Contactor is an electrical device used to convert electrical circuits. The contactor uses a lower power current control source to switch off a large current source. To make it easier to understand, I give an example as follows: Contactor uses 24VDC control source (current <1A) to control 3-phase 380VAC 3pha motor with a large capacity of 10 KW …
The contactor has the same principle of operation as the relay, however, the contactor can cut off the rated current many times greater than the relay.
Structure of Contactor
The following three are crucial components of the contactor:
+ Coil or Electromagnet: This is the most crucial component of a contactor. The driving force that is required to close the contacts is provided by the coil or electromagnet of the contactor. The coil or electromagnet and contacts are protected by an enclosure.
+ Enclosure: Just like the enclosures used in any other application, contactors also feature an enclosure, which provides insulation and protection from personnel touching the contacts. The protective enclosure is made from different materials, such as polycarbonate, polyester, Nylon 6, Bakelite, thermosetting plastics, and
others. Generally, the open-frame contactor features an additional enclosure, which protects the device from bad weather, hazards of explosion, dust, and oil.
+ Contacts: This is yet another important component of this electrical device. The current carrying task of the contactor is done by the contacts. There are different types of contacts in a contactor namely, contact springs, auxiliary contacts, and power contacts. Each type of contact has an individual role to play.
+ In addition, some high-end product lines with large switching currents often have accompanying accessories and additional magnetic suppression devices to remove the arc.
Basic specifications of Contactor:
+ Rated current: The current flowing through the contactor’s main contact system when the load circuit is closed. With this value of current, the main conductor circuit of the contactor does not overheat.
+ Rated voltage: Is the voltage applied on the two poles of the main conductor circuit of the contactor.
+ Contactor closing ability: Rated by the current value that the contactor can close successfully. Usually this value is from 1 to 7 times the value of the rated current.
+ Contactor’s ability to disconnect: It is assessed by the value of the disconnecting current, at which the contactor can successfully interrupt the circuit. Usually this value equals 1 to 10 times the rated current.
+ Mechanical strength: It is the number of switching times when there is no current flowing through the contactor’s contact system. Exceeding the number of switching times, the contacts are considered damaged, no longer usable. The contactor type usually has mechanical strength from 5 million to 10 million switching times.
+ Electrical strength: Is the number of switching on the rated current. Conventional contactors have electrical durability of about 200,000 to 1 million switches.
Classification of Contactor:
There are many ways to classify contactors:
+ According to the transmission principle: We have electromagnetic contactor, steam type, hydraulic type, … Usually we have electromagnetic contactor.
+ According to the electric current pattern: DC electric contactor and AC electric contactor.
+ According to the structure: People use the contactor in height-restricted places (such as electric panels in undercarriage) and in limited widths (for example: tramcars).
+ According to the rated current: Contactor 9A, 12A, 18A, …. 800A or greater.
+ By pole: Contactor 1 phase, 2 phase, 3 phase, 4 phase. The most common is a 3-phase contactor.
+ According to voltage level: Medium-voltage contactor, low-voltage contactor.
+ According to suction coil voltage: ACAC 220VAC, 380VAC, … DC coil 24VDC, 48VDC, …
+ By specialized functions: Some manufacturers make specialized contactors for a specific application, for example, special contactor for capacitor banks of Schneider, …
Operating Principle of a Contactor:
The current passing through the contactor excites the electromagnet. The excited electromagnet produces a magnetic field, causing the contactor core to move the armature. Main contacts and auxiliary contacts (if any) will simultaneously switch to the operating status.
The pairs contact NO to NC, NC to NO or close to open, open to close.
When stop supplying electricity to the suction district, the contactor returns to its original, inactive state.
Advantages of Contactor:
Compact size can take advantage of the narrow space for installation and operation that the circuit breaker cannot perform. Remote control switch has an arc cover to protect the outside, so it is absolutely safe for the operator of the electrical system, fast switching time, high durability, stable operation, … because of the advantages The point on contactor is widely used to control switching in low voltage circuits especially used in industrial plants.
Application of Contactor:
Contactor is a control device to switch on and off the power supply for the device so it is used very popular in electrical systems.
In industry, Contactor is used to control the operation of electric motors or equipment for safe operation. This is an automation solution by the electromechanical method. This method does not handle complicated processes but it is simple and has high stability, easy to fix.
In today’s automation industry that requires the processing of complex and difficult tasks, it requires the intervention of a processor, so the mechatronic method was born to meet the advanced manufacturing processes. up. Contactor is still a device used in many industries and civil:
+ Motor control contactor: power supply for direct start motor. The contactor is used in combination with a thermal relay to protect the motor from overload.
+ Star / delta starting contactor: change the operating mode of the engine from the star-shaped diagram at start-up to the triangle diagram when the engine has been running stably, with the purpose of reducing the starting current.
+ Contactor control capacitor: switch capacitor on / off to compensate for reactive power. The contactor used in the automatic compensation system is controlled by the capacitor controller to ensure switching of capacitors suitable for the load.
+ Contactor control lights: can control the contactor by time relay or PLC to switch the lights to turn on / off the lights according to the prescribed time.
