Liang Xidong

Investigation on hydrophobicity and pollution status of composite insulators in contaminated areas

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.

Investigation on composite insulators in contaminated areas

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.

Hydrophobicity transfer properties of silicone rubber contaminated by different kinds of pollutants

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.

Study of water droplet discharge by electric field computation and high-speed video

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.

Effective Contaminant Deposit Density-a new concept of the pollution level of composite insulators

Effective Contaminant Deposit Density (ECDD)-a new concept of the pollution level of silicone rubber composite insulators is introduced in this paper to study the transferency of hydrophobicity and the artificial contamination test method of composite insulators. A solid contamination layer method is adopted. The effective contaminant is defined as the dissolved salt from the contamination layer when the polluted sample or insulator is wetted. It is found that the ECDD is much less than the original artificially polluted salt deposit density (SDD). This phenomenon means that only part of the salts could be dissolved out when the polluted silicone rubber sample is wetted. Hence the lower ECDD is also the important reason why the silicone rubber insulator could always keep its excellent pollution performance besides the well-known reason that hydrophobicity caused an uncontinued water film on the insulator surface. Then ECDD or the ratio of ECDD/SDD, called solved ratio, could be used to describe the transferency of hydrophobicite. The lower solved ratio represents the more sufficient transference.<<ETX>>

Study of tracking wheel test method under DC voltage

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.

Experimental study on the pollution flashover mechanism of polymer insulators

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.

Research on the brittle fracture of FRP rods and its acoustic emission detection

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.

Application of acoustic emission technology on structure design and quality control of composite insulators

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.

Laboratory study on hydrophobicity and pollution flashover properties of polymer insulators

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.