Research and product development of the hottest ga

2022-09-23
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Research and product development of inflatable high voltage shunt capacitor

Abstract: through the analysis of the market, this paper puts forward the research of inflatable high voltage shunt capacitor, and introduces the characteristics of the developed products

key words: research and development of inflatable high-voltage shunt capacitors

1 preface

with the rapid development of China's economy and the continuous improvement of people's living standards, the demand for power is increasing, and the safety and environmental protection issues are increasingly concerned. There is an urgent need for fire-resistant, explosion-proof, non polluting transmission and distribution equipment. The clear guiding ideology for the construction and transformation of urban and rural electricity in China is to develop towards less oil and no oil. Oil free products are increasingly welcomed by the power sector, and the demand is growing. With the continuous progress of power technology, new technologies are developing with each passing day, and new product development is emerging in endlessly. At present, oil-free dry-type insulated combination appliances, mutual inductors, transformers, reactors, and circuit breakers have been more and more widely used, but there is a lack of cheap and high-quality dry-type oil-free high-voltage capacitors. Now, in the high-voltage parallel compensation package, other supporting equipment can be easily oil-free. Only high-voltage parallel capacitors can realize oil-free products due to the particularity of their working medium, which is very difficult. At present, only a small number of dry-type oil-free high-voltage capacitors are in operation. Their technology is not very mature, their performance is not very stable, and their cost is high, which is difficult to be widely used. Therefore, less oil, fire-resistant and explosion-proof inflatable collective shunt capacitor came into being. The traditional oil filled high-voltage shunt capacitor is very popular with users because of its simple wiring, convenient installation, use and maintenance, and small floor area. However, because it contains a large amount of insulating oil, it does not conform to the trend of oil-free power system. The new gas filled high-voltage shunt capacitor is developed on the basis of the oil filled shunt capacitor, which has been mass produced and has more than ten years of manufacturing and operation experience. It uses non combustible insulating gas to replace a large amount of insulating oil, so that the advantages of the original product can be retained and brought into play, and it is in line with the concept of safety, environmental protection and less oil. The successful development and popularization of gas filled high-voltage shunt capacitors meet the requirements of the market and are very popular with users. Please log in: power transmission and distribution equipment to browse more information

2 Research on inflatable collective high-voltage shunt capacitor

traditional oil filled collective shunt capacitor, because there are hundreds to thousands of kilograms of flammable insulating oil (transformer oil or alkylbenzene oil) between the large box shell and the unit capacitor, the product has defects such as easy to leak oil, flammable and explosive under fault conditions, environmental pollution, heavy weight and so on. Replacing the above insulating oil with non combustible insulating gas can overcome its shortcomings. However, compared with insulating oil, insulating gas has worse insulation and heat dissipation performance than insulating oil under general conditions, and the gas is more difficult to seal. Therefore, how to choose the appropriate insulating gas, reduce the heat generation of the product as far as possible, and solve the problems of heat dissipation, insulation, sealing, etc. are the main research contents of developing the product, among which the heat dissipation problem is the focus and difficulty of the research

2.1 heat dissipation

sf6 gas is a poor conductor of heat, and its heat dissipation performance is much worse than that of insulating oil. If the oil of the oil filled collective capacitor is simply replaced with gas, the temperature rise of the capacitor unit will be too high, and the performance will be degraded, resulting in thermal breakdown damage. Therefore, to solve the problems of thermal stability and thermal breakdown of inflatable collective capacitors, and to reduce the temperature rise of unit capacitors as far as possible to maintain their good operation state is the focus and difficulty of this project. For full film capacitors, the temperature of the hottest spot inside should not be greater than 80 ℃, and in order to reduce the difficulty of reducing temperature rise in other aspects, the temperature rise between the hottest spot of the unit and the unit shell should be controlled below 6 ℃

in order to ensure that the operating temperature inside the capacitor unit does not exceed the allowable value, the loss of the unit must be strictly controlled. The factory standard is tan δ Not more than 3 × 10-4。 Practice has proved that the existing technological level of the enterprise can be achieved. In general, the tangent Tan of the dielectric loss of the unit δ Not more than 2 × 10-4。

in addition, add a certain number of stiffeners on the box shell, and try to increase the heat dissipation area of the well-known shell, so as to reduce the temperature rise of the large shell to the ambient air

how to minimize the temperature rise between the shell of the capacitor unit and the large box is the key content of our research. For this reason, we have done a lot of research work. First, carefully arrange the structural layout of the capacitor unit in the large box, so that the wiring is simple and the insulation is reliable, and the heat flow is smooth without local overheating, so that the heat energy of the capacitor unit can be effectively transmitted to the large box through conduction, convection and radiation without adding additional forced heat dissipation measures. In order to ensure that the performance of the capacitor unit will not be degraded due to poor heat dissipation, after research, we have taken more effective forced heat dissipation measures, applied the heat pipe heat dissipation technology adopted in the aerospace field to this product, and installed a heat pipe heat dissipation device between the capacitor unit shell and the large box shell, which is an effective and practical result of our research in this project. The working principle of the heat pipe (see Figure 1) is as follows. The heat absorption section of the heat pipe absorbs heat and transfers it to the working medium in the heat pipe. Due to the particularity of the working medium under certain environmental conditions, the absorbed heat changes from liquid phase to gas phase. Under the action of the internal differential pressure power in the heat pipe, the working medium in the gas phase can reach the cooling and heat dissipation section by transferring the concrete pressure testing machine. Due to the low temperature of the cooling section, the working medium changes from gas phase to liquid phase to release heat energy. The heat pipe heat transfer has small thermal resistance and large transmission power, which can realize long-distance variable direction heating, and has fast startup, good transmission speed and remarkable heat dissipation effect. Generally, there is a high negative pressure in the heat pipe. In order to ensure the service life of the heat pipe, we use the heat pipe under normal pressure, that is, when the temperature of the working medium reaches its vaporization temperature under normal pressure (0.1MPa), it can vaporize, and can normally condense and dissipate heat

in order to test the heat dissipation effect of the heat pipe, we have carried out many comparative research tests on the test object with and without heat pipe, in order to determine the best structure of the heat pipe. Table 1 shows the thermal stability test data of the test object. The test method is according to the standard jb7112-2000, and the test voltage is 1.2 times the rated voltage

the key to the development of inflatable collective capacitor is to solve the problem of temperature rise. We believe that using heat pipe for heat dissipation is a very effective solution. We have carried out extensive, in-depth and difficult exploration and research experiments from the aspects of the principle of heat pipe, various factors affecting heat dissipation and heat transfer, processing and manufacturing technology, as well as the installation and use of heat pipe radiator, overcome various difficulties, and finally made a breakthrough. We have developed an internal heat pipe heat dissipation device suitable for this product, with excellent performance and convenient installation, so as to solve the long troubled problem of temperature rise. The type test of the product proves that the temperature rise meets the requirements, and there is a certain margin to ensure that the capacitor unit will not be thermally damaged due to poor heat dissipation, so as to ensure its safe operation, so as to meet the explosion-proof and fire-proof requirements. Only when the problem of temperature rise is reasonably solved, the inflatable collective capacitor can play its due advantages. The successful use of the built-in heat pipe radiator ensures the safe operation of the product

2.2 insulation

insulating gas is responsible for the external insulation of the capacitor unit in the large box shell and the insulation and heat dissipation between the capacitor unit and the box shell in the inflatable collective high-voltage shunt capacitor. Sulfur hexafluoride (SF6) gas is a kind of gas with very stable physical and chemical properties and excellent insulation and arc extinguishing performance, which was discovered in 1900. Industrial production began after the 1930s. Because of its excellent physical and chemical properties and insulation arc extinguishing performance, it began to be used in power equipment in the 1940s. At present, SF6 gas and its mixture have been widely used in circuit breakers, mutual inductors, GIS and other power equipment. There is no doubt that SF6 gas or its mixture is a natural and ideal choice for inflatable collective capacitors. The problem is that the pressure range of the gas and how to choose the ratio of SF6 gas to each mixed gas must be carefully studied and determined

10kV and 35 kV voltage, therefore, strain fatigue analysis method must be adopted to accurately predict the fatigue life level. The insulation level of the collective capacitor is 75/42 (kV) and 95/200 (kV) respectively. Since the insulating gas of the inflatable collective shunt capacitor only undertakes the external insulation of each high-voltage charged body in the large box shell, and the structural arrangement is easy to increase the insulation distance with less cost, in order to make the product operate reliably, we have fully studied and tested, and selected the appropriate insulation structure and insulation distance, so that the product can pass the type test of all electrical properties under the air state of 0 gauge pressure. Considering the convenience of sealing, the mechanical strength of the box shell and other factors, after experimental research, we chose the gas pressure range of 0.001 ~ 0.06mpa (this paper refers to gauge pressure), which satisfied the requirements of all aspects, rather than using a higher pressure like SF6 circuit breaker and GIS. Considering the manufacturing habits of the assembled capacitor, high air pressure does not bring much benefit to the inflatable assembled capacitor, but complicates the product manufacturing and operation and maintenance. In order to make the operation convenient, this product is not considered to be equipped with a complex automatic air replenishment system

in order to prevent the interior of the box from being immersed by external moisture during the operation of the product, the positive pressure should be maintained in the box. Since our factory has many years of gas seal manufacturing experience in SF6 standard capacitors and inflatable CVT products in recent years, the annual gas leakage rate of 0.5% can be achieved for inflatable collective capacitors under the pressure of 0.065 MPa. Therefore, the determination principle of rated air pressure (20 ℃) is to calculate the annual gas leakage rate of 0.5%. After 20 years, at the lower limit of ambient temperature, the gauge pressure in the box shell should not be less than 0.001mpa when the products are not put into operation, Based on this, the rated air pressure can be calculated as 0.032mpa. Similarly, according to the upper limit of the ambient temperature of the product and the temperature of the product during operation, the upper limit of the normal pressure in the box can be calculated as 0.06mpa

in fact, due to the guarantee of process conditions, the annual gas leakage rate during the factory test of products is below 0.03%. Therefore, under normal operating conditions, the product does not need air replenishment during its 30-year service life. Although SF6 gas has excellent electrical performance, its price is slightly expensive and it is sensitive to the inhomogeneity of electric field. Considering the convenience of manufacturing, although some measures have been taken, the uniformity of electric field is not very ideal. The mixing of SF6 and cheap N2, as long as the proportion is appropriate, can not only save costs, but also reduce the sensitivity of pure SF6 gas to the uniformity of electric field in terms of electrical performance, so as to ensure better electrical strength, without making great efforts to improve the uniformity of electric field

at present, SF6 mixed gas is gradually used to replace pure SF6 gas at home and abroad. The commonly used N2/SF6 ratio is 50%/50% or 60%/40%. Through research and experiments, we have achieved good results by adopting the appropriate volume ratio of SF6 to N2

as mentioned earlier, in order to facilitate sealing and increase reliability, the "0" gauge air state is used as the design basis of lead insulation strength. All conductors in the shell of inflatable collective capacitor (except the internal insulation of the unit itself

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