both phase-to-phase and phase-to-earth fault operatingcharacteristics should be considered.To avoid load encroachment for the phase-to-earth measuring elements, the setresistive reach of any distance protection zone must be less than 80% of theminimum load impedance.0.8 loadRFPEZx Z EQUATION792 V2 EN-US (Equation 69)Equation 69 is applicable only when the loop characteristic angle for the singlephase-to-earth faults is more than three times as large as the maximum expectedload-impedance angle. For the case when the loop characteristic angle is less thanthree times the load-impedance angle, more accurate calculations are necessaryaccording to equation 70.min2 1 00.8 cos sin2 1 0loadR Zx R ZxRFPEZx Z X Zx X Zx EQUATION578 V5 EN-US (Equation 70)Where:∂ is a maximum load-impedance angle, related to the maximum load power.To avoid load encroachment for the phase-to-phase measuring elements, the setresistive reach of any distance protection zone must be less than 160% of theminimum load impedance.load1.6 ZRFPPZx EQUATION579 V3 EN-US (Equation 71)Equation 71 is applicable only when the loop characteristic angle for the phase-to-phase faults is more than three times as large as the maximum expected load-impedance angle. For other cases a more accurate calculations are necessaryaccording to equation 72.load minR1ZxRFPPZx 1.6 Z cos sinX1Zx IECEQUATION2307 V2 EN-US (Equation 72)All this is applicable for all measuring zones when no Power swing detectionfunction ZMRPSB is activated in the IED. Use an additional safety margin ofapproximately 20% in cases when a ZMRPSB function is activated in the IED,refer to the description of Power swing detection function ZMRPSB.Section 7 1MRK 505 393-UEN BImpedance protection128 Line differential protection RED650 2.2 IECApplication manual
