Selective partial discharge measurements on assembled outer-cone cable plugs for on-site routine tests of rail vehicles

Summary

Medium voltage cables with assembled outer-cone type plugs (also called T-plugs) are widely applied in 15 kV- and 25 kV-supplied railway rolling stock. They connect the roof-mounted switchgear with the inside- or underfloor-mounted traction transformer. Poorly assembled or badly connected plugs are not reliably detected during routine voltage withstand tests on train level. In recent years this fact has led to several incidents on rail vehicles due to electric breakdown of plugs. These incidents affected the nearby equipment negatively without yet a safety impact on persons. After-installation partial discharge (PD) tests on train level can reveal poor assembly and plugging. A major problem of on-site PD measurements on assembled and connected plugs is the high environmental noise and PD from less PD-sensitive, nearby equipment (e.g. the connected traction transformer). This paper proposes a selective measuring method to identify PD in T-plugs and to separate it from superimposing external PD and disturbances. Therefor the PD pulses are measured synchronously in the earthing leads of the plug and the cable. A comparison of the two measured pulse charge heights allows an effective distinction of plug-PD and external pulses as e.g. PD from the connected transformer. Using common digital PD measuring systems, implemented visualization tools provide a convenient practical implementation of this method. The method has been successfully tested in a highly disturbed setup with a cable connected to a traction transformer by T-plug, including several sources of PD and disturbances.

Additional informations

Authors

Gürlek Akif, Shirvani Ali, Nourirad Ghasem