Study on Detection Method of Composite Insulator Ageing Based on Hyperspectral Technology

Abstract

Thanks to excellent hydrophobic and low cost, silicone rubber composite insulators have been widely used in power systems in recent years. The silicone rubber composite insulator is a high molecular polymer, the main chain is a Si-O bond. With the increase of working years, The properties of silicone rubber materials will also change, resulting in powdering, Hydrophobic loss, material embrittlement and so on. At present, the detection methods of composite insulator ageing are mainly divided into direct and indirect measurement methods. The direct methods include voltage measurement, electric field measurement, leakage current method and so on. The indirect methods include Fourier transform infrared spectroscopy, ultraviolet imaging, X-ray imaging and so on. However, there are many defects in the above methods. The direct method requires the operation by boarding pole, the indirect method is complicated, and the efficiency is low. Therefore, finding a non-contact, fast and non-damaging ageing detection method is of great value for maintaining stable operation of the power system and ensuring national economic security. Under the action of long-term corona discharge, the internal organic polymer's chemical bonds will be destroyed and then generate a large amount of free radicals, causing the material properties of the material to change. The change of the material will absorb and generate electromagnetic waves of different wavelength bands. Therefore, the ageing state of the composite insulator detected by hyperspectral have become a possibility. In order to study a new method for ageing detection of composite insulators based on hyperspectral technology, get the ageing silicone rubber composite insulation by conducting corona ageing experiments in the laboratory. The experiment uses the multi-needle-plate electrode system recommended by the CIGRED1.14 working group of the International Large Power Grid Conference. The silicone rubber composite insulator's size is set to $80\times 80\times 3\mathbf{mm}$ , and the ageing time was set to 50h, 100h, 150h, 200h, 250h, 300h, respectively. Taken out and then place the simple in a dry and clean environment for 24 hours, finally imaging sample with a hyperspectral imaging system to obtain a surface spectral reflectance intensity of a total of 256 bands of the silicone rubber insulator in the range of 400nm to 900nm. Black and white correction of the acquired spectral data to obtain a relative spectral reflectance with a relative value in the range of 0-1. The collected spectral line information is analyzed to establish a response mechanism between the spectral line and different ageing times. After obtaining the spectral data of the sample, extract the band number which can best reflect the ageing state of composite insulator. Using the hyperspectral image processing software to enhance the single-band grayscale image at the extracted band number, and an enhancement process is performed to obtain a visualization of the highlight distribution of the surface change of the insulator. According to the final result, the hyperspectral image of the sample at different ageing time has obvious difference. As the ageing time increases, the spectral curve of the silicone rubber insulating material shows a decrease in reflectance in the near-infrared band. The hyperspectral line has a peak at 750 nm, and the peak height increases with the ageing time, the reflectivity decreases. The band that can highly reflect the surface change of the composite insulator is concentrated in the range of 600 nm-900 nm bands. By analyzing the spectral information of the insulator collected by hyperspectral technology, the researcher can obtain the ageing state of the composite insulator.