Tracking Insulation Degradation of Railway Traction Induction Motors using High-Frequency Differential Current

Abstract

Degradation of stator insulation is usually a slow developing process influenced by diverse operating and environmental factors that can end up in serious stator faults unless continuously monitored. During the progressive insulation degradation, a distinct change in the high-frequency parameters of motors gradually transpires. In practice, a notable percentage of motor capacitance change occurs before insulation breakdown. In this work, changes in capacitance will be tracked through the analysis of transient current responses to inverter-imposed voltage steps for winding insulation monitoring. The contribution of this paper is the use of a single current transducer to measure the differential current to track both ground-wall and turn-turn insulation degradation prior to faults without voltage sensors. Measuring differential current has the advantage of reduction of signal processing efforts due to absence of inductive current behavior. It will be shown that small-emulated changes of groundwall and turn-turn capacitances can be tracked by the proposed high frequency differential current analysis in a medium-voltage railway traction motor.