Chenlong Zhao

Influence of environmental factors on hydrophobicity transfer property of silicone rubber material

Silicone rubber materials have been widely used as external insulation for power systems due to their good hydrophobicity and hydrophobicity transfer. However, pollution flashover accidents of composite insulators occurred from time to time in recent years. The influence of environmental condition on hydrophobicity and hydrophobicity transfer property of silicone rubber material needs further research. In this paper, incubator and saturated salt solution were used respectively to control ambient temperature and humidity precisely. Hydrophobicity measurement method were studied and regulated. Using incubator and special temperature control platform, hydrophobicity transfer property of silicone rubber material in different temperature was deeply studied, and the results were analyzed. The results showed that hydrophobicity transfer speed of silicone rubber slowed down with temperature decreased. Meanwhile, the results showed that ambient humidity had a great influence on hydrophobicity transfer property of silicone rubber. Flashover performance of silicone rubber samples with different hydrophobicity was analyzed. The results showed that the pollution flashover performance of composite insulators is closely related to the hydrophobicity state of the polluted surface.

Analysis of characteristic of natural pollution test and artificial simulation method

Pollution flashover has serious impact on power system and jeopardizes the safety of its operation. Many measures to avoid pollution flashover have been taken by the utilities through long term experience, while the mechanism of pollution flashover remains further research. Artificial pollution test is an effective method to estimate the electrical performance of the insulation system, but its equivalency to the natural pollution test has not been verified. Study on the natural pollution insulators on transmission line in Jiangsu Province, China, is presented in this paper. Possible explanations of the difference between the artificial pollution test and natural pollution test are proposed by comparing pollution flashover performance of artificial pollution insulators with the natural pollution insulators. A new method to apply natural pollution insulators is presented, with which leakage current and flashover voltage of artificial pollution insulators and natural pollution insulators are acquired. Comparison on the SEM structure of natural and artificial pollution is also taken to analyze the wetting properties of them. It is found that due to the compactness of the natural pollution, the Moisture rate of natural pollution is lower than that of artificial pollution, which leads lower leakage current and increased flashover voltage in the same conditions. In this paper, artificial pollution of non-uniform ESDD distribution has been used to simulate natural pollution and some conclusion has been made.

Development of contamination flashover pre-warning system and analysis of operating experience

Pollution flashover has been a serious threat to the operation safety for the power system. Online monitoring is one most important way for the operation and maintenance of power system. The leakage current on insulator surface is a comprehensive reflection of the insulator surface contamination, environmental conditions and other affecting factors. The purpose of outdoor insulation state on-line monitoring could be achieved by measuring and monitoring the leakage current on insulator surface. This paper showed that close relationship existed between leakage current in both low humidity and saturated moisture conditions. A negative exponential relationship exists between pollution flashover voltage and a new parameter I* which could reflect the insulator shape and the maximum leakage current under saturated humidity. The flashover voltage under saturated humidity could be predicted through current obtained under low humidity conditions. A contamination pre-warning system was constructed in accordance using this mathematical model combined with some hardware system. Pilot systems were established in some typical polluted area in Jiangsu Province. The results showed that the system could achieve online monitoring purposes.

Pulsed infrared thermography to inspect the internal defects of composite insulators

A non-destructive testing method for internal defects detection is desperately needed due to wide and increasing application of composite insulators in the power grid. In this study, a novel approach based on pulsed infrared thermography was investigated with the aim of testing and evaluating the state of composite insulators. In pulsed infrared thermography, an external source of energy is required to induce a temperature difference between defective and nondefective areas in the specimen under examination. The thermal changes can be detected with an infrared camera and recorded for later analysis. The recorded data is analyzed by images sequence processing technology to yield information for the recognition quantification of internal defects. Preliminary study based on experimental tests in laboratory concerning the detection of plate specimen with flat-bottom holes was conducted. The validity of the proposed testing method is proved with a series of experiments performed on specimens containing defects of different sizes at different depths. It is concluded that pulsed infrared thermography is attractive and promising for detecting internal defects of composite insulators because of its rapid, contactless, remote imaging and quantitative defect estimation capabilities.

Study and application of portable leakage current monitoring system

Measuring the leakage current of insulator surface is an implementable and effective method to evaluate the insulator contamination. This paper proposed a portable leakage current monitoring system for site outer insulation studies. Difference mode has been applied in this system for common mode signal reduction. The synchronous sampling rate can reach 20kS/s, which can record full information in the leakage current data. Resistor sensor has been applied in this system, which has a good electromagnetic interference performance. This system has a wide measuring range from 0.1mA to 5A, relative error can be controlled within 2%. Applied voltage values on the insulator can also been measured through this system when correlating with a voltage divider. LabVIEW has been applied for software platform building of the system, which is easy to operate, rich in functions and extendible. Features of this system are light weight, small volume, economic and convenient to implement. This system can fit varies site applications for research institutes.

Analysis on flashover performance of polluted porcelain insulators in high conductivity fog environment

Except from the two basic and conventional contamination accumulation modes, the common slow solid mode and the rapid liquid mode, there is another kind of rapid contamination accumulation mode which is even easier to cause the pollution-flashover. It is related to human activities, such as burning straw and setting off firecrackers, or natural factors as forest fire and acid rain. Those factors result in the weather condition of high conductivity and high humidity, due to whom the rapid contamination accumulation is added to the normal one. In this paper, the relationship between flashover voltage and the fog conductivity is researched, by doing artificial polluted tests using porcelain insulators of XP-70. Contrast to the process of the pollutions getting wet under the clean fog, the variation characteristics of flashover voltage under the high conductivity fog is systemically studied. It is pointed out that the high conductivity fog decreases flashover voltage, which is more notable on low salt deposit. After studying the changing law of the flashover voltage under different fog conductivity and salt deposit, the relational expression among them was obtained. According to the local meteorological environment, the warning model was revised, by using the expression. It also can be decided if the insulation configuration should be improved.

Influence on voltage distribution of composite insulator by inserting metal electrodes in weather sheds

The uneven distribution of voltage along the composite insulator strings harmed their electrical and mechanical properties heavily, which threatened the safety of power system. Inserting metal electrodes in the silicone rubber sheds of composite insulator helps increase their self-capacitance, thereby ameliorating the voltage distribution along the string. In this paper, a new structure of weather sheds with metal electrodes inserted has been designed. Tests on composite insulators with different metal electrodes setup were conducted to examine their voltage distribution performance. Corona inception voltage of the mentioned composite insulators was obtained by a remote monitoring system as a criterion of the voltage distribution performance. Simulation model of the insulators were set up and calculation of their voltage and electric field distribution were carried out by finite element method (FEM). The calculation result was in good compliance with the experiment result. The applied voltage at the live end of composite insulator decreased by 4% when inserting electrodes in the weather sheds, which was verified by both experiment and simulation results.