Phase-Ground Fault Current Analysis and Protection of a High-Resistance Grounded Power System

This paper provides a closer-look at a high resistance grounded (HRG) power system using symmetrical components. It addresses the industry confusion, “how system charging current flow direction reverses during bolted phase-ground fault condition without reversal of system voltage that causes fault current flow”. In this paper, the theory of symmetrical components has been used for analysis of phase-ground fault to illustrate ground fault current flow directions and its phasor diagram. The industry concept, “phase-ground fault current flows from the faulted location to ground before it returns to the power source” has been used in the analysis. This concept has not been used in the IEEE Std. 142 -2007, causing ground fault protection confusion for HRG power systems. The fault current flow direction clarification will help in the application of a sensitive voltage polarized ground fault protection relay for HRG. Under phase-ground faults with very low arcing fault currents which pose a sensitivity issue on ground fault protection relays, some relevant technical papers providing techniques of fault detection are referenced in this paper. Clarification on the limitation of HRG grounding contained in IEEE Std. 142–2007 for phase-ground fault current not to exceed 10A and power system voltage not to exceed 4.16 kV is also included in this paper.