Low voltage electrical appliances
Low-voltage electrical appliances refer to electrical equipment that operates in circuits with AC voltage less than 1200V and DC voltage less than 1500V , serving functions of switching, protection, control, or regulation, as well as electrical equipment that uses electrical energy to control, protect, and regulate non-electrical processes and equipment. The vast majority of the load in the power system is supplied by low-voltage electrical appliances. Most of the various production machinery and equipment of power users are powered by low voltage. In the vast low-voltage power distribution and consumption systems, a large number of low-voltage electrical appliances are needed for control and protection.
Low-voltage electrical appliances are components or devices that can manually or actively connect or disconnect circuits according to external signals and requirements, in order to switch, control, maintain, detect, transform, and regulate circuits or non-electrical targets. Control electrical appliances can be divided into two main categories based on their operating voltage: AC 1200V and DC 1500V . In general, low-voltage electrical appliances can be divided into two main categories: distribution electrical appliances and control electrical appliances, and are the basic components of complete sets of electrical equipment. In industry, agriculture, transportation, national defense, and residential electricity consumption sectors, low-voltage power supply is mostly used; therefore, the quality of electrical components directly affects the reliability of the low-voltage power supply system.
High voltage electrical appliances
High-voltage electrical equipment is widely used in power systems, but in my country, due to the lack of a clear standardized definition, the meaning of this term varies in different contexts. This section introduces the concept presented in higher education textbooks and is generally accepted.
Overview
High-voltage electrical equipment is widely used in power systems, but in my country, due to the lack of a clear standardized definition, the meaning of this term varies in different contexts. This section introduces the concept presented in higher education textbooks and is generally accepted.
1. Definition of high voltage electrical appliances
The internationally recognized dividing line for high-voltage electrical appliances is 1kV for AC ( 1500V for DC ). Appliances above 1kV are considered high-voltage, while those at 1kV and below are considered low-voltage. High-voltage electrical appliances are devices used in high-voltage lines to perform closing, opening, maintenance, control, regulation, and measurement. Typical high-voltage electrical appliances include switching devices, measuring devices, and current-limiting and voltage-limiting devices. However, transformers are sometimes also included in high-voltage electrical appliances (e.g., by the High-Voltage Electrical Appliances Subcommittee of the Chinese Electrotechnical Commission).
The Xi'an High Voltage Electrical Apparatus Research Institute was established in 1958 with the approval of the Ministry of Machine Building, based on the planned central laboratory of the Xi'an Switch and Rectifier Factory. At that time, the institute was specifically designed to conduct research and development and experimental services for the switch, porcelain, capacitor, insulation and transformer factories under construction in Xi'an, covering various specialties such as switches, transformers, maintenance electrical appliances and measuring electrical appliances. Therefore, it was named the High Voltage Electrical Apparatus Research Institute, and this name has been used ever since.
2. Classification and Functions of High-Voltage Electrical Appliances
2.1 Switchgear
It is a high-voltage electrical device primarily used to switch normal and faulty circuits on and off, or to isolate power sources and achieve safe grounding.
1 ) High-voltage circuit breakers: They can not only close and open normal load currents (including air transformers, air lines, air cables, etc.), but also close fault currents. In the event of a short circuit fault (or other abnormal operating conditions, undervoltage, overcurrent, etc.), they can automatically trip and automatically reclose. Therefore, high-voltage circuit breakers are multi-functional automatic switches.
2 ) Fuse: Commonly known as a safety device. It automatically melts and breaks the circuit when the load current exceeds a certain value or when a fault current occurs. It is divided into current-limiting fuses and ejector fuses.
3 ) Load switch: It can switch the load current (including capacitive and rational load current), and sometimes it can close the short circuit current but cannot interrupt the short circuit current.
4 ) Contactor: A contactor is a device that can close, open, and handle normal and regular overload currents with only one rest position, without manual operation. It is generally used for frequent control of large electrical equipment (such as large motors).
5 ) Isolation switch: Used to isolate circuits or power sources. When closed, it can carry normal current and regular short-circuit current. Sometimes it can interrupt very small capacitor current and no-load current of transformers with small capacity. Sometimes it can switch bus switching current.
6 ) Grounding switch: Used to perform maintenance grounding on equipment or lines under maintenance.
Sometimes it is required that load switches, contactors, and grounding switches close the short-circuit current.
7 ) Recloser: A switchgear that can perform opening and closing operations in a predetermined sequence in the conductive circuit, and then automatically reset, open or close, with its own control and protection functions (without external power).
8 ) Sectional switch: A switching device that can actively detect line faults and recall the number of times the line fault current is interrupted, and automatically trips the circuit breaker when there is no voltage or no current after the set number of interruptions are reached.
Some sectionalizers may have the ability to close short-circuit current (active reclosing function) and to interrupt and close load current, but they do not have the ability to interrupt short-circuit current.
2.2 Measuring electrical appliances
1 ) Current transformers: Used to convert and measure the current in lines and busbars for metering and maintenance. Traditional current transformers are oil-paper insulated electromagnetic types, while epoxy-cast and SF6 current transformers are now available, and the latest are photoelectric current transformers. To meet the needs of mechatronics equipment, linear current sensors are now available.
2 ) Voltage transformers: Used to measure line and bus voltage for metering and relay maintenance. Traditional voltage transformers are oil-paper insulated electromagnetic types. Currently, lightweight and compact capacitive voltage transformers are used in high-voltage and ultra-high-voltage ranges. Internationally, photoelectric transformers have been developed and are being commercialized.
2.3 Current-limiting and voltage-limiting electrical appliances
1 ) Reactor: It is a choke coil used to confine fault current, and is made of insulated wire. Now it is also made by epoxy casting, which is small in size and has higher insulation and mechanical strength.
2 ) Wave trap: It is also a type of inductor, primarily used in carrier communication to restrict high-frequency carrier waves from entering the substation.
3 ) Surge arresters: Used to restrain overvoltages and protect electrical equipment in the power system from damage caused by atmospheric and internal overvoltages; they are energy dissipation devices. The simplest type is the protective gap, followed by tubular surge arresters, valve-type surge arresters, and magnetic blow-out surge arresters. The newest type is the zinc oxide surge arrester, which has relatively good protective characteristics.
Note: Current-limiting fuses are also a type of maintenance electrical appliance that quickly limits current (amplitude).
3. Basic Functional Requirements of High Voltage Electrical Appliances
Various indoor and outdoor high-voltage electrical appliances within the power system should be able to withstand normal and abnormal voltage and current effects, as well as various environmental factors, without damage. Therefore, they are required to possess the following functions.
3.1 Electrical Functional Requirements
