In order to clarify the characteristics of lightning strokes, it is necessary to study not only striking events but also physics of lightning discharge. It is expected that the characteristics of lightning discharge will be clarified in more detail by the simultaneous electromagnetic field measurement.
CRIEPI has been measuring the electromagnetic field with automatic measuring system. But there sometimes were some troubles such as recording memory was overflown, and so on. In order to avoid such troubles, CRIEPI has developed a new remote control measuring system using a telephone line. This system have a special merit to check whether the trouble occurs or not. It is possible to do remote control of a digital oscilloscope and to transfer a large amount of data from each measuring site “Hokuriku” to the control site “Tokyo”.
In this paper, the new remote control measurement system is described and some results of electromagnetic field measurement by this system are presented.

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Lightning occurrence frequency is an important factor for lightning protection design. The IKL map has been used to estimate the lightning occurrence frequency, but recent progress of lightning location systems such as the LLP system and LPATS shows a possibility to make a more accurate map than that used now. In order to make such a map, present status of lightning location systems in Japan is surveyed and detection efficiency of the systems is clarified. A method to make the lightning frequency map with these data is proposed and an example of the map is shown.

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In this paper, a simple thunderbolt prediction system under fuzzy reasoning scheme is proposed. To predict the lightning location, Shikoku island and its environs are divided into a hundred areas, and the thunderbolt location and the rainfall in each area are measured by a LLS (lightning location system) and a weather radar respectively. In the proposed system, the measured thunderbolt data, its change data and the rainfall data in each area are used as the input data to the antecedent part of the fuzzy rules, and the lightning locations after thirty minutes are inferred. To achieve high accuracy prediction, the fuzzy reasoning rules are tuned by a learning law so that the prediction results match the past thunderbolt data. The learning algorithm is described in detail. By using the tuned rules, the thunderbolt locations for another day are predicted. These results demonstrate the possibility of the proposed system for prediction of the thunderbolt locations.

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A new technique of lightning location utilizing data of arrival time difference and direction of electromagnetic waves from 2 stations or 3 stations is evaluated. Combination of available modes in this time-difference and direction (TDD) technique can achieve accurate lightning location in a wider coverage area than that of the time-of-arrival technique. Simulation shows that TDD technique is capable of retrieving the site error curve in the magnetic direction finding considerably accurately. Systematic timing error associated with propagation effect deteriorates the accuracy of the TOA lightning location, especially in the exterior base line area. The existence of this phenomenon is confirmed by analyzing real lightning data.

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The authors have investigated the internal structure of thunderclouds in winter season using an X band dual polarization Doppler radar in the Wakasa Bay district from 1993. This paper deals with elapsed time transitions of the distribution and the Doppler velocity of precipitation particles in thunderclouds, and the relationship between the heights of radar echo top and of the equivalent potential temperature. In this observation, we have detected the tendency that the region of large echo intensity is maintained in the upper level of thunderclouds about 5 minutes before the lightning discharge, although descends to the lower level about 10 minutes after the lightning discharge. And we have found the relationship between the heights of the echo top and the equivalent potential temperature.
Also, referring to the recent electrification theory of thunderclouds, we have discussed the relation ship between the temperature of the graupel accumulating region before lightning discharge and the difference of lightning discharge occurring locations, and we have estimated that the difference is caused by the terrain characteristic of the Wakasa Bay.

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In Hokkaido Electric Power Co., Inc we made research on a thunderstorm forecasting problem in order to assure a safe and efficient operation of electric power system. The study was started in the research on reliability of electric power system, led to development of the thunderstorm forecasting system. This report is one attempt to the thunderstorm forcasting technique upon which the system is based and describes an outline the system.

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The winter thunderclouds that frequently come the southeastern coastal area of the Sea of Japan were investigated by field works, operating two weather radars (one is C-band, another is X-band), the sferics direction-finding system, the car-borne fieldmill, and the SAFIR system.
The grade of lightning activity is restricted by the upper air temperature. When cold airmass is advected in lower part of the Hokuriku district, the clouds exhibit weak or no lightning activity. Furthermore, the very good relation between the temporal variation of radar echo and lightning discharges detected by the SAFIR system was confirmed.
The SAFIR system can be sufficiently adapted with detecting winter thunderclouds lightning activity in the Hokuriku district.

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The possibility of forecasting cloud-to-ground discharges is investigated. It is empirically well known that the cloud-to-ground discharges occasionally follow the cloud discharges, and the objective of this paper is to convince if it is true or false using the SAFIR data for a couple of years. Since the development of thunderclouds is going together the movement of its active area, the coordinate fixed to the moving thunderclouds is applied for the analysis.
The analyzed results suggests that the possibility of forecasting cloud-to-ground discharges in tens minutes advance for both summer and winter thunderstorms.

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The authors observed the thunderclouds in winter season using a C band dual polarization radar in 1989, 1990, 1992 and 1993. We have investigated the distribution and the movement of the precipitation particles, especially graupel and ice crystals which play an important role in the riming electrification theory that is perceived as an potent electric charge generation mechanism in the thunderclouds. As a result, we have reported that there is a close relationship between the mixing of graupel and ice crystals and the lightning discharge.
In this paper, we denote the validity of the discriminating method of the precipitation particles, namely graupel and ice crystals by the radar reflectivity (Z_H) and the differential radar reflectivity (Z_DR) of the dual polarization radar in comparison with the sonde data, observed simultaneously.
Also, we have proposed two types of predictable parameters for the lightning discharge occurrence based on the discrimination method of the precipitation particles mentioned above, and we discuss the applicability of these predictable parameters.

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Pulse trains superimposed on the initial stage of Japanese winter lightning are investigated. The characteristics of these pulse trains seem to be significantly different from those of summer lightning. The shapes of pulse trains are divided into three categories: (1) consecutive small bipolar pulses similar to the summer ones. (2) a large bipolar pulse which has a static electric field change. (3) a large oscillating waveform. A correlation between the meteorological conditions and the type of these three waveforms is investigated. Each pulse included in the pulse trains is a normal bipolar waveform and its width takes the value from 5 to 52 microseconds with the mean of 18 microseconds. The time interval between successive pulses takes the value from 10 to 180 microseconds and has the mean of 52 microseconds. For each bipolar pulse, the ratio of the peak amplitude of the initial polarity to the maximum overshoot amplitude is statistically about 1.4-1.7.

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The lightning location system and weather radar system have made it possible to track lightning activities and to assume lightning occurrence precisely. These system are useful to reduce the influence of lightning failure in the power system. If lightning occurrence is forcasted several hours and one day before, more effective operation and restoration of power facilities can be realized. In an attempt to develop lightning forecast system, we researched correlation between lightning information and weather elements observed before and during lightning activities. One of important factors is air-mass stability index. We developed new type of stability index which is specifically used for lightning forecast. New type of lightning forecast algorithm has been also developed. Some case studies indicate the new lightning forecast algorithm has good accuracy.

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Electric filed changes due to lightning discharges are analyzed by means of Wavelet. Since the electric field changes are the non-stationary phenomena, the conventional Fast Fourier Transform (FFT) Analysis is not sufficient to investigate the transition of electric field spectra as functions of time. The main objective of this paper is to discuss the feasibility of the forecasting of lightning to the ground to consult the transition of electric fields. For this purpose the typical electric field changes of the positive cloud to ground strokes, which were observed during winter thuderstorms, are analyzed. The transition of spectra corresponding to the preliminary breakdown pulses, return strokes and continuing currents with pulses are shown and the feasibility of forecasting is suggested.

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An imaging of lightning discharge channel in three spatial dimensions is realized by UHF interferometers observation at two stations. These system are operating at center frequency of 327MHz with a bandwidth of 6MHz and the time resolution of 1μs. We observed many lightning discharges in winter storms at Hokuriku area of Japan, and the observed results are analyzed to obtain the lightning channel image. The analysis shows that the system can give us the image of progression of both intracloud and cloud-to-ground discharges in three spatial dimensions, and a strong possibility of clear imaging of lightning channel using interferometers.

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In high voltage aerial distribution systems, a compound insulation system consisting of an insulator and the wire insulation layer exists at insulated wire supporting points. Hence, complicated discharge phenomena can occur at these supporting points due to the presence of overvoltage caused by lightning. If there is a weak point in the wire insulation, the creeping discharge generates a punch-through breakdown at this point and the arc spot is fixed at this breakdown point resulting in a disconnection. Furthermore, an aerial insulated wire in the outdoors are exposed to some kinds of weather condition, such as rain, snow, fog and humidity, and the discharge phenomena are more complicated by these conditions. The clarification of breakdown phenomena in these insulation systems will contribute to the prevention of wire melting accidents.
In this paper, we report the effect of the polarity both on the lengths and the shapes of the creeping discharge which progress on the insulated wire under dry and wet conditions.

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The photovoltaic module integrated with roofing materials is a promising candidate for cost reduction in PV systems and we have developed roof panel modules integrated with a insulating material for energy conservation in house. It is difficult to cool these modules compared with conventional modules. The increase in temperature of the modules which consist of crystal silicon solar cells usually affects its performance under sunlight. However, the photodegradated performance in a-Si solar cells can be recovered by thermal annealing effect with increasing modules temperature under sunlight. Therefore, the PV modules integrated with roofing materials is suitable for a-Si solar cells.
This paper reports the dependence of the cell performance on the temperature by analyzing the data obtained in the field test. Furthermore, we describe the integrated modules using a-Si solar cells.

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On-line fault location techniques of intermittent ground fault points on non-grounded distribution lines are necessary to supply steady electric power for customers. This paper proposes a novel method which uses frequency spectra of transient waveforms at a sending end when an intermittent ground fault occurs. The principle of this method is that if a ground fault position differs, it causes different frequency spectrum pattern of the current or voltage transients at a sending end which is decided by the surge reflection phenomena between the sending end and the ground fault point.
By comparison between experimental data of lLG fault test on a simulated overhead line (373m line length, 2 branch points) and digital simulation analyses, we found the grounded capacitance of a power source transformer was important enough to locate the ground fault point.

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Development of LV (Low Voltage) apparatuses with high performance and superb function has been encouraged. Therefore, when applying voltage varies, the change in effective power, reactive power, and power factor of the LV apparatus is deemed to give different aspects from before. When an advanced control of voltage and reactive power at a distribution network is required, it signifies to grasp these characteristics of the LV apparatus as well as the change of its own performance while applying voltage varies. This time, the measurement of these characteristics and change in performances while applying voltage varies was carried out on various 100 volts and 200 volts apparatuses. On the basis of the measurement data, a model formula of these characteristics for simulating phenomenon of the distribution networks when the applying voltage varies was worked out for each apparatus.

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