21 - Grounding Theory and Ground Fault Protection Schemes

Abstract

This chapter discusses several ground fault (G/F) protection schemas for the protection of domestic or industrial single phase system. Hazardous areas are highly sensitive areas and a little higher level of a ground fault current can be catastrophic. At such locations it is therefore mandatory to keep the ground leakage current low by maintaining a certain level of ground loop impedance and then be able to detect and isolate these currents promptly. A scheme for a ground fault protection depends on the type of system and its grounding conditions, i.e., whether the system is three-phase three-wire or three-phase four-wire. A three-wire system requires an artificial grounding while for a four-wire system the type of grounding must be known, i.e., whether it is effectively (solidly) grounded or non-effectively (impedance) grounded. Grounding protection depends upon the measurement of the residual quantities that appears across the ground circuit in the event of a ground fault. Some of the widely adopted (G/F) protection schemas are unrestricted G/F protection, protection through a single current transformer (CT), restricted G/F protection, directional G/F protection, and differential G/F protection.