Many new users like "trend" products when selecting models, and think that newly developed products must be better than old ones. In fact, each type of cable accessory has a series of advantages, but there are also some weaknesses. Moreover, a certain feature of a certain structure is an advantage in a certain use situation, and may become an undesirable disadvantage in another use situation. The following example explains:

Choice of silicone rubber composite sleeve and porcelain sleeve: All types of terminals can use silicone rubber composite sleeve instead of porcelain sleeve as the external insulation of the outdoor terminal. The manufacturer also makes a clear price for the user to choose.

Case 1. Selection of silicone rubber composite casing and porcelain sleeve:

Schematic diagram of 126kV full dry condenser cone outdoor terminal structure

Compared with porcelain sleeve, composite casing has the following advantages:

The composite casing is light in weight, convenient for transportation and on-site installation. Compared with the porcelain sleeve, the biggest advantage of the composite casing is its excellent explosion-proof performance. When the insulation breakdown occurs in the terminal, the internal pressure of the terminal increases sharply, and even the porcelain sleeve explodes. Porcelain sleeve is a brittle material, and the fragments after the explosion will damage the surrounding electrical equipment and the safety of personnel. There have been many such accidents. The flexible composite insulating material can just 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 casing.

Disadvantages of silicone rubber composite casing:

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 put into operation for a long time, sufficient and convincing data have not yet been accumulated. We can refer to the operating experience of line insulators with similar materials.

The mechanical properties, electrical properties and stability characteristics of silicone rubber composite insulating materials can all meet the operational requirements. In the future, a large number of composite insulating materials will be used as external insulating materials in my country's power transmission and transformation equipment. However, based on the operating experience of line insulators, after a certain number of years of operation, composite insulators will experience water repellency, mechanical and electrical performance degradation, and sealing deterioration.

The long-term aging performance of silicone rubber composite casing is not as good as porcelain casing. The latter has been successfully used in the power transmission and transformation industry for more than 100 years, which is sufficient to prove its reliability-electrical performance, mechanical strength and weather resistance The performance is very stable. Therefore, at least for now, there is no possibility that the silicone rubber composite sleeve will be eliminated from the porcelain sleeve.

Recommended plan:

The correct choice should be determined according to the actual conditions of use. For example, in areas with dense populations and equipment in large cities, the explosion-proof properties of silicone rubber composite bushings become more important; on the contrary, in some areas with harsh climatic conditions, porcelain bushing may be more appropriate , Because the probability of terminal explosion is very small after all.

Case 2: The choice of fully prefabricated dry synthetic insulated outdoor terminal and traditional prefabricated terminal:

Advantages of fully prefabricated dry synthetic insulated outdoor terminal:

The fully prefabricated dry synthetic insulated outdoor terminal is simple in structure and light in 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 and used horizontally, vertically or in any direction.

The fully prefabricated dry synthetic insulated outdoor terminal has passed strict qualification tests and has also been safely operated for a certain period of time. It has been proved that this type of terminal can meet the operational requirements. In the future, it will continue to be used in the 110kV cable system in my country. But this is not to prove that it is a perfect structure, or it is possible to eliminate the traditional prefabricated terminal structure.

Disadvantages of fully prefabricated dry synthetic insulated outdoor terminal:

In addition to the shortcomings of organic composite materials for external insulation, there is also an electric field problem that is of concern.

Figure 6 110kV outdoor terminal electric field distribution (isopotential line)

Calculation result 1—shielding cover 2—cable insulation 3—insulating oil 4—rubber stress cone insulation 5—conductor of rubber stress cone 6—ceramic sleeve

Fig. 6 shows the calculation result of the electric field distribution of the traditional prefabricated outdoor terminal in Fig. 1. It is not difficult to see from the figure that the concentration of equipotential lines near the stress cone is the most concentrated part of the cable terminal electric field. As we all know, the insulating strength of the insulating interface is lower than that of the insulating material body. Therefore, when designing the insulation in the terminal, the designer always tries to handle the insulation interface as much as possible where the electric field distribution is relatively uniform and the electric field strength is relatively weak.

First look at the traditional prefabricated outdoor terminal (Figure 6). There are several insulating interfaces near the stress cone (from the center to the periphery):

① Rubber insulation and insulating oil for stress cones;

②Insulating oil and the inner wall of the porcelain sleeve;

③The outer wall of the porcelain sleeve and the atmosphere.

among them,

The interface ①, that is, the interface between the rubber insulation of the stress cone and the insulating oil is the most dense, indicating that the electric field is the most concentrated here. However, the electrical strength of the interface between the rubber and insulating oil of the stress cone is relatively high and stable. The lowest electrical strength of the interface is the interface ③The 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 isopotential density here is much looser than the interface ①, that is, the electric field strength is much weaker. Therefore, the electric field distribution of the entire terminal is very reasonable. The high-strength medium (including the interface) is used for the areas where the electric field is concentrated, and the electric field strength is not high for the areas with poor medium strength.

Note:

From the above two analysis examples, it can be seen that many types of cable accessories have their own strengths, and it is difficult to determine which one is the best or which one is the worst. This is why these cable accessories can coexist in the past ten years. Reasons for development. The selection of cable accessories should be decided according to actual use

requirements, and there is no need to blindly pursue "trend", application is the best.

In summary:

For users who are new to the field of high-voltage cable accessories, it is easy to place the convenience of installation and construction too important when selecting models. The high-voltage cable accessory has a feature. The manufacturer provides rubber prefabricated stress cones, porcelain sleeves, insulating oil and other parts when they leave the factory, and they become finished products after on-site installation—a complete, quality-guaranteed accessory product. Therefore, installation and construction are indeed a very important part of the overall product quality. It can be said that for the same set of products, different levels of construction personnel install the results, and the level of the product is different. The selection guide for high-voltage cross-linked cable accessories is summarized as follows:

1. A good installation process has relatively low requirements on the on-site environment and the technical level of the operators, the installation quality is easy to control, and the product quality is easy to guarantee.

2. Strictly speaking, the installation of high-voltage cable accessories is part of the work of the manufacturer, not the user's work. For users, what is important is the reliability of the accessory products after installation.

3. Reliability is always the first important consideration in cable engineering. Only on the basis of reliability can we talk about the convenience of installation and construction and the high and low prices, otherwise the biggest trouble and the most expensive price will be obtained. Of course, to ensure the reliability of the selected accessories, in addition to the correct selection, there are also a series of issues related to manufacturing, construction and installation, and test acceptance.

4. Whether the installation process is simple or not is indeed an important condition for the selection of cable accessories, but it is not necessary to place the convenience of installation and construction in an important position.