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Understanding Contactors in the Electrical Industry

Time:2024-05-13   Author:As Beam   Browse:

1.What is a contactor? What is its function?

A contactor is an electrical component mainly used to control the switching of circuits and protect electrical equipment. Its working principle involves controlling the opening and closing of circuits by controlling the on-off state of an electromagnet, thus enabling start-stop control of electrical equipment. The main functions of a contactor include:


Switching control of circuits: Contactors can make or break circuits, thereby controlling the start, stop, or switching of electrical equipment. This control can be manual or automatic through remote control systems.


Protection of electrical equipment: Contactors have functions such as overload protection and short-circuit protection. When overcurrent or short-circuit faults occur in the circuit, the contactor can quickly cut off the circuit to prevent equipment damage due to excessive current or accidents.


Segmented control: Contactors can divide circuits into sections to achieve segmented control of electrical equipment, thereby improving operational efficiency and safety.


Remote control: Contactors can be used in conjunction with remote control systems to achieve remote control of electrical equipment, increasing the automation and intelligence level of electrical equipment.

Contactor in Power Cabinet.jpg


2.What components make up a contactor?

Contact part: This is the core part of the contactor, with the function of conducting and breaking current. It typically consists of fixed contacts and moving contacts. When the contactor is de-energized, the moving contacts separate from the fixed contacts, thereby interrupting the current flow. The contact system includes main contacts and auxiliary contacts. Main contacts are used to make or break the main circuit, while auxiliary contacts are used to control other parts of the circuit.


Electromagnetic mechanism: The electromagnetic mechanism consists of a coil, moving iron core (armature), and static iron core. Its function is to convert electromagnetic energy into mechanical energy, generating electromagnetic force to drive the movement of contacts. When the electromagnetic coil is energized, it causes the armature to attract under the action of electromagnetic force, directly or through lever transmission, bringing the moving contacts into contact with the static contacts, thus closing the circuit. When the electromagnetic coil is de-energized, the armature returns automatically under the action of reset springs, separating the contacts and opening the circuit.


Insulation part: Mainly composed of insulation materials, used to isolate electrical parts from mechanical parts, preventing current leakage or electric shock hazards.


Mechanical part: Used for connecting and fixing contacts and insulation parts, including switch handles, springs, and other mechanical components, used to control the operating state of the contactor.


AC contactors may also include special components such as arc extinguishing covers (used to extinguish arcs when contacts open), contact pressure springs (used to maintain contact pressure between contacts), and action-reaction springs (used to quickly separate contacts after the electromagnet is de-energized).

Contactor Contruction.jpg


3.How to select a contactor?

When selecting a contactor, multiple factors need to be considered to ensure it meets specific application requirements. Here are some common requirements for reference:


Determine the nature of the load: Select the type of contactor based on the nature of the load (such as AC or DC, motors, or other loads). The type of contactor should be compatible with the load.


Voltage rating: The voltage rating of AC contactors should be the same as the load, and the rated voltage should be greater than or equal to the operating voltage of the main circuit. Also, the rated operating voltage of the contactor should not exceed its rated insulation voltage.


Current rating: The rated current should be greater than or equal to the rated current of the controlled circuit. The closing current of the contactor should be greater than the starting current of the load, and the breaking current should be greater than the current required to break the load during operation. For motor loads, the rated current should be appropriately increased or decreased according to the operating mode. Conventional calculations can be made based on the load's rated current multiplied by 1.4-7 times.


Coil voltage and frequency: The rated voltage and frequency of the coil should match the selected voltage and frequency of the control circuit. Additionally, consider the length of the circuit and voltage drop to ensure the contactor can operate normally within 85% to 110% of the rated voltage.


Auxiliary contacts: The number and current capacity of auxiliary contacts should meet the wiring requirements of the control circuit.


Operating frequency: If the operating frequency of the contactor exceeds the specified value, the rated current should be appropriately increased.


Operating environment: Consider the operating environment of the equipment, such as temperature, humidity, dust, vibration, etc., to select the appropriate contactor model.


Installation and dimensions: Consider the installation method and size of the contactor to ensure it can fit within the space inside the electrical product.


4.What are the classifications of contactors?


(1) Classified by the voltage of the control coil: DC contactors: Contacts and electromagnetic relays designed for DC circuits. AC contactors: Contacts and electromagnetic relays specifically used for AC circuits.

(2) Classified by operating structure: Electromagnetic contactors: Use electromagnetic attraction to close or break motor circuits or other load circuits. Hydraulic contactors, pneumatic contactors.

(3) Classified by operating mode: Direct-acting contactors, rotary contactors.

(4) Classified by the nature of the main contact current: AC contactors, DC contactors, AC/DC contactors (for some contactors that control AC circuits in the contact system but connect to DC circuits).

(5) Classified by operating mode: Manual, electric, electromagnetic attraction.

(6) Classified by installation method: Fixed, movable.

(7) Classified by the form of the main contacts: Normally open type, normally closed type.

(8) Classified by structure: Electromagnetic contactors and permanent magnet contactors.

(9) Classified by the environment where the main contacts are located: Air-type contactors, vacuum-type contactors.

(10) Classified by the number of main contacts: Single-pole contactors, multi-pole contactors.

(11) Classified by rated current and power: Small, medium power, large contactors, and low, medium, high power contactors, chosen based on the required current and power load.

Eaton Contactor.jpg


5.What are the main applications of contactors?

In industrial control systems, contactors are one of the most common components. They are widely used in control systems of large machinery and equipment to control the operation of motors, lighting, and other devices by switching circuits. Contactors can also be used to control pneumatic and hydraulic systems, as well as various automated control systems in factories. In transportation systems, contactors also have important applications. For example, in places like trams, subway stations, and train stations, automatic doors and barriers on pedestrian walkways are controlled by contactors. Additionally, contactors can be used to control headlights, power windows, and air conditioning systems in ordinary vehicles. In building automation systems, contactors also have certain applications, especially in large commercial and residential buildings, where they can control the switching, regulation, and coordination of lighting and air conditioning systems through circuit switching, thus achieving energy savings and intelligent control.


6.How to explain the working principle of a contactor?

The working principle of a contactor is mainly based on electromagnetic principles. When the contactor coil is energized, the coil current generates a magnetic field, which exerts electromagnetic force on the static iron core inside the contactor, causing it to attract the moving iron core. The movement of the moving iron core drives the contactor's contact system, causing the normally closed contacts to open and the normally open contacts to close (both are interlocked). Specifically, the contactor's contact system includes main contacts and auxiliary contacts. Main contacts are typically used to make or break the main circuit, while auxiliary contacts are used to control other parts of the circuit, such as conducting control circuits. These contacts are usually made of silver-tungsten alloy, which has good conductivity and high-temperature resistance. When the coil is de-energized, the electromagnetic force disappears, and the moving iron core is released under the action of return springs, restoring the contact system to its original state, i.e., the normally open contacts open, and the normally closed contacts close. In this way, the contactor completes the control function of the circuit.


7.What is the relationship between a contactor and the Internet of Things (IoT)?

In electrical systems, contactors can be part of the Internet of Things (IoT), used to achieve intelligent control and management of electrical equipment. For example, contactors can be used in conjunction with sensors to detect the status or environmental parameters of electrical equipment, and then control the on-off state of the electrical equipment through the contactor. In this way, IoT systems can achieve functions such as remote monitoring, fault diagnosis, and intelligent control of electrical equipment, improving the operational efficiency and safety of electrical systems.



8.What do interlocking, interlocking, and self-locking mean in relation to contactors?

Interlocking, interlocking, and self-locking have different roles in electrical control systems, but they are all designed to ensure the safety and stable operation of the system. Detailed analysis:


Interlocking: Interlocking refers to two or more contactors mutually constraining each other in the same circuit to prevent them from closing simultaneously and causing a short circuit. Specifically, when one contactor closes, its normally closed contacts open, triggering the coil circuit of another contactor to de-energize, thereby preventing both contactors from closing simultaneously. Interlocking is mainly used in applications such as motor forward and reverse circuits to ensure the safe operation of the circuit.


Interlocking: Interlocking, sometimes also referred to as interlocking, refers to using auxiliary contacts of one circuit to control the coil circuit of another circuit to achieve state holding or function limitation. This control method is usually used to prevent two or more operations from occurring simultaneously to ensure the safe and stable operation of the system. For example, in manual gearbox transmissions, the function of the interlocking mechanism is to prevent two gears from being engaged simultaneously.


Self-locking: Self-locking refers to the phenomenon that AC contactors keep the coil energized through their normally open auxiliary contacts. When the contactor coil is energized, its normally open auxiliary contacts close, forming a self-locking circuit. In this way, even if the start button is released, the contactor can maintain the closed state, realizing the continuous operation of the equipment. Self-locking is commonly used in the continuous operation control of motors to improve the stability and reliability of equipment.

Contactor interlock control forward and reverse circuit.jpg


9.How to use a multimeter to check the condition of a contactor?

Preparation: First, you need a multimeter, ensure that its battery is fully charged, and it can work properly. Select the resistance range: Adjust the multimeter to the resistance range, usually choose a lower resistance range for more accurate measurement of the contactor's resistance value. Disconnect the contactor power: Before checking the contactor, make sure the power to the contactor is disconnected to avoid the risk of electric shock.

Measure coil resistance: Connect the two test leads of the multimeter to the two ends of the contactor coil, and observe the resistance value displayed by the multimeter. Generally, the resistance value of the contactor coil should be between tens to hundreds of ohms. If the resistance value is too large or too small, it may indicate contactor damage. Measure contact resistance: Next, measure the contact resistance of the contactor. Close the contacts of the contactor, and then connect the two test leads of the multimeter to the two ends of the contacts. If the contacts are normal, the multimeter should display a small resistance value, close to zero. If the resistance value is large or infinite, it may indicate poor contact or damage to the contacts. Observe the testing process: During the measurement process, pay attention to whether the multimeter display is stable. If the display is unstable, there may be problems such as sticking or jitter of the contactor contacts during operation. Judge the result: Based on the above measurement results, judge whether the contactor is good or bad. If the coil resistance and contact resistance are within the normal range, and the testing process is stable, then the contactor should be normal. Conversely, if the resistance values are abnormal or the testing process is unstable, it may indicate contactor damage or other issues.

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TAG:   Contactors AC Contactor Eaton  Electrical