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Discussion on the development of metal enclosed switchgear

Discussion on the development of metal enclosed switchgear

(Summary description)1.Overview of the country Metal enclosed switchgear (commonly known as switch cabinet) is the largest and most widely used distribution switch equipment. In the past ten years, especially after the start of urban and rural power grids, market demand, the incentive of foreign advanced products, private enterprises, Sino foreign joint venture into the rise, effectively promoted the development of domestic switchgear, product technology and production equipment have been greatly improved, its main features:

Discussion on the development of metal enclosed switchgear

(Summary description)1.Overview of the country
Metal enclosed switchgear (commonly known as switch cabinet) is the largest and most widely used distribution switch equipment. In the past ten years, especially after the start of urban and rural power grids, market demand, the incentive of foreign advanced products, private enterprises, Sino foreign joint venture into the rise, effectively promoted the development of domestic switchgear, product technology and production equipment have been greatly improved, its main features:

Information
1.Overview of the country
 
Metal enclosed switchgear (commonly known as switch cabinet) is the largest and most widely used distribution switch equipment. In the past ten years, especially after the start of urban and rural power grids, market demand, the incentive of foreign advanced products, private enterprises, Sino foreign joint venture into the rise, effectively promoted the development of domestic switchgear, product technology and production equipment have been greatly improved, its main features:
 
1.1 Product technology begins with international practice
 
A number of technical parameters, performance, quality and the international level of the equivalent or close to the product line. The general assembly structure, composite insulation, miniaturization of the main switch, high-quality composite materials such as tibnor etc.. More representative products, such as:
 
1)ANSEN developed GZS1 (KYN28-12) handcart cabinet series, 12KV, 630-3150A, 20-40KA. The structure features are available as: tibnor (multiple bending) shell, circuit breaker, mid cylindrical epoxy insulation tube phase insulation structure, multi touch left bundle plug circular spring.
 
2)XIGAO developed by the KYN port -40.5 hand cart cabinet, 40.5KV, 1600A, 31.5KA. The structure is characterized in that: the compound insulation structure is adopted, and the cabinet width can be up to 1200 millimeters, and the floor type hand cart can be used.
 
3)XIGAO developed by the KGN6-12 fixed cabinet series, 12KV, 1250A, 3l.5KA (3l50A, 40KA is in development). The client: assembly type structure, the floor type circuit breaker, composite insulation, knife type = three position isolation switch.
 
4)A number of development of the HXGN port -12 ring network cabinet series. 12KV, 630A, 20KA (50KA peak). The structure features are available as: using SF6 isolation load switch, and a three-phase switch is arranged in a longitudinal direction, and the majority of the bus arrangement, outlet using the load switch with fuse box.
 
In addition, there are many units are developing inflatable cabinet, and some have completed the test type inside such as inflatable cabinet high in the West and the development of the 40.5KV, 1250A, 25KA; some are design stage.
 
1.2 Using new technology and equipment
 
1)Processing technology and equipment in sheet metal processing has been a considerable part of the factory has CNC punching, shearing, bending equipment, or on the basis of the flexible manufacturing system; some factories are equipped with laser cutting machine, CNC machining equipment bus, improve the processing precision of the shell and the bus and the production efficiency.
 
2)Widely used epoxy resin automatic pressure gel technology (APG process) and advanced vacuum casting technology, including the selection of high precision and finish of the mold. Obviously improve the inner quality and appearance level of insulation parts.
 
3)The surface of advanced coating technology widely used, such as electrostatic spraying, flow coating and Dacromet technology, including the corresponding pretreatment process. The anti rust ability and appearance of new products.
 
1.3 The application of computer in the design and production of switch cabinet
 
1)The application of engineering design, including the panel opening, the two line layout, the shell and the other parts of the modification design, and some factories also extends to the NC machining programming, project quotation, etc..
 
2)The use of computer design (CAD), including three-dimensional modeling design, drawing the engineering drawing, interference check or simulation.
 
3)Analysis of product design for computer (CAE), the calculation software for the insulation of two-dimensional or three-dimensional electric field calculation and Optimization on stress components such as inflatable casing stress and deformation analysis, provide the basis for product design, reduce design errors.
 
4)Management of the production of switch cabinet with computer. Raw materials and other components, purchased in switch cabinet pieces of large volume, annual output of some big factories began to use computer logistics and production management software, and achieved good results.
 
1.4 Quality Assurance
 
Most factories have passed the certification of IS09000 quality management system. To create a good foundation for quality management, but the implementation is not the same. There have been a number of factories have achieved good quality management level.
 
In short, the switch cabinet industry has made remarkable progress, but compared with the international advanced level, there is a big gap, especially the product of independent innovation and development capabilities need to be further strengthened.
 
 
 
2 Foreign product overview
 
In accordance with the requirements of power system for the high availability of power equipment, maintenance, miniaturization and intelligent, the switch cabinet has made great progress in the past ten years:
 
2.1 The development of air insulation cabinet
 
2.1.1 The development of hand cart cabinet
 
In the circuit breaker in the cabinet body (height) in the main features of the built-in cabinet as a distribution of current movable switch cabinet advanced mainstream products, technical parameters of a switch cabinet for general 24KV and below, to 2500, 3l50A (4000
A forced air cooling), to 40, 50KA; its typical products such as:
 
1) ZSl ABB company, is the cabinet introduced earlier, the split phase insulation tube for vacuum interrupters insulation and mechanical support (VD4 type), D type three-phase busbar, vertical setting internal fault pressure relief channel, configuration of intelligent control unit REF542, its dimensions (width X X, 1250A, 3l.5KA, 650x1300x2200mm) with the following. In recent years, the cabinet ZSl plus new series of high reliability, with no maintenance of VMl type circuit breaker, with a sealed insulation structure of the permanent magnetic actuator, the mechanical life of up to one hundred thousand times. Further improve the technical level of the cabinet.
 
 
2) NXair type of Siemens, the phase splint insulation structure as the vacuum interrupter main insulation and mechanical support, the level of bus arrangement, internal fault pressure relief channel, configuration of SIPROTEC4 control and protection unit. Its outline dimension 800xl554x2200mm
 
 
3) PIX type of ALST0M, the phase composite insulation structure, compatible with vacuum circuit breaker (HVX) and SF6 circuit breaker (FPX), set the internal fault pressure relief channel, using DCX control unit and MiC0MPl2l protection relay, size 650xl405x2l30mm.
 
 
4) VISAX ALST0M, which is consistent with special Dian bus circuit breaker level three-phase longitudinal arrangement from the horizontal, vacuum interrupter with isolation contact, when opening the vacuum interrupter firstly, and then the isolation contact rotate 90 degrees to form a visible isolation fracture. Outline dimension 650xl460x2l50mm
 
2.1.2 The development of the fixed cabinet
 
Maintenance free or less switch, a variety of insulation technology more mature, Xian fixed type switch cabinet advantages, in recent years, the handcart cabinet mainly in Western Europe also appeared as a fixed cabinet distribution, such as:
 
1)AX1 ABB company, which is characterized in that the switch equipment with solid insulation encapsulation, circular bare copper busbar in triangular arrangement, all in the same way a back shell and is provided with the (internal) fault arc eliminator, internal arc generated within ten milliseconds of arcing grounding to eliminate arc discharge. The pressure from the internal fault of the channel; the interval between the bus by using a round spring contact connection, the cabinet can be compatible with SF6 circuit breaker (HX) and vacuum breaker (VMl) circuit breaker, bus side set three position isolation switch, feeder side isolation components; the size of 650xl050x2020mm.
 
2)FKI company (UK) of the Fclipse type, the main parameters for the 630-2000A, 25KA, as between a distribution and two power distribution products. The cabinet breaker three-phase longitudinal arrangement and horizontal arrangement of bus line, vacuum circuit breaker with monostable permanent magnetic actuator, a bus side knife type three position isolation switch, feeder side isolation element with internal fault pressure relief channel, size of 500xl125x2100mm.
 
2.1.3 The development of the two power distribution fixed cabinet
 
To meet the two requirements of the power distribution switch cabinet cabinet is basically fixed, its main features: parameter is not high, the rated current is dominated by 630A, 1250A, a thermal current is 20KA, a 25KA, rated voltage 12-24KV, a general 36KV; the main switch to isolate the load switch (including main load switch fuse box), there is a part of a circuit breaker. Typical product is:
 
1)SM6 company's ALST0M type, FLU0KIT company's ABB type, UNISWITCH company's VEI type, UNIFLU0RC company's SCHNEIDER type and so on series. Its main features are: three main switch along the longitudinal arrangement is consistent with the level of bus arrangement; load switch with gas compressor, early in the last century the majority, in mid 90s after the SF6 three position load switch, at present, the products have the following changes: stainless steel shell to replace epoxy resin casting shell for circuit breaker; the series three-phase cabinet in the longitudinal direction, the circuit breaker and current transformer or sensor combination, compatible with vacuum circuit breaker and SF6 circuit breaker, and configure the corresponding intelligent control and protection unit. Contour dimension (load switch cabinet) 375-500xl000x1635mm.
 
2)ZS8 company's ABB type, the series is a box type cabinet, bus has a separate compartment. Using a new type of direct acting pneumatic isolation load switch (C4 type), three-phase switch arrangement, positive charged body insulation encapsulation, selection of VD4/VM1 circuit breaker, for control and protection of bus breaking contact and wire spacing (1250A) and its dimensions: load 600x800xl900mm, circuit breaker cabinet cabinet 650xl000xl900mm switch.
 
2.2 Development of gas insulated tank
 
The cabinet is developing very fast inflation over the past ten years, the main products are: increased technical progress * and safety, especially the sealing elements and * safety and internal fault conditions.; to achieve scalability by coupling different from SF6 gas field processing, intelligent control; configuration a protection unit and a variety of sensors, control, measurement, protection and degree of distribution automation functions; performance, structure, process and appearance improvement and innovation. Gas filled cabinet products are also developed at the two levels of distribution and the two power distribution, and are described as follows:
 
 
2.2.1, primary power distribution cabinet
 
 
A distribution of gas filled tank main technical parameters: 12-40.5KV, 1250-2500A, 25-40KA; in general, the circuit breaker main switch, requires a double bus scheme; the typical products are:
 
 
1) the main characteristics of the series of products ZX2 ABB company are: single, double bus level arrangement, the use of plug-in bus connector is directly connected between the cabinet and the cabinet bus, selected straight three position isolation switch, horizontal vacuum breaker, combined current and voltage sensors, cone type cable interface and internal fault the pressure relief device and channel configuration, REF542 control and protection unit pressure and displacement monitoring sensor. The outline dimension is 600xl7l0x2300mm.
 
 
2) SIEMENS-p.htm "target=" _blank "title=" SIEMENS PDF "data sources and main features of the series of products NXPLUS >SIEMENS company are: single bus level arrangement, component connection method of the cabinet and the cabinet bus connection, does not involve SF6 gas, vacuum circuit breaker level layout, selection of rotary three position isolation the switch and the interface of the outer cone or cone type cables and internal fault pressure relief device and channel, voltage and current transformer (SF6 external gas outdoor), configure the SIPR0TEC4 integrated protection and control unit and pressure, displacement sensor etc.. The outline dimension is 600x1600x2450mm.
 
 
2.2.2, two electric power distribution cabinet
The two parameter distribution of gas filled tank with the same 2.1.3. In recent years, this kind of product is a common bus, switch in a pneumatic chamber, and adopts modular structure that a plurality of interval shared an inflatable shell, to simplify the bus connection, save space and cost; solve the scalability with various couplings or connection mode, eliminate on-site installation of gas treatment main work; the switch load switch scheme, generally equipped with electric operating mechanism, there are circuit breakers and configuration scheme, intelligent control and protection unit, the corresponding other schemes, such as load switch, combination appliances are also equipped with digital control device; the product can be a ring network cabinet with extended switch cabinet of the arrangement, can also be a standard the 3, 4 or 5 loop; typical products:
 
 
1) the main characteristics of the ZX0 type ABB CaLor Emag series of products for the company: current bus and feeder can reach l250A; circuit breaker and three position isolation switch combination, space saving and convenient match, l250A uses the straight type three position isolation switch, 630A uses the knife type circuit breaker; sealing structure VD4 type; bus connector and ZX2 type; interval control scheme with optional REF542PLUS control protection of single charge, or CCl control unit; rated pressure is l.3bar. The size of 400x900x2l00mm (l250A for width of 600mm).
 
 
2) the main characteristics of SIEMENS-p.htm "target=" _blank "title=" SIEMENS and PDF "data sources of the series of products of 8DHl0 >SIEMENS company is: a series of technical parameters for 24KV and below, 630A, 20KA; three position isolation switch for rotary type load isolation switch; bus in the chamber bottom cabinet or cabinet and combination the insulation plug busbar, circuit breaker horizontal transmission rod, welding bellows seal to ensure SF6 gas chamber in the circuit breaker operation by l.5bar; the rated pressure, size of 350x780xl400 (load switch cabinet), 500x780x2000mm (circuit breaker cabinet).
3) the main characteristics of the series of products CGM of 0RMAZABAL company is: this series of technical parameters for 36KV and below, 630A, 20KA; the SF6 circuit breaker, cabinet or cabinet and the combination between the busbar connection dimensions of silicone rubber using plug-ins, 370x850xl800mm, circuit breaker cabinet width 480MM.
 
 
4) the main characteristics of the series of products SEFEPLUS ABB AS company is: this series of technical parameters for 24KV, 630A, 2lKA and below; the vacuum circuit breaker, cabinet or cabinet and combination with cable connector connection on top of the cabinet, the series according to the different number of loop composed of ring network cabinet series, and SaFeRing install the external bus, the bus current increased to l250A; the rated pressure is l.4bar. The size of 3Z5x75lx2096 mm.
 
 
5) the main characteristics of the series of products GMB of ALST0M company as the technical parameters of 24KV and below, l250A, 25KA; vacuum circuit breaker with vertical arrangement, interlocking between the isolating switch and grounding switch; bus cabinet or cabinet and between modules via a coupling device; a size of 600x800x2300mm, the circuit breaker cabinet the depth is 1000mm.
 
 
 
3 Analysis and discussion
 
Throughout the development of switchgear products, attention to the recent relevant literature, the development of the switch cabinet is as follows:
 
3.3 Safety of switch cabinet
 
3.3.1 According to the revised draft of IEC60298 (l7C/266/CD), the classification of the switch cabinet is no longer according to the product structure (armour, and box, and in accordance with the interval) compartment function classification (SClA, SClB and SC2). Obviously this change from the use of the Department, the product design requirements are more clear, is conducive to the development of products, especially for the case of the element can improve the sex, can simplify some of the structure.
 
Safety improvement has the following progress:
 
3.3.1.1 The internal fault arc test has been widely implemented, and many research papers published, there are methods and detection of gas pressure to actively prevent internal fault quickly cut off the fault. The experimental data of the internal fault arc pressure and temperature characteristics, but also for the reduction of results of material selection and design method of fault effect. These results will be helpful to improve the safety performance of the switch cabinet.
 
3.3.1.2 The structure of security measures, such as the use of integrated mechanical switch position simulation map, only the operation of all switches with the door closed the case, to reduce the misoperation, strengthen the safety of operating personnel.
 
3.3.1.3 A new system that limits the internal fault arc has been configured in the AXl type ABB cabinet of the company. The system uses optical fiber sensor for detecting the monitor cabinet monitor detects the arc, arc, arc is generated immediately trigger the rapid connection within l0MS in arc, eliminating the arc and prevent internal arc of person and equipment damage. Therefore, the pressure relief channel of the internal fault arc of the switch cabinet can be avoided. With the rapid decrease of internal fault arc grounding damage has been used in high voltage GIS, but the optical fiber sensing arc suppression system for medium voltage switchgear and l0mS arc is the first time, the safety and economy of concern.
 
3.4 Edge structure technology
 
The insulation structure is the most important part of the coordination of the insulation level and miniaturization:
 
3.4.1 Uniform electric field is still a means to be considered. Using the rounded copper busbar and type D bus is very common, but the bus and branch bus are connected by a bolt, the electric field is poor, the weak link of Tuan insulation cabinet. The AXl type uses the prefabricated T to connect the circle bus, the connection of the bus becomes the butt joint of tubular direct bus, the electric field is greatly improved. The scheme enables the bus bar to be segmented according to the cabinet, which increases the number of bus bars, and has good tubular connection structure. But bus site installation is convenient.
 
3.4.2 Progress of composite insulation. The development of epoxy resin vacuum casting and automatic pressure gel technology has created the conditions for the progress of composite insulation:
 
1) the epoxy resin coating of the vacuum arc extinguishing chamber is not only the main insulation of the vacuum arc chamber, but also the mechanical support, the electric field distribution and the distribution of the stress distribution is better than that of the various shapes. But this must be based on a high level of insulation technology and stability of the arc extinguishing chamber mass.
 
 
2) the overall combination of electrical equipment, the use of epoxy resin superior electrical, mechanical properties and good molding process will be the integration of adjacent components. As an early adopter of the contact box and current transformer, current and voltage sensors; the recent emergence of circuit breaker and isolating ground switch (ZX0), inflatable combination circuit breaker and isolating and earthing switch in a gas chamber (AXl), are still the basis element combinations for high reliability.
 
3.4.3 Progress in gas insulation. The gas charging switch cabinet is used early, and the technical progress is that the sealing can be avoided and the gas treatment in the field can be avoided:
 
1)By using the computer analysis software (such as IDEARS), advanced CNC machining equipment, such as laser cutting, welding machinery, improve the machining precision and reduce the shell shape and position tolerances and welding deformation, using vacuum, helium leak detection, inflatable special equipment. From the design, processing, inspection and other aspects to prevent weld defects, improve the sealing of the * *;
 
2)The use of bellows actuator sealing structure, eliminate the rubber seals because of loss, reduce the aging of seal can be *;
 
3)The bus connector (interface insulation or casing connection) to solve the connection and the extension of cabinet and cabinet or cabinet and module, eliminating the problem of gas field.
 
3.4.4 Interface insulation insulation interface broadening due to small size, is matched with the gas insulated, so much for the cable connection charging cabinet, PT plug; also useful for bus structure (8DCll type), for a bus connector, to expand the scope of application of interface insulation.
 
3.5 Temperature rise Technology
 
With no oil switch, silver plating technology, the permissible temperature rise is greatly improved, reasonable design of conductor and contact structure, the application of natural ventilation and forced ventilation technology to the rated current level switch cabinet and miniaturization achieved good coordination.
 
 
In principle, the temperature rise of the switch cabinet can be calculated by software, but rarely seen in this area. According to the data and experience, summed up some points:
 
3.5.1 Rated current 630A and below, the main effect of cabinet body size is insulated and structure. More than 800A will need to consider the temperature rise factor, and the main effect (cooling area) cabinet width size.
 
3.5.2 Current product level is:
 
1)Air insulated cabinet, in general, to l250A, the small width can be 650mm, you can not do 500mm, 2000A and 800mm 2000A is larger than the width of cabinet, cabinet width l000mm (with natural ventilation measures), 4000A needs to strengthen the forced ventilation.
 
2)In addition to charging cabinet, cabinet shell radiation, between the shell and the shell of the air cooling cabinet is very important. Under normal circumstances, l250A, cabinet width 600mm, 2500A, cabinet width 800mm, heat dissipation good design cabinet width also can be 600mm.
 
3.6 Structure design technology
 
The structure design of the switch cabinet includes the general arrangement, the choice of components and general parts, the design of transmission and interlock, which is an important aspect of the miniaturization of switchgear. This is only a summary of the overall design of the practice is worth noting:
 
3.6.1 The circuit breaker is arranged in the depth direction, which is consistent with the bus bar of the horizontal layout. This approach has been popular in the two power distribution switch cabinet, and try to push the current rating of more than l250A areas, but from the existing products to see (VISAX), such as no other heat dissipation measures of small size limited;
 
3.6.2 Design ideas of the isolation switch of the fixed cabinet. In recent years, the introduction of a fixed power distribution cabinets, including inflatable cabinets, basically no feeder side isolation switch, bus side is located three station isolation, grounding switch.
 
This line of thought is not without reason: circuit breaker can  *. According to the survey of 40.5KV gas insulatedswitchboard XIHARI cancel isolation switch, the power sector as long as the cable connection can unlock, you can not set up the isolation switch. The outlet side of the 5O0KVPASS gas insulated switchgear of ABB company is not provided with the isolating switch, and the high reliability of the circuit breaker is also based on the high reliability of the circuit breaker. The overall structure, operation and interlocking of the switch cabinet will be greatly simplified, and the reliability and economy will be significantly improved if the feeder side isolation switch is canceled.
 
3.7 On the application of digital and intelligent technology
 
First is the requirement of digital and intelligent distribution automation equipment and maintenance of switch equipment, at the same time is an important aspect of improving product, switch cabinet level using high technology is to simplify the structure and improve the switch control protection level, two simplified system, improve the inevitable choice of *. For example, only the digital can choose current and voltage sensor or small current transformer, using proximity sensors to replace the auxiliary switch.
 
 
The company has production of integrated circuits, microprocessor control, measurement and protection development (interval) control unit, such as ABB REF542, SIEMENS SIPR0TEC, Scheider Sepam and so on; there will be a separate protection and control configuration, such as the AlSTOM DCX control unit and MiCOMPl2l protective relay. In addition, there is a corresponding digital control device for load switch.
 
 
However, due to the different level of distribution automation, a variety of digital intelligent product maturity varies, the use of different habits, the use of digital intelligent equipment configuration should be different. At the same time, according to the requirements of distribution automation, switch cabinet should have manual, electric operating mechanism and the corresponding switch position signal, remote communication device (RTU), DC power supply and so on.
 
 
 
4 Several points of view
 
4.1 Relationship between hand cart cabinet and fixed cabinet
 
The merits of David handcart cabinet is convenient for inspection and maintenance of circuit level, and the isolation handcart switch plug.
 
 
Cabinet in the most compact size of the upper and lower isolation structure, it is easy to meet the requirements of the hand cart cabinet SClA level of the highest security level requirements. Hand cart cabinet is easy to develop into double layer or multilayer cabinet. Handcart cabinet weakness: handcart push pulled out, plug, valve opening and closing, and a switching signal connection and interlock related linkage isolating contacts, involves many other moving part, assembling a little careless, would lead to the rise of temperature, insulation and mechanical failure; cabinet push out by mid the truck with small size and light weight and improve the precision of the track, the valve drive simple hand car * operation can be greatly improved. But the disconnector operation only move the knife movement, compared with push pull which is still weak. In addition, when the vehicle is used in the double bus bar, the size is bigger, the cost is higher, and the lack of competition ability.
 
 
The outstanding advantage of the fixed cabinet is that in addition to the provisions of the switch operation or action (including the relevant interlocking), there is no moving parts, the relative high * * *. It is easy to meet the requirement of double bus scheme. Our country has always had the habit of choosing a fixed cabinet.
 
 
The weakness of the fixed cabinet is the maintenance is not convenient, the size is too large. With the circuit breaker no less maintenance maintenance maintenance issues are relatively close to targets, desalination, inflatable cabinet promotion illustrates this point. At the same time, according to the new draft standard to select the SClB level requirements, that is, the feeder side can not be provided with a separate switch, the fixed cabinet structure to simplify, size reduction, will enhance its competitiveness. Accustomed to the hands of the cabinet of the European, some companies in recent years, the introduction of a fixed cabinet to illustrate this point.
 
 
Therefore, the two types of cabinet type parallel development of the situation still need to continue a considerable period of time.
 
4.2 About inflation
 
Fixed tank filling cabinet belongs to high technology, it must have high reliability components based on high precision sheet metal processing, welding equipment, SF6 gas processing technology to the design and production of sophisticated inflatable cabinet products.
 
4.2.1 The advantage of the gas charging cabinet is:
 
4.2.1.1 High availability. Design of charging cabinet must be selected for high reliability of the switching element, enough insulation margin level makes gas insulatedswitchboard become no maintenance or less maintenance (a small amount of lubrication, adjustment mechanism part of the switch cabinet). At the same time, a loop in the inflated the influence of the external environment is not affected by the shell, filling SF6 or nitrogen containing no oxygen, moisture content control in a very low level, can prevent the insulation failure of metal parts and oxidation corrosion caused by the contamination, condensation; in principle, it can be used in damp, filthy, dust etc. harsh applications, high altitude and other non normal conditions.
 
4.2.1.2 Miniaturization. Low pressure SF6 has a very high insulation performance and low sensitivity to the electric field, therefore, compared with the air insulated cabinet, the air charging cabinet has the smallest size. The nitrogen inflating cabinet, insulation structure because of not considering the condensation and filth and simplified, size also decreases. This advantage is particularly significant for high voltage levels such as 40.5KV products.
 
4.2.1.3 The gas filled tank is suitable for double bus system, and has the advantages of compact structure and strong competition ability.
 
4.2.2 Inflatable cabinets also have their weaknesses, mainly worried about the SF6 gas leakage caused by the failure of processing and the negative impact on the environment. The leak worried, leak to SF6 high voltage switch equipment for many years is the most common defect, but at present in the sealing structure, materials and process has been greatly improved, more mv-gis for its favorable conditions, can be explained in two aspects:
 
4.2.2.1 Gas seal. Effective measures have been taken to ensure the sealing performance:
 
1)Medium small volume and low pressure pneumatic shell, stainless steel plate is thin, bending, welding process, weld length is shorter; housing can be in the factory cutting, bending, welding, leak detection line, can ensure the quality of welding can be sealed.
 
2) generally use the static sealing rubber ring sealed detachable, due to low pressure, and the pressure is small, easy to ensure the sealing performance.
 
 
3) transmission can be used to seal the sealing structure of high pressure GIS, medium voltage switch due to a small stroke, but also the use of corrugated pipe for the dynamic sealing structure, sealing performance is better.
 
4.2.2.2 SF6 gas and environment of the gas filled cabinet
 
1) SF6 gas is one of the six kinds of greenhouse gases, the United Nations Framework Convention on climate change "published, but the effect of SF6 on emissions of greenhouse gases accounted for only six of the total effect of 0.0l% that its influence is only 1/10000. For high-voltage electrical appliances and equipment accounted for about half of the total amount of SF6 gas gas global SF6, and medium voltage switchgear was high and super high voltage switch 1/10, less than 1/200000 of the visible effects of charging cabinet.
 
 
2) the air leakage rate is less than l%, so the leakage discharge is very little. SF6 gas mv-gis in, is gas recycling, recycling of SF6 CIGRE to develop guidelines for recycling and treatment of the use of specific provisions. Gas recycling has greatly reduced the amount of SF6 gas emissions.
 
 
3) the abnormal leakage of gas filled tank, such as installation, operation, damage or internal arc caused by gas leakage, which is the most worried about the accident. The [10] of 36KV switchgear are analyzed respectively in different situations with and without arc decomposition, different arc energy, the harmful gas concentration calculation results and requirements of State Industrial Hygiene Association valve limit (TLV) comparison, the conclusion is: in SF6 as insulation and 36KV underground medium or basement fault in substation of power plant, equipment repair after using period and normal life of the equipment, from the health point of the operator, accidentally leaked SF6 will not cause any harm. So it's not necessary to worry too much about it.
 
4.2.3 Another weakness is (Part one) maintenance is not convenient. As mentioned earlier, charging cabinet should be no maintenance or less maintenance equipment, the medium voltage switch level has reached or close to no maintenance or less maintenance, over the years, there are many inflatable ring net cabinet inflatable box is not open maintenance, good operation effect. Description of high * * * Don't have to worry too much about maintenance. On the other hand, many still consider charging cabinet in case of need for maintenance of the structure, such as a hand hole, or the use of explosion-proof device hole.
 
Therefore, the inflatable cabinet is urgent to develop high-tech products, development of the time it takes a large amount of money and longer; on the other hand, for new products, with a weak left, the user may have a longer time to accept.
 
4.3 The relationship between one power distribution and two power distribution switch cabinet
 
Along with the development of the product, the difference and the characteristic of the first power distribution and the two power distribution switch cabinet are becoming more and more clear:
 
4.3.1 technical parameters. Is mainly rated current and thermal stable current is different. Primary power distribution is 630-4000A and 20-40KA, the two power distribution is less than 630-l250A, l6-25KA.
 
 
4.3.2 security level. A distribution generally requires higher security level, according to the old standard armoured type or interval type, new draft standard SClA or SClB level; the two distribution reduced box or SC2.
 
 
4.3.3 performance and price. Due to the use of different occasions, once in the head end power distribution feeder, distribution in the middle or at the end of two, the importance of the former than the latter, the use of the latter number several times in the former, the first distribution focused on performance, the two distribution to ensure the performance but also pay attention to the price.
 
 
For many years China's main switch cabinet in the development of a distribution, in recent years, the secondary distribution cabinet has made great progress, but there is a large gap between the demand and the distribution system, should intensify efforts to improve the two level distribution cabinet products.

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