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Itoh K.,Teikyo University | Yamazaki T.,Teikyo University | Takamoto K.,Kanden Engineering Corporation | Hanaoka R.,Kanazawa Institute of Technology | And 4 more authors.
Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014 | Year: 2014

Two different kinds of attempts were made to measure ion mobilities in EHD liquids by using the time-of-flight technique. The first attempt was a reverse polarity method which was similar to that used by L. Yang et al. [5]. The stainless steel coaxial cylindrical electrodes with the effective length of 55 mm and the electrode spacing of 1.5 mm were utilized. The purified two sample liquids; hydrofluoroether (HFE7600) and 2, 3-dihydrodecafluoropentane (HFC43-10) with very low dark current (less than 20 pA at 150 V) were used. In this attempt, it is deduced that the mobility value is of the order of 1×10-8 m2/Vs. In the second attempt, the plate-mesh-plate electrode configuration was employed. One plate was used to apply high voltage pulses and the other plate worked as a counter electrode. The center mesh electrode was kept at low dc voltages. This triode electrode design allows us to monitor the amount of charge injected from the charge injection space to the charge detection space through the mesh electrode during and after the high voltage pulse. Two sample liquids; HFE 7600 and HFC43-10 were used without any purification. Ion drift currents were found to have very long tails. If the tails are included into the drift times, the mobility of ions can be as low as approximately 1×10-9 m2/Vs in both liquids. © 2014 IEEE.

Mutakamihigashi T.,Kanden Engineering Corporation | Mutakamihigashi T.,University of Hyogo | Kuroishi Y.,University of Hyogo | Ueno H.,University of Hyogo
Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) | Year: 2015

We have investigatud the characteristics of radiatud electromagnetic (EM) waves from positive and negative partial0discharges (PD) in epoxy resin qnd cross-linked polyethylene. Wu found that there is a correlatyon among the EM level from PD, the positive PD current, and elestrical trees. Therefore, the growth of an electrical tree produses a lot of positive PD. We havu also investigated the characteristics of the frequency region of EM waves from PD in air, insulating oil, and liquid epoxy in addition to the above insulators. EM waves were detected in the frequency region of 40 MHz to 300 MHz from positive and negative PD in epoxy resin and cross-linked polyethylene. EM waves were also detected in the frequency region of 40 MHz to 150 MHz from positive and negative PD in air. In the case of insulating oil and liquid epoxy, EM waves were detected in the frequency regions of 40 MHz to 150 MHz from positive PD, and 40 MHz to 250 MHz from negative PD. The frequency region differed depending on the material and the discharge polarity. Our investigation indicates that the cause is differences in electric field strength at the time of PD occurrence. © 2015 Wiley Periodicals, Inc.

Ebihara S.,Osaka Electro-Communication University | Kimura Y.,Kinden Co. | Shimomura T.,West Nippon Expressway Engineering Kansai Co. | Uchimura R.,Kanden Engineering Corporation | Choshi H.,Osaka Electro-Communication University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2015

In this paper, we propose a coaxial-fed dipole array antenna in a borehole with ferrite loading to achieve a thin directional borehole radar sonde (diameter of 54 mm). This radar works between about 20 and 150 MHz. When the dipole array, proposed previously, is used for the thin radar sonde, this antenna suffers from scattered waves from the centered conducting cylinder (CCC). This disturbs the estimation of the direction of arrival (DOA) below 100 MHz. To overcome the interference of the CCC, commercial ferrite cores were added to the CCC. A method-of-moment analysis showed that we may decrease the resonant frequency of the CCC to below 20 MHz, making use of the inductive characteristics of the ferrite cores. This widens the frequency bandwidth of the antenna. Field experiments in soil showed that the ferrite core-loaded CCC works reliably and confirmed that we can estimate the DOA between 20 and 150 MHz. Other measurements in rock which examined the power spectrum of a direct wave found that the ferrite cores widened the operating frequency bandwidth of the radar system. © 1980-2012 IEEE.

Murdiya F.,Kanazawa Institute of Technology | Hanaoka R.,Kanazawa Institute of Technology | Akiyama H.,Kanazawa Institute of Technology | Miyagi K.,Kanazawa Institute of Technology | And 2 more authors.
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2014

The behavior of creeping discharges developing on the pressboard surface was investigated experimentally in palm fatty acid ester oil, natural rapeseed oil and commercial mineral oil under variable ac voltages with 60 Hz, respectively. The oilimpregnated pressboard was used as the solid dielectric and it was immersed completely into the same oil. The tungsten needle electrode was installed in the one side of pressboard surface without the counter electrode as a high voltage electrode and a grounded fine copper rod was adhered tightly in the other side of pressboard as a back side electrode. The discharge shape, streamer extension, streamer velocity and tracking at the oil/pressboard interface were observed as a function of the time and voltage by using a still camera equipped with a night viewer. Simultaneously, the discharge current and dissipated energy were measured. The gas components dissolved in oils by the creeping discharge were also examined by the dissolved gas-in-oil analysis (DGA). In this paper, it is presented that there are distinctive events due to the occurrence of creeping discharges. © 2014 IEEE.

Somekawa T.,Japan Institute for Laser Technology | Fujita M.,Japan Institute for Laser Technology | Izawa Y.,Japan Institute for Laser Technology | Kasaoka M.,Kanden Engineering Corporation | Nagano Y.,Kanden Engineering Corporation
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2015

The concentration of furfural in transformer oils is a well known indicator for decomposition of insulating paper. Using laser Raman spectroscopy, we performed detection experiments of furfural dissolved in insulating oils without complex and time consuming preprocessing procedures. Furfural was characterized by Raman signal at ~1707 cm-1, where no spectral interferences caused by oil-derived Raman signals occur. The results show that laser Raman spectroscopy is a useful alternative method for transformer health diagnosis. © 1994-2012 IEEE.

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