Study On The Joint Time-Frequency Analysis Of Partial Discharge Signal During The Thermal Aging

Aging phenonenon is always an importance study item in insulation subject. After insulation diagnosis and lifetime prediction on electronic devices, there will be greatly benefitial to electronic system and economic performance. Meanwhile, a lot of insulation diagnosis systems which are advanced, convenient and reliable was formed. As a kind of insulation material, epoxy resin is widely used in electric and electronic devices and its insulation properties will directly affects performance safty and reliable of equipment. Partial discharge detection is an effective means which is used in high-voltage electrical equipment insulation diagnosis, but Partial discharge signal is non-stable signal and its frequency may change with time. while, need to use the joint time-frequency analysis whith is a practical tool to analyze and deal with non-stable time-change signal.For these reasons, the research used samples made of epoxy resin, designed an aging box specially. 80℃and 120℃were selected for the temperature to accelerate the aging of the aging two batches of samples, 8h aging cycle for a total of four aging cycle. After each aging cycle, we measured and recorded data of partial discharge signal, meanwhile used joint time-frequency analysis method to get characteristics of discharge signal, as aging time changing, judged partial discharge changes as well as distinction under both temperatures and aging insulation sample.Study shows that time-frequency analysis technique was applied to analysis and management of partial discharge signal, which could clearly reveal the changing process on time-frequency plane of partial discharge signal and demostrate time-varying characteristics of partial discharge signal accurately. Moreover, it becomes more simpler and more intuitive. The research provides a more accurate and reliable method to recognize partial discharge signal's pattern. It can be seen from analysis results: in different stages of aging, partial discharge frequency characteristic significantly, and with the aging time increasing, in the low-frequency region continued to discharge and changes in small, but high-frequency spectrum region characteristic peak, and with the aging lengthen the duration of peak decreased significantly, but the frequency increased. High or low of aging temperature has quite weak affect distinction on partial discharge in low-frequency signals parts while influences the high-frequency part more significant. Therefore, partial discharge of high-frequency part of the characteristics of more help to determine the status of aging.