Chengrong Li

Study of Corona Discharge Pattern on High Voltage Transmission Lines for Inspecting Faulty Porcelain Insulators

The corona pattern from porcelain insulator strings on high voltage (HV) transmission lines has been investigated for inspecting faulty insulators on-line. Corona patterns from HV conductive line, metal accessory, and discharge patterns from bad connection, power stations, have also been studied for background pulse noise elimination. A pattern recognition method for inspecting faulty porcelain insulators is proposed, which consists of several criteria. It is found that the harmonics and carriers from the transmission lines influence the recognition seriously, which can be eliminated by choosing a high frequency band of sensors (2 MHz-20 MHz). Based on the above investigations, an instrument was developed and used on the field measurements in Lanzhou and Zhengzhou power utilities in China. The field results show a strong support for this method. On the measurement of 76 towers, the measuring accuracy of inspecting faulty insulators was about 87.5%.

On-line estimating the level of hydrophobicity of composite insulators using the digital images

The hydrophobicity of composite insulators is a very important property for composite insulators used on transmission lines. An off-line test to indicate the hydrophobicity of a composite insulator has been developed by STRI, but it can not be used under on-line conditions. The objective of this paper is focused on an on-line estimation of the hydrophobicity of composite insulators using the digital images taken in the field. In order to identify the hydrophobic class of an insulator based on the digital images taken in the field, four algorithms were studied for imaging analysis, which include the improved ANE (the average of normalized entropies) method, the SPS (the seed point statistic) method, the FMA (the frequent magnitude analysis) method and the improved SF (the shape factor) method. The results from our study indicate that the improved SF method shows the best results for estimating the hydrophobicity of composite insulators in service. The way to measure on-line the hydrophobicity of composite insulators has been developed. It consists of a set of portable devices and the relative measuring rules. The devices include a sprayer with an insulated operating arm, a digital camera, and software. For every composite insulator in service, the upper surfaces of three sheds closest to the tower are chosen for the measurement. The way to spray distilled water on to the surface of the insulator has been investigated and an operating method suitable for on-line testing has been developed. The photo analysis for an indication of hydrophobicity is also carried out in our laboratory. The results from our study show that it is possible to determine the hydrophobicity of the composite insulators from the photos taken in the field based on our hydrophobicity analysis software with the aid of the operator. On site testing for determining the hydrophobicity of composite insulators has carried out on certain 220 kV transmission line in central China on three occasions. The results from on-line measurement show that the method we developed is suitable for on-line measurement and several composite insulators on this line exhibited poor hydrophobicity (HC7). The reasons for the degradation of the hydrophobicity of the insulators are being investigated

A method to detect the deterioration of HTV silicone rubber under corona discharge

This paper has investigated the thermally stimulated current (TSC) characteristics of the deteriorated HTV silicone rubber under varied corona discharge duration, the hydrophobicity, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) of the corresponding test samples have also been measured. The experimental results show that the TSC characteristics of HTV silicone rubber gradually varied with the corona deterioration process, and it has relationship with the change of its hydrophobicity, SEM, and also FTIR. As a result, it could be suggested that the TSC characteristics might be used as an effective index for assessing the corona deterioration of HTV silicone rubber.

The relationship between surface partial discharge and carbon trace in oil-impregnated paper insulation

In this paper, high voltage, which was raised step by step, was taken on an oil wedge model. Partial discharge (PD) signal was measured by normal IEC 60270 method. And the carbon trace on the pressboard was checked. Using Weibull function, the changes on the type of the PDs, were analyzed. Furthermore, the relationship between the carbon trace and the change of PDs was though about. From the results of the experiments, the PDs changed their type during the high voltage increasing. At the beginning, the PDs were small and produced dim carbon trace. This situation kept on for a long time and the carbon trace gradually extended its range and depth. Then, new type of PDs with very big amplitude appeared just before the breakdown, which we believed produced the breakdown point and due to the breakdown.

Hydrophobicity Loss of HTV Silicone Rubber after Corona Discharge

This paper presented the results of a study on the hydrophobicity loss of HTV silicone rubber under the different corona discharge conditions. The experimental results show that the speed and grade of hydrophobicity loss vary with the corona discharge time and the corona intensity. Moreover, it is noticed that the hydrophobicity would not become worse as long as the corona intensity keeps below a certain level.

An outdoor investigation on hydrophobicity of silicone rubber insulators in the Temperature Zone

This paper summarizes the common hydrophobicity change characteristics of silicone rubber insulators in the North Temperature Zone, according to the results of a series of outdoor tests. The tests were conducted for over a year on an outdoor experimental flat roof in Beijing, China, which belongs to the North Temperature Zone. All samples were not energized and suffered from the various natural environmental stresses. The samples were investigated using the HC method. The test results show that the hydrophobicity of SIR insulators can decrease and even lose in winter. After winter, with the change of season, different samples have the different hydrophobic recovery capacity. The influences of several typical environmental stresses such as ambient temperature, precipitation and ultraviolet radiation, to the hydrophobicity of silicone rubber insulators are also analyzed. Finally, based on the test results, the dynamic hydrophobicity monitoring method of silicone rubber insulators in the North Temperature Zone is discussed.

Effect of Corona on the Hydrophobicity Recovery Characteristics of HTV Silicone Rubber

This paper has investigated the hydrophobicity recovery characteristics of HTV silicone rubber after different corona deterioration time using the static contact angle method. The experimental results show that the hydrophobicity of HTV silicone rubber can get some recovery after the corona deterioration, and the procedure of hydrophibicity recovery would be varied with the corona deterioration condition, moreover, the hydrophobicity would not recover back to the initial value after a certain condition of corona deterioration, even if the storage time is long enough.

Effect of corona intensity on the hydrophobicity recovery characteristics of HTV silicone rubber

This paper has investigated the influence of corona intensity on the hydrophobicity recovery characteristics of HTV silicone rubber (SIR) deteriorated by corona discharge. The accelerating aging experiments of HTV silicone rubber were carried out with five levels of corona voltage. The hydrophobicity recovery with time was measured by static contact angle method. The experimental results show that the hydrophobicity of HTV silicone rubber can get some recovery after the corona deterioration, and the corona intensity play an important role on static contact angle of HTV SIR. In general, the procedure of hydrophibicity recovery would be varied with the different corona intensity and varied corona deterioration duration. And the hydrophibicity would not be recovered as original when the corona intensity is high enough under an certainty deterioration duration time.

TSC of HTV Silicone Rubber during Corona Deterioration

In order to investigate the micro-electric characteristics of HTV silicone rubber during corona deterioration, the corona accelerating deterioration was conducted and the thermal stimulation current (TSC) was measured for HTV silicone rubber samples at different deterioration stage. Experimental results show that the TSC curves were changed gradually with different corona deterioration procedure. There are trend to move the current peak from a relatively low temperature to a high temperature, and the trapped charges increase with the increase of corona discharge time. Considering the calculated trap parameters, it is confirmed that not only more traps are produced by corona deterioration processing, but the trap energy levels are gradually improved by corona deterioration procedure.

Mechanism analysis on hydrophobicity decrease of operating silicone rubber insulators

Through a series of on-site hydrophobicity-measuring tests for the silicone rubber insulators operated in Henan electric power grid of China, some insulators were found having the bad hydrophobicity performance. The objective of this paper is focused on the mechanism analysis of the hydrophobicity decrease of these insulators through a series of laboratory tests. As a comparison, some new samples were also investigated. Firstly, the hydrophobicity of the tested insulators was measured using the HC method before and after washing the contamination layer away. In addition, the scanning electron microscopy (SEM) and the attenuated total reflection infrared spectroscopy (ATR-FTIR) were also used to analyze the effect of aging on the hydrophobicity of the operating insulators. The test results show that the difference of the hydrophobicity performance of silicone rubber materials between the operated insulators and the new ones is negligible. The contamination deposition is the main factors causing the surface hydrophobicity decrease of these operating insulators. Some aging phenomena were found through SEM and ATR-FTIR tests. But the relationship between these aging phenomena and the hydrophocity decrease of the operated insulators was not found.