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SUMMARYThis paper describes the phenomenon of internal pressure-rise due to arcs ignited between metal rod electrodes in air. First, the internal pressure-rises in a closed chamber due to arcs were measured at currents within the range of 1 to 12.5 kA. The rod electrodes were made of copper, iron, and aluminum, and were 20 mm in diameter. The measurements showed that the maximum pressure-rise distinctly differed with each electrode material at the same total arc energy, namely, the maximum pressure-rise was the highest in the case of the aluminum electrode and was the lowest in the case of the iron electrode. Next, to quantitatively verify this difference, the internal pressure-rise was estimated, taking into account the energy balance in the closed chamber on each electrode material. It was found that the estimated pressure-rise approximately agreed with the above experimental results by taking into consideration oxidation reactions of the electrodes, melting and vaporization of the electrodes, and radiation loss of the arcs under certain realistic assumptions.

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Some strands of composite fiber-optic ground wire (OPGW) are sometimes melted and broken by high-energy lightning strikes. DC arc tests simulating lightning strikes have been performed to obtain the melting and breaking characteristics of OPGW strands. The tests have to be performed under many conditions concerning the arc (e.g., current, duration, polarity, gap length) and the OPGW (e.g., size, type, and number of strands) to clarify the melting and breaking characteristics of the strands. In this paper, the calculations regarding the melting characteristics of strands are performed considering the transferred heat and its area from the arc to the strands under the aforementioned conditions. The melting characteristics of strands are calculated with an arc current of 1-100 kA considering the measured current of actual lightning. The calculation results of the strand melting duration depending on arc current show good agreement with the experimental values obtained in dc arc tests.