Overhead distribution conductor motion due to short-circuit forces

Overhead distribution conductors move as a result of short-circuit conditions. In some cases, this motion can lead to conductors swinging together closer to the source. The subsequent fault causes higher stresses on the substation transformer and causes a backup overcurrent protective device to operate, having a negative impact on reliability. This paper reports on an investigation involving conductor motion on Dominion Virginia Power’s overhead distribution system. It builds upon prior work dealing with compact overhead transmission lines. The author extends the model to typical overhead distribution lines and provides guidance to the distribution engineer as to when conductor swinging might become a problem. The characteristics of the most vulnerable spans led to the development of time-current curves depicting regions where spans are likely to have problems from short-circuit forces. The resulting critical clearing time curves have been adopted by the author’s company to minimize problems from swinging conductors.