At the supporting point of an insulated wire in a high voltage areal distribution system, there appears the compound insulation system consisting of an insulator and the insulation layer of the wire. Hence, complicated discharge phenomenon is to occur at the supporting point due to the penetrated overvoltage by the lightning, as reported in the earlier work.
Recently it has been found that polarities of successive lightnings in the districts along the Japan sea in winter were frequently intermingled with the positive and the negative. With such successive lightnings the discharge phenomenon is supposed to be much more complicated.
In this work, two successive impulse voltages whose polarities were intermingled with positive and negative, were impressed on the wire, and they were intermitted in time interval of 30s. Under these conditions, the leaders progressing from the tip of binding wire along the surface of the insulated wire were observed. In consequence, it was clarified that there were remarkable differences in the progression characteristics of the leaders in comparison with those due to a single stroke of lightning.
Finally it is pointed out that it is necessary to take care of the weak point of insulation layer of the wire not only in the neighborhood of the supporting point, but also in the farther range.

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With the diffusion of the earth leakage breakers (ELBs), its unnecessary operation (false operation) which might be caused by lightning surges has been reported. The false operation of the ELBs is a problem in the modern society and it is an important problem in view of the stable supply of the electric power.
The currently available methods of evaluating the false operation put emphasis on the peak value of applied lightning impulse voltage and does not take lightning surge current that flows through circuits into consideration. When we consider the operational mechanism of ELBs, it is required to take notice of the lightning surge current that flows circuits.
In this paper, attention was paid to the surge current that flows the ground return circuit. A 8/20μs standard impulse current waveform and a 0.5μs-100kHz ring waveform were used to make an experimental study of the evaluation of the false operation of ELBs due to lightning surges while considering the characteristics of a surge absorber element.

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This paper describes the water tree diagnoses of 6.6 kV class XLPE cables by DC component method. The DC current component is measured by energizing the cable with AC high voltage, therefore, it would be suitable for on-line diagnoses. The DC component is considered to appear due to the rectifying effect of water trees inside the insulation.
In the laboratory test, the DC component showed a good correlation with the degradation. However, almost no correlation was seen in the on-site measurement. The authors found that the cause of this bad correlation is galvanic effect inside the jacket. This generates the noise current through the grounding circuit when the jacket resistivity is low. Based on this finding, the equivalent circuit of on-site measurement was proposed.
Considering the equivalent circuit, this paper proposes 9 methods for discriminating the DC component due to water tree from noise current. And, this paper describes the analytical results of each method. Furthermore, the on-site or laboratory tests show some of them are effective to separate the DC component due to water tree from noise current.

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Global warming due to increasing atmospheric carbon dioxide(CO₂) is a matter of serious concern. Energy efficiency improvement has been said to be the most effective strategy for reducing CO₂, emissions. The acceleration of R&D for energy technologies which have large effects on CO₂, emission reduction should be effective to abating global warming.
In this study, the author proposes a method for evaluating the effects of energy efficiency improvement on CO₂ emission reduction. This method utilizes a compact energy system model combined with analytical calculations.
Using this method, effects of energy efficiency improvement in Japan in the year 2030 are analysed. Energy efficiency improvement in thermal power generation, nuclear power generation, and heat utilization are especially effective for reducing CO₂, emissions. The author estimates that CO₂, emissions per capita can be stabilized at the present level by energy efficiency improvement.

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In a photovoltaic system, the prediction of long-term performance may require a statistical knowledge of solar spectral distribution for some types of PV cells. However, the measuring items of current PV plant monitoring does not contain any spectral observation. To attain it in an easy manner the author discusses the capabilities of ‘skipped sampling’. It can be classified to; (1) sampling with equidistant wavelength interval, and (2) sampling with non-equidistant wavelength boundary. The former is further classified to discrete sampling and average sampling. All the cases have been systematically studied for 5 types of PV cells by numerical methods. The analysis adopted plural different sampling phases to assure possible maximum estimation errors.
Major conclusions are; (1) Average sampling allows larger sampling interval approximately 3 to 5 times as much as discrete sampling, (2) it is demonstrated that non-equidistant sampling having appropriate wavelength boundary can decrease the required number of spectral bands compared with equidistant one, and (3) a proposed 6 band spectroradiometer gives precisions within -4 to +2.5% for efficiency evaluation and -2 to +1% for its seasonal deviation evaluation. It can be adopted as a practically excellent solution for system performance evaluation.

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The pictures of lightning taken by a photo camera or a video camera give us important informations, such as the paths, the intensity and the falling point of lightning. It is necessary to change the analog data on pictures into digital ones, in order to analyze the information objectively. In this study, a CCD camera with a microcomputer is used to obtain digital image data. By using the digitalization, it is able to abstract the clear lightning channel path from the illegible picture by the new digital filter, and further it is possible to compare with the intensity distribution of each channel branch.

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Power system control and protection equipment has required higher sensitivity and operational reliability than conventional one.
Studies of digital signal processing suitable for electric power systems fulfill this objective using fast sampling and digital filtering by a 32-bit floating point DSP (Digital Signal Processor). The sampling rate of 3kHz is carefully selected in order to separate the power spectrums of the A-D conversion output errors from the signal bandwidth. The new 12-bit A-D conversion unit equipped with a recursive-type digital filter achieved the equivalent high resolution of 14-bit conversion.
This paper describes the design concept and the characteristics showing applications to current differential relays, distance relays and power system controllers.

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In this paper, energy conversion characteristics of a new type wave power device are discussed. In the new system, water valves without any mechanical operation are combined with a few air chambers. Advantage of this system is that the rectifying valves (Water Valve) without moving parts suffer less frequent failures.
To examine the efficiency of this system, the hydraulic model experiment with water valves and a small sized turbine generator was carried out in regular and irregular waves.
The method to calculate electric output in waves by the wave power device was proposed and theoretical calculations were carried out.
Results obtained by model experiments and theoretical calculations are summarized as follow.
(1) In regular waves, the efficiency of the air chamber is roughly 50_??_60% and that of the water valve is about 60_??_70%. In irregular waves, the total efficiency of the new system is about 5_??_6%.
(2) Results of theoretical calculations almost agree with those of experiments both qualitatively and quantitatively.

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Analysis of decomposition gas products offers the most promising method for the diagnosis of gas-insulated transformers due to its capability of detecting the two important faults, overheat and discharge, in transformers. Although many studies have been made on SF₆ decomposition, quite few are readily available to gas-insulated transformers because of the variety in their faults.
An experimental survey over the main components of the decomposition products generated by various faults in gas-insulated transformers was carried out through simplified model tests. The modeling was made on three important phenomena of the faults in transformers, namely, overheat, partial discharge and electrical arc, taking the actual materials related to each fault into account. Gaschromatograph and ionchromatograph were employed in the analyses of the decomposition products.
Decomposition gases characteristic to each fault were identified by the experiments. For example, SF₆ decomposition by an overheat of a metal gives SO₂ and an overheat of winding insulation CO₂ and CO. Discharges in SF₆ gas have given characteristic SO₂F₂ gas while arc currents at insulated wires have shown SF₄ gas instead. A development of a diagnostic method for gas-insulated transformers is under way by use of a quantitative study on this results.

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This paper proposes three new total systems which treat municipal refuse by pyrolysis and highly refine the generated pyrolysis gas and then use it as the fuel of a cogeneration system for district heating and cooling. The characteristics of the proposed systems were also evaluated comprehensively. As the result of evaluation, a cogeneration system is recommended which is constructed by a combined cycle power generation system with two gas turbines and a bleeder/condensate steam turbine. In the recommended system, two mass-produced conventional gas turbines are partially modified so as to make it possible to utilize the refuse-recovered low calorific gas as its fuel. It has high power generating characteristics, and is economically superior compared with a conventinal sytem, which is constructed by a garbage incinerating furnace and bleeder/condensate steam turbine power generation unit, if the extra electric energy of the system can be sold to various municipal facilities. It was also revealed from the simulation results that in the recommended system the average exergetic efficiency is 1.59 times higher, and the amount of NO_x and CO₂ emission is 71% and 41% less, respectively, compared with the conventional system.

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Partial discharge (PD) detection on live UHV/EHV power cables and accessories is one of the most important technique to prevent cable systems from serious troubles caused by slight mistakes in jointing the cables. New PD detecting method is proposed in this paper. REDI (Resonance Type Partial Discharge) sensor is developed for detecting PD occuring inside the joints of live XLPE insulated cables. This sensor pickes up the high frequency components of PD current pulses on the surface of live cables, so that the output signals can be clearly observed at the noiseless area (for example, 10_??_60MHz)
This new method was applied to the initial AC breakdown tests with three different types of joints of UHV/EHV power cables. PD pulse sequence was detected before their breakdown in all cases. The charge quantity and the number of pulses extremely increase just before the breakdown. In addition, the phase of PD pulse against the applied voltage (φ-q characteristics) changes with time or progress of deterioration. According to this experimental results, REDI sensor can be applied to the insulation diagnosis of live power cable joints.

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