Anomalous Phenomenon of Δtanδ in Insulation Diagnosis for Electric Machines Kenji Natsume, Non-member, Kazuhisa Hatano, Non-member, Makoto Nakahara, Member (Shinko Electric Co., LTD), Masayuki Nagao, Member (Toyohashi University of Technology), Masamitsu Kosaki, Member (Gifu National Collage of Technology)
In the tanδ test of the stator winding for the high voltagen electric machine, the anomalous phenomenon that the decrease of tanδ sometimes appears when the voltage increases. In case of this anomalous phenomenon, we can't use the conventional judgement of the Δtanδ for the insulation diagnosis.
In this study, the experiment and the numerical calculation were conducted to clarify this anomalous phenomenon. As the result, the tanδ of the coil inserted into the core slot shows a peak when the contact resistance between the coil surface and the slot increases due to the deterioration, around a certain specific value of contact resistance. Around this specific value of the contact resistance, the apparent contact resistance becomes smaller due to the high electrostatic nonlinear phenomenon and the partial discharge which are caused by the increase of applied voltage, and this leads to the decrease of tanδ with the increase of applied voltage.

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In the present work, prebreakdown phenomena in dielectric liquids which have various molecular structure, especially turning our attention to chlorine atoms or fluorine atoms and some double bonds included in moleculer formula, are observed in detail for positive and negative point polarities, under the application of an impulse voltage (1.1/225 μs) to the point electrode. As test liquids, cyclic hydrocarbon liquids such as cyclohexane, benzene, chlorocycl ohexane, monochloro benzene, hexafluorobenzene and cyclohexene, are used. Results obtained in these liquids are compared with ones obtained in straight-chain hydrocarbon liquids.
As a result, the propagation of negative streamers, especially in dielectric liquids with chlorine atoms or fluorine atoms in molecular formula, is promoted, on the other hand the propagation of positive streamers in dielectric liquids with some double bonds is promoted. The former is related to large electron affinity, the latter is due to π electrons, for both cyclic and straight-chain hydrocarbon liquids.

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In order to realize the practical application of DC polymer insulated cables, much research work has been done to clarify the characteristics of space charges which significantly affect the electrical properties of the cables.
So far, we had information of the space charge behavior in thick insulating specimen in order to understand the DC characteristics in thecables.
And we found out the existence of acetophenon influenced space charge phenomenon. So in this paper, in order to clear up the effect of acetophenon, we investigated the dielectric property of oil with ionic impurity and acetophenon.
We found that the tan δ of the oil increased and ρ decreased suddenly when both ionic impurity and acetophenon were added to the oil simultaneously. We assumed that the phenomenon was due to emulsion formation.

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The guideline and procedure to select the outdoor silicone rubbers having the best electrical performances from candidates by using slab samples and inclined-plane and salt-fog tests are introduced. Inclined-plane test, which eliminates the material hydrophobic effect, can make evaluations which do not correlate with actual outdoor use to silicone-based materials. However, good understandings on it and the combination with salt-fog test enable an appropriate and valid material selection. It is shown that proposed modified salt-fog method which involves dust deposit has a possibility to produce significant differences among excellent silicone rubbers and to evaluate their performances in considerably severe conditions. The recommended procedure will be helpful for users and manufactures in evaluating and screening silicone rubbers for outdoor insulation.

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The fundamental properties of room temperature vulcanizing silicone rubber (RTV) coatings, which have been applied to improve contamination performances of ceramic insulators, are investigated. Leakage current on plastic substrates and actual ceramic insulators coated with RTV in salt-fog and rotating wheel dip tests are evaluated. Roles of alumina trihydrate (ATH) filler level, filler particle size, filler surface treatment and type of coating substrates on electrical performances and lifetimes of RTV-coated insulators are investigated. In salt-fog conditions, RTV coatings can successfully suppress leakage current and dryband arcing on bisphenolic epoxy, acryl and ceramic insulators. The reduction magnitude of leakage current levels is not dependent on ATH filler level in the range of 0-50% wt. When RTV coatings are dipped into saline water and then energized (in rotating wheel dip test), leakage current and dry-band arcing accompanied by it are allowed to develop. ATH filler level, filler particle size, filler surface treatment and type of coating substrates, all the parameters affect electrical performances and lifetimes of RTV-coated insulators. It is revealed that, for RTV coatings, neat coating preparation and adhesion between the substrates and coatings are more important than tracking and erosion suppression by adding high level ATH filler.

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We proposed an one-dimensional conduction model in a discontinuous medium in order to consider the behavior of carriers and excitons in the double-layer organic light-emitting diode (TPD/Alp3). We assumed that each emitting molecule corresponds to a hopping site for the actual charge transport. When the electron mobility is 100 times higher than the hole mobility in the emitting layer, the distribution of electron density was independent of the position, and holes accumulated near the anode in the emitting layer.
The electron-hole recombination agreed to the hole distribution. The hole accumulation dependented on the field. The field distortion caused by the hole accumulation was negligibly small in the bulk. We also discussed the time dependence of the electron-current and hole-current.

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In this paper, we report an investigation using pulsed electroacoustic (PEA) method on electrical breakdown phenomena in a low-density polyethylene (LDPE) film. A space charge distribution and an external circuit current were simultaneously measured up to electrical breakdown in a 100μm thick LDPE film with a semi-conducting electrode under DC voltage. An electric field distribution and conduction current were estimated based on these experiments. An electric field distortion due to a positive charge accumulation was observed at room temperature near the breakdown field. At 60 and 90°, an electric field distortion due to a negative charge was observed but the electric field distortion was not so large even near the breakdown field. The estimated conduction current reached to about 10mA/m2 before the electrical breakdown in each measurements. From obtained results, it is suggested that the LDPE film becomes quasi-conductive for negative charge near the breakdown field, the electrical breakdown is more affected by the conduction current than by the maximum electric field within the LDPE film.

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For the practical insulation design of high temperature superconducting power apparatus, it is necessary to elucidate partial discharge (PD) inception characteristics in liquid nitrogen (LN2). However, most of investigations have been limited to breakdown characteristics in LN2. Furthermore, the influence of thermal bubbles on PD inception characteristics should also be taken into account.
In this paper, we investigated PD inception characteristics in LN2/solid composite insulation system under practical operating conditions with thermal bubbles. Especially, we focused on V-t characteristics for PD inception under different bubble conditions. Experimental results revealed that (1) PD inception voltage was mainly influenced by the gas density in thermal bubbles, and mutually affected by the volume rate of thermal bubbles in the gap space. (2) n value of V-t characteristics for PD inception was 86-106 under small thermal bubble disturbance, while 38-54 undr large disturbance. (3)Pressurization of LN2 largely contributed to the enhancement of PD inception voltage, while little influenced on the n value of V-t characteristics for PD inception.

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Recently, high repetition rate pulsed power generators have been developed using a magnetic pulse compression circuit(MPC) and semiconductor switches. We have studied and developed a new all solid-state pulsed power generator for a high repetition rate excimer laser and an ozonizer. The all solid-state generator consists of a semiconductor switch and the MPC with saturable inductors(SI) and a saturable transformer(ST). The semiconductor switch is a high speed gate turn off(GTO) thyristor. The GTO thyristor was improved in the switching speed, therefore a switching loss decreased.The ST with a Fe-based nano-crystalline magnetic core has two functions of a step-up transformer and a magnetic switch. The high speed GTO thyristor and the new MPC realized the high-performance and simple all solid-state pulsed power generator.

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The history study of technology provides an engineer with several important suggestions to understand the essence of technology with the aim to expand his understanding of human nature and to establish his own identity to be an engineer so that his social status shall be improved. Activities for the history study of technology must be directed towards the new century and the new world not only to find the identity of an electro-engineer but also to make the public well understood of his role.
The method of history study in Japan is to find the Japanese unique technology that was born through the high standard of her education system and the devotion of excellent engineers. A model study is advisable as a scientific and an effective method to analyze the history. "The history study as an engineering, " newly composed of the engineer, by the engineer and for the engineer, must be the way for an engineer to analyze the historical facts to get the suggestion for the development of technology in the future.
The products of history study will be continuously revised and refreshed through the study of the process to face the new century and to create an ever brighter future. It should be seriously taken into account that Japanese engineers are expected to contribute to the global society by way of technology transfer to the developing countries.

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The microdischarge dynamics of high-frequency silent discharge has been studied to improve the ozone generation efficiency. The silent discharges in oxygen atmosphere were generated using a parallel-electrode type and a screw-electrode type geometries. The electric power generators of frequencies of 50kHz, 10kHz and 60Hz were utilized. The ICCD measurement showed that the number of the microdischarge with average diameter of 100μm and average current of 0.65mA increases with the applied voltage.
In the screw-electrode type system, highest ozone generation efficiency of 302g/kWh under high ozone concentration 17.1gO3/m3 was attained at an electric power of 13.6W (10kHz) and a O2 gas flow of 4.0l/min.

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Nitrogen ions were implanted into aluminum alloy (A1-7Si) for casting mold materials by plasma-based ion implantation to enhance wear resistance and hardness of the target. The negative high-voltage of pulse with the voltage of 10kV, pulse width of 10μs, and repetition rate of 100Hz was applied to the target immersed in the nitrogen plasma produced by the filament discharge. The AES analysis indicated that the depth profile of implanted nitrogen had two peaks corresponding to N+ of 10 keV and N+ of 5keV for the short implantation time less than about 0.5 hour. For the implantation time longer than 0.5 hour, however, two peaks merged each other. The AES analysis also indicated the formation of AIN by implantation of nitrogen ions. The AIN was formed in the surface region than in the nitrogen ion range. The wear resistance test by the ball-on-disk method showed that the nitrogen ion implantation resulted in the reduction of friction coefficient from 0.6 to 0.1 and the wear resistance was increased by one order of magnitude.

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We have derived analytic expressions of the potential and electric field generated by a triangular surface charge that has a second-order or third-order charge density distribution on each element. These, expressions are applicable to the surface charge method (SCM) for electric field calculations in three-dimensional arrangements. In general, the higher-order charge density expression improves the accuracy of the SCM. Moreover, the SCM with analytic expressions needs no troublesome treatment of singular points inevitably involved in the SCM using numerical integration. We have also confirmed the validity of these derived analytic expressions by comparing the calculated results with those by the numerical method.

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We propose a tool with which everybody can learn logic circuits. After opening the program window, subwindows for (1) random NAND circuit, (2) arbitrary NAND circuit and (3) logic circuit learning program are displayed for selection. Once for instance the item (2) is chosen, a truth table will be prompted for input. Then either the true value (1) or the false value (0) will be clicked by a mouse, for circuit's input condition. Next, using MA method, a preliminary circuit composed of NAND gates only is generated. The circuit can be altered later. Also by choosing the item (3), one can easily understand the relationship between the input and output logics in the various basic logic states.

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