SUMMARYThe Tokyo Electric Power Company, Inc (TEPCO) plans 1100 kV power network system in Japan in order to meet the steady increasing demand for electricity. Four-hundred kilometer 1100-kV-designed double-circuit transmission lines have already been constructed and are now operated at 550 kV. 1100-kV substation equipment has also been developed.To realize the best design technically and economically throughout the transmission line and the substation, important technical solutions for network problems peculiar to the ultra high voltage (UHV) system have been introduced. They include insulation coordination, overvoltage countermeasures, and fast multi-phase reclosing systems with high speed earthing switches (HSESs). The overvoltage countermeasures are realized by high performance metal oxide surge arresters (MOSAs), gas circuit breakers (GCBs) with closing/opening resistor, and disconnectors (DSs) with resistor. These sophisticated technologies realize highly reliable and economical UHV substations and transmission lines. This paper describes important, fundamental, and specific requirements for UHV substations such as their compactness, economical view, and environmental harmony. There are many technical/economical aspects to be considered on UHV substation and based on those considerations: (a) compactness, (b) less impacts to the environment, (c) optimizing cost, could be fulfilled. This paper also describes the technologies addressed to UHV class components such as the introduction of new concept ''on-site assembly transformer,'' VFTO reduction countermeasure and the necessity of fullscale seismic qualification test.
Japan suffered from the Great East Japan Earthquake followed by the nuclear disaster. As a result, we experienced rolling outages for a few months in the Tokyo and Tohoku area. Japan's power transmission system consists of 50 Hz AC and 60 Hz AC in eastern and western Japan respectively. When the nuclear disaster occurred in Fukushima, enough electricity hasn't been supplied in eastern area. Power interchange capacity between east and west was small because of small redundant T&D system design. Based on this rolling outage and some present electricity supplying issues in Japan, METI (Ministry of Economy, Trade and Industry) has set the electricity system reform committee to improve this situation and make a good T&D system for the future. This committee reported the discussed issue to the Japanese METI and METI proposed policy on Electricity System Reform to the Japanese Cabinet. As a result, the Japanese Electricity System Reform policy was adopted. This future T&D system deals with redundant T&D systems between east and west, how to handle large amounts of renewable electrical energy, and how to fully de-regulate the distribution market. HVDC (VSC system) will be introduced between Hokkaido and Honshu as a subsea cable transmission system and HVDC transmission system between eastern area and western area. This paper describes recent and future Japan's T&D systems. This will be helpful to understand how to solve the issues of Japan's T&D system.
Interaction faults caused by a flawed external system designed by a third party are a major issue faced by interconnected systems. Fault injection is a valuable tool for evaluating the dependability of such scenarios. Several types of errors caused by interaction faults may be injected by existing approaches, even though previous work focused on other types of faults, such as hardware and software faults. This is not the case of inconsistent values -data that is correctly received and syntactically correct, but inconsistent with what it should represent. In this paper, we propose a novel methodology to inject inconsistent values caused by interaction faults, including hand-defined, random and semantically significant values. We also describe a simulation tool which implements the proposed mechanism to aid dependability evaluation in a system that uses the Universal Plug and Play standard to communicate.
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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