Magnetic contactor

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Contactor - magnetic starter is an important device. It is widely used in electrical control system in industry and daily life. Should attract the attention of many people. So what is its function? What is the structure and working principle of Contactor?... The answer will be revealed right in the content of the article below.

1. What is the word starter contactor? How is the function?

Contactor is a low-voltage electrical instrument, performing the switching of electrodynamic circuits, remote control. Contactor is known as a particularly important electrical device in the power system. Thanks to it, we can control devices such as motors, capacitors, lighting systems, etc. simply through push button, automatic mode or remote control.

Carry out the switching operation of the Contactor by means of an electromagnetic mechanism, a pneumatic mechanism or a hydraulic mechanism. But the most common are electromagnetic contactors.

2. The history of formation and development of Contactor magnetic starter

In the 1890s, manual starters were used to start DC machines. Engineers find it difficult to separate the machine from the mains supply.
In the 1950s, the definite purpose contactor was developed. Since then, we have observed various changes in the contactor's design. Today we can make many different types of starters with different purposes.

Magnetic starter

A magnetic starter is a device designed for the purpose of powering an electric motor. It includes a contactor as the key component. In addition, there are overcurrent protection, short cut, undervoltage, and overload.

Vacuum contactor

The vacuum contactor uses a vacuum bottle to enclose the contacts and extinguish the arc. This arc quenching allows for further miniaturization of the contacts. Also, uses less space than air-powered trip contacts at higher currents. Since the contacts are encapsulated, vacuum contactors are widely used in contaminated environments, such as mining.

Mercury contactor

Mercury contactor is also known as mercury displacement contactor, mercury contactor. It's a relay that uses liquid mercury in an insulated sealed box. And it acts as the closing/cutting component

Mercury absorbent contactor

A mercury-infused contactor is a form of contactor, usually a reed contactor. In which the contacts are impregnated (impregnated) with mercury. They are not considered contactors because they are not intended for designs with currents greater than 15 amps.

3. Structure and working principle of Contactor starting from


Contactor is divided into 3 main parts:
Electromagnet: Includes the following details:

  • Coil used to generate magnet attraction;
  • Iron core;
  • The spring acts to push the lid back to its original position.

Contact system: Includes main contacts and auxiliary contacts.

  • Main contact: Has the function of allowing large currents to pass through. The main contact is usually open and closed when supplying power to the magnetic circuit of the Contactor starting from the electrical cabinet, causing the magnetic circuit to absorb again.
  • Auxiliary contact: Function for the current to pass through the contacts less than 5A. The auxiliary contact will have two states: normally closed and normally open.

Arc extinguishing system: An electric arc will appear when switching, causing the contacts to burn and wear out. Therefore, an electric arc system is required.

Working principle of Contactor

Image simulating the working principle of Contactor

When the power supply in the control circuit is equal to the rated voltage of the Contactor at the two ends of the coil winding at the previously fixed magnetic core, the generated magnetic force will attract the mobile magnetic core. Then form a closed magnetic circuit. At this time, the magnetic force will be greater than the reaction of the spring. Following that, the Contactor starts the active state.

Thanks to the mechanical interlock between the movable magnetic core and the contact system, the main contact will be closed. At that time, the auxiliary contact changes state (when normally closed will open, when normally open will close). This state will be maintained. When power is stopped to the coil, the Contactor will be in a resting state and the contacts will return to their original state.

4. Contactor classification starting from

There are many types of contactor starters. You can rely on the following classifications:

  • According to the principle of transmission: Electromagnetic contactor, slightly pressed type, hydraulic type, etc. Electromagnetic contactor will be the more common type.
  • According to the form of current: DC Contactor and AC Contactor.
  • According to structure: Contactor is used in places with limited height such as electrical panels under the car and in places with limited width such as train compartments.
  • According to rated current: Contactor 9A, 12A, 18A,.... 800A or can be larger.
  • According to the number of poles: Contactor 1 phase, 2 phase, 3 phase, 4 phase. Among them, the most popular is the 3-phase contactor.
  • By voltage level: Medium voltage contactor and low voltage contactor.
  • According to the suction coil voltage: AC suction coil 220VAC, 380VAC,... DC suction coil 24VDC, 48VDC,...
  • By specialized function: Some manufacturers make specialized contactors for a particular application. For example, contactor specialized for capacitors of BTB Electric.

5. How is the magnetic starter contactor manufactured?

Pictures of automatic contactor production line

Contactor is manufactured on modern production lines including the following 8 steps:
1. Distributing components to the line by AGV
By using the AGV, an automated transport vehicle, the component delivery operation follows instructions from the central control system with programmed addresses.
2. Supply components for assembly line
After being delivered the components to the conveyor belt by AGV, the robotic arms distribute the components sequence to the assembly line automatically.
3. Mount the components and test
Individual components are fully automated by the robotic arms, each cycle is checked by sensors before being attached to the device housing to avoid errors during assembly.
4. External inspection
Through visual inspection, we check the assembly of the external auxiliary contact of the product, check for missing parts such as the nameplate position cap and the print status.
5. Noise test
Carry out a test for abnormal vibrations, during the movement test of the main and auxiliary contacts. For the purpose of determining the presence of abnormal sounds in the product.
  6. Automatic loading of goods
The products after inspection, loaded automatically by the robot, are transferred to the packing line.
7. Packaging each product
Depending on the product type, individual packaging boxes are automatically supplied and inserted with instructions for use and accessories.
8. Multi-layer packing and stacking
The products are individually packed and packed into cartons and loaded automatically by the robot.

6. Contactor's app starts from

Magnetic starter contactor is a control device to switch off the power supply to the device. Should be very commonly used in power system.

In industry, contactors are used to control the operation of motors or electrical equipment for safe operation. Because this is an automation solution by electromechanical method. Although this approach does not handle complex processes, it is simple and highly stable and easy to repair.

In the automation industry, it requires handling complex jobs. Furthermore, the difficulty requires processor intervention. So the mechatronic method was born to meet the advanced production processes. Contactor is a device widely used in life and industry:

  • Motor control contactor: To supply power to the direct-start motor. Then, the contactor is used in conjunction with the thermal relay for the purpose of motor overload protection.
  • Star-delta starting contactor: It is used to change the operating mode of the motor. From the star diagram to the triangle diagram when the engine has operated stably. For the purpose of reducing the inrush current.
  • Capacitor control contactor: It has the effect of switching capacitors to the grid to compensate for reactive power. The magnetic starter contactor is used in the automatic compensation system, it is controlled by the capacitor controller to ensure the switching of capacitor levels in accordance with the load. The unique feature of this contactor line is the ability to limit the starting current of the capacitor.
  • Contactor to control lights: can control the contactor with a time relay or PLC to switch off the power supply to the lights to turn on or off the lights at a specified time.
  • Contactor protection: Ordinary contactor when used with overcurrent, voltage, phase protection relays. When the above relays release the contact, the contactor also opens the circuit behind the device, which will lose the protective power for the above fault device.

7. CLIP guide to select Contactor to boot from

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