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The dielectric response of filled high temperature vulcanized (HTV) silicone rubber has been measured in the frequency range 10−4∼100 Hz and in the temperature range 20∼60°C. The complex relative susceptibility of filled HTV silicone rubber was calculated from the measured complex capacitance by removing the effect of infinity frequency capacitance and taking the geometrical sample factor into consideration, then a master curve of complex susceptibility was constructed. The complex susceptibility results and the master curve were found to have the frequency dependence characteristic of low frequency dispersion (LFD) process. The origination of the LFD process in the dielectric response of HTV silicone rubber was analyzed in depth by taking the microstructure of HTV silicone rubber into consideration.

In order to further utilize the transmission line cooridor, meanwhile, achieve a relatively friendly electromagnetic environment, composite cross arm is developed and employed in the transmission system. The electric field distribution as well as the electromagentic environment of composite cross arm deserves a detailed and in-depth study to verify its performance. In this research, the three-dimension (3D) finite element method (FEM) was employed to calculate the electric field distribution of composite cross arm. The electromagnetic environment was characterized by electric field intensity on the ground, radio interference and audible noise and these parameters were investigated and analysed. Calculation results indicated that by using proper metal hardware, composite cross arm could obtain a relatively suitable distribution of electric field and potential. The electromagnetic environment calculation results demonstrated that composite cross arm could meet the standard design requirement. Furthermore, some suggestions were made based on this research to achieve an optimization use of composite cross arm.

The pollution flashover characteristics of insulators are tightly related to the salt dissolving out of pollution layer which makes contribution to surface conductivity of insulators in wetting process. For hydrophobic pollution layer on silicone rubber (SR) insulator, both the process of salt dissolving out and the process of salt running off are more complicated in wetting process. The concept of Effective Equivalent Salt Deposit Density (EESDD) is used to characterize the effective salt in wetting process, which is defined as the amount of salt dissolved in water on insulator surface minus the amount of salt ran off from insulator. Actual measurements indicate that EESDD of SR insulators increases in initial half of the wetting period and decreases in ending half of the wetting period. Hydrophobicity of pollution layer, NSDD, polluted manner all have significant influence on EESDD in wetting process. The wetting process of SR specimen keeps 6-9 times as long as that of glass specimen. For naturally polluted SR insulators, maximum percent of EESDD is about 15% of the total ESDD, which is another reason why SR insulators have higher pollution flashover voltage.

The development of composite insulators in China dates back to the early 1970's. In the 1990's they have become widely used in China. At present, up to 600000 composite insulators are operating on 35 to 500 kV ac overhead transmission lines. They are to be introduced into the 500 KV HVDC transmission schemes. In China all composite insulators in service are silicone rubber and are operating in various Contamination conditions. They have successfully and efficiently avoided serious pollution flashover, which occurred frequently when conventional ceramic insulators were used, and radically reduced the maintenance cost of transmission lines in pollution areas. Study of composite insulators is very active in China. The main aspects include properties of materials such as silicone rubber and fiberglass reinforced polymer (FRP) rods, electrical and mechanical performance, aging as well as evaluation and inspection of composite insulators. These fruitful works greatly promote the development of composite insulators in China.

The hydrophobicity and hydrophobicity transfer property of silicone rubber composite insulators not only prevents the formation of continuous water film, but also make the salt in the pollution layer more difficult to dissolve out. In order to study the regularity of salt dissolving process, a model based on mass transfer laws was established in this paper and the second order partial differential equation for describing the salt dissolving process was obtained. The correctness of this model was verified by measuring the salt dissolving process of a site contaminated composite insulators in our laboratory.

In this paper, leakage current obtained by laboratory was derived to calculate the pollution flashover voltage of porcelain insulators. On this basis, this paper analyzed the basic theory of prediction of pollution flashover based on leakage current monitored in service. At the same time, the calculation results and the test results of pollution flashover voltage were compared. The results showed that the difference of flashover voltage between calculation results and test results was less than 5%. It is proved that the calculation method for evaluating the flashover risk by monitoring the leakage current proposed in this paper was effective.

For long-term operating outdoor insulation, contamination accumulation has become an increasingly serious problem. In this paper, atomic force microscopy was used to measure the adhesion force of glass, silicon rubber, porcelain, stalinite samples. Test results showed that adhesion force of silicon rubber was the largest, approximately larger than the other three samples by one or two orders of magnitude. Furthermore, silicon rubber surface exhibited a long-range attractive force and multiple points contact, probably due to the electrostatic interaction and surface roughness. It might be a theoretical proof which accounts for the different contamination accumulation between composite insulator and porcelain or glass insulator.

As a simple aging test method for composite insulators, the tracking wheel test has been studied for many years, it is easy to be repeatable due to its simple operation, reproducible results and good equivalence. Recently the tracking wheel test is considered to be published as an IEC standard. More and more composite insulators have been used in HVDC transmission line, and thus their long-term properties are cared. As an aging test method, how about the properties of the tracking wheel test method being used under DC voltage are not clear. In this paper, different voltages such as positive DC voltage, negative DC voltage are applied to the sample to study the DC tracking wheel test. Several kinds of samples are also used in the tests. Comparing with AC tracking wheel test, some differences are shown in the tests, and different samples also show some interesting differences in the test.

It is well known that the excellent pollution performance of silicone rubber (SR) insulators originates from its hydrophobicity and hydrophobicity transfer properties. With the sustainable growth of composite insulator usage in China, a convenient method should be given to judge the hydrophobicity properties and to help the utilities choose proper products. In this paper, a four-parameter method used in the evaluation of hydrophobicity status was introduced. The four parameters are hydrophobicity on clean surface, hydrophobicity loss property, hydrophobicity recovery property and hydrophobicity transfer property named H/sub c,/ H/sub l,/ H/sub r/ and H/sub t,/ respectively. Relative values of the four parameters, which were based on the research work of hydrophobicity, were also given. This method has already been used in some parts of China for its easy operation and effectiveness regarded. In addition, the mechanism of hydrophobicity transfer property was further investigated and the difference of the results between contact angle and hydrophobicity classification was also discussed in detail.

In this paper, model of composite insulators were designed to study distortion, movement of the water droplets when discharging occurs on the shed surface of composite insulators applied with uniformity electric field. The distortion and movements of single and multiple water droplets on the surface of insulator in ac and dc electric fields were studied. The results show that the water droplets gradually increase in length in the action of electric field, and the distortion considerably increases with the increase of the electric fields. From these results, the effect of water droplets on flashover voltage is analyzed.

Publisher Summary This chapter presents the influences of annealing method on the space charge properties in low-density polyethylene (LDPE). LDPE films are prepared by three kinds of annealing methods, which are different in cooling velocity. The crystallinity of the LDPE samples are measured and compared. Surfaces of samples are observed. Higher cooling velocity results in lower crystallinity. High DC negative voltage is applied on the samples and then samples are open-circuit. Space charge formed in samples is measured during the above procedure. The space charge properties based on crystallinity and morphology are discussed.

The lightning transient characteristics of a substation grounding grid are analyzed in detail, especially considering the dynamic and nonlinear effects of soil ionization around grounding conductors and the inductance between grounding conductors. The analysis results are calculated by a loss transmission-line model with distributed time-variable parameter. The influences of grid structure, feed point location, and shape of the lightning impulse current on the transient characteristics of grounding grids are discussed.

A loss transmission-line model with distributed time-variable parameter for the calculation of transient characteristic of a grounding system under lightning to consider the dynamic and nonlinear effect of soil ionization around the ground electrode is proposed. The influences of the length of grounding electrodes and location of feed point on the transient characteristic of ground electrodes are analyzed. Grounding electrodes have impulse effective length under impulse current. The model has been validated by comparing the numerical results with experimental tests.

The usage of composite insulators in various contaminated areas is increasing prominently in recent years. Most of composite insulators are operating in heavy or medium pollution environment in China. As the exposure time in the field prolonging, the change of hydrophobicity and the build-up of pollution layer directly affect pollution performance of the composite insulators. This paper is based on the work of investigation on the pollution performance and aging of nearly 40 composite insulators operated in Jiamusi city, the north east area of China. These composite insulators were removed from 110 kV lines, and they are all made of HTV silicone rubber and mostly are in service for nine years. Four aspects of hydrophobicity of these insulators are studied after the measurement of pollution status.

A laboratory method to simulate the different hydrophobicity status of contaminated or aged polymer insulators is presented in the paper. It is found that kieselguhr, used as the non-soluble contaminant in the simulation, is more suitable and convenient than kaolin. Based on the method, the influence of hydrophobicity on pollution resistance properties is investigated. A remarkable difference between the artificial pollution test outcome of hydrophobicity of un-recovered polymer insulators and that of ceramic ones is found. Furthermore, the applicability of static contact angle and hydrophobicity class (HC) is discussed.

The mechanisms of tracking and erosion failure of high temperature vulcanized HTV silicone rubber were studied by means of the inclined-plane test. Test conditions were varied by using different kinds of electrolytic contamination solutions instead of the stipulated NH/sub 4/Cl. Arc current I, arc burning, and extinguishing time t/sub a/ and t/sub 0/ were all recorded. Therefore, both the energy E/sub a/ dissipated on the sample surface in each t/sub a/ and the average energy E/sub t/ dissipated on the sample surface per minute could be calculated. Boiling temperatures T/sub b/ of different saturated contamination solutions were also measured. The tracking and erosion test results of silicone rubber showed a good correspondence with E/sub a/ and T/sub b/, but a poor correspondence with E/sub t/. The higher the E/sub a/ and T/sub b/, the severer the tracking and erosion damage of test samples. This means that the tracking and erosion failure of silicone rubber in the inclined-plane test is mainly caused by the heat absorbed on a simple surface in each arc burning time, and the actions of successively burned arcs are independent. >

The usage of silicone rubber insulators in various contaminated areas has increasesd prominently and still keeps rising. In the case of China, more than 90% of the 800000 composite insulators are operating in heavy or medium pollution environments. As the exposure time in the field is prolonged, the change of hydrophobicity and the build-up of pollution layer directly affect pollution performance of the composite insulator. The paper is based on part of the work of a system investigation aiming at inspection and evaluation on pollution performance and aging of the composite insulator in service. More than 40 composite insulators, all made of HTV silicone rubber, were removed from 110 kV-220 kV HV lines. The service time changes from 1 year to 10 years. Hydrophobicity status and pollution status of these insulators are reviewed in the paper. Data from the field provide important references for the research on aging and pollution property and for the build-up of relevant test methods.

The application of Acoustic Emission (AE) technology on the production of composite insulators, especially with crimped end fittings, is studied in this paper. In the production process of crimped end fittings of composite insulators, the establishment of an effective detection method is the key problem. With the adoption of AE detection, a method of structure design and quality control in the manufacturing process of crimped end-fittings is realized. Composite insulators made by this method show good mechanical properties according to IEC 1109 and other standards.

Brittle fracture of composite insulator FRP rods has aroused widespread attention in China. In the laboratory, two load-applying methods are used to simulate the brittle fracture process. One is constant tensile load method, which is used to test the resistance of FRP core against stress corrosion. The other is decreasing tensile load method, with the purpose to simulate similar appearance of brittle fracture section in service. Some important factors that influence the brittle fracture process, which are not well described in IEC Drafts are discussed and clarified. Finally, the acoustic emission (AE) feature of the brittle fracture process is analyzed. It is in great difference from normal short-term tensile failure process.

Considering various contaminated environments in the field, research on the hydrophobicity transfer properties of different pollutants is necessary for the proper selection and maintenance of polymeric insulators. In the paper, hydrophobicity of SR polluted by several kinds of pollutants such as kieselguhr, kaolin, Tonoko, metal oxides and inorganic salts were investigated. Contact angle measurement and FTIR analysis have been used to trace the hydrophobicity transfer process. It is found that the inherent chemical properties and the physical morphology of pollutants play important roles on the hydrophobicity transfer property.

For an extensive understanding of the pollution flashover mechanism on hydrophobic surfaces, a series of experiments were designed to investigate the relationship between hydrophobicity, pollution severity and pollution withstand property of polymer insulators. Rain tests with the conductivity 100 /spl mu/S/cm to 100000 /spl mu/S/cm were conducted on the silicone rubber insulators presenting various hydrophobicity statuses. It is found that the electric conductivity and accumulating status of water droplets or zones on the hydrophobic surface is tied closely to the sequence flashover voltage, even in the case of complete hydrophobicity. The accumulating status and the conductivity of water droplets on the contaminated polymer insulators depend both on the hydrophobicity and on the pollution severity. It suggests that the pollution flashover voltage on the hydrophobic surface relates not only to the hydrophobicity but also to the pollution severity. Based on the results, pollution flashover mechanism on the hydrophobic surface is discussed.

Based on the simulation of contaminant deposit, hydrophobicity status and wetting process in the laboratory, an artificial pollution test method suitable for composite insulators is recommended in this paper. It is found that hydrophobicity status and pollution level jointly determines composite insulator's pollution performance. Neither of them can separately describe the overall pollution capability of the insulator. This suggests that composite insulators' outdoor insulation evaluation in the field be achieved by regularly inspecting these two parameters.

Brittle fracture of composite insulators occurred in China makes it a subject concerned by many people, and it is urgently necessary to put forward a test method on the resistant of FRP core against stress corrosion. The brittle fracture caused by stress corrosion is simulated in two similar ways The fracture modes are analyzed, and the measures to improve the stress corrosion resistance are studied. As the results, a modified stress corrosion test method is suggested, and the stress corrosion resistance of FRP rod is improved greatly when E glass fiber is still adopted.

In this paper, the pollution regularity versus time and various weather conditions and the distribution of contamination on the surface of a porcelain insulator is discussed in detail using a partial surface conductivity method. The results illustrate that the self-cleaning ability of rain has a notable influence on the contamination of each kind of insulator. Compared with the conventional equivalent salty deposit density method, the partial surface conductivity method is an effective measurement and also a practical one to inspect the contamination density and research into the pollution regularity of the insulator.

The conductor-conductor gap is a practical operation parameter in transmission lines. In the past, the insulation distance between conductors was determined only by a simple impulse voltage. But for compact lines, a more precise model of sparkover characteristics should be studied in detail. In this paper, the influence of a pre-stressing AC and floating electrode on the U/sub 50%/ composite sparkover voltage for a conductor-conductor gap is discussed.