LAUSR

This article provides a closer look at a high resistance grounded (HRG) power system using symmetrical components. It addresses the industry confusion, “how system charging current direction reverses during phase-ground fault condition without reversal of system voltage that causes fault current flow.” It presents fault current phasor diagram that caused industry confusion which lead IEEE Std P3003.1 published without the phasor diagram with the consensus of working group members including the author of this article. In this article, 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. During 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 article. Clarification on the limitation of HRG grounding contained in IEEE Std. 142-2007 for phase-ground fault current not to exceed 10 A and power system voltage not to exceed 4.16 kV (for delayed clearing of first phase-ground fault) is also included in this article.