Isamu Kitani

Fractal character of DC trees in polymethylmethacrylate

The fractal dimensions of DC trees in polymethylmethacrylate have been investigated using the self-correlation function. The fractal-established range is proportional to the tree length for both positive and negative polarities of the applied voltage. For positive polarity, the fractal dimension increases with increasing inception voltage and saturates at 1.5 to 1.6. For negative polarity, the fractal dimension is nearly constant, approximately=1.5, as a function of voltage. >

Analysis of Anomalous Discharge Current in Low-Density Polyethylene

An anomalous discharge current flowing in the same direction as the charging current was observed in a low-density polyethylene film with evaporated silver electrodes at room temperature (25°C) after the application of a very high field above 2×108 V/m. The discharge transient current was computer-analyzed numerically by an explicit difference method. The anomalous current was attributed to the large amount of two types of injected space charge (electrons and holes) with ohmic electrodes, and not to one type of injected space charge (electrons or holes) with blocking electrodes.

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.

Very Faint Light Emission in Low-Density Polyethylene Films under dc Field

Faint light emission in low-density polyethylene films was detected by using a photon-counting system. The photoncount response rose to a maximum value at a time greater than 1 minute after a step voltage was applied. The emission spectra ranged between 300 and 540 nm. The light-emission process was attributed to a recombination between trapped electrons and trapped holes.

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.

Effect of Prestressing on the ns Range Electrical Breakdown in Polymeric Insulating Films

The electrical impulse breakdown of prestressed polymer films was investigated in the ns range. The effect of prestressing on the breakdown was observed in polyethylene terephthalate (PET) and polycarbonate (PC), but not in polystyrene (PS) or polypropylene (PP). The amount of space charge estimated from the transient currents was large enough to induce electric field distortion in the bulk for all specimens. The effect in PET and PC is attributed to field distortion due to space charge accumulation near the electrodes, which can be estimated as electrons at the cathode and holes at the anode. The reason why the effect was not observed in PP and PS can be explained as the result of their own high breakdown strength in strong non-uniform fields.

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.