SUMMARYThis paper describes the outline and results of the lightning impulse tests for a 275-kV full GIS substation. The behavior of lightning surges is a very important factor for the rational design of substations and low-voltage and control circuits inside the substations. For the above reason, we carried out lightning impulse tests for a new 275-kV full GIS substation. In these tests, we measured voltage induced in low-voltage and control circuits, transient characteristics of grounding grid, injected voltage and current waveforms, and so on.By investigating these data, we confirmed the behavior of lightning surges inside the substation. We also compared simulated waveforms by EMTP analysis with the measured waveforms. The simulated results agreed well with the measured results.

SUMMARYInvestigations were conducted on the VFT (Very Fast Transient) surges that propagate into a 500-kV transformer. The disconnector restriking surge and ground fault surged were discussed. It was regarded that a large part of the surge voltage was applied just at the entrance of the transformer winding for the VFT surges. Thus, an equivalent circuit that models the windings was used for the analysis. The overvoltages that appear between the first winding sections at the entrance of the transformer were computed. The following was established.(1) The overvoltage between the first winding sections becomes greater when the magnitude of the voltage change at the transformer terminal is larger. The overvoltage between the first winding sections is not affected by the magnitude of the transformer terminal voltage. (2) For the disconnectors that are not connected directly to the transformer, the voltage change at the transformer terminal is not so large. (3) In the case of a ground fault at the GIS near the transformer, the voltage change at the transformer terminal is the same as that for a disconnector directly connected to the transformer. (4) In actual GIS, the disconnector that is connected directly to the transformer is not usually used. In this situation, the overvoltages that threaten the transformer insulation will not be generated by the restriking of the disconnectors.

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The examination of the present flood control plan for the Yodo River System based on simulated flood damages by the recurrence of the largest recorded flood in Lake Biwa basin People living at Lake Biwa shoreline areas have suffered from inundation damages from the ancient time, they strongly desire to relieve themselves from these damages. The largest recorded flood in Lake Biwa basin after Meiji Restoration occurred in 1896, but it occurred long time ago so that little hydrological and hydraulic data such as rainfall data , discharge data of the rivers which are basic information for preparing a flood control plan are left. Therefore we can't take this flood into consideration when we make the flood control plan for Lake Biwa basin. Based on the importance of the analysis of the largest recorded flood, we tried to collect as much data as possible about this flood and simulate this flood correctly based on collected data. And we also analyzed the damage by this flood. Due to the results of the analysis, if this flood occurred now, the water level of Lake Biwa would be higher than the present design flood level even if Setagawa Barrage, which was constructed at the outlet of Lake Biwa, were totally opened. On the other hand , the precipitation in the Kizu and Katsura River basins would be not very large, so the present river-related facilities would be enough for the prevention of the flood damage even if Setagawa Barrage were totally opened. But for the Uji River basin, it is clear that further counter measures for this flood must be taken because the discharge in the river would exceed the actual capacity of flow .

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