On-Line PD Monitoring of Coils Subjected to Electric-Thermal Combined Ageing

For High Voltage (HV) rotating machines, an important aspect of the evaluation of insulation system is its behavior when subjected to electrical and thermal stress at the same time. For this purpose, international standards propose different kind of procedures, usually focusing on the ability to withstand higher stress than what would be the working conditions for a defined timeframe without failures [1] . This approach has an intrinsic limit when there is the need to study how insulating materials parts of the system are affected by combined stress, since it doesn’t focus on the development of the ageing. Once on the field, HV rotating machines status is monitored using Online Partial Discharge (PD) recording, but this technique can be used also during evaluation phase of insulation system, giving the opportunity to compare the behavior of different materials combinations.