The problems related to grounding systems of substations and power plants include geological structure analysis of substation site, the precise design of grounding system, the technology to decrease grounding resistance of substation in high soil resistivity area, corrosion diagnosis of grounding system, precise measurement of grounding resistance of substation, and impulse characteristics of grounding devices. Up to present, these six aspects related to grounding technology of power system have been widely studied, and achieved satisfied results in China. These achievements were systematically introduced in this paper.

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Surges on a rolling stock's body will occur when the train raises its pantograph. These surge cause damage or malfunction to on-board equipment. Expansion and vibration of the surge in the end car are found. Making clear those phenomena is required to design rolling stock that reduces a surge. In this paper, experiment and basic analysis confirm that inductance of a ground wire of a car body has close relation to behavior of surges.

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It has been found from measurements for 13 sets of GSU transformers that a transfer voltage of a generator step-up (GSU) transformer involves one dominant oscillation frequency. The frequency can be estimated from the inductance and capacitance values of the GSU transformer low-voltage-side. This observation has led to a new method for simulating a GSU transformer transfer voltage. The method is based on the EMTP TRANSFORMER model, but stray capacitances are added. The leakage inductance and the magnetizing resistance are modified using approximate curves for their frequency characteristics determined from the measured results. The new method is validated in comparison with the measured results.

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JLDN (Japanese Lightning Detection Network) is a large-scale lightning location system, which covers from Hokkaido to Southwest Islands of Japan. It observes LEMP (lightning electromagnetic impulse) in the frequency ranges from VLF to LF, and estimates location and current amplitudes of lighting return strokes. The present study evaluates its ability to discriminate LEMP from return-strokes by comparing its output with the observation of a fast-antenna network constructed on Fukui Plain. It turns out that about 90% of the sources of LEMP, interpreted by JLDN as positive return strokes in the 10kA range in summer, are not cloud-to-ground strokes but in-cloud discharges. The number of termination points on ground produced by negative cloud-to-ground strokes in summer is about 1.3 to 1.4 times of the number of negative flashes observed by JLDN.

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A hot gas simulation in self-blast type GCBs was performed and revised. As a result, it was foundto be important to consider the thermodynamic and transport properties of SF₆-PTFE gas at high pressures and temperatures. Moreover, modelling arc diameters are also important in the chamber. They have become the main factors in determining the rise of puffer pressure in self-blast type GCBs, while they were not relevant in conventional puffer-type GCBs.

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Arc jets that spout from electrodes as a result of high current fault arcs cause damage to the surrounding apparatus. This paper describes the results of spectroscopic observation of 10-50kA AC arc jet. The electrodes used were iron of 40mm in diameter. The temperature and the iron vapor concentration of the arc jet were determined by considering the self-absorption of two spectral lines of iron atom. As the arc current increased from 10kA to 50kA, the temperature gradually decreased from 14,000K to 10,000K, and the iron vapor concentration (molar rate) in the arc jet increased abruptly from 1% to 50%. The energy density was calculated and it was found that the energy density of the arc jet did not change greatly (8×10⁵J/m³) as the arc current increased from 10kA to 50kA.

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SF₆ has been identified as a greenhouse gas with a long atmospheric lifetime. In the long term, it is preferable to reduce the amount of SF₆ used. Therefore, it is important to discuss the possibility of using environmentally friendly gases as alternative insulation gases for practical gas-insulated apparatuses. In the selection of an alternative gas, it is thought that high-pressure natural gases, such as air, nitrogen (N₂), and carbon dioxide (CO₂), are promising environmentally friendly candidates. In this paper, we describe the basic insulation characteristics of N₂ and CO₂ in the high-pressure range of up to 2.0MPa under a quasi-uniform electric-field gap and under a non-uniform one in the presence of a metallic particle, and the characteristics are compared with those of SF₆. Moreover, we discuss the estimation of the cross-sectional size of a gas-insulated apparatus using high-pressure N₂ or CO₂, based on insulation and thermal designs.

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Upward lightning is often observed on the coast of the Sea of Japan in winter season. Space charges by corona discharges at the grounded structures and on the ground or from the sea surface greatly affect the upward leader initiation, however, no studies of the effect of space charges have been carried out yet. In this paper, we calculate the electric fields around a conductor considering the effect of corona discharge from the conductor itself and on the ground using the DC ion flow calculation program that was developed by CRIEPI. Calculation results show that the upward leader initiation criteria are difficult to be satisfied for small conductors than large conductors because space charge reduces the electric field for the small conductors, and that space charge from conductors gives remarkable effects including polarity change on the ground level electric field in the downwind area.

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Study on reliability of vacuum interrupter (VI) such as detection method of the slow leak has been extensively carried out, while study on discharge properties in low vacuum of VI is still insufficient. In this report, we experimentally investigated discharge properties inside VI under closed contact and open contact conditions of main contactors in low vacuum of VI to simulate vacuum leakage. We also measured current waveforms and spectrum of electromagnetic wave (EMW) emitted by discharges in VI. Furthermore, we discussed the relationship between partial discharge against the product of pressure and gap spacing, and compared the results with the Paschen's curve of air. We also discussed flowing path of the discharge current in an experimental circuit including VI.

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When steep lightning surge enters a pole-mounted distribution transformer, the voltage distribution of the internal windings is unbalanced. It is known that a layer-to-layer short or a turn-to-turn short occurs where the voltage distribution of windings is high. In this paper, the voltage distribution of the windings was measured at the primary and secondary sides of the transformer using a testing transformer. The point of the windings where the highest voltage occurred was clarified. At the primary windings, large voltage occurs at the layer nearest the primary bushing, and the possibility of breakdown at this point is high. By field test using several types of surge arrestor, it is found that the lower the operating voltage of the surge arrestor installed in the primary side, the lower the voltage occurring at the primary windings. At the secondary windings, large voltage occurs at the layer closer to the neutral terminal, and the possibility of breakdown at this point is high. The lower the operating voltage of the surge arrestor installed in the primary side, the lower the voltage occurring at the secondary windings, too. Adding the surge arrestor in the secondary side, although effectively reduce line-to-line voltage, does not effectively reduce the voltage of the secondary windings.

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Switching of induction motors with vacuum circuit breakers continues to be a concern. In this paper the influence on statistical overvoltages of the stochastic characteristics of vacuum circuit breakers, high frequency models of motors and transformers, and network characteristics, including cable lengths and network topology are evaluated and a general view of the overvoltages phenomena is presented. Finally, a real case study on the statistical voltage levels and risk-of-failure resulting from switching of a vacuum circuit breaker in an industrial installation in Hong Kong is presented.

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This paper has proposed a genetic algorithm based approach to determine a grounding electrode model circuit composed of resistances, inductances and capacitances. The proposed methodology determines the model circuit parameters based on a general ladder circuit directly from a measured result. Transient voltages of some electrodes were measured when applying a step like current. An EMTP simulation of a transient voltage on the grounding electrode has been carried out by adopting the proposed model circuits. The accuracy of the proposed method has been confirmed to be high in comparison with the measured transient voltage.

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