Many new users, when choosing a model, like "trendy" products, think that the newly developed products must be better than the old products. In fact, cable accessories of each structure have a series of advantages, but there are also some weaknesses. Moreover, a certain feature of a structure is an advantage in one case of use, and may become an undesirable disadvantage in another use case. The following example is explained:
Choice of silicone rubber composite sleeve and porcelain sleeve: All kinds of terminals can use silicone rubber composite sleeve instead of porcelain sleeve as the outer insulation of outdoor terminals, and the manufacturer also makes a clear price for users to choose.
Case 1: Selection of silicone rubber composite sleeve and porcelain sleeve:
Schematic diagram of 126kV full dry capacitor cone outdoor terminal structure .jpg
Schematic diagram of 126kV dry capacitor cone outdoor terminal structure
Advantages of composite casing compared to porcelain sleeve:
The composite casing is lightweight and easy to transport and install on site. Compared with the porcelain sleeve, the biggest advantage of the composite sleeve is that it has excellent explosion-proof performance. When the insulation in the terminal breaks down, the pressure inside the terminal increases sharply, and even the porcelain sleeve explodes. The porcelain sleeve is a brittle material, and the debris after the explosion will affect the safety of other electrical equipment and personnel in the surrounding area. There have been many such accidents. The flexible composite insulation material can overcome this weakness of the porcelain sleeve and ensure the safety of the surrounding personnel and equipment. This is the outstanding advantage of silicone rubber composite sleeve.
Disadvantages of silicone rubber composite sleeve:
Silicone rubber composite sleeve is an organic composite material, and its stability is worse than that of inorganic material porcelain sleeve. Since the composite casing has not been in operation for a long time, sufficient convincing operational information has not yet been accumulated. We can refer to the operating experience of line insulators with similar materials.
The mechanical, electrical and stable properties of silicone rubber composite insulation materials can meet the operating requirements. In the future, a large number of composite insulation materials will be used as external insulation materials in China's power transmission and transformation equipment. However, according to the operating experience of line insulators, composite insulators will have hydrophobicity, deterioration of mechanical and electrical properties, and deterioration of seals after a certain number of years of operation.
The long-term aging performance of silicone rubber composite casing is not comparable to that of porcelain sleeve, which has been successfully used in the power transmission and transformation industry for more than 100 years, which is enough to prove its reliability - electrical properties, mechanical strength and weather resistance are very stable. Therefore, at least for now, there will be no possibility that silicone rubber composite sleeves will eliminate porcelain sleeves.
Recommended Scheme:
The correct choice should be determined according to the actual use conditions, such as in large urban population and equipment dense areas, the explosion-proof nature of silicone rubber composite casing highlights the importance; On the contrary, in some areas with harsh climatic conditions, porcelain sleeves may be more appropriate, because the probability of terminal explosion is very small.
Case 2: Selection of fully prefabricated dry type synthetic insulated outdoor terminal and traditional prefabricated terminal:
Advantages of fully prefabricated dry type synthetic insulated outdoor terminals:
Fully prefabricated dry synthetic insulated outdoor terminals have simple structure and light weight, especially on-site installation is very convenient. Since there is no insulating oil and gas in the terminal, the possibility of oil and gas leakage is completely eliminated, giving users a sense of security without hidden dangers. The flexible structure allows it to be installed horizontally, vertically or in any orientation.
Fully prefabricated dry-insulated outdoor terminals have passed rigorous qualification tests and have also operated safely for a certain period of time, which has proven that this type of terminal meets operational requirements. In the future, it will continue to be used in China's 110kV voltage level cable system. But this is not proof that it is a flawless structure, or that it is possible to eliminate traditional prefabricated terminal structures.
Disadvantages of fully prefabricated dry type synthetic insulated outdoor terminals:
In addition to some disadvantages of organic composites as external insulation, there is also a concern about the electric field problem.
110kV outdoor terminal electric field distribution (allele) .jpg
Figure 6 Distribution of electric field in 110kV outdoor terminal (allele)
Calculation result 1 - shielding case 2 - cable insulation 3 - insulating oil 4 - rubber stress cone insulation 5 - conductor of rubber stress cone 6 - porcelain sleeve
Figure 6 shows the calculation results of the electric field distribution of the conventional prefabricated outdoor terminal in Figure 1. It is not difficult to see from the figure that the densest allele near the stress cone is the part of the cable where the electric field at the end of the cable is most concentrated. As we all know, the insulation strength of the insulation interface is lower than that of the insulation material body. Therefore, when designing the insulation in the terminal, the designer always tries to dispose of the insulation interface in a place where the electric field distribution is relatively uniform and the electric field strength is relatively weak.
Looking at the traditional prefabricated outdoor terminal (Figure 6), there are several insulating interfaces (from the center to the periphery) near the stress cone:
(1) Rubber insulation and insulating oil of stress cone;
(2) Insulating oil and inner wall of porcelain sleeve;
(3) The outer wall of the porcelain sleeve and the atmosphere.
thereinto
Interface (1), that is, the interface alleles of the rubber insulation of the stress cone and the insulating oil are the densest, indicating that the electric field is the most concentrated here. However, the interface electrical strength of the rubber and insulating oil of the stress cone is still relatively high and stable. The part with the lowest electrical strength of the interface is the interface (3) the outer wall of the porcelain sleeve and the atmosphere, and the insulation strength is unstable due to the influence of atmospheric conditions such as pollution, moisture, and ultraviolet rays. But the allele density here is much looser than interface (1), that is, the electric field strength is much weaker. Therefore, the electric field distribution of the entire terminal is very reasonable, and the part where the electric field is concentrated is a high-strength medium (including the interface), and the part with poor dielectric strength has a low electric field strength.
Concentrate:
From the above two analysis examples, it can be seen that many types of cable accessories, each with their own strengths, it is difficult to determine which one is the best or which is the worst, which is why these cable accessories can coexist and develop in the past ten years. The selection of cable accessories should be decided according to the actual use requirements, do not blindly pursue "trendy", the application is the best.
Heat shrink cable attachment 3
Sum up:
Users who are new to the field of high-voltage cable accessories are easy to put the convenience of installation and construction too important when selecting. High voltage cable accessories have one feature. Manufactured at the factory, parts such as rubber prefabricated stress cones, porcelain sleeves, and insulating oils are supplied at the factory, which become finished products after on-site installation – complete, quality-assured accessory products. Therefore, installation is indeed a very important part of the overall product quality. It can be said that the same set of products, the results of installation by construction personnel of different levels, the level of the product is also different. The selection guidelines for high-voltage cross-linked cable accessories are summarized as follows:
1. Good installation process has relatively low requirements for the on-site environment and the technical level of operators, easy to control the installation quality, and easy to ensure product quality.
2. Strictly speaking, the installation of high-voltage cable accessories is part of the work of the manufacturer, not the work of the user. What matters to the user is the reliability of the accessory after installation.
3. Reliability is always the first important consideration of cable engineering. On the basis of reliability, it is possible to talk about the convenience of installation and construction and the high price, otherwise you will get the biggest trouble and the most expensive price. Of course, to ensure the reliability of the selected accessories, in addition to the correct selection, there are also a series of issues involving manufacturing, construction installation and test acceptance.
4. The simplicity of the installation process is indeed an important condition for the selection of cable accessories, but there is no need to put the convenience of installation and construction in too important a position.
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