Low-voltage electrical appliances can be seen everywhere around us, and their application fields are very wide: from electric power, industrial control, communication, commercial and civil buildings, almost all walks of life can not do without it. Low-voltage electrical appliances and electrical distribution, lighting and control circuits composed of low-voltage electrical appliances almost penetrate into all power consumption fields. Low-voltage electrical apparatus is the foundation of reliable operation of low-voltage electrical system and an important guarantee for safe electricity use. Electrical (industrial) employees must master relevant knowledge and technology skillfully in order to be handy in their work.
This paper is a detailed introduction to the basic knowledge of low-voltage electrical appliances: the definition of electrical appliances and low-voltage electrical appliances, and the classification of low-voltage electrical appliances.
First, the definition of electrical appliances
Electrical equipment refers to electrical equipment that can automatically or manually turn on or off the circuit according to external requirements or applied signals, so as to continuously or intermittently change the parameters or state of the electrical network, so as to realize the switching, control, protection, detection and throttling of the circuit or non-electrical objects. Simply put, electrical appliances are electrical appliances or devices that connect or disconnect circuits or adjust, control and protect circuits and equipment.
Electrical appliances can be divided into high-voltage appliances and low-voltage appliances according to the working voltage.
Second, the definition of low-voltage electrical appliances
Low-voltage electrical appliances generally refer to electrical appliances that play the role of on-off, protection and control in circuits with AC 50Hz, rated voltage below 1000V and DC rated voltage below 1500V V.
I would like to remind you that some books say: "Low-voltage electrical appliances generally refer to electrical appliances with rated voltage below 1200V at 50Hz AC."? This is a normative statement. According to the definition of national standards, low-voltage electrical appliances generally refer to "electrical appliances with AC 50Hz and rated voltage below 1000V".
Third, the types of low-voltage electrical appliances
There are many types of low-voltage electrical appliances, with different functions, applications and structures, and different working principles. There are many classification methods for low-voltage electrical appliances.
Commonly used low-voltage electrical appliances are classified as follows:
1, according to the purpose and function classification
(1) Low-voltage distribution appliances
Mainly used in the main circuit of low-voltage distribution system. When the system fails, it can act accurately and work reliably, and has corresponding physical and chemical stability (dynamic stability, thermal stability, light stability, etc.) under specified conditions.
Commonly used power distribution appliances include: lighting switch, knife switch, transfer switch, load switch, isolating switch, circuit breaker, fuse, lightning arrester, integrated terminal appliance, etc.
(2) Control electrical appliances
It is mainly used in control loop and auxiliary circuit to control the power receiving equipment to work according to the expected requirements. It requires long service life, small volume, light weight, accurate and reliable operation and high operating frequency.
Common control appliances include: contactors, relays, starters, master controllers, electromagnets, transformers, proximity switches, transfer switches, sensors, etc.
(3) starter
The starting principle of various starters of three-phase asynchronous motor is based on relay logic control principle, which is composed of switching electrical level protection appliances. The relay logic control circuits (systems) that realize these starting modes are collectively called starters in national standards, including star-delta starters, autotransformer decompression starters, soft starters (solid-state decompression starters), variable resistance starters (H-class starters) and so on.
(4) Industrial automation equipment
Industrial automation equipment is a general term for many automation products. Automation equipment automatically completes the tasks of workflow according to the set instructions or procedures without human intervention. It can include edge controller, programmable logic controller (PLC), universal frequency converter, soft starter, sensor, etc.
Hainan distribution box
2. Classification by operation mode
(1) Automatic electrical appliances
Depending on the change of its own parameters or the action of external signals, it can automatically complete the on-off and other actions of the circuit, such as contactors and relays.
(2_ Manual electrical appliances
Electrical appliances that are switched by manual operation, such as knife switches, changeover switches and buttons.
3, according to the presence or absence of contact type classification
(1) Electrical appliances with contacts
By using the on-off switching circuit of contacts, the advantages of electrical appliances with contacts are reliable action and good mechanical strength, but the disadvantages are slow action speed, high power consumption, low sensitivity and large volume, and easy wear of mechanical parts, such as contactors, knife switches and buttons.
(2) Contactless electrical appliances
The electrical appliance without mechanical contact uses the switching effect of electronic components to realize the on-off control of the circuit. Its advantages are fast action speed, high operating frequency, low power consumption, high sensitivity, small size, light weight, long service life and strong function, but its disadvantages are that it cannot achieve ideal electrical isolation, poor overload ability, poor temperature characteristics and poor anti-interference ability. Such as proximity switch, Hall switch, electronic time relay and solid state relay.
(3) Hybrid electrical appliances
In order to foster strengths and avoid weaknesses, contact and contactless electrical appliances are used together, such as hybrid relay with transistor relay as sensing element and contact relay as executing element.
4, according to the working principle of classification
(1) Electromagnetic appliances
Electrical appliances that operate according to the principle of electromagnetic induction, such as contactors, relays and electromagnets.
(2) Non-electric control appliances
Electrical appliances, such as change-over switches, travel switches, speed relays, pressure relays and temperature relays, which operate by external forces (manpower and mechanical forces) or non-electric signals (such as speed, pressure and temperature).
5, according to the working voltage type classification
According to the type of working voltage, low-voltage apparatus can be divided into AC electromagnetic low-voltage apparatus and DC electromagnetic low-voltage apparatus.
6. Classification by application industry and occasion
According to the working conditions, low-voltage electrical appliances can be divided into general industrial electrical appliances, general electrical appliances, distribution electrical appliances, traction electrical appliances, explosion-proof electrical appliances, vacuum electrical appliances, chemical electrical appliances, mining electrical appliances, aviation electrical appliances, ship electrical appliances, building electrical appliances, agricultural electrical appliances, smart home electrical appliances and so on.
Hainan transformer
7, according to the classification of low-voltage electrical appliances.
According to the model of low-voltage electrical appliances, low-voltage electrical appliances can be divided into knife switch H, fuse R, circuit breaker D, controller K, contactor C, starter Q, control relay J, main electrical appliance L, resistor Z, rheostat B, regulator T and electromagnet M.
Common low-voltage appliances according to their models.
8, according to the protection form classification
The first type of protection, the second type of protection,
9. Classification by IP protection level
According to the IP protection level, it is divided into indoor appliances, outdoor appliances and control equipment.
Today, the sharing of basic knowledge of low-voltage electrical appliances, such as the definition of electrical appliances and low-voltage electrical appliances, and the classification of low-voltage electrical appliances, is over. If you think it is helpful to your work, please like it and collect it! Please pay attention to me! Wonderful content, full of dry goods to share regularly, don’t miss my sharing!