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Characteristics and Development Stage Recognition of Air-Gap Discharge within Oil-Paper Insulation Considering Effect of Cavity Size
Pages: 49-58
Year: Issue:  10
Journal: Transactions of China Electrotechnical Society

Keyword:  Oil-paper insulationcavity sizepartial discharge characteristicsclustering-random forestsstage recognition;
Abstract: Oil-paper insulation is commonly used in power transformer. Air-gap discharge, especially the discharge in large cavity will threaten the oil-paper insulation. In order to comprehensively evaluate the risk of air-gap discharge, five types of cavity configurations were manufactured, and the effects of their cavity sizes on partial discharge(PD) were studied. Then PD signals throughout the accelerated deterioration experiments were analyzed. In addition, based on Clustering-Random Forests, PD development stages of large and small cavities were recognized. Results show that, compared to small cavity PD, large cavity PD possesses lower inception field, higher charge magnitude and higher inception phase, moreover when air-gap PD comes to the last stage, positive PD in large cavity fails to expand to the negative half cycle and vice versa. Lower surface electron emission rate and lower reverse field in the large cavity are the main reasons of higher inception phase. Through clustering, PD development stages for large and small cavity models are both divided into three stages, i.e. initial discharge stage, weak discharge stage and outbreak discharge stage. For the development stage recognition, the accuracy of Random Forests is 93.15%, showing better performance than those of RBF Neural Network and Kernel Based Support Vector Machine. Experiment results provide reference for more precise evaluation of the air-gap PD development stage.
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