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Grounding wires and enclosed ZnO elements have been incorporated generally in 6.6‐kV distribution systems by TEPCO for the reduction of lightning overvoltages. At present, the reliability to lightning surges is tolerably good. However, the facility of grounding wires is not inexpensive and its maintenance is hard due to corrosion and disconnection in some areas. A typical model simulating TEPCO field adopting enclosed ZnO elements has been developed and we have evaluated relative failure risks systematically according to conditions with and without grounding wires against lightning overvoltages. Two kinds of failures discussed in the paper are the flashover of insulation and the overduty of ZnO elements, and two kinds of induced and direct lightning overvoltages are studied in flashover. The greatest problem with no grounding wire is the increase of ZnO elements' duty, but it was demonstrated that a short partial grounding wire around ZnO elements or the selection of heavier ZnO elements provides a solution. The main objectives of this study are to clarify the relative failure risks systematically according to realistic field conditions, the risk of small stroke currents having long duration to ZnO elements' duty, and countermeasures against ZnO elements' overduty. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 1–10, 1999

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Mechanism of Lightning Damage on Low-voltage Distribution Equipment due to Arc dynamic currentTakahiro Otsuka,member (Toko Electric co.)Masanori Matsuoka,member (Toko Electric co.)Shigeru Uchiyama,member (TEPCO)Ichiro Sumitani,member (TEPCO)The lightning damage on low-voltage power distribution systems is almost burning of low-voltage distribution equipment due to flashover and arc dynamic current.The lightning overvoltage causes flashover of low-voltage distribution equipments. After that, the flashover causes burning, because of impressing the commercial frequency voltage.Two kinds of experiments were conducted by the authors. The first was using real scale low-voltage distribution line model.The second was using a low-voltage distribution equipment. According to the first experiment, a lightning overvoltage causes burning at an equipment or two equipments on a low-voltage power distribution system. In the second experiment,the authors suggested that flashover current due to lightning overvoltage become 0 ampere at once when flashover current switches to arc dynamic current.

Grounding wires and enclosed ZnO elements have been incorporated generally in 6.6‐kV distribution systems by TEPCO for the reduction of lightning overvoltages. At present, the reliability to lightning surges is tolerably good. However, the facility of grounding wires is not inexpensive and its maintenance is hard due to corrosion and disconnection in some areas. A typical model simulating TEPCO field adopting enclosed ZnO elements has been developed and we have evaluated relative failure risks systematically according to conditions with and without grounding wires against lightning overvoltages. Two kinds of failures discussed in the paper are the flashover of insulation and the overduty of ZnO elements, and two kinds of induced and direct lightning overvoltages are studied in flashover. The greatest problem with no grounding wire is the increase of ZnO elements' duty, but it was demonstrated that a short partial grounding wire around ZnO elements or the selection of heavier ZnO elements provides a solution. The main objectives of this study are to clarify the relative failure risks systematically according to realistic field conditions, the risk of small stroke currents having long duration to ZnO elements' duty, and countermeasures against ZnO elements' overduty. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 1–10, 1999