Investigative summary of the July 1993 Nebraska Public Power District Grand Island-Moore 345 kV transmission line failure

Nebraska Public Power District (NPPD) lost 64 miles (406 structures) of 345 kV transmission line to a severe wind storm on July 8, 1993. Transmission lines with the characteristics of this line are all at high risk of catastrophic, costly failures. NPPD investigated the failure of the line with the assistance of POWER Engineers, Inc. The probable mechanics of the failure were identified and recommendations were offered to reduce the costs associated with such catastrophic failures. Most of the recommendations are broad in nature and of value to the designers and owners of similar lines everywhere. This paper describes the transmission line, its failure and the recommendations useful to avoiding such costly events in the future