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2020

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02

Power Capacitors - Development Trend of High Voltage Electrical Appliances in China


1. Combination and complete sets of electrical appliances have emerged to meet the needs of small size, small footprint, high performance, and high reliability. In addition to switchgear, FC cabinets, and multi-layer cabinets, various combinations such as load switch fuse combination capacitors, high-voltage contactors fuse combination appliances (used for FC cabinets), load switches, drop fuses, and lightning arrester combinations, as well as lightning arresters, isolation switches, voltage and current inductors, have emerged, and have developed into advanced types of combination complete devices, such as gas filled cabinets (C-GIS) and fully enclosed combination appliances (GIS), And the entire substation combination, such as prefabricated substations (including box transformers and high and low voltage electrical appliances).  
2. Large capacity and high parameters Due to the rapid growth of modern daily electricity consumption, the increase in industrial and agricultural electricity consumption, and the formation of high-voltage and large capacity power grids, the capacity and various parameters of high-voltage electrical appliances are required to be rapidly improved. At present, the rated current of the main power transmission and distribution equipment has been increased from 1000A to 2500A to 4000A, and the short-circuit current has been increased from 16-20kA to 31.5-50kA, or even higher. The number of single pole fractures in the 550kV circuit breaker has been reduced from 4 to 2, and the development of single fractures is being intensified. If the main power transmission and distribution voltage in our country cannot be rapidly increased, then the demand for large capacity and high parameters of high-voltage electrical appliances in our country's power grid will not decrease (the emergence of higher transmission voltage can unlock some loops of the subordinate distribution voltage to reduce the short-circuit current of these power grids).  
Due to the development of computer and sensor technology, as well as the improvement of power grid automation, the demand for intelligent functions of high-voltage electrical appliances is more urgent. The combination of strong current equipment and advanced weak current technology can significantly expand the functions of high-voltage electrical appliances, providing better conditions for grid automation, telecontrol, and online detection. The traditional electromagnetic relay protection devices, electrical instruments, and control devices with large volume, heavy weight, and single function will be replaced by multifunctional computers and sensors.  
4. Minimal and maintenance free products. With the widespread use of excellent insulation and arc extinguishing media such as SF6 and vacuum in high-voltage capacitor products, as well as the implementation of production processes based on advanced high-tech (such as CAM), the maintenance cycle of products can be extended to 10 years, and even the product is maintenance free for life. And with the development of electronics and information technology, online detection technology is becoming more practical, and user departments have the conditions to achieve the transformation from fault maintenance to condition based maintenance. The operation and maintenance will also implement "fewer people, higher efficiency, safety, and reliability". In the next decade or so, there will be a significant development of products with minimal or no maintenance, and they will gradually occupy a certain position in the power system.
5. With the development of high voltage and large capacity power grids, excessive closing overvoltage and large short-circuit current in the system are detrimental to the safety and reliability of the power system. The selection of phase and closing of no-load lines for circuit breakers is possible today with the rapid development of electronic control technology. Selecting the phase to close the no-load line can minimize the closing overvoltage, which is very important for reducing the insulation level and improving the technical and economic level of the ultra-high voltage power grid. However, breaking large short-circuit currents (especially in cases of 50kA or above and large asymmetric currents) places a heavy burden on the breaking of high-voltage circuit breakers. If favorable phases can be automatically selected for breaking (i.e. shorter arc time and less than half wave), the breaking capacity of high-voltage circuit breakers can be improved, and the safety and reliability of the power system can be improved. Therefore, utilizing advanced electronic control technology to achieve phase selection, opening, and closing of high-voltage circuit breakers is one of the development directions of high-voltage circuit breakers.
6. In the high-voltage electrical industry, oil-free switchgear has been used as an insulation medium and arc extinguishing medium for over a hundred years, and is still widely used in transformers and switches to this day. However, the oil medium is a flammable and explosive substance, and it is not convenient for operation and maintenance. With the rise of SF6 and vacuum switches in switching appliances, the use of oil switches is decreasing (oil switches are no longer used at 363kV and above). It can be said that "oil free" is a development trend and an important equipment policy for switchgear.
However, oil switches are relatively economical and have rich experience in use, so in the next 10 years, there will still be a certain proportion of medium and high voltage switches.
The above are only recently developed switching appliances. There are also some medium to long-term potential developments in switching appliances, such as superconducting switches, static electronic switches (non mechanical switches), high environmental protection switches, etc. However, due to technological and economic limitations, it is difficult to achieve substantial start-up and development in the near future.
7. The trend of integration of various professions In the 1950s and 1970s, various professions of power transmission and transformation equipment, such as transformers, switches, lightning arresters, transformers, and secondary control protection measurement systems, had clear division of labor and clear boundaries, and each professional field did not interfere with each other. Nowadays, with the emergence of GIS, C-GIS, mechatronics integrated switchgear, and prefabricated substations, various specialties of power transmission and transformation equipment, as well as strong and weak current specialties, have been tightly intertwined and difficult to separate. Therefore, the high-voltage electrical equipment profession should not only adapt to the trend of integrated development among various professions, penetrate each other, break down professional barriers, but also penetrate and integrate with electronic technology, computers, and secondary systems. In summary, we should have a clear understanding of the development trends of the high-voltage electrical appliances listed above, especially for manufacturers engaged in the high-voltage electrical appliance industry. They should adapt to market trends, readjust their professional configurations, and moderately develop products with technical reserves to welcome the arrival of the new generation of high-voltage electrical appliances.
Conclusion: In terms of high-voltage capacitors, SG6 technology, vacuum technology, combination technology, etc. have been applied to the product structure and have basically achieved "oil-free". In the process, there have been introduced shell production lines, vacuum epoxy casting and injection molding equipment, mechanical processing centers, and so on. At present, based on market research, transaction rates in the high-voltage electrical appliance market, and customer feedback, domestic equipment with voltage levels of 500KV and below can meet domestic needs, and its technical parameters have approached or reached the national advanced level.