Insulator surface discharge is a common cause of insulation failure of switch cabinets. However, traditional surface discharge detection methods characterized by electromagnetic and acoustic signals can hardly meet the requirements in field application. Based on light radiation, another intrinsic nature of discharge, optical detection method has been applied for discharge diagnosis, performing strong anti-interference and high detection confidence. Further, spectral analysis provides a light wavelength information dimension for refined discharge diagnosis, but it is not practical because of the limitation of sensing equipment. In this paper, a practical discharge spectral detection sensor named SiPM-based multispectral discharge sensor (SMDS) is introduced to study the optical radiation characteristics and the evolution laws of multispectral characteristics during the surface discharge development process of insulators, moreover, a strategy for severity diagnosis of surface discharge based on the characteristics of multispectral pulse evolution are proposed.
First, based on the new generation solid state photoelectric sensors, SMDS with seven specific band channels and one full band channel are adopted to acquire multispectral pulses of surface discharge. Second, the evolution stages of surface discharge are distinguished into three stages, named slight, moderate and severe stage, respectively, according to the derivative of full-band light pulse intensity at different voltages. Third, multispectral characteristics of surface discharge at different stages are analyzed. For the phase-based multispectral characteristics, the light intensity of each band increases significantly with the applied voltage independent of the phase, while the light intensity proportion of each band shows different evolution trends. In the slight stage, the light intensity at 450nm is the largest, accounting for about half of the total light intensity. While the light intensity of 400nm band has the smallest proportion. In the moderate stage, the proportion of light intensity at 450nm decreases slightly, while the proportion of light intensity at 400nm increases slightly. In the severe stage, the proportion of 450nm band decreases obviously with the increase of 400nm band. In terms of the phase distribution, the phase range expands continuously from the slight stage (20°~100° and 175°~280°) to moderate stage (0°~90° and 180°~270°) and to severe stage (0°~90°, 170°~300° and over 340°). At the same time, six characteristics named maximum pulse amplitude, average pulse amplitude, pulse repetition rate and their proportions of each band are defined as the non-phase-based multispectral characteristics. In addition, the first three characteristics perform the significant positive liner correlations with the applied voltage. However, for the maximum pulse amplitude proportion, all the components show a significant correlation with applied voltage, with the 450nm component showing a negative correlation and the 650nm component showing relatively low linearity. For the average pulse amplitude proportion, all the components are significantly correlated with the applied voltage, and the 450nm component is negatively correlated. For the pulse repetition rate proportion, all components show significant correlation with applied voltage, among which 400nm and 450nm show a negative correlation. Finally, discharge risk assessment models with a deep neural networks (DNN) based on the non-phase-based multispectral characteristics are built. The results reveal that the correct rates based on multispectral average pulse amplitude proportion, maximum pulse amplitude proportion and pulse repetition rate proportion are 96.75%, 93.45% and 95.25%, respectively.
The following conclusions can be drawn from the multispectral analysis: ①For the phase-based multispectral characteristics, in the slight stage, the 450nm band has the highest pulse amplitude and the widest phase distribution, while the 500nm wave pulse has the smallest amplitude and narrow phase distribution. With the development of the discharge, the amplitude of the whole band pulse increases obviously in the moderate and severe stage, and the phase distribution shows a significant “left shift”. ②For the non-phase-based multispectral characteristics, with the development of discharge stage, maximum pulse amplitude, average pulse amplitude and pulse repetition rate are significantly increased, and the band maximum pulse amplitude proportion, average pulse amplitude proportion and pulse repetition rate present decrease trends for 450nm and increase trends for other bands. ③The multispectral proportion characteristics can effectively reflect the microscopic characteristics of the discharge development process. The accuracies of the discharge severity evaluation model based on the multispectral proportion characteristics and DNN (over 93%) are higher than that of the traditional phase statistical characteristic models (87.15%).
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