RCCN WeChat QrCode
Mobile WebSiteThe electrical discipline is still one of the thriving sciences. With the rapid development of the national economy and the modernization of national defense construction, more and more demands are placed on electrical appliances. At present, the structure and working principle of electrical appliances are constantly improved and innovated, and the variety and specifications are one of its characteristics. So what is an electrical appliance? All powered appliances can be collectively referred to as electrical appliances.
In terms of voltage level, the highest working voltage has been developed to above 765kv, and prototypes of 1500kv ultra-high voltage electrical equipment have also been developed, with a minimum voltage of a few volts or less.
In terms of current rating, the maximum operating current reaches tens of thousands of amps, and the minimum operating current reaches mA or less electrical equipment or components.
In terms of power frequency, well-known DC and 50 Hz or 60 Hz industrial frequency AC power sources are still widely used. In addition, low-frequency, ultra-low frequency, intermediate frequency, high-frequency ultra-high frequency and pulse power supply electrical components and devices are also widely developed and applied.
At present, the structural size of electrical equipment or components has grown from half a match size to a huge number of buildings. It is of practical significance to rationally organize the production and use of electrical appliances, scientifically and reasonably divide the voltage and current levels, and reduce the specifications and models of the series products as much as possible. It is very important to develop "combined", "building blocks", "standard units", and parts and components, and interchangeable electrical appliances or components. Especially in the current economic reform process, it is very important to strengthen macro-lead and actively carry out scientific and academic academic exchange activities of disciplines. In this way, we can mobilize the various disciplines to cooperate with each other and learn from each other.
2, high voltage electrical appliances
The development of high-voltage electrical appliances is closely related to the development of transmission and distribution networks. At present, power plants of 2 to 3 million kw have emerged, and large-capacity power stations of 10 to 12 million kw are inevitable trends, such as the Yangtze River Three Gorges Water Conservancy Project and the Southwest Water Conservancy Project. However, small and medium-sized power stations with small rivers are also being built everywhere. In order to economically transmit electrical energy, it is one of the important methods to increase the operating voltage of the transmission line. To this end, there will be a series of technical problems waiting for electrical scientists to study and solve. For example: 1) the limit working voltage and current of various electrical appliances, that is, the study of the ultimate economy and possible output capacity; 2) the study of overvoltage protection, study the causes and hazards of overvoltage generation, and thus adopt corresponding restrictions, reduction or elimination. The measure of overvoltage is very meaningful. For example, the amount of copper used in a 500kv transformer is almost as small as the insulation weight. It can be seen that the study of reducing the overvoltage is of practical significance for reducing the insulation withstand voltage level. At present, there are methods to limit the distribution of voltages in the range of 1.5 to 2.0 times, 3) study of internal insulation free discharge, anti-aging and dirt, and study of long-gap air external insulation discharge characteristics; 4) arc The new principle of extinction and the study of new media. For example, vacuum switches, sulfur hexafluoride, etc., as well as traditional methods to increase compressed air up to 150 atmospheres; 5) research on new principles and new structures. For example, capacitive voltage transformers, photoelectric current transformers (magneto-optical effect, optical pulse repetition frequency modulation, etc.).
In addition, due to the successful development of high-voltage, high-current thyristor components, it provides conditions for the development of DC transmission grids. To this end, the requirements for switching the switch and electrical equipment of the DC transmission grid are proposed. At present, China has adopted a DC power supply system of 22kv or above on the electrified railway line, and has a test circuit with a voltage of 500kv in Shanghai and Xi'an. Generally speaking, it has moved from trial type to operational type in China. At present, many scientists have made new progress in theory and technology. There are already ultra-high DC transmission grids running around 1000kv in foreign countries. This system has a relatively large economic value for over-distance transmission.
The research on the flexibility and the usability of high- and low-voltage switchgear is also a topic of great interest.
The automatic reclosing device that automatically disconnects the short-circuit fault and then automatically closes is also a subject of practical value and economic benefit. The leakage prevention and maintenance of sulphur hexafluoride and compressed air and vacuum switches are also important issues to be solved. Oil circuit breakers are still in use.
3, low-voltage electrical appliances
Low-voltage electrical appliances are the main electrical equipment for low-voltage power supply and electricity use. In most cases, it is installed in a control panel (or cabinet) for use as a complete set of appliances. The appliance (or component) is also used alone in individual cases. The low voltage switch is one of the main products in the field of low voltage electrical appliances. The current key technical issue is to improve the service life and reliability issues. This point has been taken seriously at home and abroad. It involves electromagnetic structure and theory, mechanism theory, technology and material technology, as well as impact vibration and wear resistance of various moving parts (such as springs, short-circuit rings, contacts, etc.). For example, the current short circuit of the AC electromagnetic switch is made into an in-line type, which is one of the effective methods to improve its service life.
Nowadays, in the civil buildings, new automatic switches have been used to replace the traditional knife-switches-fuses, especially when used on buildings with frequent overload or short-circuit faults. Although the investment is slightly higher, it can not only improve the quality of the power supply, but also save a lot of fuses. At the same time, recovery after failure can be*. Therefore, the development, promotion and application of low-voltage electrical appliances are very important.
The emergence of new components such as semiconductors and thyristors, combined with electromagnetic devices, can be used to make automated devices with various functions, which will be widely used in the national economy, national defense and life. For example, medium-frequency power supply stationary devices for various purposes replace rotary motors (devices that have been manufactured for several hundred watts to tens of thousands of kilowatts), magnetic semiconductor devices, semiconductor switches, magnetic semiconductor regulation and stabilization devices, and the like. In order to comprehensively solve the above technical problems, it is often necessary to develop electrical equipment such as "composite", "building block" or standard unitization and component generalization. This is a new trend that is currently needed or already under intense research and development.
Household appliances are another new technical field for low-voltage electrical appliances. Technical indicators in terms of aesthetics, application, noiselessness, safety, power saving, excellent functions, and ease of maintenance and use should be met as much as possible in order to be highly competitive in the market, and to enter foreign markets and be subject to thousands of households. welcome.
Due to the successful development of large-scale and medium-scale integrated circuits, micro-machines and electronic appliances have been widely used in many aspects. This has a great impact on the miniaturization of electrical appliances, instruments and meters. Therefore, many samples of weak electrical appliances, micro electrical appliances, and instruments and meters have been developed.
Despite this, the current domestic and international magazines have introduced more articles on electrical basic theory and electromagnets. The application of magnetic amplifiers has been improved, especially in terms of electrical isolation and high-precision measurement and control of the primary and secondary sides, which are incomparable to semiconductors and other devices. The exact calculation method of the air gap permeability gδ=f(δ) and the derivative dg8/ds of the electromagnet is not completely solved by the arc extinguishing theory and calculation method. It is still approximated by *experience data or formula. Finally, it is still solved according to the * test.
4, electrical materials
Electrical materials mainly include insulating materials, conductive materials, magnetic materials, and semiconductor materials.
Insulating materials have been developed in the synthesis of new materials such as high temperature resistance, pressure resistance, infrared radiation, and ultra-low temperature. Therefore, an enameled wire having a high temperature resistance of 200 ° C has been widely used, and an enameled wire having a high temperature resistance of 250 ° C has also been developed. The research work on aluminum-based copper has been applied in some electrical equipment.
At present, there are many new varieties of magnetic materials. The high-quality low-coercivity alloy steel sheets can be rolled into a thickness of 0.1 mm, and the permanent magnet materials with high coercive force, such as br=12000gs, hc=3000oe, and br=6000gs. Magnetic ceramics with hc=6000oe have also been developed.
Further, a heat-sensitive magnetic core, a magnetic bubble, a filter element made of a magnetic single crystal, or the like. High magnetic permeability and high strength magnetic materials are also under development.
Semiconductor materials manufacturing processes continue to improve, transistor, thyristor, turn-off thyristor components, triacs, thermal, magnetic, gas sensitive, force sensitive, photosensitive and other special semiconductor devices have been developed. Medium and large-scale integrated circuits can skillfully implement various control logic functions, making automation of production processes easier to implement.
