Phasor diagram of a single-phase-ground fault current in a high-resistance grounded power system

Abstract

This paper clarifies the bolted single-phase-ground fault current flow directions and its' phasor diagram for a high-resistance grounded (HRG) power system. The paper clarifies that the system charging current 3ICO (vector sum of currents from un-faulted phases to ground) flow direction remains unchanged, whereas the same current called the capacitive component of the phase-ground fault current (ICGF) flow is in the reverse direction to 3ICO. This follows the mathematical relationship, ICGF = − 3ICO at the fault location and at the power system neutral. Many publications fail to apply this concept to phasor diagrams of phase-ground fault current, showing the phase-ground fault current power factor lagging, with respect to faulted phase-neutral voltage, which is questionable. Other publications, including the IEEE Std. 142-2007 contains figures of HRG systems that do not use the relationship ICGF = − 3ICO, causing application confusion. This paper recommends use of the relationship ICGF = − 3ICO for HRG power systems and se of “phasor” instead of “vector” to present phase-ground fault currents with respect to faulted phase-neutral voltage, and faulted phase to two un-faulted phases voltages.