M. Ieda

Measurements of partial discharges by computer and analysis of partial discharge distribution by the Monte Carlo method

The mechanism of partial discharge (PD) occurring in the CIGRE Method II (CM-II) electrode system, which is a representative closed-void model system is discussed in the context of a computer-aided PD measuring system. Measurements of PD are made for the CM-II electrode system. Effects of the pressure and gas inside the void on the PD are examined. Taking into account the experimental results, a model for the PD mechanism is proposed. This model assumes that the statistical time lag of discharge depends on the overvoltage and that the residual voltage depends on the PD magnitude. A Monte Carlo simulation of the PD distribution is made on the basis of this model. The computed results agree well with the experimental data and the appearance of swarming pulsive micro discharges. The physics of the model are discussed. >

Study of space charge in polyethylene by direct probing: effects of oxidation

By utilizing the laser-induced pressure-pulse technique, the authors have quantitatively studied the behavior of space charge in unoxidized and oxidized low-density polyethylene (PE) samples whose thickness ranged from 100 mu m to 1 mm. The distribution of space charge changes with applied field, temperature, extent of oxidation and the thickness of the samples. Prominent negative space charge was formed near the cathode in oxidized PE, indicating that oxidation enhanced the electron injection from the cathode. The amount of negative space charge increased with applied field, and this suggests that the electron injection is enhanced by the applied field. The depth of charge centroid from the cathode became larger with increasing temperature and applied field. This indicates that electrons become more mobile as temperature increases. The complicated behavior of the space charge suggests that space charge formation is determined by the following competing processes: electron injection from the cathode, transport, trapping, detrapping, and charge exchange at the anode. >

Study of space-charge effects on dielectric breakdown of polymers by direct probing

Direct and quantitative probing of space charge was carried out to study effects of space charge on dielectric breakdown of polymeric insulating materials. In poly-p-phenylene sulfide, in which dielectric-breakdown characteristics were explained in terms of space-charge formation, positive homo space charge was observed. The amount and the depth of space charge detected could explain the dependence of impulse breakdown strength on prestressing both qualitatively and quantitatively. In oxidized polyethylene, negative homo space charge was observed. This also agreed well with the prestress dependence of the breakdown characteristics. The injecting electrode during the prestressing or the region nearby was suggested to be important in the breakdown process of both materials. >

Effect of additives on DC treeing breakdown in polyethylene under divergent fields

The effect of additives on DC treeing breakdown phenomena and space-charge formation in polymeric materials is studied under divergent fields. Experimental results are presented to show that: (1) The DC treeing breakdown phenomena are considerably affected by the space charge. (2) The presence of acetophenon in low-density polyethylene (LDPE) enhances the amount of accumulated space charge, while blending with ionomer or polyamide suppresses it. (3) Blending ionomer or polyamide into LDPE improves the DC tree resistance. >

Ultralow-frequency dielectric properties of EPR with filler

The dielectric properties in the ultralow-frequency regions of ethylene propylene rubber with fillers are studied. These are important materials, especially for electrical cables and wires in nuclear power generating stations. The dielectric parameters alpha , tau /sub o/, and in /sub ro/- in /sub r infinity / in the Cole-Cole equation are obtained by fitting the theoretical curve with the experimental results on the discharge current. The present polarization is caused by the interfacial polarization between EPR and the fillers. Assuming that part of the filler clusters and takes the form of spheroids, the relaxation time is correlated with the shape of the spheroid. The observed distribution of relaxation times is interpreted as being due to the dispersion of various shapes of spheroids. As the concentration of filler increases in the low-concentration region, the characteristic relaxation time tau /sub o/ decreases. The decrement of tau /sub o/ can be understood with the variation of the cluster shape with the filler concentration. >

Effects of interface on electrical conduction in epoxy resin composites

The effects of the epoxy-resin interface on electronic conduction were studied by using photocurrent and thermally stimulated current techniques. The electrical properties of epoxy-filler composites are greatly affected by the interfaces in various ways depending on applied field, temperature, carrier species, and mechanical stress. At low temperature, electronic carriers transported from the epoxy layer in epoxy-alumina composites can pass through the epoxy-alumina interface and move in the alumina bulk, increasing the conduction current in the alumina, but they are accumulated at the interface and lead to interfacial polarization at room temperature. At low fields and low temperature, electronic carriers from the alumina layer can pass through the epoxy-alumina interface and increase the conduction current in the epoxy resin, but they are accumulated at the interface at high field and the conduction is explained by the Maxwell-Wagner model. At room temperature, electronic carriers from the alumina layer are blocked by the potential barrier at the interface. However, electronic carriers from the epoxy layer can pass through the epoxy-silica interface and increase the conduction current in the silica at low and room temperature.<<ETX>>

Space charge and solid insulating materials-in pursuit of space-charge control by molecular design

Recent development of direct and quantitative space-charge probing techniques has provided with various information on the nature of space charge and has enabled quantitative discussion of effects of space charge. This paper briefly describes what was clarified by the conventional techniques and what has become possible by the recent developments, and stresses the importance of the study in pursuit of space-charge control by molecular design.

Third-harmonic generation and growth mechanism of vanadyl-phthalocyanine single crystals prepared on KBr substrate by molecular beam epitaxy

Abstract Vanadyl-phthalocyanine (VOPc) single crystals were prepared on KBr (1xa00xa00) substrate by molecular beam epitaxy (MBE). The second and third-harmonic generations of nonlinear optical thin films are proportional to the square of the thickness. Therefore, it is important to prepare a large nonlinear optical single crystal. However, the conditions to prepare a large nonlinear optical single crystal are not well understood yet. In this paper, we succeeded to prepare a large nonlinear single crystal. It was obtained with the control of substrate temp., evap. time and annealing time. The orientation and nonlinear property of VOPc single crystal prepared by the MBE method were also studied. The size of maximum single crystal prepared on KBr is 4×9×0.16xa0μm. The absorption spectrum of sample has an absorption peak at 790xa0nm. It reveals that the growth of single crystal gradually grow to a large crystal merging small crystals and also suggest that the VOPc single crystal is monoclinically grown from the results of RHEED pattern and UV/VIS spectrum. We estimated the third-order nonlinear optical susceptibility χ (3) from the TH intensity for VOPc single crystal monoclinically grown on KBr. Its χ (3) value estimated is 8.5×10 −10 esu. The value is 3 times higher than the value reported recently.

Fundamental aspects of interfacial phenomena in solid insulating systems

The authors summarize interfacial phenomena involved mainly in solid insulating systems. Emphasis is placed on charge injection and accumulation, electrochemical reaction, carrier transport, carrier trapping, mechanical stress, swelling, and streaming electrification. It is pointed out that various kinds of interfacial effects manifest themselves in various ways in affect the electrical properties of composites. The discussion is limited to interfaces inside solids or solid-liquid composites.<<ETX>>

Electrical properties of EPR with filler

The authors have investigated the electrical properties, especially the conductivity and the dielectric characteristics in the ultraflow-frequency region of EPR with hard clay. They first investigated the relation between the electrical conductivity and the content of filler. It was found that, as the content of filler was increased, the conductivity decreased initially and then increased abruptly. The authors have explained the decrease and increase in conductivity by the action of carrier traps at the interface between the EPR and filler and the formation of highly conductive paths of the filler between the electrodes, respectively. Secondly, the authors studied the dielectric properties in the ultralow-frequency region which was obtained from the discharge current. The observed variation of the relaxation time with the filler can be interpreted as being due to the variation of cluster shapes in the composite materials.<<ETX>>