Experimental application of digital PD measurements to the diagnostics of railway system drives insulating systems

The present work explores the possibility of introducing, in the service monitoring of electrical drives for railway systems (or for similar transportation systems), a diagnostic tool of the relevant insulating system, based on the digital measurement of partial discharges (PD) by means of PRPDA (Phase Resolved Partial Discharge Analyser) devices. The relevant investigation regarded both new and "aged" (that is having a record of 3500 service hours) asynchronous rotating machines, which, after a specific optimisation of the testing procedure and of the testing circuit, have been subjected to several PD measuring campaigns, run at four different AC voltages. A suitable analysis of the relevant PD data, performed through an "ad hoc" software, allowed to identify several indicators (derived quantities and/or statistical parameters related to the acquired PD patterns) which have a potential for a clear discrimination between new and "aged" insulation. Therefore the results of this preliminary work evidence that a correct application of digital PD measuring techniques can offer a sound basis to develop a tool to monitor the conditions of the insulating system of electrical drives for railways systems.