Clearing of single phase to ground faults

Abstract

This paper considers problems with selective clearing of single phase to ground faults. Actual fault currents are sometimes lower than calculated, and directional relays sometimes determine the wrong direction. Considering lower than calculated fault currents, the paper proposes several adaptions to present fault calculations that yield more accurate results. New values for the zero sequence impedances are calculated taking into account the earth return path. A method to integrate the fault resistance in the calculations is suggested. And the capacitive contribution of all connected cables is shown to be non-negligible. Considering direction determination extreme phase angles of the current are determined for forward and backward faults and a recommendation is given for selective clearing of earth faults.

Date of Award	28 Feb 2014
Original language	English
Supervisor	Johan Morren (Supervisor 1)