Sakae Nishimoto

Repetitive Discharges in a Corona Reactor Produced by a Reciprocal Traveling Voltage Pulse in a Coaxial Cable

We propose a new method for a gas cleaning system with repetitive discharges produced by a reciprocal voltage pulse in a coaxial cable. When the cable is charged with a dc voltage and then grounded at one end of the cable without any resistance, a traveling wave is reciprocated in the cable because of a negative reflection at the grounded end and a positive reflection at the other end. The reciprocal traveling wave results in a voltage oscillation with a very high frequency. The repetitive pulsed discharges between a point-plane electrode gap with a dielectric barrier were observed for various charging voltages.

Effect of pre-charging to plasma reactor on repetitive barrier discharges produced by reciprocal traveling wave voltage pulse

This paper describes an experimental study for NO/sub x/ decomposition using repetitive streamer discharges produced by reciprocal traveling wave voltage pulse from a direct-grounded coaxial cable. When the cable is charged and then grounded at one end of the cable without any resistance, a reciprocal traveling voltage pulse is repeatedly applied to a barrier-type reactor at the opposite end with a change in its polarity. High-speed photographs of discharge light indicated that the voltage oscillation caused by one switching induced alternate propagation of positive and negative streamers with a very high frequency. The 50% streamer initiation voltage with the reciprocal pulse generator was much smaller than that with a single pulse generator having a matching resistance. The reason for the difference in the 50% voltage was explained by the effect of pre-charging to the dielectric barrier. In the case of the reciprocal pulse, a large number of space charges were accumulated on the barrier surface during the cable charging, so that the field strength in the gap was strongly enhanced after the polarity reversal. In the test of NO removal from a flue gas, high NO removal ratio was obtained under the low applied voltage when the reciprocal pulse generator was used. Removal weight of NO per unit discharge energy in the reciprocal pulse generator was lower than that in the single pulse generator. However, the total efficiency calculated with the stored energy in the reciprocal pulse generator gave a better performance.

Space charge effect for streamer initiation and propagation in water subjected to reciprocal traveling wave voltage pulse

This paper deals with initiation and propagation processes of streamer discharges in water subjected to high-speed repetitive voltage pulse. The 50%-duty repetitive pulses were produced by the reciprocal traveling wave in a pulse forming cable which was connected with a point-plane electrode gap in a water-cell. Laue plot of time lag distributions for the streamer initiation indicated that the initiation probability during the second pulse application became much higher than that during the first pulse application. We concluded that the change in space charges distribution due to internal field during the rest-time after the first pulse enhanced the streamer initiation probability at the second pulse application. Temporal development in the positive streamers during the repetitive pulse application was observed using a gated image intensifies. When the pulse was relatively high, the streamer discharges started the propagation at the first pulse and then the discharge channel became long step by step at the subsequent pulse applications. It was also found that the periodical emission due to excitation of OH radicals was detected for a long period after the development of the streamer discharge in a spectroscopic measurement

Study on application of wavelet analysis for degradation diagnosis of partial discharge in a void

Waveforms of partial discharge (PD) current and sound wave emission by PD are measured in a void between a polyethylene terephthalate (PET) film and an electrode. The measured waveforms of PD current and sound wave are transformed by Gaussian and Mexican hat wavelets. The relation between the obtained results and degree of insulation degradation is discussed. As a result, it was clear that wavelet analysis results could be used in degradation diagnosis of an insulator.

Two-Dimensional Kerr Electrooptic Measurement of Nonuniform Electric Fields by CT Method

It is very difficult to measure nonuniform electric field distributions in insulators. The optical measurements of the electric field were investigated in nitrobenzene using the Kerr effect. A sphere-to-sphere electrode or a sphere-to-plane electrode system was used to produce the nonuniform electric field. A rectangular test cell was made of teflon with two glass windows. A He-Ne laser was used for a light source. The intensity of the light transmitted through the cell was measured with a photodiode. The two-dimensional electric field distribution expressed in absolute value was reconstructed by the computed tomography (CT) method. The measured electric fields were compared with the theoretical one and good agreement was obtained.

Photographic observation system for DC prebreakdown phenomena in dielectrics using the long image guide scope

The observation technique for dc prebreakdown in dielectrics was established by the use of a long image guide scope which was set in front of an image intensifier with a high speed gate. The passage time of a prebreakdown image through the scope was longer than the response delay time of the gate. Therefore the gate could be closed as soon as the prebreakdown image arrived at the image intensifier.

Surface potential on LDPE and PP films after removal of the upper disk electrode

The potential distribution was measured on the free surface of low-density polyethylene (LDPE) and polypropylene (PP) films which had been inserted between plane electrodes after the removal of the upper brass disk electrode. The polarity of the surface potential was always the same as that of the applied step voltage which had been subjected to the upper electrode for a while and then shorted. The absolute value of the surface potential tended to increase to a constant value of /spl sim/650 V with increasing applied voltage and application time for both polarities. There was no appreciable difference in the surface potential between PP and LDPE when the applied voltage and its application time changed. However, the increase in the shortcircuit time tended to increase the surface potential for LDPE only, while it did not change that for PP. The effect of a longer shortcircuit on the surface potential increase for the LDPE films for both polarities could be explained by bipolar injection.

Study on degradation diagnosis of partial discharge in a void by wavelet analysis

Waveforms of partial discharge (PD) current and sound waves emitted by a PD are measured in a void between a polyethylene terephthalate (PET) film and an electrode. The measured waveforms are transformed by Gaussian and Mexican hat wavelets. The analyzed patterns are obtained on a plane using both time and frequency information. Then, the relation between the obtained results and the degree of insulation degradation is discussed.

Photographic observation of DC prebreakdown in silicone-oil/PET-film composite using the long image guide scope

The paper describes the results of photographic observations on the complete breakdown in silicone-oil/PET-film composite under point-cathode/plane-anode conditions by the use of an optical system.

The charge spreading due to micro discharges on insulating films from an evaporated metal electrode subjected to a DC ramp voltage

The charge spreading phenomena on polymeric insulating films from a circular evaporated electrode were studied in the atmospheres of air and nitrogen gas atmospheres on the application of a slowly increasing dc ramp voltage. The flash over voltage between the circular and its opposing concentric ring electrodes on the film was also measured. The observation on very faint light using an image intensifier camera revealed that micro discharges occurred repeatedly at the surrounding region of the circular electrode as the voltage increased. When the positive voltage was applied to the circular electrode, several or more streamer-like micro discharges occurred in a row at the same time in both atmospheres. In the negative polarity, a single fan-shaped micro discharge occurred at a time in air and luminous regions were observed as one or a few small spots at the electrode edge in nitrogen gas. The electrons created by the negative micro discharges in nitrogen gas had a major role of the expansion of charging region. The flash over voltage in air was higher than that in nitrogen gas in both polarities; more remarkable difference in the flash over voltage was obtained in the negative polarity. The voltage for the negative polarity was much higher than that for the positive polarity in air, while the former was rather slightly lower than the latter in nitrogen gas.<<ETX>>