Hideki Ueno

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.

© 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. Ozone has much attention in many industrial fields. To materialize higher ozone generation efficiency, it is necessary to elucidate the relationship between discharge characteristics for discharge electrode system and ozone generation concentration. To clarify the improvement of mechanism on the multiple needle-to-plane configurations, the discharge characteristics and ozone generation characteristics for a multiple needle electrode system with various needle tip distances have been investigated. In this experiment, the maximum ozone yield at needle tip interval of d = 0.5 mm was improved by the minimum discharge power, the local maximal at d = 0.5 mm of discharge volume and the same ozone generation compared with those for d = 0 mm and d = 1 mm. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

© Springer Nature Switzerland AG 2020. The abstract should summarize the contents of the paper in short terms, i.e. 150—250 words. Partial discharge characteristics of new developed foamed wire with various insulated layers with low dielectric permittivity by including small air cavities in insulating layer have been studied. Partial discharge inception voltages (PDIV) have been investigated. PDIV depends on insulation layer of enamelled wire clearly, that is, PDIV for enamelled wire using an insulator with lower dielectric permittivity foamed polyimide becomes higher by increasing air cavities in the insulated layer. Furthermore, possibility of partial discharge generation in air cavities in the insulating layer has been also studied. By theoretical electric field analysis, electric field of each cavity is relaxed lower than that at the gap between wires due to presence of a great number of cavities in foamed insulating layer, resulting in suppression of partial discharge in the cavities. Partial discharge initiates in gap between wires before discharge generation in cavities of the new developed wire. From V - t characteristics measurements, the evaluated lifetime for enamelled wire using foamed wire is improved comparing conventional unfoamed one.