8.5.3 Setting guidelines8.5.3.1 GeneralThe settings for the Full-scheme distance protection, quadrilateral for earth faults(ZMMPDIS, 21) function are done in primary values. The instrument transformer ratiothat has been set for the analogue input card is used to automatically convert the measuredsecondary input signals to primary values used in ZMMPDIS (21) function.The following basics should be considered, depending on application, when doing thesetting calculations:• Errors introduced by current and voltage instrument transformers, particularly undertransient conditions.• Inaccuracies in the line zero-sequence impedance data, and their effect on thecalculated value of the ground-return compensation factor.• The effect of infeed between the IED and the fault location, including the influenceof different Z0/Z1 ratios of the various sources.• The phase impedance of non transposed lines is not identical for all fault loops. Thedifference between the impedances for different phase-to-ground loops can be aslarge as 5-10% of the total line impedance.• The effect of a load transfer between the IEDs of the protected fault resistance isconsiderable, the effect must be recognized.• Zero-sequence mutual coupling from parallel lines.8.5.3.2 Setting of zone1The different errors mentioned earlier usually require a limitation of the underreachingzone (normally zone 1) to 75 - 90% of the protected line.In case of parallel lines, consider the influence of the mutual coupling according tosection"Parallel line application with mutual coupling" and select the case(s) that are valid in yourapplication. We recommend to compensate setting for the cases when the parallel line isin operation, out of service and not grounded and out of service and grounded in both ends.The setting of grounded fault reach should be selected to be <95% also when parallel lineis out of service and grounded at both ends (worst case).8.5.3.3 Setting of overreaching zoneThe first overreaching zone (normally zone2) must detect faults on the whole protectedline. Considering the different errors that might influence the measurement in the sameway as for zone1, it is necessary to increase the reach of the overreaching zone to at least120% of the protected line. The zone2 reach can be even higher if the fault infeed fromSection 8 1MRK 506 369-UUS -Impedance protection294 Line distance protection REL670 2.2 ANSIApplication manual
