Method and directional element for fault direction determination in a capacitance-compensated line

In combination with an electrical power system including:

• a transmission line for transmitting electrical power;
• series capacitance compensation series-coupled to the transmission line adjacent one end thereof, the series compensation including a capacitance having a value (−j XCAP);
• and
• a protective relay at the one end of the transmission line for monitoring line voltages and line currents on the transmission line;
• an apparatus upon sensing a fault for determining a direction of the sensed fault, the apparatus comprising:
• a calculating element calculating a Δ-impedance ΔZ of the line based on the monitored line voltages and line currents before the sensed fault and the monitored line voltages and line currents after the sensed fault;
• an adjusting element adjusting the calculated Δ-impedance ΔZ according to the value of the capacitance of the series compensation (−j XCAP) to result in a modified Δ-impedance ΔZMOD;
• and
• an examining element examining the phasor angle of ΔZMOD to determine the direction of the sensed fault, the fault being in a first direction if the phasor angle is between X and X+180 degrees, and being in a second direction opposite the first direction if the phasor angle is between X+180 and X+360 degrees.