GE Multilin D30 Line Distance Protection System 5-1715 SETTINGS 5.6 GROUPED ELEMENTS5The positive-sequence restraint must be considered when testing for pick-up accuracy and response time (multiple ofpickup). The positive-sequence restraint is removed for low currents. If the positive-sequence current is less than 0.8 pu,then the restraint is removed by changing the constant K to zero. This results in better response to high-resistance faultswhen the unbalance is very small and there is no danger of excessive CT errors, since the current is low.The operating quantity depends on the way the test currents are injected into the D30. For single phase injection:• Iop = ⅓ (1 – K I injected for I_2 mode.• Iop = (1 – K I injected for I_0 mode if I_1 > 0.8 pu.The directional unit uses the negative-sequence current (I_2) and negative-sequence voltage (V_2).The following tables define the negative-sequence directional overcurrent element.Table 5–21: NEGATIVE-SEQUENCE DIRECTIONAL OVERCURRENT UNITTable 5–22: NEGATIVE-SEQUENCE DIRECTIONAL UNITThe negative-sequence voltage must be greater than 0.02 pu to be validated for use as a polarizing signal. If the polarizingsignal is not validated neither forward nor reverse indication is given. The following figure explains the usage of the voltagepolarized directional unit of the element.The figure below shows the phase angle comparator characteristics for a phase A to ground fault, with settings of:ECA = 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)MODE OPERATING CURRENTNegative-sequence I op = |I_2| – K I_1|Zero-sequence I op = 3 × (|I_0| – K × |I_1|) if |I_1| > 0.8 puI op = 3 × |I_0| if |I_1| ≤ 0.8 puDIRECTION COMPARED PHASORSForward –V_2 Z_offset I_2 I_2 1ECAReverse –V_2 Z_offset I_2 –(I_2 1ECA)Forward –V_2 Z_offset I_2 I_2 1ECAReverse –V_2 Z_offset I_2 –(I_2 1ECA)
