Guan Zhicheng

Development of composite insulators in China

The development of composite insulators in China dates back to the early 1970s. In the 1990s 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 3~500 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.

Discharge performance of different models at low pressure air

There is a large area at high altitude in China where it is necessary to build high voltage transmission lines and substations. Studying the discharge characteristics of several important types of electrical field is a very important topic in the development and building of power systems in a high altitude area. In this paper a series of tests have been done in a chamber, in which the air pressure could be changed. The tested models included sphere-sphere gap and point-plane gap. The discharges along dry clean, wet clean and wet polluted surfaces were also studied at different air pressures under both AC and DC voltages. The discharge characteristics of the above models at different pressure air were analysed and discussed.<<ETX>>

Study on the hydrophobic transfer based on the theory of absorption and cohesion

Room temperature vulcanized (RTV) silicone rubber (SIR) coatings are used increasingly on outdoor HV porcelain and glass insulators and bushings when subjected to heavy pollution. An important property of the RTV-SIR coating is its ability to restore the hydrophobicity of the surface after a layer of contamination has built up on it, and thus continues to suppress the development of leakage current, dry band arcing and flashover. As hydrophobicity is the key to the superior contamination performance outdoor insulation, the present study was undertaken to better understand this phenomena. In this paper, the hydrophobic migrations of RTV SIR coating with the pollution of kieselgur and kaolin were measured. The virgin kieselgur and kaolin and them with hydrophobicity were analyzed using Scanning Electron Microscope. The theory of absorption and cohesion is introduced and applied to explain the mechanisms of hydrophobic transfer.

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.

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 on the various pollution performance of the post insulators in exceeding high voltage in high altitude area

The 750 kV alternating voltage of transmission lines plan to be built in the northwest of China, where the altitude is from 1800 m to 2800 m, and the climate is very serious. In the design of the lines, we contrast the ability against the pollution flashover of the post insulators. For three types of typical high intensity, big diameter post insulators, the artificial contamination tests are carried out in four pressure cases corresponding to the altitude from 0 m to 3000 m and in two typical kinds of equivalent salt deposit density (ESDD). The test results show that the flashover voltage of polluted insulators at high altitudes regularly decreases with the dropping of the air pressure. And there is certain relationship between voltage and the shed shape. Also, with a normal post insulator with RTV coating, the artificial contamination tests are carried out in the four pressure cases. The test shows, in the same ESDD and the same pressure condition, the ability to prevent the pollution flashover of the post insulator with RTV coating is much too stronger than that without RTV coating. And the rule that the flashover voltage decreases with the dropping of the air pressure is almost the same.

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.

A study on the leakage current along the surface of polluted insulator

The leakage current of a polluted insulator not only depends on pollution degree and damped situation, but also depends on insulator shape, insulator string length, operation voltage etc. This paper studies the relationship between the leakage current and factors such as the pollution degree, the damped state of contamination, the shape of insulator, the operation voltage, etc. Based on the above research, a method to determine the warning value of leakage current is proposed.<<ETX>>

Flashover mechanism of RTV coated insulators

The use of room temperature vulcanized (RTV) silicone rubber (SIR) coatings for improving the contamination performance of existing ceramic insulation has become popular. RTV SIR coatings work on the principle of providing a high surface resistance even in the presence of moisture and contamination, hence, limiting the leakage current to harmless levels. This paper deals with the flashover mechanism and performance of contaminated RTV SIR coated insulators under wet conditions. Four types of profiles of insulators with RTV SIR coating were evaluated. The withstanding voltage and flashover tests were performed on these insulators. The equivalent salt deposit density and the non-soluble deposit density were measured. Based on the analysis of leakage current monitored, the flashover mechanism of RTV SIR coated insulators was proposed in this paper.

Influence of fillers on silicone rubber for outdoor insulation

HV outdoor insulating systems such as line and station insulators, surge arresters and bushings, using silicone rubber for outdoor insulation have become very popular. This paper presents the mechanical behavior and electrical behavior of silicone rubber blend with different fillers. Various loadings of alumina trihydrate (ATH) and silica are added to silicone rubber and their performance are evaluated. Different types of silica such as fumed silica and precipitated (ppt) silica are studied. It was found the type of different silica filler makes difference in mechanical properties and dielectrical properties. And it was also found silane treatment of precipitated silica have great influence on the performance. The test results show that the more addition of ATH, the better the erosion resistance is achieved, but will result in declined mechanical properties.