The Ninth International Workshop on High Voltage Engineering (IWHV2014) was held on November 7^th and 8^th of last year at Faculty of Engineering, University of the Ryukyus, Okinawa. It has been held biennially under the joint supervision of the Institute of Electrical Engineers of

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Terahertz (THz) waves are electromagnetic waves in the frequency region 100GHz-10THz, and are useful for nondestructive testing of dielectric materials, such as polymers, plastics, and ceramics. In this report, application of THz waves to inspection of thermal barrier coating (TBC), corrosion evaluation and detection of rust under paint, and improvement of spatial resolution in THz imaging is presented. TBC is applied to high temperature components in gas turbines, and consists of a ceramic topcoat and a metallic bondcoat. THz waves were shown to be effective for measuring the topcoat thickness, which is an important factor which determines the thermal resistivity. Early stages of corrosion of metal substrates covered with paint are difficult to detect by visual inspection, but could be visualized using THz waves. In imaging using THz waves, the spatial resolution is mainly limited by the effective spot size. Frequency filtering of THz waves and combination with image processing techniques were found to be effective for improving the spatial resolution. This was demonstrated in THz imaging of an IC card.

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In scenarios involving an increased risk of damage to electrical and electronic equipment due to lightning, it is important to protect equipment by employing protection mechanisms such as surge protective devices (SPDs). However, it is difficult to achieve effective protection when the protective devices have incorrect specifications, or when incorrect connections are made for the equipment to be protected. In this study, we develop circuit simulation models to investigate how the selection and installation conditions of SPDs affect their protective effect. We perform experiments and analyses using power-supply circuits of actual equipment where a single-phase alternating current (AC) voltage of 200V was supplied outdoors. By modeling in detail a varistor as a nonlinear resistance, we were able to analyze the protective effect of varistors in power-supply circuits. By installing the varistors before and after the filter unit in the power supply circuit, we can realize the protective coordination of multiple varistors because the filter unit functions as a decoupling element.

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It is of importance to detect a partial discharge (PD) in a gas-insulated switchgear (GIS) and to estimate its current magnitude and charge amount. In this paper, electromagnetic fields generated by a PD in an 84-kV-class three-phase test GIS have been measured with a differential voltage probe installed on the outer surface of an insulation spacer of the GIS tank, and the corresponding simulations have been carried out using the finite-difference time-domain (FDTD) method. FDTD-computed time-domain voltages across spacers agree reasonably well with the corresponding measured ones.

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This paper has proposed a new fundamental investigation technique on arc behaviors in decaying and re-ignition processes under gas flow condition. This technique utilizes power semiconductors like insulated-gate bipolar transistors (IGBTs) to control the arc current and voltage with a high accuracy in time domain. The free recovery condition was created by switching-on an IGBT connected in parallel with the arc device to investigate decaying process of the arc plasma under gas flow condition. Then, the quasi-transient recovery voltage (quasi-TRV) was intentionally applied between the electrodes in the arc device under the free recovery condition by turning-off the IGBT again, to study the re-ignition process of the arc plasma. At the same time, the arc behavior in a nozzle was observed by a high speed video camera at a frame rate of 200,000 fps. In the present work, arc behaviors in gas flow such as SF₆ and CO₂ in a nozzle was fundamentally investigated under free recovery condition and then after quasi-TRV application. In addition, the timing of the quasi-TRV application was changed to examine the recovery property of residual arcs in SF₆ and CO₂ gas flow. Through these experiments, the probability of arc successful interruptions were statistically measured for these gas flow arcs. These results provide fundamental data for comparison of the arc interruption capability of different conditions.

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For the analysis of back-flashover phenomena in transmission lines, accurate evaluation occurrence of flashover at the arcing horns is necessary. In this paper, parallel gap flashover phenomena are experimentally studied using real arcing horns and an impulse generator. The occurrence probability of concurrent flashover is theoretically estimated based on statistical analysis of flashover phenomena. We show that the theoretically estimated probability agrees with the experimental results.

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Comparison tests between Japanese national-standard-class measuring system for lightning-impulse high voltage and reference measuring system of 5 high-voltage laboratories are carried out. The evaluated uncertainties of the measurements by the reference measuring systems are less than the requirements of IEC60060-2: 2010. Furthermore, it was confirmed by comparing with past conducted comparison tests that the voltage dividers of the reference measuring systems are stable within the range of the uncertainty of the standard measuring systems over about 10 years.

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Modeling of spallation polymer particles in polymer ablated arcs was conducted to numerically simulate its dynamics and thermal decomposition. We had found that spallation particles ejected from the polyamide materials contacting thermal plasmas experimentally. For the modeling of the particle dynamics, the temperature and gas flow fields in polymer ablated arcs were calculated as a background plasma at first. Using the calculated temperature and gas flow fields in polymer ablated arcs, we computed the trajectories of the particles flying in the polymer ablated arc, considering the time variations in the temperature and the diameter of the particles. This computation accounted for the temperature distribution inside the particle, melting and thermal decomposition of the particle. The polyamide-6 (PA6) particle in the PA6 ablated arc was dealt with. As a result, the temperature variation including the phase changes, and the decrease in diameter were simulated for PA6 particles in the PA6 ablated arc. Results also indicate that a particle with a diamater of 0.3mm and a velocity of 5m/s can reach the high-temperature arc core in a 6mm diamater PA6 tube.

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