided into two types: electromagnetic type and vacuum type.

2 Model Description

(1) The above models are standard models. In recent years, B series AC contactors have been newly developed, and their model is BXX.

(2) The electromagnetic AC contactor model is CJ. The vacuum AC contactor model is CZ.

3 The structure and working principle of electromagnetic AC contactor

(1) Structure: The contactor mainly consists of electromagnetic system and contact system , arc extinguishing system and other parts.

①Electromagnetic system: The electromagnetic system includes the electromagnetic coil and the iron core, which is an important part of the contactor, relying on it to drive the closing and opening of the contacts.

②Contact system: The contact is the execution part of the contactor, including main contacts and auxiliary contacts. The function of the main contact is to connect and break the main circuit and control larger currents, while the auxiliary contact is in the control circuit to meet the requirements of various control methods.

③Arc extinguishing system: The arc extinguishing device is used to ensure that the arc generated is reliably extinguished when the contacts disconnect the circuit, thereby reducing arc damage to the contacts. In order to quickly extinguish the arc during disconnection, the contactor is usually equipped with an arc extinguishing device. Generally, a semi-enclosed longitudinal seam clay arc extinguishing cover is used, and is equipped with a strong magnetic arc blowing circuit.

④Other parts: There are insulating shells, springs, short-circuit rings, transmission mechanisms, etc.