What is A Contactor?

Figure 1: A contactor.

Contactors are divided into AC contactors (voltage AC) and DC contactors (voltage DC). They are used in power, power distribution and electric field combination. Broadly speaking, contactor is an electrical appliance that uses the current flowing through the coil to generate a magnetic field and close the contact in order to control the load.

1. Function

In Electrotechnics, contactor is a device that can quickly cut off the main AC and DC circuits. And it can also connect and turn off the high current control (up to 800A) circuit. So, it is often used in the motor as the control object. It also be used to control the power load such as factory equipment, electric heater, working mother machine and various power units. The contactor can not only connect and cut off the circuit, but also has the function of low voltage release protection. The contactor has large control capacity and it is suitable for frequent operation and remote control. It is one of the important components in the automatic control system.

2. Working Principle

The working principle of the contactor is that when the contactor coil is energized, the coil current will produce a magnetic field. The generated magnetic field causes the static iron core to generate electromagnetic attraction attracting the moving iron core. And it will drive the AC contactor to act. The normally closed contact and the normally open contact will be closed. When the contactor coil is powered off, the electromagnetic suction disappears. And the armature will restore the contact disconnecting the normally open contact and closing the

2. normally closed contact due to the release of the spring.

3. Structure

The contactor is mainly composed of electromagnetic system, contact system, arc extinguishing system and other parts.

Figure 2: The structure of a contactor.

1. Electromagnetic system: electromagnetic system includes electromagnetic coil and iron core. It is an important part of contactor which drives the closing and opening of contacts.

2. Contact system: the contact is the executive part of the contactor including main contact and auxiliary contact. The function of the main contact is to connect.

3.Major loop: control large current, and the auxiliary contact is in the control loop to meet the requirements of various control modes.

4. Arc extinguishing system: the arc extinguishing device is used to ensure that the arc generated when the contact disconnects the circuit can be extinguished reliably and reduce the damage of the arc to the contact. In order to quickly extinguish the arc during disconnection, the contactor is usually equipped with arc extinguishing device. Generally, the semi sealed longitudinal seam ceramic arc extinguishing cover is adopted, and a strong magnetic arc blowing circuit is equipped.

5. Other parts: insulating shell, spring, short circuit ring, transmission mechanism, etc.

4. Classification of Contactors

Figure 3: Direct acting contactor (left) and Rotational contactor (right).

According to the voltage of the control coil, it can be divided into DC contactor and AC contactor.

According to the operation structure, it is divided into electromagnetic contactor, hydraulic contactor and pneumatic contactor.

According to the action mode, it can be divided into direct acting contactor and rotational contactor.

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