SUMMARY When a fault arc occurs in oil‐filled electric power equipment such as transformers in transmission and distribution systems, it generates a flammable gas and a dynamic pressure rise that may trigger an explosion. The purpose of this fundamental study is to investigate the effects of the arc under electrical insulation oil on pressure rises in a closed vessel containing air and oil. In particular, this paper is intended to investigate the relationship between the pressure rises and the generated bubble behavior by the arc. The pressure rises in both air and oil are measured under experimental conditions involving an arc current ranging from 2.3 kA to 8.9 kA, an arc duration of 10 ms or 100 ms. Experimental results show that the behavior of a bubble affects the pressure rises in the air and the oil as low‐frequency pressure oscillation comparatively.

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Zinc phosphide (Zn3P2) has attracted considerable attention as an environmentally benign and earth-abundant photoabsorber for thin-film photovoltaics. It is known that interdiffusion occurs at the Mg/Zn3P2 interface, which is a component of the record device, but the micro- and nanoscopic structures of the interface after interdiffusion have been controversial for over three decades. Here, we report on the formation of a Mg–P–Zn ternary semiconductor, Mg­(Mg x Zn1–x )2P2, at the Mg/Zn3P2 interface. Interestingly, Mg­(Mg x Zn1–x )2P2 is epitaxially grown on Zn3P2 with the orientation relationship of [21̅1̅0](0001)Mg(Mg x Zn1–x )||[100]­(011)Zn3P2 due to interdiffusion. The lattice mismatch of the Mg­(Mg x Zn1–x )2P2 layer on the Zn3P2 substrate is less than 0.5%, and this is favorable for carrier transport across the interface. Mg­(Mg x Zn1–x )2P2 is the material suggested as “n-type Mg-doped Zn3P2” or “a Mg–P–Zn alloy” in the previous studies. Thus, only the optimization of Mg treatment as conducted in the previous studies is insufficient for the improvement of the cell performance. This work clarified that a suitable microstructure and band structure around Mg­(Mg x Zn1–x )2P2/Zn3P2 heterointerface should be established.

When a fault arc occurs in oil-filled electric equipment, it generates a flammable gas and a dynamic pressure rise. In this study, the pressure rises due to the arc are measured in a closed vessel containing air and oil for different arc depths. The pressure rises in air and oil with different depth are measured under experimental conditions involving an arc current 6.6 kA, an arc duration of 100 ms. Experimental results show that the frequency of pressure fluctuation varies with the depth of the arc. Our approximate calculation of the pressure fluctuation with consideration of the oil flux is consistent with the experimental results. C⃝ 2017 Wiley Periodicals, Inc. Electr Eng Jpn, 202(2): 43-53, 2018; Published online in Wiley Online Library (wileyonlinelibrary.com).