Evolving Fault Performance of Vacuum Switchgear on an 11kV Distribution System

The evolving fault, a fault condition in which a fault rapidly changes in physical nature immediately after its initiation, has long been known to exist but has rarely been examined on a power distribution system. This paper describes a series of tests which were performed on the Egyptian Electricity Authority's 11kV distribution system in Cairo, and which included simulations of the evolving fault. The paper also describes the capability of the vacuum interrupter to successfully interrupt the evolving fault, and some very unusual, unanticipated, fault current levels.