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| Time and Frequency Domain Characteristics of Spatial Electric Field During the Discharge of Polluted Insulator |
| Zhang Dongdong1, Luo Wei1, Huang Xiaoning1, Zhang Zhijin2, Han Xuechun3 |
1. School of Electric Power Engineering Nanjing Institute of Technology Nanjing 211100 China;
2. State Key Laboratory of Power Transmission Equipment Technology Chongqing University Chongqing 400044 China;
3. State Grid Jiangsu UHV Company Nanjing 211102 China |
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Abstract Transmission corridors inevitably cross complex environmental areas such as coastal, industrial, and heavily polluted areas, resulting in ongoing pollution flashover accidents. With the development of technology, emerging non-contact pollution monitoring technologies have been continuously proposed, but a unified consensus has not yet been formed. At present, the main problems in non-contact pollution monitoring of insulators are as follows. First, difficult to implement on site. Methods such as visible light method, sound wave method, etc., are greatly affected by external factors such as noise, radiation, perspective, etc., and greatly limited in on-site use. Second, the characterization ability is weak. The essence of insulator string pollution flashover is a complex dynamic electrical process. However, the existing methods are based on non-electrical quantities, such as color, light waves, etc., which can only statically characterize a certain piece or part of pollution, and have poor correlation with the overall pollution of the insulator string.
In order to enrich the means of non-contact monitoring and pollution flashover prewarning for insulators, and to reveal the mechanism of pollution flashover discharge at a different level, this paper established a space electric field monitoring platform for polluted insulator discharge. With the help of artificial fog chamber to simulate operating environment, the short insulator string was used as the test object to carry out the pollution withstand tests. During the tests, the method of first applying voltage and then wetting was used, and the electric field signal at fixed point near the low-voltage end cross arm of the string was monitored. Through the test data, the spatial electric field signal waveform characteristics under different pollution levels and different discharge development stages were analyzed, and its time-frequency domain characteristic parameters were extracted and systematically studied as well.
The research results indicate that the spatial electric field signal near the low-voltage side of the insulator string can reflect its pollution flashover process. As the humidity increases, the amplitude and effective value of the spatial electric field waveform both increase. After the occurrence of arc discharge, the amplitude continues to rise and the waveform undergoes distortion, resulting in a gentle fluctuation of the effective value. For cases where no pollution flashover occurs, the amplitude and effective value increase slightly. During pollution flashover discharge, the spatial electric field waveform undergoes depressions at the peaks and valleys, and the distortion is mainly the third harmonic component. With the development of surface wetting and discharge, the third harmonic factor k3 rapidly increases, and can reach 1 when approaching pollution flashover. For cases where no pollution flashover occurs, the growth rate of k3 is relatively small, less than 0.2. The two dimensionless feature parameters, peak factor Cp and third harmonic factor k3, are significantly positively correlated with pollution level, with correlation k3>Cp. In practical engineering, the mean value of Cp and k3, during the period of damp can be calculated, and the representative salt density can be evaluated through the Exponential function fitting.
This research utilizes the relationship between the insulator surface potential distribution and the spatial electric field to reveal its time-frequency characteristic mechanism under pollution flashover discharge. The distribution of surface potential of insulator under different operating conditions has significant differences. After the pollution layer is wet and dry-bands form, the overall surface potential rises, resulting in an increase in the amplitude of the spatial electric field waveform. After the occurrence of partial arc, the surface potential distribution is mainly determined by the dry-bands’ voltage drop, so as the spatial electric field waveform. Therefore, a depression of the spatial electric field waveform occurs at the peaks and valleys of the sine curve, where the partial arc occurs and the lowest dry-bands’ voltage drop forms.
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Received: 24 April 2023
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2024, Vol. 39 
