The rapid development history of China's silicone rubber composite insulators

07-12-2021

Introduction

Since the first batch of Chinese-produced silicone rubber composite insulators were put into operation in the Shitai Line and Baocheng Line electrified railway tunnels in 1983, the development of composite insulators in China has been more than 30 years. Today, China has become the first country in the world to use organic external insulation as the mainstay in UHV AC and DC transmission systems.

In order to ensure the safety of large power grids, the power system usually adopts a conservative attitude towards new technologies. The wide application of new technologies often requires in-depth research, detailed demonstration, careful trials, and accumulation of several years of experience before they are gradually promoted. However, the speed of the application and promotion of composite insulators in China has obviously far exceeded general expectations.

The development of insulators is inseparable from the development of the power industry. China's power industry has developed rapidly for more than 30 years. In the past 10 years, it has continuously stepped up to several major steps such as 750 kV AC, 1,000 kV UHV AC and ±800 kV UHV DC. At the end of 2014, the national annual power generation capacity reached 5.545 trillion kW·h, the length of transmission lines with voltage levels of 220 kV and above reached 570,000 km, and the total length of the 9 UHV AC and DC lines currently in operation reached 13,813 km. The length of the UHV AC/DC line under construction is 11 556 km.

The construction of large-scale power grids with new voltage levels will inevitably put new and higher requirements on the performance of insulators, in addition to the substantial increase in the amount of insulators. For example, 110-220 kV transmission lines use a large number of 70-120 kN insulators, while 500 kV transmission lines must use a large number of 160-210 kN insulators for UHV AC and DC lines. It must be based on 300~550 kN; for example, the large-scale construction of DC transmission lines inevitably requires that insulators can operate safely and stably under DC voltage for a long time; in addition, as the scale of China's power grid continues to expand, the workload of transmission line operation and maintenance It is also becoming more and more onerous, which also puts forward new requirements for insulators.

The technological progress of China's insulators has well supported the development of China's power industry. The review of the development history of China's composite insulator technology can have many different perspectives, such as from the dosage, voltage level, manufacturing technology and process progress, major accidents in operation, hot issues, etc. This article chooses to review the development of composite insulators in China from the perspective of the development of composite insulators and their applications in power systems.

1. Three key development opportunities for composite insulators

In the 30 years of rapid development of composite insulators in China, from the perspective of external conditions or development environment, there are 3 development opportunities worthy of special attention, which can be called 3 key opportunities for the development of composite insulators: 1) Large-scale pollution flashover Opportunities; 2) DC transmission opportunities; 3) UHV opportunities. When these three special development opportunities are coming, power grid development has encountered new and major problems. If only based on the past experience of porcelain insulators or glass insulators, it is difficult to meet the external insulation requirements of the power system when the three opportunities are coming. If any new technology can be recognized by the power operation department and accepted by the power system during the critical period of power grid development, its application in the power system will be greatly accelerated.

1.1 Large-scale pollution flashover opportunities

The first opportunity appeared in the late 1980s and early 1990s (around 1989-1992). This opportunity is called the "large-scale pollution flashover opportunity". China's first 500 kV transmission line was put into operation in 1981. The 500 kV power grids in various provinces and the inter-provincial 500 kV backbone grids in North China, Northeast China, Central China and East China did not begin to take shape until the end of the 1980s. At the same time, many serious large-scale pollution flashover blackouts occurred in major power grids across the country.

In January 1989, heavy fog in East China caused pollution flashovers and 12 trips in 5 of the 6 500 kV lines that are the main grid of East China Power Grid. In December 1989, two 500 kV lines of the East China Power Grid were polluted again, and the porcelain insulators of the Doudu line fell to the ground due to the explosion of iron caps, and the lines were suspended for nearly a week. In February 1990, under the rare heavy fog in North China for more than ten consecutive days, all four 500 kV lines were out of pollution flashover, and the Beijing-Tianjin-Tangshan power grid was dismantled twice. On the 500 kV Fangbei line, on February 10, the porcelain insulator pollution flashover iron cap exploded, causing the wire to fall to the ground, and the delivery point was returned 5 days later. The 500 kV Dafang line was shut down for 60 hours on February 17 and the power supply was resumed on the 19th.

Immediately, the then Ministry of Electric Power held the National Pollution Flashover Work Conference for three consecutive years from 1990 to 1992. It is very rare to convene a national conference for three consecutive years for a topical issue of external insulation that has not received much attention. This shows that the large-scale pollution flashover accident has attracted the attention of the Chinese power sector. At that time, the anti-pollution flashover measures that could be taken immediately were mainly the traditional "increasing the number of insulators or replacing large creeping distance insulators to increase the creepage distance of the insulator string, strengthening the manual power failure cleaning of the transmission line in the dirty area, and painting some hydrophobicity. Coatings", among these measures, the first two are the most important. It should be pointed out that the power sector is obviously not satisfied with these measures.

Composite insulators (silicone rubber insulators), as one of the country’s "seventh five-year" key tasks, reached Tsinghua University and Wuhan Institute of Water Conservancy and Electric Power in 1986. The 110~500 kV silicone rubber synthetic insulators developed by the two schools passed the technical appraisal in 1988-1990, and subsequently transferred their respective silicone rubber umbrella skirt formulas and hardware connection methods to different power equipment manufacturers for mass production. . That is to say, when a large-scale pollution flashover occurred in China's power grid, China's silicone rubber composite insulators also came into the factory from the laboratory of the university, and they have the ability to be adopted by the power system.

The excellent pollution flashover resistance of silicone rubber composite insulators is considered to be the most attractive feature, but the light weight and high specific strength are not the most concerned. The first name for composite insulators in China is "anti-pollution flashover insulators"; and in China, "composite insulators" and "silicone rubber composite insulators" are used exactly the same. Oxygen resin and polytetrafluoroethylene composite insulators are hardly recognized. In addition, the price of silicone rubber insulators at this time is about 2 to 3 times that of ordinary porcelain insulators. Even though the price of silicone rubber insulators was so high at that time, the power sector still adopted them for their excellent pollution flashover resistance. The aging problem of organic materials when used for outdoor insulation is temporarily put aside at this time. After all, the aging resistance of silicone rubber materials is very good among organic materials. All in all, during this period, the advantages of high pollution flashover voltage of silicone rubber insulators overwhelmed the high price and the power sector still worried about their long-term aging performance.

It can be said that the large-scale pollution flashover accidents that frequently occurred in porcelain insulators from the late 1980s to the early 1990s provided a rare opportunity for the development of silicone rubber composite insulators. Completed the research and development of composite insulators in China. The power sector responded positively to this new silicone rubber insulator and placed high expectations, which greatly accelerated the trial operation progress of silicone rubber composite insulators and laid the foundation for the rapid development of composite insulators in China. The proactive research work of the composite insulator research department has provided sufficient preparation for composite insulators to seize the "large pollution flashover opportunity", and provided technical measures for the power system to solve large-scale pollution flashover.

1.2 HVDC opportunities

The second opportunity occurred during the construction period of the Three Gorges Power Transmission Project around 2000 (around 1998-2002). This opportunity can be called the "HVDC opportunity". A total of 9 000 km of AC and DC transmission lines are involved in the Three Gorges Project. The pollution of DC insulators is more serious than that of AC insulators, and the pollution flashover of DC transmission lines is far more serious than that of AC lines. The famous pollution flashover accident on the US West Pacific DC link provides an important reference for the construction of China's DC transmission lines.

The ±500 kV Geshang Line (Gezhouba-Shanghai, 1 045 km, 1.2 GW) built in 1990, even if the DC insulator fouling will be more serious, it has increased the insulation design margin, but in actual operation Porcelain insulators continue to suffer from pollution flashover. This increased the number of other DC projects that were about to be constructed at that time, such as sending the Three Gorges to East China and South China (Longzheng Line, Sanguang Line, Jiangcheng Line, etc., each line is about 1,000 km, and each line is 3 GW) Concerns about pollution issues in China.

It needs to be pointed out that when the "DC transmission opportunity" is coming, the key problems of composite insulators in the early stage of operation have just been broken and resolved. Avoid the long-term mechanical strength drop of the external wedge insulator. In addition, clear research results have been made on the hydrophobicity evaluation of silicone rubber materials, resistance to direct current corrosion, shed damage during operation, and abnormal flashover. These early technical reserves and successful solutions to existing problems provide an important guarantee for composite insulators to seize the "DC transmission opportunity".

The "±500 kV DC rod suspension composite insulator technical requirements", which was compiled in 1998, was formally promulgated in 2002 and became the Chinese power industry standard DL/T 810-2002 (the standard was revised in 2012). The standard carefully analyzes and absorbs the research experience and operating experience of my country's AC composite insulators, the research results on DC composite insulators that began in the mid-1990s, and the operating experience of DC lines in other countries. This is the first technical standard for DC composite insulators. The promulgation of this standard is an important symbol of my country's new generation of composite insulators. DL/T 810-2002 is not only of great significance for the quality assurance of AC and DC composite insulators, improving the mechanical and electrical reliability of long-term operation, but also important for the standardization of UHV composite insulators in a few years. The successful operation experience of composite insulators in AC power transmission systems, the performance improvement of composite insulator umbrella skirt materials, the successful development of composite insulators acid-resistant core rods, the successful development of composite insulators crimping joint structure, and the technical standards of DL/T 810-2002 The promulgation has strengthened the confidence of the power design department and operation department in composite insulators, which paved the way for the large-scale use of composite insulators in DC lines, and composite insulators also provided technical support for DC transmission projects.

In addition, the high prices of DC porcelain and glass insulators due to ion migration issues have also contributed to the significant price advantage of silicone rubber composite insulators. The price of silicone rubber DC composite insulators is only 1/3 of the price of DC porcelain and glass insulators, which is completely different from the situation of AC, which increases the attractiveness of DC silicone rubber composite insulators.

The typical doubt of the design institute at that time was: if the tower head is designed according to the configuration of composite insulators, the size of the tower head may be smaller than the size of the tower head configured according to porcelain and glass insulators; but if the tower head is designed to be smaller, If the composite insulators are aging in the future, it is impossible to go back and replace the composite insulators with porcelain or glass insulators. Especially when a large number of composite insulators are used, how to deal with the aging phenomenon of composite insulators at the same time? Will the power equipment companies and power operation departments have time to produce and replace? The answer to this concern is actually very simple: if the first batch of composite insulators are several years later It is really aging. It is also replaced by another batch of new composite insulators. In short, it is impossible to return to the state of using porcelain and glass insulators. Porcelain and glass insulators have learned too many pollution flashovers, and the treatment of large-scale air pollution cannot be completely solved in a short period of time. Moreover, the price of silicone rubber composite insulators is only 1/3 of the price of porcelain and glass insulators. As for the possible aging problem, don’t worry too much. The aging of composite insulators is related to many factors, such as natural sun and rain, environmental attack, moisture, and surface discharge. The operating conditions of composite insulators vary greatly, and it is impossible for the composite insulators along the line to age to the extent that they need to be replaced immediately. If composite insulators really need to be replaced, power equipment companies and power operation departments also have enough time.

After the construction of the Three Gorges DC transmission and transformation project, the application of silicone rubber composite insulators in China has taken a big step forward. By the time the Sanguang DC was put into operation in the summer of 2004, the number of silicon rubber composite insulators used on the four ± 500 kV DC transmission lines of Geshang Line, Tianguang Line, Longzheng Line and Sanguang Line had reached 9,750, far exceeding the others. The total amount of DC composite insulators in various countries. The large proportion of composite insulators in the DC transmission system is widely used, which in turn strengthens the power operation department's confidence in the further promotion and expansion of the application of composite insulators in the AC transmission system.

1.3 UHV opportunities

The third opportunity appears in the period of construction of AC/DC UHV transmission and transformation projects, that is, around 2006-2010. This opportunity can be called the "UHV opportunity."

When the State Grid Corporation of China and China Southern Power Grid began to actively launch AC/DC UHV transmission and transformation projects from the end of 2004 to the beginning of 2005, all parties at home and abroad still had great concerns about the difficulty of UHV projects, including UHV transmission. Concerns about substation equipment. Concerns about UHV insulator strings are firstly their pollution performance, and secondly there are mechanical properties and electric field control.

According to the operating experience of porcelain insulators at that time and the artificial pollution flashover test data of large-tonnage porcelain insulators, the string length of 1,000 kV AC porcelain insulators will also reach 10.5 m in lightly polluted areas, and it will reach 12~15 in moderately polluted and heavily polluted areas. m, even longer. The length of ±800 kV DC porcelain or glass insulator strings will reach 12.7~15.6 m in moderately polluted and heavily polluted plain areas.

The length of the insulator string designed according to porcelain and glass insulators obviously exceeds the insulation requirements for lightning and operating overvoltages, and does not conform to the principle of equal strength design in engineering. At the same time, such a long string of insulators will cause the tower head to be too large, the line cost soaring, the line construction is difficult, and the cleaning and maintenance cost of the line operation is high. This is obviously unacceptable for the power operation department.

The successful development of crimping large-tonnage composite insulators and the good operating experience of composite insulators for more than ten years have provided strong support for them to win the "UHV opportunity". Just as composite insulators can seize the "DC transmission opportunity", when the "UHV opportunity" comes, China's composite insulators have completed the preliminary technical reserves and operating experience accumulation to seize the opportunity. These operating experiences include the good performance of composite insulators in polluted areas, the excellent tensile strength and long-term creep performance of crimped composite insulators, and the prevention of brittle fracture accidents by non-boron and acid-resistant core rods. The price advantage of silicone rubber composite insulators in UHV and large tonnage levels also provides strong support for its development.

The large-area pollution flashover accident of porcelain insulators from 1989 to 1990 and the second large-area pollution flashover accident of porcelain insulators in 2001 made the power department's memory still fresh. In areas where porcelain insulators frequently suffer from pollution flashover, once the line insulators are replaced with silicone rubber insulators, the pollution flashover is successfully avoided; while the lines that have not been replaced with silicone rubber insulators continue to have pollution flashovers. The extensive use of silicone rubber insulators has been very successful in avoiding power grid pollution flashover accidents. From 1971 to 1999, there were more than 4,000 line pollution flashovers and more than 2,000 substation pollution flashovers in 35-500 kV systems. After extensive use of silicone rubber composite insulators, since 2007, the State Grid Corporation of China and China Southern Power Grid Corporation, pollution flashovers have been ranked almost the last among various tripping and outage factors of transmission lines.

As organic insulators, the aging performance of silicone rubber insulators has naturally been questioned. Some experts believe that UHV power transmission is already a project that challenges the limits of technology. You should not put all your eggs in the same basket, and you should not put immature technologies including composite insulators in the first UHV project at the same time. Come.

After detailed demonstration and testing in 2006-2008, silicone rubber composite insulators finally won the opportunity of UHV. A total of 7,200 silicone rubber insulators were used on China's first 640 km long 1,000 kV AC UHV line. The line has been in safe operation for 6.5 years since it was put into operation in January 2009. The first three ±800 kV UHV DC lines (Yun-Guang Line: 1 417 km, 5 000 MW; Upward Line: 1 895 km, 6 400 MW; Jin-Su Line: 2 059 km, 7 200 MW) were in 2010. It was put into operation in June and July of 2012 and December 2012. On these three lines, the amount of silicone rubber insulators exceeds 2/3 of the total amount of insulators, and these silicone rubber insulators have been in safe operation so far.

China has become the first country in the world to focus on organic external insulation in UHV AC/DC systems. Among all three AC UHV lines that have been put into operation, the amount of composite insulators calculated in series is about 60%; In all six DC UHV lines that have been put into operation, the amount of composite insulators calculated in series exceeds 85%.

2 The four stages of composite insulator development

The 30-year rapid development process of composite insulators in China can be divided into four successive development stages, namely development, promotion and application, mass use and conventional products, as shown in Figure 2. Each development stage has its own characteristics and focus of attention.

2.1 Development stage

The development stage is roughly the first 10 years in the development history of composite insulators in China. In the research and development stage, the research institutes completed the research and development of composite insulators in China, and through the transfer of technological achievements, the power equipment enterprises have mastered the manufacturing process of composite insulators. At this stage, composite insulators are mainly in the development stage of laboratories and process workshops. Research institutes and power equipment companies mainly introduce and emphasize the characteristics and performance of composite insulators as a new product at this stage to facilitate the power sector Get to know. During the development of composite insulators, the characteristics and performance of composite insulators such as pollution flashover resistance, strong surface hydrophobicity, tracking resistance, and aging resistance have also received special research and attention.

Silicone rubber composite insulators have "high pollution flashover and wet flashover voltage", "light weight", "high specific strength", "not easy to break", "easy to transport and install", "not easy to man-made damage", "short production cycle", and " "Composite insulators have excellent mechanical and electrical properties" is the most common introduction term in the development stage. Its purpose is to try to give composite insulators excellent performance, and to introduce that it can solve the problems that traditional porcelain and glass insulators cannot solve, so that the electric power department can understand and be familiar with this new insulator.

2.2 Promotion and application stage

From the early 1990s to around 2000, the development of composite insulators in China entered the stage of popularization and application. At this stage, the application scale of composite insulators in the power system is expanding. At the same time, many problems and accidents of composite insulators also occurred during this period, such as brittle fracture of composite insulators, long-term mechanical performance decline, and unexplained flashing. Damaged network, umbrella skirt, etc.

During this period, the research institute was mainly concerned about how to solve various problems and accidents in the operation of composite insulators, and provide technical support for the optimized application of composite insulators. At the same time, during this period, the production scale of power equipment manufacturers has gradually expanded. While introducing the excellent performance of composite insulators to the power sector, manufacturers are more willing to show their production processes, production lines and mass production capabilities.

2.3 Mass use stage

After about 2000, China's composite insulators entered the stage of mass use. Composite insulators are widely used in key projects such as 500 kV AC and ±500 kV DC. Competition among factories has intensified, especially price competition has become fierce. How to ensure the quality of composite insulators while reducing prices and controlling production costs, especially how to ensure the long-term performance of composite insulators has become the focus of attention at this stage.

It needs to be pointed out that the quality of power equipment is judged by standards. The important role and significance of standards is to screen out inferior products, rather than select a few high-quality products from a large number of products. It is not easy to judge the long-term performance of composite insulators with a small amount of short-term tests.

Inappropriate standards are also an important reason for dissatisfaction with quality. If the defective product cannot be eliminated, the standard itself is inappropriate. In 1992, IEC 1109 was the first international standard for composite insulators. At the beginning of its birth, it did promote the development of composite insulators. However, in the late 1990s, it gradually exposed to the elimination of inferior products (especially It is the product with poor long-term performance.) The effect is not good enough. The international community is also worried that because the standards are not effective enough, manufacturers excessively reduce costs, causing insulators that "conform to the standards" but actually have poor long-term performance into the power grid, which will eventually damage the entire industry.

The difficulty in standard formulation lies in its lack of adequate test and evaluation methods for the long-term performance of composite insulators. One direction is to develop complex long-term performance test methods. This is necessary, but it is more difficult and requires a lot of research work. The other direction is to develop material performance test, which can make up for the defect that only the overall performance of insulators is ignored in the previous standard. It is based on this consideration that DL/T 810-2002 introduced several requirements for the material of the umbrella skirt and core rod of composite insulators, and managed to ensure long-term performance by controlling the performance of the material. For example, DL/T 810-2002 puts forward the test method and acceptance criterion for evaluating the hydrophobic migration and recovery characteristics of umbrella skirt material, the test method and acceptance criterion for DC tracking resistance of umbrella skirt material, and the test method and acceptance criterion for silicone rubber composite insulators. Artificial pollution test method, test method of stress corrosion resistance of core rod material and acceptance criteria, etc.

2.4 Conventional product stage

As the AC and DC UHV successfully realized organic external insulation, China's composite insulators began to enter the period of conventional products from the special product of "anti-pollution flashover insulators". From January 2012 to September 2015, the consumption of composite insulators accounted for 55% of the new insulator market in the National Grid project, which is much higher than 26% of porcelain insulators and 19% of glass insulators calculated by string. .

Good insulator performance means not only qualified materials, reasonable design, and excellent manufacturing, but also proper selection, compliant transportation and installation, and proper maintenance. Therefore, at this stage, how to use and maintain composite insulators more reasonably has become the focus of attention.

3 Problems faced in the development of composite insulators

Compared with traditional porcelain and glass insulators, silicone rubber insulators are brand new products after all. Although silicone rubber insulators have won the above three key development opportunities, there have been some accidents or accidents in the long-term operation. These accidents or accidents have undoubtedly become the main problems faced by silicone rubber insulators in their large-scale applications.

3.1 Brittle fracture

The brittle failure of a 220 kV composite insulator that occurred in Guangdong in December 1994 was the first brittle failure of a composite insulator in China. The accident caused the wire to fall, and the accident insulator only operated for about 4 years. The accident prompted research units, manufacturers, and users of composite insulators in China to have to pay attention to this kind of vicious accidents that have occurred in foreign countries. Another brittle fracture accident occurred in 1998 when a 500 kV composite insulator in Zhejiang was brittle fracture. In 1999, there were 4 brittle failure accidents of 500 kV composite insulators, and imported and domestic products accounted for 1/2. In 2001, there were 6 unprecedented brittle failures of 500 kV composite insulators, of which 5 were imported composite insulators. .

After the brittle fracture accident occurred in 1994, Tsinghua University strengthened the research on the mechanism and development process of composite insulator brittle fracture, and proposed brittle fracture simulation test methods and factors affecting brittle fracture during insulator production. Several mandrel manufacturers developed boron-free mandrels with good stress corrosion resistance in 2000-2001. In the power industry standard DL/T 810-2002 promulgated in 2002, the test method and acceptance criteria for the stress corrosion resistance of the mandrel were clearly specified. The universal application of stress corrosion-resistant core rods and DC composite insulator standards have successfully avoided the brittle fracture accident of composite insulators. These clear measures to prevent brittle fracture also eliminate the worry of the power sector about the brittle fracture of composite insulators.

3.2 Decreased mechanical strength of external wedge insulators

In the middle and late 1990s, the power department discovered that the mechanical strength of composite insulators with external wedge joint structure decreased significantly after running for a short period of time. A province conducted spot checks on 44 100 kN external wedge 110 kV and 220 kV composite insulators that had been in operation for 2 to 5 years, and only 1/3 of them passed the 1 min rated mechanical load (SML) endurance test. The damage load is only 60%~80% of SML, and the lowest has dropped to 50% of SML. Another province conducted sampling tests on 9 70-100 kN external wedge composite insulators that had been in operation for 1 to 5 years, and only one passed the 1 min SML endurance test. The tensile failure load of 8 insulators is only about 80% of SML.

From 1997 to 1999, Tsinghua University studied the structure of crimping joints, and since 1999, it has provided optimized crimping control technology to major manufacturers. The tensile strength of core rods with diameters of 18 mm and 24 mm reached 750 MPa and 700, respectively. MPa, and the standard deviation of the tensile failure load is very small, and the long-term mechanical creep characteristics are excellent. With reference to the original IEC 61109:1992 standard, in the 600-day long-term creep characteristic test, the creep slope is only -2.07% Mav per logarithmic unit time (Mav is the average failure load of 1 min). This creep slope is not only better than the usual composite insulators, but also significantly better than the outer wedge composite insulators.

The timely research and development of composite insulator crimping technology and the introduction of anti-brittle breaking measures dispelled the concerns of the power sector when the DC opportunity for composite insulators arrived. Subsequently, Tsinghua University cooperated with manufacturers to successfully develop 300-550 kN composite insulators, and conducted research on the mechanical strength and stability of large-tonnage composite insulators, and provided reliable technology and technology for UHV when UHV opportunities arrived. product.

3.3 Unexplained flashover

In the late 1990s, especially around 1996-1999, unexplained flashovers of composite insulators were reported everywhere. These flashover accidents mainly occurred in the 110~220 kV voltage level, and the flashover occurred mainly in the early morning. In these accidents, almost all the transmission lines with flashover can be reclosed successfully, and the composite insulators with flashover are retrieved, and their electromechanical properties and the physical and chemical properties of the umbrella material are also normal. However, because the cause of flashover is unknown, there is no corresponding preventive measures, which makes the power sector worry about the large number of applications of composite insulators.

The simulation test of Tsinghua University from 1999 to 2000 clearly showed that the vast majority of these flashover accidents should be caused by bird droppings on the line insulators before taking off for food in the early morning. The countermeasures to prevent this type of flashover are immediately clear, and the consequences of this type of flashover on the power grid are immediately clear, thus dispelling the concerns of the power sector.

3.4 Umbrella damage

Around the mid-1990s, many composite insulators became hard and brittle after running for a period of time, or even after running for a short period of time, and the umbrella skirt was prone to damage and breakage. This problem has caused the electric power department to worry about the long-term aging resistance of composite insulators, and also caused discussion and research on how to adjust the silicone rubber formulation to balance the hydrophobic migration performance and tracking performance of silicone rubber materials. Fortunately, the damage of composite insulator umbrella skirts is mainly concentrated on the products of some manufacturers. Related manufacturers quickly improved the formula, and other manufacturers also learned experience in time, optimized the formula, and the problem of composite insulator umbrella skirt damage was solved.

3.5 Bird Pecking Damage

Bird-pecking damage to the umbrella skirt and sheath of composite insulators rarely occurred in China before, but before the UHV composite insulators were put into operation, hundreds of composite insulators were found to be injured by birds. The damage mainly occurs on the top of the I-type string composite insulator and the lower part of the V-type string composite insulator. Finally, some composite insulators with severe damage were replaced before the UHV line was formally charged. It should be noted that the phenomenon of bird-pecking composite insulators only occurs on individual lines in individual areas, and is not a universal problem faced by composite insulators. And after the line is electrified, the bird pecking phenomenon will be greatly reduced. Therefore, bird pecking is not the main factor threatening the safe operation of composite insulators. However, in the future, the further application of composite crossarms, composite insulator V-strings and tensile strings may make the problem of bird-pecking composite insulators more prominent, which still needs further attention and research.

3.6 Rotten fracture

In recent years, a new abnormal fracture mode of composite insulators under low mechanical load has appeared. The cross section of the core rod is not smooth, the texture of the core rod has become crispy and shaped like rotten wood, and the core rod has powdered, glass fiber and resin. Separate. This new abnormal fracture mode is obviously different from brittle fracture. Since 2008, there have been 8 such accidents of 500 kV composite insulators. Among them, 5 are imported products, 2 are domestic products, and one manufacturer is unknown.

We named this newly-appearing abnormal fracture of composite insulators "crisp fracture". Some progress has been made in related laboratory simulations. The main characteristic of decay fracture is the degradation and deterioration of the epoxy resin matrix in the glass fiber reinforced plastic core rod. The occurrence of decay fracture is closely related to the failure of the interface between the umbrella skirt and the core rod of the composite insulator, and the composite insulator will have a local temperature abnormality before the decay fracture occurs. The decay and fracture phenomenon of composite insulators is worthy of further study by researchers.