Partial Discharge And Insulation Deterioration Mechanism For Locomotive Cable Terminal In Alpine Area

With the rapid development of railway electrification in the western region,the application of electric locomotive in the northwest area has also been expanded.The locomotive cable are facing the challenge of the environment in the northwest alpine regions.In recent years,the shortcomings about the application of flexible terminal in the alpine regions began to be gradually exposed.The cable flexible terminals of locomotive which running in the northwest regions often occur insulation breakdown accidents during winter operation,which makes locomotive shutdown and seriously affects the reliability of electric locomotives in the northwest and alpine region.In order to study the phenomenon of frequent explosion on the locomotive cable flexible terminals,a test system for PD(Partial Discharge)has been set up which can reproduce the low temperature environment and the low atmospheric pressure environment.The PD characteristics of the flexible terminals at different temperatures and atmospheric pressure were studied,including the initial voltage of PD and extinct voltage of PD,discharge rule and PRPD(Phase Resolved Partial Discharge)spectrograms.Meanwhile,the left avertence,sharp and the asymmetry of positive and negative half-cycle in PRPD spectrograms are analyzed by the characteristics of PRPD spectrograms.The results show that,the change of the atmospheric pressure factor is not obvious to the PD of the flexible terminal.When the temperature is below-10 degrees,the initial voltage of partial discharge decreases rapidly,and the PD develops faster and more severe as the temperature continues to decrease.The low temperature factor is the main factor which leads to the insulation deterioration of the flexible terminal of the locomotive cable in the alpine region.Based on the research mentioned above,the mechanism of PD of flexible terminal in low temperature environment was studied and analyzed in this paper.Firstly,the serious discharge trace was found in the interface between the stress control tube and main insulation by dissecting a cable terminal.It is indicated that the low temperature condition causes the discharge of the stress tube-main insulation interface,which leads to insulation decline of the flexible terminal.Secondly,insulation material DSC test and interfacial stress test indicated that EPDM of the main insulating material in the locomotive cable flexible terminal is highelastic state,and the stress tube is the glass state at the low temperature.The deformation of the main insulation and the stress tube is not consistent at low temperature,which leads to the reduction of matching ability between stress control tube and main insulation.The research shows that the interfacial stress between the stress control tube and main insulation at 40? decreases by about 30% compared to the normal temperature,which leads to the gas gap in the interface,and thus the discharge occurs.Finally,a measure that can improve the insulation performance of the interface between the stress control tube and main insulation at low temperature is introduced,and the reliability of the measure under low temperature was verified.