Automatic reclosure requirements on heavy loaded transmission lines

Increasing number of unsuccessful attempts to close the transmission feeders either automatically or manually as a result of increased loading of the ESKOM EHV transmission system prompted an investigation into possible improvements of automatic reclosure (ARC) philosophy. Analysis of failures led to increased settings of permitted synchronizing angles between incoming and running voltages, reduced required synchronization voltage levels as well as changes to the ARC cycle. In this paper recommended changes and evaluation of their possible impact on the transmission´s customers are presented. Described changes are presently being implemented on the ESKOM transmission system with an aim to enhance restoration of supply and prevent development of system incidents into a major events thus improving system reliability particularly in most onerous, heavy loaded conditions