A new Approach for Form Wound Machine Goundwall Insulation Diagnosis by Means of High Frequency Model Parameter Monitoring

This paper investigates a new approach for stator winding insulation diagnosis. The guiding principle consists in modelling the input-output behavior of the groundwall insulation system in a high-frequency (HF) domain, ranging from several kHz to hundreds of MHz. The first motivation of this work is that this frequency area has been seldom used by conventional insulation diagnostic techniques such as partial discharge monitoring or time domain measurements. Another originality consists in modelling the groundwall insulation system with a diagnostic dedicated modelling approach, i.e. searching for the best tradeoff between simplicity for system identifiability and complexity for diagnosis abilities. More specifically, we try to distinguish between winding contamination (moisture, coal or metallic dust) and insulation material ageing because the maintenance procedures and their induced costs are very different for high voltage (HV)) machines ranging from a few to several kilovolts or more. At last, the theoretical and industrial constraints impose to use very efficient identification algorithms. Experiments have been carried out in order to appreciate the feasibility of this approach. A high voltage MOSFET pulse generator with ultra fast rise time has been specially designed. It allows to apply a high energy input excitation covering the wide frequency range required for the ground-wall insulation system identification. In order to isolate numerous phenomena which could be mixed together in an entire winding, the experiments first deal with stator bars and coils taken from high voltage induction machines. The first results are promising.