5-252 L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUALGROUPED ELEMENTS CHAPTER 5: SETTINGS5Table 5-38: Negative-sequence directional unitThe negative-sequence voltage must be greater than the VOLTAGE CUTOFF LEVEL setting specified in the PRODUCT SETUP DISPLAY PROPERTIES menu to be validated for use as a polarizing signal. If the polarizing signal is not validated, neitherforward nor reverse indication is given. The following figure explains the usage of the voltage polarized directional unit ofthe element. It shows the phase angle comparator characteristics for a phase A to ground fault, with settings ofECA = 75° (element characteristic angle = centerline of operating characteristic)FWD LA = 80° (forward limit angle = ± the angular limit with the ECA for operation)REV LA = 80° (reverse limit angle = ± the angular limit with the ECA for operation)The element incorporates a current reversal logic: if the reverse direction is indicated for at least 1.25 of a power systemcycle, the prospective forward indication is delayed by 1.5 of a power system cycle. The element emulates anelectromechanical directional device. Larger operating and polarizing signals result in faster directional discrimination,bringing more security to the element operation.Figure 5-139: Negative-sequence directional characteristicThe forward-looking function is designed to be more secure compared to the reverse-looking function, so use the forward-looking function for the tripping direction. The reverse-looking function is faster compared to the forward-looking function,so use the reverse-looking function for the blocking direction. This allows for better protection coordination. Take this biasDirection Compared phasorsForward –V_2 + Z_offset × I_2 I_2 × 1∠ECAReverse –V_2 + Z_offset × I_2 –(I_2 × 1∠ECA)Forward –V_2 + Z_offset × I_2 I_2 × 1∠ECAReverse –V_2 + Z_offset × I_2 –(I_2 × 1∠ECA)
