A system for determining a system charging current in a three-phase power system has a first grounding circuit that joins a neutral of the power transformer with a ground through a first resistor. System charged capacitance voltage in one phase is discharged through a second resistor in a second grounding circuit joining the one phase of the power system with the ground. A magnitude of the currents in the first and second grounding circuits are measured when the one phase is short circuited to ground. The preliminary system charging current is calculated as the root of the difference between the squares of the measured currents grounding circuits. The same procedure may be repeated for different values of the first resistor and for each of the phases, and the calculated preliminary system charging currents may be averaged to arrive at a net system charging current.