Technical problems of inflatable cabinet accessories:

1. Inflatable cabinet accessories sealing problem:

The air leakage rate of inflatable cabinet accessories has always been the focus of attention of various manufacturers and users. The annual leakage rate of SF6 load switches and inflatable cabinets is less than 1%/year. The service life of the switch is generally about 30 years. The seal should take into account the factors of compression life, aging, and reliability of the sealing elements.

When the SF6 gas pressure in the box drops to atmospheric pressure, it seems that the internal and external pressures are equal, and there is no leakage of gas. However, from the perspective of penetration, the concentration of SF6 gas in the box is obviously higher than that outside the cabinet, and the SF6 gas still seeps out, on the contrary, the concentration of air outside the box is higher than that inside the cabinet, and the air will enter the box through the gap. Over time, although the gas pressure in the box is still atmospheric pressure, the gas composition changes. When the percentage of SF6 gas decreases, when the proportion of SF6 drops to 40%, there is a possibility that accidents may occur due to the deterioration of insulation performance, so the sealing problem must be paid attention to.

SF6 load switches generally use sealing rings to achieve dynamic and static sealing of gases (such as ABB's SFG and Schneider's SM6 switches);

There are also some sealing forms that combine stainless steel welding and sealing rings (VEI's SF6 switch);

The sealing methods of C-GIS inflatable cabinet include welding seal, sealing ring seal and metal bellows sealing.

The welding seal is adopted, to ensure the airtightness of the weld, the general welding equipment and welding technology can not meet the requirements, at least use argon arc welding or laser welding equipment for welding (at present, there are several domestic companies that have introduced welding manipulator production equipment from abroad) to ensure the welding quality.

There are two commonly used SF6 gas leak detection methods in inflatable cabinet accessories: 

First, the qualitative leak detection of inflatable cabinet accessories, that is, the leakage point;

second, the quantitative leak detection of inflatable cabinet accessories, that is, the gas concentration in the sealing volume is measured after 24 hours of sealing to calculate the annual leakage rate;

In addition, the impact of environmental factors on sealing performance should be considered, such as whether the sealing performance meets the requirements under high or low temperature conditions;

2. The gas moisture content of inflatable cabinet accessories:

The moisture content of SF6 gas is one of the main detection indicators of SF6 switch quality, and its size directly affects the insulation level of the switch.

When the amount of water in SF6 gas is lower than the saturation value at the temperature of this state, the content of water in the gas state is one of the main detection indicators of SF6 switch quality, and its size directly affects the insulation level of the switch.

When the content of water in SF6 gas is lower than the saturation value at the temperature of this state, the water content exists in SF6 gas in the gas state, and the test proves that the insulation performance of SF6 switch is basically not affected. If the moisture content of the gas exceeds the saturation value, some of the water vapor will condense on the surface of the solid insulation inside the switch, which will reduce the flashover voltage along the surface, which will also affect the arc extinguishing performance of the switch. Therefore, DL/T596-1996 "Preventive Test Regulations for Power Equipment" stipulates that the moisture content of SF6 switches shall not exceed 150ppm after new operation and overhaul, and shall not exceed 300ppm during operation.

The sealed box is put in an appropriate amount of dried adsorbent, which is mainly used to absorb water to ensure that the moisture content in the sealed box does not exceed the standard specifications. sealing the parts in the box (including sealing box, transmission parts, contact blades, etc.);

Standard parts should be baked strictly according to the baking temperature and baking time of each component, strictly control the moisture content of the parts themselves, and ensure the packaging time of the parts.

When the SF6 switchgear is vacuumed and inflated, the inflatable pipeline is cleaned with high-purity nitrogen or sulfur hexafluoride gas, the moisture content in the pipeline is controlled, and the production process of SF6 switchgear is formulated.

3. Quality problems of inflatable cabinet accessories and parts:

The quality of inflatable cabinet accessories is directly related to the quality of the product. SF6 load switches and inflatable cabinets are maintenance-free or low-maintenance switchgear, once the parts in the sealing box have quality problems, they may be scrapped as the entire switchgear;

To ensure the quality of inflatable cabinet accessories, it is necessary to strictly control the material, processing technology and inspection method of the parts, and its mechanical strength, electrical properties and other parameters meet the requirements of the product. Stricter inspection of the parts required to be loaded, and stricter process control and process inspection control are required for the entire assembly process to ensure the correctness and consistency of assembly. In particular, the lubrication of the transmission link and the surface of the contact in the sealing box should be permanently effective throughout the product life cycle, the contact pressure of the contact should be strictly controlled, and the resistance value of the main circuit of the switch should meet the technical requirements of the product during the life cycle.

With the rapid development of social economy, the continuous growth of urban electricity load, the requirements for power supply reliability are getting higher and higher, high-performance ring network power distribution, multi-circuit power distribution, switchgear, etc. have become one of the irreplaceable important equipment in the secondary power distribution system, especially the compact and scalable SF6 switchgear has become the leading equipment in the secondary power distribution system. With the wide application of digital technology, integration technology and mechatronics technology, SF6 switchgear will be further developed.