The plain Mho circle has the characteristic as in figure 49. The condition forderiving the angle β is according to equation 6.β = −( ) − ( )⋅arg argU I Z UL L L L set pol1 2 1 2 1IECEQUATION15027 V1 EN-US (Equation 6)whereU L1L2EQUATION1790 V2EN-USis the voltage vector difference between phases L1 and L2I L1L2EQUATION1791 V2EN-USis the current vector difference between phases L1 and L2Z set1is the positive sequence impedance setting for phase-to-phase fault in zone directionFor Zone 1,Z R PPZ j X PPZset1 1 1 1 1= + ⋅IECEQUATION15011 V1 EN-US (Equation 7)whereR1PPZ1 is the positive sequence resistive reach for phase-to-phase fault for zone 1X1PPZ1 is the positive sequence reactance reach for phase-to-phase fault for zone 1For Zone 2-5 and RVZ R Zx j X Zxset1 1 1= + ⋅IECEQUATION15012 V1 EN-US (Equation 8)whereR1Zx is the positive sequence resistive reach for zone x (x=2-5 and RV)X1Zx is the positive sequence reactance reach for zone x (x=2-5 and RV)Upolis the polarizing voltageOperation occurs if 90°≤β≤270°1MRK 505 394-UEN A Section 7Impedance protectionLine differential protection RED650 2.2 IEC 127Technical manual
