K. Arii

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. >

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 growth of polypyrrole with a fractal pattern and dependence of pattern on polymerization condition

Polypyrrole with a fractal pattern has been prepared by electrochemical polymerization method with the needle-circle electrode configuration in electrolyte solution of acetonitrile containing sodium p-toluenesulfonate and monomer. Under certain polymerization conditions, the polypyrrole has been polymerized not only on the needle but also on the bottom surface of the cell and has grown to the circle electrode with branching. The growth patterns on the cell are classified into three types: broad leaf-like, DLA-like and needle-like patterns. The patterns depend on the polymerization conditions such as applied voltage and concentrations of electrolyte and monomer. The patterns can be controlled by the polymerization conditions. A neural network pattern has been synthesized by changing the condition during the polymerization. The fractal dimension of the pattern has been calculated from the self-correlation function, which is obtained using a fast Fourier transform technique.

Impulse Tree and Discharge Light in Pmma Subjected to Nanosecond Pulses

The partial breakdown of PMMA subjected to one or several successive square pulses of 7 ns rise-time and about 40 ns duration in a point-plane electrode system has been investigated by observing the discharge light using a fast photomultiplier and a close-up camera. The tree is longer and the discharge light more intense for a positive point than for a negative point. The discharge channel can initiate from a point anode when the field strength at the tip exceeds 10 MV/cm. Trees grow more rapidly with alternate application of positive and negative impulses than with successive positive impulses. However, repeated negative impulses cannot cause new extensions of a tree but they broaden the existing channel, emitting intense light. These results can be explained by space charge remaining in the channel from the preceding impulse.

Separation of noise from partial discharge signals by wavelet

There have been many works on detection of partial discharges in insulators. In solids, technique of the detection have been much progress in deterioration of solid insulating materials. This paper will concern a new detection technique of partial discharges, current and sound signals.

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.

DC voltage breakdown in silicone-oil/polymer-film composite

Breakdown phenomena in a silicone-oil/polymer-film composite subjected to DC ramp voltage (0.5 kV/s) and a step voltage were studied with point-plane and plane-plane electrode systems. When the film was placed on the plane anode, the breakdown voltage of the composite with the ramp voltage was less than that for oil alone for both electrode systems as long as the film thickness was thin. Although the breakdown of the film due to charge deposition caused the complete breakdown of the composite for both systems, there was a difference in the transition process from the film breakdown to the complete breakdown. For both electrode systems, when the film was placed on the plane cathode, the increasing rate of the breakdown voltage with the increase in the film thickness was less than that for the film on the anode. In the point-plane system though the film breakdown was brought about by the charge deposition, it could not cause the complete breakdown. The breakdown of the composite was completed by the positive propagation from the point anode. In the plane-plane system, the magnitude of depositing positive charges on the film was too little to cause film breakdown under the ramp voltage. The complete breakdown was induced by the discharge in oil.<<ETX>>

A 3-D numerical simulation of partial discharge acoustic wave propagation in a model transformer

In this paper, the authors present a three-dimensional numerical simulation of partial discharge (PD) acoustic wave propagation that has been developed to provide time-domain signal representation in a model transformer. The numerical modeling of acoustic PD data is used to support interpretations of laboratory experimental data and to enhance the understanding of acoustic wave propagation in a structure like the power transformer, and hence PD source location in the same. It is intended that an extension of the work presented here, to account for real transformer geometry and also to visualize the propagation of acoustic wave fronts, will later be compared with field results. The three-dimensional wave equation, given by c/sup 2//spl nabla//sup 2/P=/spl part//sup 2/P//spl part/t/sup 2/, where c is the acoustic velocity and P the pressure wave field, defines an initial value problem and describes time evolution. The goal of the numerical code is to track that time evolution with some desired accuracy taking into consideration the boundary conditions that govern the evolution in time of points on the boundary of the spatial region of interest. This is particularly important for the satisfactory modeling of a complex structure like power transformer. In solving the above equation using the finite-difference method, of particular interest are the conditions of numerical stability. In this paper, the authors apply the stability analysis method originally developed by Von Neumann. The simulation results are in agreement with the results obtained from the laboratory experiments.

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.

Learning effect of composite conducting polymer

Conducting polymers with fractal patterns have been polymerized electrochemically under some conditions. The pattern of neuron-like conducting polymer has been prepared by controlling the polymerization conditions. Furthermore, the network of neuron-like conducting polymer has been prepared. If this kind of conducting polymer has the properties of learning effect and non-linearity, it works as neuron device. In this article, the method for adding the learning effect to the channel of conducting polymer has been investigated. In conducting polymer gels, the dopant easily moves in or out of conducting polymers in some solvents and in this time the gel swells or shrinks. On the other hand, polypyrrole is stable in such solvents. A composite film of polypyrrole and conducting polymer gel, poly(3-hexylthiophene), has been used to suppress the change of shape of conducting polymer gel. The technique of neural network was used as a method of learning effect. A simple network has been used instead of actual complicated conducting polymer network. It was confirmed that the conductivity of the channel network changed for correspondence to a teacher signal flow.