1. What is a contactor?
A contactor is an electrical device used in industrial electricity that uses the magnetic field generated by current flowing through a coil to close contacts, thereby controlling the load. Because it can quickly disconnect AC and DC main circuits and frequently connect high-current control circuits, it has been widely used in electrical engineering.
2. Working principle of a contactor
A contactor consists of an electromagnetic system (iron core, stationary iron core, electromagnetic coil), a contact system (normally open contacts and normally closed contacts), and an arc-extinguishing device.
Contactor working principle: When the contactor's electromagnetic coil is energized, it generates a strong magnetic field, causing the stationary iron core to produce an electromagnetic attraction that draws in the armature, thus actuating the contacts: normally closed contacts open; normally open contacts close, and the two actions are linked. When the coil is de-energized, the electromagnetic attraction disappears, and the armature is released by the release spring, causing the contacts to return to their original position: normally closed contacts close; normally open contacts open.
3. Common Classifications of Contactors
According to the type of controlled current:
AC contactors (commonly used) and DC contactors.
AC contactors mainly consist of an electromagnetic mechanism, a contact system, and an arc-extinguishing device; DC contactors are generally used to control DC electrical equipment, with energized coils, and their operating principle and structure are basically the same as those of AC contactors.
Classified by application (the scope of application is in parentheses):
General purpose contactor (for commonly used loads);
Contactor for switching capacitors (used in reactive power compensation cabinets, for switching capacitors);
Reversible contactor (for dual power supply switching and forward/reverse control of motor equipment).
Clamping contactor (for electrical equipment such as cranes in metallurgical and steel rolling enterprises);
Building contactors (homes, hotels, apartments, office buildings, public buildings, shopping malls, etc.).
Key parameters for contactors include: rated current, coil voltage, frequency, number of main contacts (pole number), and auxiliary contacts. On the Gongpin Hui website and mobile app, you can easily and conveniently select the contactor product you need based on these parameters.
4. Applications of contactors
Contactors are mainly used for frequently connecting or disconnecting AC and DC circuits. They have a large control capacity, can be operated remotely, and can be used with relays to achieve timed operation, interlocking control, various quantitative control, and undervoltage and overvoltage protection. They are widely used in automatic control circuits. Their main control object is the electric motor, but they can also be used to control other electrical loads, such as electric heaters, lighting, welding machines, and capacitor banks.
Contactors not only connect and disconnect circuits, but also provide low-voltage release protection, making them one of the most widely used low-voltage electrical components in electric drive automatic control circuits.
5. The difference between contactors and relays
Contactors are used to connect or disconnect loads with high power, while relays are generally used in electrical control circuits to amplify the contact capacity of miniature or small relays in order to drive larger loads.
Contactors and electromagnetic relays operate on essentially the same principle, so how do you distinguish them? See their specific applications↓↓↓
The main function of a relay is to detect, transmit, transform, or process signals. The circuit current it switches is usually small, so it is generally used in control circuits (as opposed to "main circuits").
The primary function of a contactor is to connect or disconnect the main circuit. The main circuit refers to a circuit whose operation is determined by whether it is connected or disconnected. The concept of the main circuit corresponds to the control circuit. Generally, the current flowing through the main circuit is greater than that of the control circuit. Therefore, large-volume contactors are usually equipped with arc-extinguishing shields (because disconnecting a large current will generate an electric arc, and without an arc-extinguishing shield, the contacts will burn out).
6. Causes and solutions for poor contact of contacts
Unreliable contact between the moving and stationary contacts will increase the contact resistance, leading to excessively high contact surface temperature, turning surface contact into point contact, or even causing non-conductivity.
The causes of this malfunction are:
1. The contacts have oil, lint, or foreign objects.
2. With prolonged use, the contact surface oxidizes;
3. Arc erosion can cause defects, burrs, or metal shavings.
4. There is a jamming phenomenon in the moving parts.
The following are the solutions:
1. For oil stains, lint, or foreign objects on the contacts, you can wipe them with a cotton cloth dipped in alcohol or gasoline.
2. If the contact is made of silver or silver-based alloy, the formation of an oxide layer on the contact surface or slight burns and blackening under the action of an electric arc generally does not affect operation. It can be cleaned with alcohol and gasoline or carbon tetrachloride solution. Even if the contact surface is burned and uneven, only use a fine file to remove the spatter or burrs around it. Do not file too much, so as not to affect the contact life.
For copper contacts, if the burn is minor, simply use a fine file to smooth out the uneven areas. However, do not use fine sandpaper to polish them, as this may leave quartz sand particles between the contacts and prevent good contact. If the burn is severe and the contact surface is low, the contacts must be replaced.
3. If there is any jamming in the moving parts, it can be disassembled for inspection and repair.
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