Diagnostic tools for condition monitoring of insulating materials

Partial discharge measurement based on the IEC270 guidelines is a useful technique for detecting flaws in an insulating construction. This technique has, however, its limits when it comes down to an estimation of future performance. New methods of measuring discharges and of dealing with the discharge data have become available in recent years. It is shown in this paper that a combination of these techniques can successfully be used for the assessment of the performance of insulating systems. A new diagnostic tool is presented for assessing the condition of insulating materials during the ageing process caused by partial discharges. This method makes use of pattern recognition techniques for the evaluation of both time-resolved and phase-resolved data. Based on a large number of ageing tests until breakdown it is shown that the degradation process of insulating materials is characterized by a number of stages. Each stage can be detected with the proper measuring equipment and it is shown that with the proposed diagnostic method a start can be made with the assessment of the time to failure. The measuring equipment and the diagnostic tools that are needed for these tests are discussed