Whichever power swing detector is responsible for applying PSB, the removal of PSB is defined by two settings –the PSB Reset Delay and (if an unblocking philosophy is employed) the PSB Unblock dly.3.6.1 SETTING THE RESISTIVE LIMITSThe Zone 7 quadrilateral should encompass all distance elements to be blocked during a power swing condition.The Zone 8 quadrilateral should be set smaller than the minimum possible load impedance. The security marginfor both conditions should be at least 20%, also a margin of at least 10% should be provided between Zone 7 andZone 8:R8 > 1.1(R7)We recommend setting the magnitudes of R7’ and R8’ equal to R7 and R8 respectively:R7’ = -R7, R8’ = -R8.V02750Zone 8Zone 7Resistive forward (+R)Resistive reverse (R’)Maximum Load+jX½ Rx Ph. ResistiveDistance zones to be blocked(only phase-to-phase)Figure 124: Setting the resistive reaches3.6.2 SETTING THE REACTIVE LIMITSThe inner Zone 7 should be set in excess of total impedance ZT , which include local source impedance ZS , lineimpedance ZL and remote source impedance ZR. Only positive sequence impedances should be considered. Thesecurity margin for this condition should be at least 20%. The recommended margin between Z7 and Z8 settings is10%:Z8 = 1.1(Z7)We recommend setting the magnitudes of Z7’ and Z8’ equal to Z7 and Z8 respectivelyZ7’ = -Z7, Z8’ = -Z8The angle Alpha should be set equal to the angle of the total impedance ZT:a =ÐZTChapter 10 - Power Swing Functions P446SV238 P446SV-TM-EN-1
