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タイトル: Propagation of Surface Leader Discharge in Atmospheric Air
その他のタイトル: 大気圧空気中における沿面リーダ放電の進展
著者: Deng, Junbo
著者(別言語): 邓, 军波
発行日: 2010年10月14日
抄録: Surface discharge is a kind of discharge which propagating on the surface of insulators, such as an interface between gas/solid, an interface between liquid/solid, and an interface between gas/liquid. The flashover electric field of the surface discharge is relatively weak. The surface discharge occurs from triple junction, firstly as a streamer and then transforms into a leader. Compared with the streamer, the leader can develop over a longer distance with a lower potential gradient, and leads to flashover on the insulator. For designing highly reliable electric power apparatus, it is of great importance to clarify the process of discharge propagation, especially the transformation process from a streamer to a leader. In this thesis, the investigations are performed with a cylindrical insulator configuration in atmospheric air. There are two ring electrodes and one rod back-electrode. The distance between two ring electrodes is aligned from 100 mm to 300 mm. One of pair ring electrodes is grounded and 1.2/50 μs standard lightning impulse voltage or 50Hz-ac voltage is applied to the other ring electrode so that a surface discharge occurs and propagates on the insulator surface. Two cameras are used to observe the discharge. One is a high speed video camera (10(6) frames/s), and the other is an ultra high speed framing and streak camera (10(8) frames/s, streak duration: 1μs). From a series of measurement, the propagation characteristics of AC surface discharge are summarized as follows: With increasing the voltage, leader discharges are recognized, whose occurrences concentrate in negative half-cycles of AC voltage applications. When the application voltage is enough high, some positive leader discharges are also observed. The maximum length of surface discharge LMAX under AC voltage can be denoted by LMAX ∝ Vpn, where Vp is the amplitude of the AC voltage and n is 1.5 to 3.3, whereas the propagation length of the surface discharge under impulse voltage is denoted by L ∝ Vn, where V is the peak value of the impulse voltage and n is 3 to 5. The residual charge distributions of impulse surface discharges are also measured with an electrostatic probe (measuring range: ±20kV), which utilizes a voltage feedback to the probe housing to null the electric field between the charged surface and the probe. With keeping 1mm air gap, the electrostatic probe moves in axial direction to the pipe and measures the surface voltage at every 0.25 mm. After measuring one line the pipe is rotated by 2 degree and the probe is moved back rescanning the surface. When the applied voltage is too high, the potential caused by the residual charge of a surface discharge will be very high and unexpected discharge will occur between the probe and the insulator surface. To reduce the surface potential, a two-layer structure is also designed. It can successfully reduce the surface potential during the measuring process with the electrostatic probe. With the two-layer structure pipe, the leader discharge propagation is studied on a clear insulator surface. The charge, electrical field, and potential distributions on the pipe are calculated from the distribution of the probe outputs. The information on the residual charge distributions of impulse surface discharges reveals the structure of the discharge, which consists of leader part and streamer part: in streamer part, the potential gradient is from 0.5 kV/mm to 1.0kV/mm; in leader part, it is from 0.12 kV/mm to 0.15 kV/mm. The dividing point of the leader and streamer parts is 6-8 kV corresponding to 350-600 pC/mm2. From the calculated electrical field distribution, it is found that the electrical field is very low and the conductivity is very high in a thin leader channel. The electrical field is 0.1-0.3 kV/mm around the thin leader channel. In the streamer zone, the electrical field is 0.5-1.0 kV/mm and it is estimated to reach 3 kV/mm in its tip region. The residual charge of surface discharge changes the electrical field distribution on the insulator and strongly influences the propagation characteristics of the subsequent surface discharge. In this research, the propagation of surface discharges on a PET film under impulse voltage applications are observed by high speed cameras and their residual charge distributions are measured with an electrostatic probe. Due to the residual charge of a previous opposite polarity discharge on an insulator, the propagation velocity increases three to eight times as large as that of the surface discharge on a clear insulator without residual charge. The peak current of surface discharge with residual charge also becomes much higher than that without residual charge. When 25-times consecutive impulse voltages are applied with changing its polarity, the propagation length of the surface discharge increases gradually from 79 mm to 164 mm and hardly converges. On the other hand, the propagation length of ac 50-Hz discharge under the same peak voltage is 40 mm at most. Under the application of consecutive impulse voltages, the potential gradient in the leader part decreases with the consecutive number of impulses, while that in the streamer part keeps constant and the value is 0.5-0.6 kV/mm. This phenomenon indicates that the surface discharge propagates unexpected length under polarity-reversed repetitive pulse voltages when the wave front time of pulses matches the required time for the formation and development of surface discharge.
内容記述: 報告番号: 甲26471 ; 学位授与年月日: 2010-10-14 ; 学位の種別: 課程博士 ; 学位の種類: 博士(工学) ; 学位記番号: 博工第7387号 ; 研究科・専攻: 工学系研究科電気工学専攻
URI: http://hdl.handle.net/2261/49744
出現カテゴリ:021 博士論文
1132020 博士論文(電気工学専攻)


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