Ground Selector for Ungrounded Three-Phase Distribution Systems

Ever since three-phase distribution has been known, a controversy has been going on with respect to the relative merits of grounded and ungrounded neutral. The inability of locating and isolating a ground fault is the chief disadvantage of the ungrounded neutral system, this being the reason why lately the grounded neutral has been given preference. The purpose of the so-called ground selector is to provide means to permit the selective clearance of a ground fault in an ungrounded neutral system. The device thus eliminates the mentioned disadvantage and raises the ungrounded neutral system to the same operating ating standard as the grounded neutral system, retaining at the same time the many other advantages inherent to the ungrounded system. The paper describes the functioning of the ground selector and compares in detail the two systems. Two ground selector installations on largely different systems are described and the practical operating results are reported and discussed. The conclusion is reached that the ungrounded neutral system equipped with a ground selector combines the advantages of the ungrounded and grounded neutral systems without being afflicted with their respective disadvantages.