Masayuki Yoda

Artificially triggered lightning experiments to an EHV transmission line

In a triggered-lightning experiment carried out on a mountain in Japan, thirteen strikes were obtained for the winter seasons of 1986 and 1987. The lightning occurred on the conductor and the tower of a 275 kV test transmission line, on the ground, etc. The authors outline the triggering method and the experimental results obtained from electrical and optical observations. Comparatively intense lightning with a current greater than 50 kA or a charge greater than 200 C was obtained. >

Forecasting variation of solar radiation and movement of cloud by sky image data

This paper describes a forecasting method for photovoltaic (PV) power by using the sky image data. The presented method is able to forecast the PV power one or two hours earlier at the PV generation site. The authors have forecasted and estimated the short period variation of solar radiation by analyzing sky image data as observed by a camera. To establish the forecasting methodology for a short-period variation of the PV power, the variation in solar radiation and cloud movement were estimated using sky image data. In this study, we used the sky image obtained from a camera with a fish-eye lens, a ceilometer (quantity and height of cloud), and a pyranometer installed on the roof of the building in our campus and neighboring areas.

Residual dc charge decay mechanism in a transmission line under fine and dry weather conditions

Authors once measured time constants of residual dc charge decay in a 500 kV transmission line during five fine and dry days of winter season. The results showed a large scattering without depending on the simultaneously measured weather conditions, such as temperature or humidity. Then the authors have performed an additional experiment in a laboratory to discuss the factors that affect the residual dc charge decay in a dry condition. And it is shown that dusts blown up and transported by wind play an important role for the charge decay.

Comparison of surface leakage current between clean and polluted insulators under dry weather conditions

We investigate surface leakage current on porcelain insulators under dry weather conditions. Clean and polluted insulators are compared. And the relationship between their surface leakage current and weather conditions is studied. As a result, the polluted insulator gives a larger leakage current than the clean insulator. Also, it is shown that the leakage current of the clean insulator is strongly dependent on the absolute humidity.

Characteristics of lightning surges observed at 77 kV substations

In order to improve power supply reliability, it is necessary to prevent lightning faults in transmission lines and substation apparatus. However, faults are caused occasionally in lower-voltage power systems, particularly at the 77 kV level. The governing factor for insulation strength of substation apparatus is the lightning impulse voltage, and it is necessary to know the voltage level and distribution in a substation caused by lightning surges in order to investigate rational insulation coordination. For this purpose, the authors measured lightning surges at two 77 kV conventional substations from 1990 to 1993. In this paper, the characteristics of induced lightning surges and back flashover lightning surges are described. Comparisons of related surge voltages at two substations, the power line phases in grounding faults, and the equivalent capacitance of the substations are also discussed.