Solid Insulation Ring Main Unit Becomes New Main Force of Intelligent Distribution Network

The position and role of the power grid in the human economic production and life are more and more important. The power grid is becoming one of the most active areas of global innovation activities. The strong and environmentally friendly smart grid will provide solid guarantee for the sustainable development of mankind and build a strong environmental protection. Smart grids have also become one of the most important innovation tasks facing humanity today. The distribution network is in an important position in the power grid, and it is an important task for distribution technology suppliers and distribution network construction companies to carry out strong technological innovation and accelerate the pace of building a strong and environmentally friendly smart distribution network. The ring network cabinets that were born in the 1970s provided new power for the distribution system. The distribution technology suppliers and application units have carried out continuous innovation and application promotion for the ring network cabinets for decades. The most significant innovation and upgrading has played an increasingly prominent role in the distribution network system.

With the continuous advancement of science and technology, human beings are demanding more and more power distribution products. Environmental protection, energy conservation, intelligence, maintenance-free, high reliability, and low cost have become the development direction of RMUs. In this context, Solid insulation ring network cabinet came into being. After entering the 21st century, several Chinese national enterprises with invention and creation capabilities pioneered the new product of solid insulated ring main unit in China, providing new technical support and products for the construction of a strong and environmentally friendly smart distribution network in the new era. Protection. After more than five years of active promotion and application, solid-insulated RMUs are entering a stage of large-scale application in China, and have become the new main force for the construction of a strong and environmentally friendly smart distribution network.

Development history of RMUs RMUs (Ring Power Supply Units, RMUs) first appeared in 1978 when German Driescher exhibited the world’s first SF6 RCH at Hannover Messe, and since then many companies have developed Its own unique ring network cabinet.

The new ring network cabinet is used to divide the load current, breaking short-circuit current and transformer no-load current, certain distance from the charging current of overhead lines and cable lines. It plays a role of control and protection, and is an important switch for ring power supply and terminal power supply. equipment. The core components of the RMU are load switches and fuses, which have the advantages of simple structure, small size, low price, improved power supply parameters and performance, and power supply security. RMUs are widely used in terminals of urban power grids. The power distribution mode is flexible and expandable, and quickly enters into large-scale applications. As a result, it has achieved great development in recent years.

With the rapid deployment and application of RMUs, users have put forward new requirements for RMUs. With the advancement of related technologies, the design, production and manufacturing technologies of RMUs have also been continuously developed and improved. The medium is becoming more and more abundant, and the voltage level covered by it is further broadened.

The insulating medium of the RMU is subjected to air insulation, mixed air and SF6 gas insulation, full SF6 gas insulation, and finally solid insulation.

Air-insulated ring main unit. This ring main cabinet is mainly air-insulated, the main switch adopts gas-producing type, air-pressure type or vacuum load switch, the load switch has side-mounted and positive-mounted, and the operating mechanism is installed in the front. The air-insulated RMUs are large in size. If the main switch is a vacuum load switch, an isolation switch must be added before designing the load switch.

Air and SF6 gas hybrid insulated ring main unit. The product main switch is generally selected SF6 load switch, designed to be placed in a fully sealed epoxy or stainless steel housing, filled with low pressure SF6 gas as insulation medium and arc extinguishing medium. Other high-voltage live parts such as a busbar, primary connection cable, voltage/current transformer, and lightning arrester are installed in the air. The air and SF6 gas hybrid insulation ring main unit has excellent electrical performance. The size of the switch cabinet is much smaller than that of air-insulated RMUs of the same type, and the three-station position can be achieved. The switchgear is fully functional, convenient to combine and easy to implement distribution network automation.

SF6 gas fully insulated ring network cabinet. The product is sealed with a high-voltage live conductor (three-station switch and connecting bus, etc.) in a stainless steel housing filled with low-pressure SF6 gas, using SF6 gas as the insulating and extinguishing medium. Stainless steel shell strength, corrosion resistance, heat dissipation and reliable grounding, can guarantee personal safety. To facilitate maintenance and replacement, the operating mechanism and high-voltage current-limiting fuses are installed in the air. The ring network cabinet also uses prefabricated silicon rubber insulated cable terminations to achieve cable insertion, which reduces the volume and improves the convenience of installation and the safety of maintenance.

Solid insulated ring network cabinet. Around 2007, domestic enterprises took the lead in the introduction of solid-insulated RMUs. The ring network cabinet eliminates the application of pressure vessels. The internal insulation and arc extinguishing of the switch body adopts vacuum medium. The external insulation adopts the insulation cylinder to solidify the switch components, and each circuit is connected by a closed bus. The insulating cylinder adopts the technology of solid sealing pole, organically combines the vacuum interrupter, the main conductive circuit and the insulating support, and realizes a fully insulated, fully sealed and maintenance-free structure. The insulating tube is made of epoxy resin and the busbar is encapsulated with silicone rubber. This structure effectively reduces the corrosion of the power supply body due to the isolation of air, moisture, dust, and hot and cold gas sources.

The solid insulated ring network cabinet was first proposed by Beijing Shuangjie Electric Co., Ltd. and it was successfully developed in 2 years and 7 months. It fills the domestic gap and has won international invention patents and four domestic invention patents. Other domestic companies also One after another introduced this product.

The ideal product for building a strong, environmentally-friendly, smart distribution network The new features of modern distribution networks are safety, environmental protection and intelligence, while the solid-insulated RMUs use pole-based sealing technology to eliminate the use of SF6 pressure gas in safety, intelligence, and flexibility. The environment, environmental protection, and harsh environment are all significantly higher than those of the traditional RMUs, and are very suitable for the construction of a strong smart grid that China is currently advancing vigorously.

The safety of equipment is an important basis for the safe and stable operation of intelligent distribution networks and reliable power supply to society. At present, the most commonly used inflatable ring network cabinet is the SF6 gas ring network cabinet. With sulfur hexafluoride as the insulating medium, in the actual operation process, leakage problems are often encountered, causing great hidden dangers and dangers to the operation of the switch. Relatively high-pressure GIS equipment is centralized and easy to manage. Inflatable ring network cabinets are widely distributed. It is difficult to perform full-scale supervision and management in actual operation, and it also brings hidden troubles to operation. The solid insulated ring main cabinet has completely eliminated the SF6 gas and the corresponding air box components in terms of structural principle. The insulating sleeve is used to solidify the switch parts, and the closed buses connect the various circuits to realize totally-enclosed full insulation. In terms of manufacturing, phases and phases are separated; from the electrical point of view, there is no short circuit between phases. It does not have pressure air boxes, pressure relief valves, anti-skid parts, etc., and it is truly maintenance-free.

Strong is the foundation and guarantee of smart grid. Compared with SF6 RMUs, solid-insulated RMUs have outstanding resistance to harsh environments, and have obvious advantages in harsh environments such as severe cold, high altitude, humidity, and strong winds. In the event of a weather of minus 40 degrees, SF6 in the SF6 RMU will liquefy, and the air pressure in the air box will also decrease, resulting in a decrease in insulation and arc extinguishing performance. In the high altitude position, the SF6 RMU will automatically expand due to the reduction of atmospheric pressure, causing air leakage and short circuit. Solid Insulated RMUs have absolutely no concerns in this regard. The solid insulated ring main cabinet is completely enclosed by the entire mechanism and there are no transmission parts outside, so it can be used with ease in a strong windy environment. In the coastal or high-humidity areas, RMUs are most afraid of rust caused by springs, gears, etc., resulting in unusable equipment. The solid-insulated RMUs pass through salt spray test chambers to imitate rust tests under conditions of high salt and high humidity. There will be no rust in the year or 30 years.

As a major innovation in transforming the development mode of the power grid, the smart grid also imposes stringent requirements on environmental protection. At present, more than 90% of the medium voltage full-enclosed ring network cabinets rely on SF6 gas as the insulating medium. This gas will inevitably leak and discharge in the process of inflating, running, and recycling, and become a major source of pollution in the atmospheric environment. Countries around the world have legislation to reduce or even prohibit the use of SF6 in power equipment. The solid insulated ring network cabinet is totally independent of sulfur hexafluoride gas from the principle of manufacturing, and provides a basic guarantee for the emission reduction and environmental protection in the field of distribution network equipment, which is in line with the requirements of smart grid construction.

The automation of distribution network automation control must achieve electrical control. Inflatable ring network cabinets are not the same as the manual and electric structures. Changing the manual mode to the electric mode is extremely difficult. At present, many inflatable SF6 ring network cabinets can not meet the needs of automation of distribution network transformation. The solid insulated ring network cabinet is extremely intelligent, and the site can be connected to the PT power supply according to the user's needs. The cable connector can realize on-line monitoring, giving the user the temperature value at the scene, at the same time the data arrives at the control terminal, the operation and maintenance is strengthened, and many practical problems are solved for the user. Solid insulation ring network cabinet load switch instantaneous breaking, to provide protection for multi-level distribution automation.

After 5 years of design, manufacturing capacity enhancement and small-scale application, the solid insulated ring main unit has received the attention of all parties and gained valuable first-line engineering application experience. In 2010, Tibet’s power supply bureaus purchased 30 solid insulated ring network cabinets produced by Beijing Shuangjie Electric Co., Ltd. in the transformation of the old city power grid. There have been no security accidents in use for more than two years, creating a high-risk ring network cabinet. The miracle of stable operation in the region. Solid Insulated RMUs are fully adapted to the climate and environment of the plateau. Compared with traditional SF6 RMUs, they have obvious advantages in the ability to withstand harsh environments such as high temperatures.

Recently, solid insulated ring network cabinets were included in the National Grid Corporation's document No. 1285 and the State Grid Corporation's "Twelfth Five-Year Plan", and became the corporate standard of the State Grid Corporation of China, which stipulates that the newly-insulated RMU investment in the solid insulated ring network cabinet To reach a certain proportion. On the other hand, the domestic solid insulated ring main cabinet manufacturing enterprises represented by Beijing Shuangjie Electric Co., Ltd. have already possessed strong R&D and manufacturing capabilities and are at the forefront of the world.

The solid-insulated RMUs in China's power distribution market are entering a period of large-scale deployment and will play an outstanding role in the construction of smart distribution networks, becoming the emerging main force for the construction of a strong environmental protection smart grid.