Introduction to the Use Environment and Procurement Points of Inflatable Cabinets

The inflatable cabinet is a new generation of switchgear. The main switch can use either a permanent magnet mechanism vacuum circuit breaker or a spring mechanism vacuum circuit breaker. The whole cabinet is combined with air insulation and sulfur hexafluoride gas compartment, which is compact and expandable. , suitable for distribution automation. The inflatable cabinet has the characteristics of compact structure, flexible operation, and reliable interlocking. It can provide satisfactory technical solutions for various applications (especially places with harsh environments) and different user requirements. The adoption of sensor technology and the latest protective relay, coupled with advanced technical performance and light and flexible assembly scheme, can fully meet the different needs of users. The inflatable cabinet is suitable for small secondary substations, switching stations, box-type substations, residential quarters, industrial and mining enterprises, and large shopping malls in the power system, especially for airports, subways, railways and other occasions that require high power consumption.


Inflatable Cabinet


1. The use environment of the inflatable cabinet


1.1 Ambient air temperature: maximum 40°C, (24h average value does not exceed 35°C), minimum -25°C;


1.2 Altitude: no more than 3000m (coordinate with the manufacturer if it exceeds 3000m);


1.3 Air humidity: the average daily relative humidity is not more than 95%, and the average monthly relative humidity is not more than 90%;


1.4 The amplitude of electromagnetic interference induced in the secondary system shall not exceed 1.6kv.


2. Features of the inflatable cabinet


2.1 Cabinet structure: The inflatable compartment is made of 3~5MM thick stainless steel plate, which is welded by welding robot after CNC machine tool processing, with less welding deformation and good air tightness. The rest of the compartments are made of high-quality cold-rolled steel plate, which is bent by CNC After welding, it has the characteristics of high precision and good strength; each functional unit is an independent module, and the assembly is extremely convenient. Each sealed compartment of the cabinet is equipped with an independent pressure relief channel to maximize personal safety and equipment operation.


2.2 Applicable standards: GB/T 11022-2011 "Common Technical Requirements for High Voltage Switchgear and Control Equipment Standards"; GB/T 3906-2006 "3.6kV~40.5kV AC Metal Enclosed Switchgear and Control Equipment";


2.3 Protection level: IP67 for air-filled isolation; IP4X for low-voltage cabinet.


3. Key points for purchasing inflatable cabinets


China's terrain is higher in the west and lower in the east, with mountains accounting for about 33% and high-altitude areas accounting for about 26%. The average altitude of the Qinghai-Tibet Plateau is above 4000m, and the vast plateaus and basins to the north and east of it are mostly at an altitude of 1000m to 2000m. The climate in high-altitude areas is complex and diverse, and it is often attacked by humidity, condensation, salt spray and typhoons; in addition, after the development of the west, the industry and transportation are increasingly prosperous, which also makes the power grid switchgear extremely prone to pollution and corrosion. The traditional air-insulated switchgear used in the distribution network, limited by the environmental conditions, can no longer meet the requirements, and has begun to be gradually replaced.


Although the inflatable cabinet has only started in my country for a few years, it has gradually become a new choice due to its small footprint, high degree of intelligence, maintenance-free, and full working conditions. In recent years, Sichuan, Yunnan and Guizhou have successively organized several large-scale power grid switchgear renovations, changing the traditional 15-20 year update cycle into continuous and frequent updates. Especially for some newly started power grid projects, starting from the design source, choose to configure 12kV inflatable cabinets to meet the necessary conditions for normal application within a certain period of time. At present, there are more and more applications of inflatable tanks in the fields of metallurgy, petrochemicals, mines, development zones, urban rail transit and high-rise buildings.


4. Application status and selection of inflatable cabinets


4.1 Type selection

4.1.1 Mainstream selection of imported products

The cabinet type C-GIS is the most selected by users, accounting for about 70%-85% of the total demand; the second is the cylinder type, which is similar to GIS above 72.5kV. The selection is mainly focused on the top 8 products that dominate the market. For example, the C-GIS of some companies in Europe is quite eye-catching. It is not only suitable for the requirements of complex network nodes or user terminals, but also meets the needs of various secondary substations for the flexible use of compact switchgears, so that more and more users are interested in it. In addition, because the quality of my country's power grid is still not up to the international first-class requirements, the instability of the power grid requires C-GIS to increase the rated parameters and strengthen the insulation of the product. At present, the C-GIS used by users on the 10kV power supply network should choose 12kV Switchgear for rated voltage.


4.1.2 Mainstream selection of domestic products

Because C-GIS has extremely high requirements on process equipment and processing is very difficult, domestic enterprises have developed a batch of applicable cabinet-type C-GIS through introduction, digestion and cooperation, which not only passed the type test, but also entered mass production. Some have formed serialization, such as Xigao Institute, Xi'an Senyuan, Zhenjiang Longyuan, Tianshui Great Wall, Shanghai Tianling (see Table 2), Guangdong Shunde, etc., which adopt sealed pressure system and protection measurement and control technology, and apply insulation aging Online detection technology and temperature rise wireless sensing technology, new products that have improved the quality of C-GIS status monitoring and fault diagnosis technology, have received special attention.


4.2 Choice of structure

Due to the large differences in shape and structure of switch cabinets of different manufacturers and models, the selection principles of users also have their own emphasis. Among them, a common concern is that the user's busbar structure has restrictions on the overall structure of the 12kV C-GIS. Therefore, when purchasing, more attention is paid to products that combine and develop C-GIS technology with conventional switch technology. The busbar is easy to install on site, and will be determined according to its own busbar structure. According to the relative position among the three main modules of busbar, disconnector and circuit breaker in the primary main circuit, it can be divided into three types of structures:


4.2.1 Top, middle and bottom layout

This is the choice of using plug-in solid insulated busbar and inflatable busbar room + busbar connector structure, and its typical product is HS-X12 of Mitsubishi, Japan


4.2.2 Bottom, middle and top layout

This is the choice of using an inflatable busbar room + busbar connector structure. Its typical products are N2S from Shanghai Tianling and ZX1.2 from ABB. This arrangement is not very convenient to realize double busbars.


4.2.3 Rear, middle and front arrangement

This is the choice of using gas-insulated busbar and gas-filled busbar room + busbar connector structure, and its typical product is ALSTOM's WS


4.3 Choice of performance

4.3.1 Insulation level and volume

The foreign C-GIS determines the insulation level according to the IEC standard, and the withstand voltage value of the primary main circuit and the isolation fracture is lower than that of the domestic product, because the domestic product must meet the IEC standard and the national standard. The size difference of domestic and foreign products is also relatively large, and the domestic products have relatively large distances between phases, relative ground and creepage, and are larger in size and heavier in quality. Plateau users choose 5 types of products with high cost performance: Products using new solid interface insulation plug-in technology for connection of high-voltage components such as gas chambers, cabinets, voltage transformers and arresters. Use solid insulated busbars or inflatable busbar compartments + busbar connectors, and products that do not require vacuuming and inflating for on-site installation. Simplify the main wiring once, and there is no product with line-side isolating switch. Products that use a large number of current/voltage sensors, position sensors, density sensors, etc. Install the PT on the top of the switch cabinet, saving a PT cabinet product.


4.3.2 Current carrying capacity

The rated current of foreign C-GIS is generally higher. For example, the rated current of foreign busbars reaches 2500A, while that in China is basically 1250A. The main reason is that it is affected by the overall design level of the product, especially the heat dissipation design level, as well as the limitation of the current flow capacity of the insulated busbar and the cable connector itself. The current carrying capacity often affects the selection orientation of products.


4.3.3 Serialization

Large foreign companies started early, and after years of development, they have formed serialized products. The main switch can be either a load switch, a vacuum circuit breaker or an SF6 circuit breaker; Various needs of users. The domestically produced varieties are relatively single, and there is little room for choice. Some manufacturers still have time to serialize their products.


4.3.4 Manufacturing process

Chinese and foreign leading manufacturers have adopted modern processing equipment, processing technology and welding technology. For example, European products that use more SF6 gas have advanced gas filling tanks and first-class quality monitoring technology. The box-type shell is welded by robots, which has no air leakage and occupies a small area. Domestic mainstream manufacturers also rise up to meet the challenge, using advanced plate blanking, bending and welding equipment, the sealed box adopts thin stainless steel welding structure, and uses laser welding, helium mass spectrometer leak detection and other technologies to make the precision and rigidity of the sealed box Increased, the air leakage rate decreased. Therefore, the cabinet structure is developed into an armored cabinet with flexible combination and better performance. Each air chamber is independent. flexible.


5. Application effects and defects of inflatable cabinets


5.1 The effect of the application is remarkable

5.1.1 Strong Applicability

Western my country is affected by external environmental conditions such as high altitude, condensation, salt spray and pollution, and there are more and more construction projects that require high reliability, such as high-rise buildings with small space, concentrated industrial and commercial areas, and rail transit. C -GIS has become the best power distribution equipment. Not only does it not have the influence of the atmospheric state, but the cabinet-shaped shell is small in size, which saves the floor space, and is more coordinated and adaptable to the surrounding environment in terms of layout, size and appearance, so that the comprehensive economic benefits of engineering construction are very obvious. . C-GIS was selected in the upgrade and capacity expansion projects of urban networks in Kunming, Guiyang and Chengdu, and the operation brought good benefits.


5.1.2 Good installation performance

C-GIS combines various high-voltage components into several standard modules, which can meet the requirements of various main wiring and meet the needs of various application occasions through combination. It is transported to the site as a whole, hoisted in place as a complete set, and does not involve the treatment of SF6 gas during installation. It is also very convenient to increase the number of incoming and outgoing cables through the reserved cable socket for expansion, or add cabinets to expand to one or both sides of the cabinet. The high-voltage components are set in the box-shaped air-filled shell, which makes it easier to use cables as the introduction and extraction of the power supply, more convenient to connect and arrange with the transformer, and is not limited by space, making it easier to form a system.


5.1.3 Great safety performance

Because the conductive part of the main circuit of C-GIS is sealed in insulating gas such as SF6, and the high-voltage live conductor is sealed, it has the advantages of high reliability and suitable for frequent operation, which meets the requirements of large rated current caused by the sharp increase in load of the power grid substation. , Large short-circuit breaking current, frequent operation, low overvoltage and other technical requirements; it can also accurately receive and distribute electric energy, and implement effective control, protection and detection of circuits.


5.1.4 High maintenance performance

Because the various high-voltage components of C-GIS are either sealed with gas or sealed with metal, the parts have no corrosion or rust, and there is no influence on operation and conduction caused by them, and the workload for maintenance is very small. The vacuum circuit breaker used has long service life, stable performance, and maintenance-free or less maintenance.


5.2 The main flaws of the application

5.2.1 The connection between production and demand is not secure enough Some manufacturers are still at the level of the early 1990s. The production of 12kV C-GIS only replaces the 40.5kV components with 12kV corresponding components on the basis of the early 40.5kV C-GIS. The reduction in shape is not large, or even unchanged, and such products are inferior in comparison. The market price of 12kV C-GIS is too high, and it has not been accepted by users who do not necessarily use C-GIS. It is estimated that its comprehensive cost is 1.5 times that of normal cabinets, but most of them are still about 3 times, and the price is unacceptable to a considerable number of users. Many products are still in the incomplete development stage. For example, when compressed air is used as the inflatable medium, its pressure is much different from that of SF6, which may lead to changes in the selection of materials, which may lead to changes in the performance of the equipment. For another example, according to the national standard GB3906─1991, the highest level of product power supply continuity is LSCB2, and 50% of C-GIS still use single air chamber, so it is necessary to change to double air chamber.


5.2.2 Supporting services of manufacturers have not kept up Due to some 12kV C-GIS manufacturers exaggerating the performance of their products, coupled with the extension of the prescribed maintenance period and the difficulty of system power outage maintenance, some users have relaxed their maintenance and management, and the equipment runs with problems from time to time. Cabinet insulation is broken down. For the sake of competition, the manufacturers build technical barriers, which is understandable, but when users buy products, they only get a general-purpose brief instruction manual, and lack an authoritative 12kV C-GIS repair process guide , It hinders the improvement of the user's use and maintenance skills. There are differences in the types of equipment and accessories of different manufacturers, and it is difficult to distribute the spare parts and accessories used for maintenance. There are inherent deficiencies in quality.


6. Equipment transformation and prospect of inflatable cabinet


6.1 Prepare products for prefabricated substations

In recent years, more and more prefabricated substations have been used in the transformation of urban power grids and terminal 12kV substations in rural power grids in high-altitude areas in western my country, which is convenient for construction and installation, and does not require building houses to occupy too much land. Most of its technical parameters and functions, as well as C-GIS and other major equipment, are required in accordance with the national standard GB/T17467-1998, which promotes the progress of power grid technology and equipment, so it is very popular with the operation department. However, there are also some 12kV prefabricated substation high-voltage power distribution devices and integrated automation systems that use a common shell, or a set of shells to seal them up. The connotation of the main components such as high-voltage switchgear is far from the national standard GB/T17467-1998 larger. Now, users generally put forward new requirements for 12kV C-GIS mechanical life and electrical life. Therefore, its manufacturers must not only strictly select product design, quality control, and manufacturing levels; they must also follow the relevant national technical standards for the configuration of technical parameters, mechanical characteristics, and operating methods in engineering design. Improve the overall level of electrical engineering.


6.2 To provide intelligent products for grid automation

The pace of intelligent transformation of power grids in high-altitude areas in western my country is accelerating, and the configuration of switchgear in electrical engineering design has shown a strong sense of advancement. Last year, the number of customers who purchased intelligent C-GIS increased by 10% compared with the previous year. many. Users prefer products that can realize condition monitoring, establish computer-aided maintenance systems and fault diagnosis systems, because the operating parameters recorded by it can provide information to prevent malfunctions or maintenance measures, and help prevent sudden and expensive failures. However, the current C-GIS is still insufficient for the online monitoring function of condition maintenance, such as conductor temperature, opening and closing coil disconnection, internal insulation condensation, mechanical characteristics and partial discharge, etc., which need further research and development to adapt to distribution network automation And maintenance-free new requirements.


6.3 Produce more environmentally friendly products to increase social benefits

Since SF6, the commonly used aerating medium in C-GIS, is a greenhouse gas, its usage should be reduced as much as possible. Some companies have developed compressed air as the inflatable medium, and some mainstream manufacturers no longer use high pressure and use SF6 gas less than 0.25MPa (absolute value at 20°C), and some use N2 and SF6+N2 mixed gas. This is the direction of development, and it is reasonable to develop such special products as soon as possible. It is also necessary to reduce the size of the insulators of the electric field control components, improve the pouring process level, and overcome the problems in materials and processes as soon as possible. Insulating epoxy resins are also in urgent need of replacement, and the development of resins with low dielectric constant, heat resistance, and strength is accelerated. In addition, it is necessary to reduce the cost ratio of C-GIS to about 1.5:1 through modular design and specialized production.


6.4 Add special products for power grids in different regions

The 12kV power grid in high-altitude areas requires a dedicated C-GIS, and the common switchgear on the market obviously cannot meet the needs. Manufacturers are called upon to add some personalized product series suitable for various operating environments and various operating departments in addition to the standard series as soon as possible, and leave enough margin for the insulation of the switch cabinet, and even redesign the cabinet shape, so that there is no need to use it because of the switch cabinet. Under the limitation of the existing cabinet shape, the insulation measures can be improved, so the quality of the product can be better guaranteed. This kind of targeted product must have a great market. It is true that its content is relatively wide and its development is difficult, but with the development of modern power grids and scientific and technological progress, it is bound to usher in a relatively complete intelligent, dedicated and serialized C-GIS application and development.

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