The environmental gas cabinet is easy to operate, and the control and protection are relatively simple, and the cost is low. Most of the current ring net cabinet uses six SF6 gas as insulation and breaking medium. Although SF6 gas is an excellent electrical gas, it is also a kind of greenhouse gas which is restricted by the Kyoto protocol. In recent years, some countries have even levied carbon tax on the use of SF6.  Therefore, for the switchgear, especially for medium voltage switchgear, removing SF6 is of great significance for environmental protection and becomes the direction of development. Therefore, it is very important to study the environmental protection of insulation gas in ring switchgear.

In today's environmentally-friendly gases, nitrogen and dry compressed air are the main sources. Such gases are easy to obtain, low cost, safe and reliable, and green.  However, considering that oxygen and moisture in the air have oxidation and corrosion hazards on the electrical contact position, nitrogen is chosen as the environmental protection gas matched with the ring net cabinet. However, there is still a great deal of trouble in the aspect of insulation, thermal conductivity and arc extinguishing performance of nitrogen in comparison with six sulfur fluoride.

Insulation in the gas box:

According to the physical characteristics of nitrogen and six sulfur fluoride, it is found that the electrical strength of nitrogen is 1/3 of the gas of six sulfur fluoride, and the insulation strength is 1/2 of the sulfur fluoride of six. Combined with the content of nitrogen in the air, the surface, nitrogen and air are very similar. Therefore, in order to realize the function of the switchgear and the similar size, we should focus on the following aspects, but at the same time, we should consider the possible shortcomings.

Strength of the gas box:

The structure of the gas box is filled with nitrogen, and the new design concept is produced. The strength of the whole gas box needs to be analyzed and studied so as to avoid the severe deformation or leakage of the gas box because of the lack of strength. The computer aided design software is used to analyze the strength of the gas tank. The results are as follows:

(1) the maximum deformation of the lateral stiffener of the gas box 1.79mm

(2) the maximum deformation of the vertical stiffener of the gas box 1.14mm

(3) the maximum deformation of the rear cover plate of the gas box 6.36mm

(4) the maximum deformation of the front panel of the gas box 2.81mm

It is known that the heat conduction is related to the thermal conductivity of the material, the effective heat conduction area, length and temperature difference, and the heat convection is related to the heat capacity, the effective heat dissipation area, the air duct and the temperature difference, and the thermal radiation is related to the coating material, color and absolute temperature of the conductor surface. Therefore, we should pay attention to the control of temperature rise when the conductor and core components are heated internally. In the specific structural design, we should consciously transfer the heat from the high temperature point to the low temperature rise point to realize the heat dissipation of the air box.

Welding of gas box:

The internal structure design of the loop cabinet with nitrogen as an insulating gas is different from that of the six sulphur fluoride filling cabinet. In the limited space, the welding process of thin steel plate has put forward high new requirements for the welding process. The main reason is the gap and saturation of the weld. It has a great influence on the leak detection and inflation of the subsequent pressure difference. The stress caused by the welding heat is mainly concentrated in the welding position.  In the process of long term equipment operation, the stress distribution of the weld seam may appear, the local area fatigue cracking and the temperature difference of the gas box cause the deformation. Therefore, the excellent welding technology and welding parameters must be selected strictly. In view of this problem, special cold welding technology was introduced. The cold metal transition welding can reduce the heat input of the workpiece during the welding process of the gas box, ensure the small deformation of the gas box, and ensure the reliable fit of the switch with the operating mechanism, thus solving the hidden danger of the gas box welding.

Type test analysis:

The prototype of the environmental protection gas insulated switchgear has been developed through optimization design. Shanghai electric power transmission and Distribution Test Center Co., Ltd. and the quality testing center of high voltage transmission and distribution equipment in machinery industry, in accordance with the GB3906 standard, include industrial frequency resistance, lightning shock, local discharge test, condensation test, loop resistance, temperature rise test, mechanical property test, mechanical life test, seal test and pressure. The test of force tolerance, short time and peak tolerance current test, opening and closing test, internal combustion arc test and so on, all the projects have passed all type tests successfully.

Through the rational distribution of electrified body and insulators, optimizing the shape and coordination of the electrified body and insulator, combining with the strict processing technology and assembly process, using nitrogen insulation, we can develop the environmental protection gas insulated ring network switch cabinet, not only can meet the requirements of the power grid operation, but also realize the policy and thought of green environmental protection. The road. The comprehensive use of various economic and reasonable safety methods, not only can solve the problem of temperature rise, but also can achieve a reasonable heat dissipation channel, the technology has reached the international leading level. Environmental gas cabinet does not use six sulfur fluoride, the use of nitrogen as an insulating gas, both in the design and production are feasible, can be gradually pushed to the market, through this low carbon green green way, better service to the society.