Abstract
The decomposition characteristics of a SF6 gas-insulated medium were used to diagnose the partial discharge (PD) severity in DC gas-insulated equipment (DC-GIE). First, the PD characteristics of the whole process were studied from the initial PD to the breakdown initiated by a free metal particle defect. The average discharge magnitude in a second was used to characterize the PD severity and the PD was divided into three levels: mild PD, medium PD, and dangerous PD. Second, two kinds of voltage in each of the above PD levels were selected for the decomposition experiments of SF6. Results show that the negative DC-PD in these six experiments decomposes the SF6 gas and generates five stable decomposed components, namely, CF4, CO2, SO2F2, SOF2, and SO2. The concentrations and concentration ratios of the SF6 decomposed components can be associated with the PD severity. A minimum-redundancy-maximum-relevance (mRMR)-based feature selection algorithm was used to sort the concentrations and concentration ratios of the SF6 decomposed components. Back propagation neural network (BPNN) and support vector machine (SVM) algorithms were used to diagnose the PD severity. The use of C(CO2)/CT1, C(CF4)/C(SO2), C(CO2)/C(SOF2), and C(CF4)/C(CO2) shows good performance in diagnosing PD severity. This finding serves as a foundation in using the SF6 decomposed component analysis (DCA) method to diagnose the insulation faults in DC-GIE and assess its insulation status.
Highlights
SF6 possesses excellent insulating and arc-extinguishing performance and is widely used as a medium in gas-insulated equipment (GIE) because of its ability to greatly reduce the equipment size and improve system reliability [1,2,3,4,5]
The mRMR principle is used for the feature selection for partial discharge (PD) severity diagnosis, and the Back propagation neural network (BPNN)
This research lays the foundation for the use of decomposed component analysis (DCA) method to diagnose the insulation faults in DC gas-insulated equipment (DC-GIE) and to assess its insulation status
Summary
SF6 possesses excellent insulating and arc-extinguishing performance and is widely used as a medium in gas-insulated equipment (GIE) because of its ability to greatly reduce the equipment size and improve system reliability [1,2,3,4,5]. When partial discharge (PD) occurs inside the equipment, this phenomenon can decompose SF6 and generate a series of low-fluorine sulfides (such as SF5 , SF4 , SF3 , and SF2 ) These low-fluorine sulfides react with the trace moisture and oxygen that inevitably exist in the equipment, generating some stable decomposition products, such as SO2 F2 , SOF2 , SO2 , CF4 , CO2 , HF, and H2 S and resulting in the insulation performance degradation of SF6 [12,13,14,15,16,17]. In addition to determining the discharge on the DCA [22,23,24,25], and the three-ratio was similar to oil chromatographic type, the discharge severity should be defined when assessing the insulation status of GIE.
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