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 the minimumload impedance.load1.6 ZRFPPZx EQUATION579 V3 EN (Equation 76)Equation 76 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 77.load minR1ZxRFPPZx 1.6 Z cos sinX1Zx IECEQUATION2307 V2 EN (Equation 77)8.2.3.8 Zone reach setting higher than minimum load impedanceThe impedance zones are enabled as soon as the (symmetrical) load impedancecrosses the vertical boundaries defined by RLdFw and RLdRv [4] or the lines defined byArgLd. So, it is necessary to consider some margin. It is recommended to set RLdFwand RLdRv to 90% of the per-phase resistance that corresponds to maximum load.min0.9 loadRLdFw R< ×IECEQUATION2419 V2 EN (Equation 78)min0.9 loadRLdRv R< ×IECEQUATION2420 V2 EN (Equation 79)The absolute value of the margin to the closest ArgLd line should be of the same order,that is, at least 0.1 • Zload min.The load encroachment settings are related to a per-phase load impedance in asymmetrical star-coupled representation. For symmetrical load or three-phase andphase-to-phase faults, this corresponds to the per-phase, or positive-sequence,impedance. For a phase-to-earth fault, it corresponds to the per-loop impedance,including the earth return impedance.[4] RLdRv=RLdRvFactor*RLdFw1MRK 502 071-UEN - Section 8Impedance protectionGenerator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 209Application manual
