Five-Wire Distribution System Demonstration Project

Abstract

During this demonstration project, an overhead portion of a four-wire power distribution circuit was converted to a five-wire system. The fifth wire is an isolated neutral that carries all of the unbalanced return current. The measurements suggested that a ground relay could be set much lower on a five-wire system than a comparable four-wire system for improved high-impedance fault detection. Stray voltage was also much lower when the circuit was operated as a five-wire configuration. Magnetic fields were generally lower on the five-wire circuit than at the same locations during four-wire operation. Conversion of an existing four-wire system to a five-wire system presented several unique concems including fifth-wire placement, crew safety and operations, and how to interface the five-wire system with the existing four-wire distribution system.