Distribution arrester failures caused by lightning current flowing from customer's structure into distribution lines

Distribution arrester failures have been thought to be caused by direct or nearby lightning strokes. We have, however, found that distribution arrester failure is caused by part of the lightning current which flows into distribution lines when the customer's structure is struck by lightning. We call this current "lightning backflow current". In order to clarify the influence off lightning backflow current on arrester failure, we have conducted experimental and analytical studies and observed the distribution outages. The main results are as follows. (1) The calculated failure probability of an arrester caused by lightning backflow current in winter is almost equal to that caused by a direct lightning stroke to distribution lines. (2) According to the investigation of lightning-caused failures; about half of the arrester failures are due to lightning backflow current. (3) Lightning backflow current should be considered as one off the main causes of distribution arrester failures.