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Switching and protection equipment in electric power transmission and distribution systems, such as circuit breakers, surge arresters, and switchgear, are essential components for the stable supply of electricity. The demands on the equipment, for example, low maintenance cost, long life, and environmental friendliness, have been growing. Development trends in switching and protection technology applied to gas insulated switchgear, gas circuit breakers, electric power distribution equipment, medium voltage switchgear, and surge arresters are reviewed in this paper.

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In the literature for fault location, most of research works have never been mentioned about effects of simultaneous faults. This paper presents a new decision algorithm that will be developed in order to predict precisely fault location, during simultaneous fault, in an underground distribution system using discrete wavelet transform (DWT). The advantage of the DWT is that the band of analysis can be fine adjusted so that high frequency components and low frequency components are detected precisely, consequently DWT is considered herein. The fault signal is simulated using ATP/EMTP. The DWT is used to detect the high frequency components. Coefficients of positive sequence current signals are calculated. The positive sequence current as extracted to several scales with the DWT, and the coefficients of the first scale from the DWT are investigated. The time that the fault signal uses to reach the ends of the distribution line is considered, then, applied so that the distance of fault can be calculated. Various case studies have been carried out including the single fault and simultaneous fault. The result is found that the proposed algorithm gives satisfactory both in case of single fault and simultaneous fault.

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In this study, (i) effect of deion plates on arc voltage and (ii) appropriate arrangement of the plates were investigated in order to develop a design guide of a circuit breaker which is able to interrupt fault current (> several kA). As for evaluation (i), improved effect on arc voltage under arrangement of the plates were evaluated quantitatively in association between arc voltage and the design factors which are current, arc length, internal pressure and number of the used plates. As the result, it was found that arc voltage rises 19.2V by number of split arc between the plates and electrical field in arc rises about 3V/mm under high internal pressure above 0.2MPa-g. Experimental formula constituted by the design factors for estimation of arc voltage was developed on the basis of the improved effect on the voltage. Since the formula is able to estimate actual arc voltage with a margin of error within about 7%, it would be provided as effective guidelines to design arc extinguishing chambers. As for evaluation (ii), dependences of the availability of used plates on electromagnetic force to drive arc were evaluated. As the result, it is found that the plates are used effectively by exerting above a certain electromagnetic force (e. g., above 5N in case of 5kA) on the arc between the electrode and the plate. Therefore, the improvement of magnetic design near the electrodes, especially the movable electrode, or the arranging enough space to drive the arc between the electrode and the plate would be improved availability of the used plates.

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Regarding SF₆-CO₂ mixture gases, the equilibrium compositions in a temperature range from 300 to 30,000K at 0.6MPa were calculated to find out predominant particles with high number densities. Eighty-five particles, including 47 neutral molecules originating from SF₆ and CO₂, were taken into account as the component species. At the temperatures T of about 7,000K or above, S, F, C, O, their positive ions and electrons are present as the predominant particles, for almost all of the CO₂ concentration, X_CO2 . Not only SF, SF₂, CO and CO₂ but also SO and SO₂ behave as the predominant particles in the temperature range from 3,000 to 7,000K, almost independent of X_CO2. On the contrary, the predominant particles in the temperature range from 300 to 3,000K distinctly depend on X_CO2. By way of example, for the gas of X_CO2=0.1, three particles SF₆, SO₂F₂ and CF₄ have the high number densities at T below 1,000K. By way of another example, particles CO₂, SO₂F₂, CF₄ and CO₂F₂, for X_CO2=0.6, shows the high number densities at T below 1,000K. On the basis of these results, the predominant particles present after an arc extinction are discussed as a function of X_CO2.

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The prospective transient recovery voltage (TRV) at current interruption for circuit breakers should be measured by using ideal circuit breaker. Prospective values of the TRV are obtained by drawing tangential line to the TRV waveform. But, it is difficult to draw the tangential line on the four parameters TRV waveform automatically by computer software.
This paper shows the new method to draw the tangential line on the four parameters TRV waveform. It is easy to draw the tangential line on the TRV waveform by simple waveform transform process. This method is easy to code to the computer software. Also, it was investigated to decide the current zero at prospective TRV measurements.

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High-Speed Earthing Switches (HSES) featuring fast extinction of secondary arcs for EHV/UHV class high-voltage transmission lines were firstly introduced in BPA's 500kV transmission lines in US. The equipment were also applied in Korea's 765kV transmission lines, which technology was developed based on 1990's UHV (Ultra High Voltage) system studies and field test carried out by TEPCO, Japan. For establishing an international standard on HSES, there were several technical issues that need to be addressed. Interrupting duties for the HSES vary depending on the system requirements; such as the system voltage, distance to the adjacent lines, the current flowing in neighboring phases, the parallel line lengths, reclosing scheme, number of circuits on the same tower, the faults conditions and so on. PT48 was established in IEC SC17A in 2009 which was succeeded by WG48 in 2010, and the organization has been working continuously for establishing an international standard on HSES. The aim of this paper is to introduce the technical considerations and prospects for standardization of the HSES as a result of the analyses of the requirement for the HSES system which was conducted by mostly SC17A WG48 Japanese members.

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Effects of an externally applied magnetic field on CO₂ and SF₆ arc plasmas are examined by three-dimensional time-dependent magnetohydrodynamic numerical analysis. The present numerical analysis is carried out for a cylindrical-shaped simple chamber filled with CO₂ or SF₆ under the condition of direct electric current and uniform magnetic field. The dependence of thermodynamic and transport properties, and emission coefficients of each gas on temperature and pressure is taken into account in the numerical analysis. Numerical results show that thermal constriction of arc column by applying a magnetic field is more clearly apparent in the case of CO₂. The heat transfer from arc plasma to surrounding gas for CO₂ is more intense than that for SF₆. This is because the rotational speed of arc plasma for CO₂ is about two times faster than that for SF₆, and also the thermal conductivity of CO₂ at the edge of arc column is higher than SF₆. In the case of CO₂, both of arc voltage and pressure are more greatly increased by applying the magnetic field compared with the case of SF₆.

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This study focused on the development of a DC earth leakage current sensor comprising a flux-gate. Although a flux-gate leakage current sensor has conventionally used, the fluctuation of sensitivity due to the variation of temperature occurs up to approximately ±15%. The compensation method of the temperature characteristic by taking advantage of the detected voltage of first harmonic at R. T. (298K) under the leakage current of 0mA enabled us to reduce the fluctuation under ±10%.

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The arc extinguishing limitation, (dE / dt)_lim, in a thermal re-ignition region was evaluated for CO₂ and its mixtures with N₂ and O₂ at a concentration of 0.2 to study variation in (dE / dt)_lim due to N₂ and O₂ additions. A progress effect on (dE / dt)_lim did not necessarily emerge in any arc state but arose only in a specific arc state. Further consideration led to the essential facts that the emergence condition of the progress effect depended on the arc-core temperature at the instant of an interrupting current zero. In other words, admixing N₂ with CO₂ proved to produce an increasing effect on (dE / dt)_lim, if the temperature composition in an arc-core cross-section at the current zero showed an axial temperature in a range from about 9 to 14kK. In contrast, mixture of O₂ with CO₂ was found to contribute to a distinct rise in (dE / dt)_lim, if the arc temperature composition at the current zero revealed the axial temperatures below 10kK. This rise in (dE / dt)_lim arose more pronouncedly with a lower axial temperature. The above-mentioned facts were explained, in terms of a temperature reduction factor showing a decay rate of an arc temperature with time.

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Concerning CO₂ and its mixture with N₂ at a concentration of 0.2, an enthalpy h, a specific heat C_P, an electrical conductivity σ and a thermal conductivity κ at temperatures of 300-20,000K were obtained to find out effect of N₂ addition on these high-temperature properties. For comparison, similar determination was also performed for CO₂-O₂ mixture. Admixing N₂ and O₂ with CO₂ proved to result in significant variation in C_P and κ in a temperature range from 5,000 to 10,000K. The temperature reduction factor was furthermore derived to find out the property as the arc-quenching gas. This evaluation led to the suggestion that adding N₂ to CO₂ achieves rapid decay in an interrupting arc temperature in a range from 7,000 to 11,000K, while admixing O₂ with CO₂ produces rapid diminishing effect on the interrupting arc temperature in a range from 5,000 to 9,000K. An attribution analysis successfully gave the fact that these effects on rapid decay in the temperature arise from variation in C_P due to N₂ and O₂ additions, furthermore from the reactions 2N⇔N₂ and C+O⇔ CO.

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The practical prediction method was studied and evaluated for transmission line voltage after circuit breaker open, where d.c. voltage remains. In case of reactor compensated lines, oscillating voltage appears with a frequency determined by line to earth capacitance and reactor at the end of line. As the line side voltage wave also includes subsidiary oscillation by phase to phase capacitance and dumps by charge leakage along supporting insulators, high-speed processor is required to predict the voltage wave by fitting or pattern recognition methods. Limited parameters such as line voltage frequency and its phase angle make very fast wave analysis feasible within 0.1 seconds using general purpose processors. Controlled reclosing of transmission line utilizing the prediction method is evaluated by numerical analysis to reduce switching overvoltage satisfactory.

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Recently, the need of using of direct molded (DM) air bushing in cable end terminals and transformers are increasing due to its merits of lighter weight and simpler structure comparing to the porcelain bushing. It uses epoxy resin as the main insulation material around the main conductor. Despite several merits of using epoxy resin, the field concentration around the shield fittings occurs which may cause electricity failure and insulation degradation. For the field controlling, an approach has started to use the Zinc Oxide (ZnO) microvaristors in epoxy resin. However, the measurement of electrical properties of epoxy resin filled with ZnO microvaristors exposed in high voltage (HV) is not easy. So, we have approached with circuit simulation method to understand the electrical properties of ZnO particles while injected in epoxy sheet by LTspice circuit simulator. Epoxy sheets with different volume fraction of ZnO particles were proposed and their equivalent circuits were prepared. The simulation results showed the relationship between their electrical properties with the amount and distribution of ZnO particles in epoxy sheet under HV application.

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This paper describes experimental and analytic studies on pressure rise and propagation phenomena due to high current arcs in a container with opened pipes. The shape of experimental container is decided taking into account of underground common ducts. First, the arcs were ignited in the container with varying diameter D and length L of the opened pipes under the condition of arc current of 4 to 12.5kA and the arc duration of 0.1s. Based on measured waveforms, the maximum value of pressure rise P_max and the pressure oscillation frequency P_osc were obtained. As the result, it emerged that there is a tendency that P_max becomes high with lessened D and elongated L. Moreover, D has a much greater impact on P_max. And it emerged that the tendency of P_osc with changing D and L can be explained by Helmholtz resonance approximately. Secondly, CFD model for the container with opened pipe was developed based on the experimental results, and simulations were carried out. Consequently, simulation results were found to correspond to the experimental pressure rise.

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This paper describes the influences of different nozzle shapes on the thermal interruption capability of a CO₂ model circuit breaker with H₂ inclusion using an fluid dynamic simulation under the assumption of a local thermodynamic equilibrium condition. Six nozzle shape spaces were studied in order to find the effects respectively from differences in the nozzle convergence angle and nozzle throat length. It is proved that the temperature and gas flow velocity around the nozzle inlet position are crucial for the thermal interruption of CO₂ arc with H₂ gas. Power balance in the whole arc plasma region was also studied to know the dominant power loss during the thermal interruption processes. As a result, convection loss may determine the thermal interruption capability of CO₂+H₂ arcs, which is also related with a local maximum gas flow velocity on the center axis in the nozzle throat around current zero.

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In the past, we have proposed some battery operations in a photovoltaic (PV) system using the PV output and load power forecasts. In the proposed method, we utilized multi-objective optimization for a residential area model that includes a large number of PV systems with storage batteries. To practically demonstrate that the proposed operation effectively improves the economic and environmental efficiencies, it is indispensable to evaluate the forecast error effects on operation design of PV system with storage battery. In this paper, we propose a method for evaluating the robustness of battery operation taking account of the statistical characteristics of forecast errors. Some numerical examples, which show the validity of the proposed method, are also presented.

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Installation of wind power into power systems has been limited due to the problem of frequency regulation during light-load periods at night. As a solution, frequency regulation by heat pump water heaters had been proposed and tested. In this paper, the demonstration test with three heat pump water heaters used in practical houses is described. The result shows that total power consumption had droop characteristic against frequency deviation, which means that the heat pump water heaters contribute to power system frequency regulation.

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For the effective and efficient insulation design of a power line, the return-stroke current waveform parameters are indispensable. A charge transfer is one of the important parameters when the damage to the equipments on a power line due to the energy of the lightning is discussed. The amount of a charge transfer associated with a lightning flash or individual strokes can be estimated by using the electric field change obtained with a slow antenna. The authors observe the electric field waveforms in south Kyushu for the purpose of efficient acquisition of return-stroke current parameters. In this paper, the authors discuss the relation between the negative first return-stroke current peaks and the impulse charge transfer based on the observed electric field waveforms.

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The ionomer of the cathode catalyst layer of the PEFC fuel cell needs oxygen permeability, proton conductivity and drain ability of water produced by generation of electric power. We developed a novel method to form minute holes to raise oxygen permeability and drain ability for this ionomer. In the sample after irradiation 28kHz supersonic wave for 20 minutes to the cathode catalyst, the voltage drop became small remarkably. The presence of minute holes was confirmed in observation of the catalyst surface by stereo microscope and SEM.

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