Relationship between AE Waveform Frequency and the Charges Caused by Partial Discharge in Mineral Oil

It is well-known that acoustic waves are generated by partial discharge (PD), however, the wave generation mechanism remains unclear. To this end, in this study, a PD test is performed to measure the acoustic waves caused by PD in insulating oil. A needle-plate electrode is applied to generate PD, and the acoustic waves are detected by an acoustic emission (AE) sensor. The PD current and AE signal associated with PD are simultaneously measured, and their relationship is analyzed. The results indicate that the frequency components of an AE signal vary with the PD current duration time. Therefore, the amount of PD charge used as a parameter in dielectric degradation can be derived from the time integral of the PD current. Thus, the acoustic frequency can help estimate the amount of PD charge and the degradation of oil-immersed electric equipment. Furthermore, a possibility of increasing the accuracy of the PD diagnosis method by focusing on AE signal frequency is established.