Faculty Profiles - KOJIMA Hiroki

For the downsizing of gas insulated power apparatus, we have proposed the electric field grading technique by 'functionally graded materials' with spatial distribution of permittivity (\varepsilon -FGM). In this paper, we fabricated post-type and truncated cone-type \varepsilon -FGM by a novel and practical technique 'flexible mixture casting method' (FMC method). We confirmed that \varepsilon -FGM by FMC method has the discharge inception voltage improvement effect by both experiment and simulation.

DOI： 10.1109/CEIDP.2018.8544770

Scopus

Combined Effect of Temperature and Humidity of Magnet-Wires on Partial Discharge Inception Voltage under Inverter-Surge Voltage International conference

T. Kaji, H. Asai, H. Kojima, N. Hayakawa

2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2018.10.24 IEEE DEIS

Event date： 2018.10

Language：English Presentation type：Poster presentation

Venue：Cancun Country：Mexico

We investigated the combined effect of temperature and humidity on partial discharge inception voltage (PDIV) of magnet wires under repetitive surge-wave voltages. As the results, the PDIV increased as the temperature increased under uncontrolled humidity, which is peculiar under surge-wave voltage. On the other hand, the PDIV decreased lineally as the temperature increased under controlled humidity. From these results, we found that the PDIV increase under uncontrolled humidity was attributed to the effect of the relative humidity decrease corresponding to the temperature increase. Furthermore, the PDIV was also influenced by the moisture amount in insulation film. Under uncontrolled humidity, the PDIV during the temperature increase was lower than that during the temperature decrease with the hysteresis. We found two reasons for the PDIV hysteresis. One reason is the humidity increase in the air gap due to moisture evaporation from the film. Another reason is the electron emission from the film with the lower first ionization energy. Based on the above reasons, the generation probability of initial electrons during the temperature increase is higher than that during the temperature decrease, which decreases PDIV.

DOI： 10.1109/CEIDP.2018.8544745

Scopus

Estimation of Partial Discharge Inception Voltage under Repetitive Inverter Surge Voltage by Volume-Time Theory International conference

N. Hayakawa, Y. Daicho, T. Kaji, H. Kojima

2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2018.10.24 IEEE DEIS

Event date： 2018.10

Language：English Presentation type：Poster presentation

Venue：Cancun Country：Mexico

We measured the repetition frequency dependence of partial discharge inception voltage (PDIV) of twisted-pair test samples with different specifications under repetitive surge voltages with different waveforms. We also extended the PDIV estimation method with Volume-Time theory under single shot of surge voltage to that under repetitive surge voltage, in consideration of the effect of the repetition frequency on the initial electrons generation probability. The estimated and measured PDIV agreed well under repetitive surge voltage.

DOI： 10.1109/CEIDP.2018.8544814

Scopus

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