1. National Power Corporation Beijing 100031, China 2. National Power Corporation Electric Power Research Institute Beijing 100085, China 3. National Power Corporation, Wuhan 430073, Wuhan SF6 switchgear insulation

0 Introduction

Application of Composite Insulators history of nearly 40 a, has been in the world with 27 countries and regions, the most use in North America. Early synthetic insulator material including epoxy resin, ethylene-propylene rubber, silicone rubber at room temperature until the 70′s high-temperature vulcanized silicone rubber composite insulators come out first in Germany. With the traditional cable joint and glass insulators compared to synthetic insulators with a light weight, high strength, tolerance and strong flash, manufacture and easy to maintain, use it abroad, mainly to prevent the shooting and the transportation is convenient [1], and is mainly used in China pollution prevention and control transmission and distribution equipment in the flash. Despite our late start, but the basis of lessons learned abroad, our starting point, beginning to develop and produce high-temperature vulcanized silicone rubber insulators (composite insulators under the order referred to.) In recent years, composite insulator has been recognized and praised the power system, developed very rapidly, and has become the fastest growing science and technology into productive forces an outcome. So far, the composite insulator is running in the network has reached 790 thousand years.

Development of Composite Insulators 1 3 stages

China’s electric power system research and development of composite insulators began in the early 80s, its application can be divided into three stages:
1.1 The development, achievements and products of the phase transfer

1981 to 1990 was developed composite insulator, results and products of the transfer stage. As a national key research projects, Hydropower, Wuhan University (main), East China Electric Power Test Research Institute (main), Tsinghua University and Xi’an Institute of Electric has developed a ceramic composite insulators distinctive samples, and began to test small quantities of hanging run; build power plant in Xiangfan in 1988 received the first transfer of scientific and technological achievements. 110 kV line was marked with the cross arm bar pillar of products through the identification of relevant departments, and access to the grid, then there is no uniform manufacturing standards. According to statistics, in 1990, only Beijing, Tianjin, Shanxi, Inner Mongolia, Hubei, Shanghai, Henan, Xinjiang and Gansu, a small number of power supply bureau trial of 2 000 composite insulators [2].

1.2 The pilot phase of industrial

1990 to 1994, is a synthetic insulator industrial pilot phase. To the end of 1989 to early 1990 have occurred in the east, north, northeast and other places in the large area of flashover as an opportunity to start a lot of access to the grid composite insulator; to the end of 1994, nearly 20 production plants, the annual production of 100,000, of which hang Run 50 000 mesh, mainly in multiple flashover, prone provinces [2]. Main symbol is the International Electrotechnical Commission standards-based national standard JB5892-91 “organic composite insulator technology,” the promulgation of, and according to the standards of production and put into operation a new generation of products in large quantities, especially in domestic composite insulator 500 kV Line Volume linked network operation. To protect the safety of the grid, the former Department of Energy [1993] No. 45, issued a “full-insulator process management approach”, in which the identification of synthetic insulators, operation and management of orders and put forward specific demands. Early development of the extruded type, irrigation plastic-type process is gradually phased out.
1.3 The large-scale practical stage

Since 1995, synthetic insulators entered the practical stage. It has not only been widely acclaimed run departments, and the concern caused by the design department; not only in the transport line including 500 kV lines used in large quantities transferred to climb, and the new line is also used in volume and even the whole line. Rapid increase in the amount of composite insulators network: 100 000 1995, 200 000 in 1996, the end of 1997 more than 40 million. Was marked JB/T8460-1996 “high-pressure lines Composite Rod Insulators” industry standards and the National Coordination Centre announced transfer network [1997] No. 93, issued a “use of composite insulators guidance.” To ensure network quality synthetic insulator, the National Coordination Centre transfer network [1997] No. 145, also issued a “network of quality assurance composite insulators necessary conditions.” The promulgation of these standards and regulations are designed to meet the large-scale power system using composite insulator, to regulate the production of composite insulators.

Composite insulators made in the “Eighth Five-Year” period has been included in the national high-tech products as a major science and technology promotion projects, and included “Torch Program.” The transition to the large-scale use, the first is the rapid technological improvements, such as end fittings and joining technology and constantly improve the mandrel, mandrel and sheath interface by filling plastic, extruded rapidly to the continuous extrusion, the overall injection molding and the overall change ; followed by manufacturers increased year by year, the annual production capacity has exceeded 150 million, the market is oversupply; third network to double year after year, according to statistics in 1998, reached 460,000 (see Table 1); The fourth is the national industry standards and continuous power system with the relevant provisions issued, regulating their production and use; fifth, scientific research, development and testing of new products, technology, further stepped up.

Table 1, the amount of the national network statistics Composite Insulator

Power Name Number / Name the number of branch network / support
* North 81752 Guangxi 3200
Northeast 48 595 1 260 Hainan
Northwest Yunnan 2554 40602 *
Guizhou 3265 East 121 534
Central Sichuan 1 453 54 801
Chongqing, Shandong, 820 * 38 278
Fujian 13 000
Guangdong, China Total 460 828 49 714
* The end of 1997 data.

2 Run Accident in flashover and
With the use of composite insulators lines sharp increase in recent years, the composite insulator flashover and damage to the growing number of information also, as of 1998 statistics in Table 2. Except for damage caused by external forces (mainly in construction), the current problems in composite insulator can be divided into two categories: one is led to a vicious power accident occurred product damage, and the other with the traditional porcelain and glass insulators, as will happen flashover. The former is the product quality problems; the latter have much experience with the operation which led to inappropriate use, of which flashover performance of silicone rubber are also relevant.

Table 2 Synthesis of the national electricity system, and damage to the insulator flashover accident statistics
Grid
Name of flashover / branch damage / support
      Flashover lightning bird hazard identification of strong wind force is not broken off Mandrel breakdown of the total number of interface
North 13148 * 31104942 ** 6
Northeast 54,371,911
Northwest 71081222501 ** 1
East 2463639538
Central 71,521,511
Shandong 351,141,411
Fujian 516
Guangdong 3,838,112
Yunnan 22
Guizhou 21 21
Sichuan 6633
Total 1314023 * 10451259158 *** 23
% 8.9 * 3.9 1.5 50.6 15.4 19.7 100 65.2 100 34.8 ***

* Includes rain flash 1; ** Includes mandrel extrusion 1; *** Includes mandrel extrusion 2.

2.1 Product quality synthetic insulator damage caused

2.1.1 The decline in mechanical strength
Mandrel or below the rated load, rated mechanical damage to a larger slip, ranging sealant slot, and at the end fittings from the mandrel in the extrusion, which runs a number of years in many provinces and removed the products after Mechanical strength tests have found that even inventory also significantly decreased the mechanical strength of the case. Operation even if the seal tiny cracks appear, will eventually lead to dropped calls occur. Although only the operation of individual mandrel prolapse reported, but decreased mechanical strength of composite insulators is still a potential threat. Especially with external wedge structure of the product end user connections, strict control measures to be taken, such as every 1 ~ 2 a board connecting rod end zone sampling observation sealed case, or remove a number of mechanical strength of the test product only test.

2.1.2 Mandrel breakdown and brittle fracture of the interface
Interface breakdown occurred in the case of lightning, especially the early adopters of filling plastic, extruded technology products, pay close surveillance. Particular attention is under the breakdown frequency of such incidents in the east, north and other places have been 15 cases, this is obviously a quality issue. Frequency voltage breakdown caused by the quality mandrel, put into operation occurred within a few hours; the running time required to interface breakdown is relatively much longer. Glue can not be filled with plastic, molded or extruded improper use of coupling agents and workmanship defects will lead to interface breakdown.

Fault accident mandrel to brittle fracture is most prominent. Guangdong Province, east China, north China have occurred in 4 cases. Brittle fracture is the so-called wet acid atmospheric electric discharges generated after invasive mandrel breaking glass. Therefore, we must guarantee a solid and long-lasting seal to prevent the sheathing damage, the longer term should improve the anti-acid ability of mandrel. Can directly lead to fracture mandrel dropped, with the growth of running time, such incidents are likely to increase, we must guard against.
According to statistics, the operation of composite insulator breakdown and mandrel interface fracture occurs, together with mandrel emerge from the end of serious damage to the fittings have been 23 accidents, the failure rate of about five hundred thousandths.

2.1.3 deterioration of surface properties of silicone rubber
Some run-off insulator sheds less flexible, easy to tear, which indicates that the surface of silicone rubber material has changed. Domestic and international studies have shown that UV-resistant silicone rubber and thermal stability are very good, leading to the main factor is the aging of long-term contaminated surface pitting. Insulator, but has been tested to run 1 ~ 2 a, such a serious deterioration occurs incredible. Formula should be carefully chosen the manufacturers to strengthen quality inspection of raw materials and additives, reinforcing agents with quality control.

2.2 Composite Insulator surface flashover

2.2.1 LIGHTNING
Lightning flashover flashover have been identified about 63% of aggregate expenditure, mainly in eastern and southern coast and southwestern provinces frequent lightning activity, to 35 ~ 110 kV line is particularly prominent. And compared with the length of the string of porcelain insulators, 35 ~ 110 kV composite insulator because of its relatively small diameter of umbrella reduced the discharge distance; of 220 kV and above products, many of the location and grading ring installed to shorten the length of the insulation. Therefore, the window size allowed in the tower within the appropriate increase in insulator length is necessary in order to prevent lightning strikes on composite insulator burns, multi-mined areas can be installed at both ends of composite insulators arc device.

2.2.2 bird hazard

Birds have been identified flashover flashover aggregate expenditure accounts for the number of second place in the top five grid has occurred to the western interior, the east coast is more. Guano flashover generally leave from the surface of the guano shed remnants of judgments, the traditional bird hazard prevention measures can achieve satisfactory results.

2.2.3 Flashover
Composite insulator in the continuing heavy fog, even the rain, condensation and melting ice and snow conditions, flashover has occurred in 22 cases. Although there are some reasons for the flashover controversial, but the idea that the use of synthetic insulators may prevent the flashover of view is biased. In fact, the silicone rubber is too thick smear layer leaving the surface hydrophobic dirt is difficult to migrate to the surface, the surface hydrophobicity in the long wet conditions will gradually weaken or even disappear temporarily render the phenomenon (north, northwest, etc. Some of flashover may be triggered), but also to their different hydrophobic unclean thing a major impact on the migration, which will lead to the performance of external insulation composite insulator greatly reduced. Most people in the past to understand the under artificial pollution tests the performance of its tolerance, and artificial contamination test results are often too high to simply apply the traditional porcelain and glass insulators in the test methods.

2.2.4 did not identify the cause of the flashover

Currently, 20% still did not identify the reasons for the flashover, but also called the “unknown flashover.” The test items had flashover, most laboratory tests prove that after no quality problems. To identify each composite insulators flashover with a cause and difficult to do. Should be through careful research and observation, as much as possible to find out the cause of flashover.
2.3 external damage

Including sheds destroyed, damaged and mandrel break jacket construction, including damage, and the running sheds pecked by birds, stock or construction to be rat-bite, in particular, to prevent the sheathing damage: One of these risks is difficult to found, and may directly endanger mandrel; second serious consequences, may lead to brittle fracture and the occurrence of accidents dropped.

3 application prospects and should be concerned about

Composite insulators in China should be more widely used, people need to break flash used for anti-pollution awareness, to shake the traditional porcelain and glass insulators dominance. To achieve this goal, the following issues need attention, and continue to conduct further research.

3.1 The selection of mechanical strength
The most prominent feature of Insulator Core synthesis of high strength and high specific strength. The tensile strength of up to 7 000 MPa, high-quality carbon steel than the intensity of 5 times. In some areas, departments use of synthetic insulators, mechanical strength than traditional porcelain, glass insulators to improve level, such as the use of porcelain insulators for the 160 kN, while the use of synthetic insulators to 210 kN. In fact, when using less than 40% of rated load mechanical load, can protect the reliability [3]. Therefore, fully in accordance with the method of selection of porcelain insulators composite insulators, without having to increase the mechanical allowable load values. Mandrel load deflection tests showed that synthetic insulators with good bending properties, good resistance to vibration performance dancing and the breeze [4]. Strain tower when used, can withstand a certain degree of bending moments. Connection structure of different end products in the long run, changes in its mechanical properties will be different, need further study.

3.2 than from choice

The choice of composite insulator than the distance, home and abroad have 2 observations: First, consider the deterioration of the surface of hydrophobic material, take 1:1; the second is the current national operating experience comprehensive, less than the distance may be appropriate, such as the desirability of porcelain insulator composite insulator 2 / 3 or 3 / 4. In order to standardize the dimensions of composite insulators, JB/T8460 industry standards and the National Coordination Centre “guidance composite insulators used” uniform requirements: 0 – Ⅱ level contamination areas, than the distance of 20 mm / kV; Ⅲ – Ⅳ-level contamination areas, than the distance of 25 mm / kV. In fact, this provision, for filthy clean area and the general area, higher than GB/T16434 requirements; for heavy polluted area is the porcelain insulators 3 / 4.

3.3 cleaning problems

Synthesis of the contamination is more important than insulators porcelain insulators, There is no unified opinion. Some flashover accidents and heavy polluted area over the contamination composite insulators is presented the question whether the need for cleaning. Because of high pressure composite insulator pollution lightning, even if the hydrophobic reduction or even short-term almost disappear, the pollution pressure is also higher than 20% of porcelain insulators. Therefore, the clean area, and general cleaning dirty areas to avoid. Particularly serious for the industry and the salt contaminated areas can be regularly replaced way around according to their own experience, when the surface hydrophobicity decreased, and the salt concentration is too large (eg greater than 0.2 mg/cm2), replace the new insulator, and thus determine the replacement cycle.

3.4 Evaluation of mechanical strength decrease

Decreased mechanical strength of 2 kinds: one is caused by poor end of the mandrel structure is less than the rated mechanical load in the prolapsed; two years after the mandrel is running creep caused by decreased mechanical strength. The former has occurred in the operation of the proposed institution in the regular sampling intensity will be less than 50% of the products for replacement; the latter has not yet detected, the safety factor chosen according to insulators, very little will happen the next few years of creep induced mechanical stresses problem.

3.5 Reliability Seal

Composite Insulator end fittings and sealing mandrel jacket connection has not yet attracted sufficient attention. It may be brittle and interface Mandrel breakdown of the causes of the current quality insulator is made of a weak point. Composite Insulator end connections made most use of wedge-fit structure, heavy load in the long run in the mandrel and the slip occurred between fittings is inevitable. When the sealant and gold with poor adhesion, the small slip enough to seal the slot; when the elastic sealant is not enough, they can slip over the sealant off. From this perspective, the use of push-fit end structure is one way to prevent seal damage. In addition, many of sealant silicone rubber at room temperature, was not as good as its anti-aging properties of high temperature silicone rubber, in the end there with a corona of gold may result in premature deterioration of the case. For 110 kV and the following products do not use the grading rings, or 220 kV and above voltage loop position products were installed, there will be more dangerous. In particular, none of the currently used products, strict sealing performance evaluation (IEC test methods should be revised as soon as possible write to the relevant national standard, users should be included in orders before the contract). In short, the end seal in the long-term effect of long-term maintenance of electrical and mechanical test demonstrated need and the long-running test.

Aging of silicone rubber 3.6

High-temperature silicone rubber used in the general area of not less than 15 a, 20 a foreign operation over existing products, performed well. Some running 2 ~ 3 a product appears brittle, damp or cold long after the water-repellent and difficult to restore, all reflect the formulation of silicone rubber material, there are some problems. The formula to be further optimized, and have a good hydrophobicity and mobility, less hydrophobic when exposed to moisture for a long time to slowly resume to damp rapidly.

3.7 Online Monitoring Technology

On-line monitoring technology failed to reach a breakthrough, but also a number of departments do not want to run one of the reasons large-scale use. Some of the ways described in the foreign is not mature, therefore, to speed up the development of online monitoring is needed. Because the development is very difficult, more realistic approach is to improve product quality, ensure operational reliability.

In addition to line composite insulators, the large number of synthetic coat of zinc oxide arrester and casing have been synthesized into the market outside the silicone rubber insulated power transmission equipment for the transmission project will be increasingly in a wide range of applications.

4 Conclusion

4.1 As a new generation of silicone rubber insulator composite insulator in industrial applications in China has entered the stage, the current network has reached 400,000 or more. In addition to contamination zone, it should be more widely used, greatly reducing transmission line maintenance workload, improve labor productivity. Silicon rubber insulated substation equipment outside in the power transmission projects will also be welcome.

4.2 The use of composite insulators can significantly improve the performance of external insulation of power transmission equipment, greatly reducing the pollution flashover accident rate, but it does not eliminate flashover (including pollution flashover) to the accident. To distinguish between the different regions of the contamination level, rational use.

4.3 composite insulator interface (or mandrel) is brittle breakdown and power mandrel serious accident. Such incidents have caused a number of reasons, such as the mandrel material (and coupling agents) of poor quality, seal damage, decreased mechanical properties of end connections, as well as the construction of the sheath may be damaged and so on. Therefore, we must strictly control product quality to ensure the construction of civilization.

4.4 It should also further enhance the synthesis of many properties of insulators, such as the end use of crimping structure, improved sealing technology to improve the mandrel acid strength, in order to improve product quality and the reliability-based, while the development of practical detection technology.