SUMMARYWe have investigated the characteristics of radiated electromagnetic (EM) waves from positive and negative partial discharges (PD) in epoxy resin and cross-linked polyethylene. We found that there is a correlation among the EM level from PD, the positive PD current, and electrical trees. Therefore, the growth of an electrical tree produces a lot of positive PD. We have 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. C⃝ 2015 Wiley Periodicals, Inc. Electr Eng Jpn, 192(3): 19-26, 2015; Published online in Wiley Online Library (wileyonlinelibrary.com).

We have investigated characteristics of radiated electromagnetic (EM) waves from positive and negative partial discharge (PD) in epoxy resin and cross-linked polyethylene. As a result, we found that there is correlation among EM level from PD, positive PD current and electrical tree. Therefore, growth of an electrical tree makes up a lot of positive PD. Also, we have investigated characteristics of frequency region of radiated EM waves from PD in air, insulating oil and liquid epoxy in addition to above insulators. EM waves were detected in the frequency region of 40 -300 MHz from positive and negative PD in epoxy resin and cross-linked polyethylene. Also, EM waves were detected in the frequency region of 40 -150 MHz from positive and negative PD in air. And in the case of insulating oil and liquid epoxy, EM waves were detected in the frequency region of 40 -150 MHz from positive PD, and 40 -250 MHz from negative PD. Frequency region was different depending on materials or polarity of discharge. Results of the study, we considered that the cause is difference of the electric field strength at partial discharge occurring.キーワード：部分放電，電磁波，電気トリー，エポキシ樹脂，架橋ポリエチレン Keywords：partial discharge, electro-magnetic waves, electrical tree, epoxy resin, cross-linked polyethylene