6-8 B90 Low Impedance Bus Differential System GE Multilin6.3 METERING 6 ACTUAL VALUES66.3METERING 6.3.1 METERING CONVENTIONSa) UR CONVENTION FOR MEASURING PHASE ANGLESAll phasors calculated by UR-series relays and used for protection, control and metering functions are rotating phasors thatmaintain the correct phase angle relationships with each other at all times.For display and oscillography purposes, all phasor angles in a given relay are referred to an AC input channel pre-selectedby the SETTINGS SYSTEM SETUP POWER SYSTEM FREQUENCY AND PHASE REFERENCE setting. This settingdefines a particular AC signal source to be used as the reference.If the AC signal pre-selected by the relay upon configuration is not measurable, the phase angles are not referenced. Thephase angles are assigned as positive in the leading direction, and are presented as negative in the lagging direction, tomore closely align with power system metering conventions. This is illustrated below.Figure 6–1: UR PHASE ANGLE MEASUREMENT CONVENTION6.3.2 BUS ZONEPATH: ACTUAL VALUES METERING BUS BUS ZONE 1(4)These values display the differential and restraint currents phasors for each bus zone. The magnitudes are displayed in pri-mary amperes (see chapter 8: Theory of operation for additional details).There is no cutoff level applied to the differential and restraint currents computed by the B90. Therefore, a small dif-ferential current reflecting CT inaccuracies and bus leakage current could be present during balanced conditions.This is done to achieve a more accurate differential balance and provide the user a direct indication of the real dif-ferential current, as excluding small currents or not accounting for CT errors may impose significant unaccounteddifferential current. It is advisable to set the minimum pickup for 87B protection greater than the maximum differen-tial current during normal load conditions. BUS ZONE 1BUS ZONE 1 DIFF:0.000 A 0.0°MESSAGE BUS ZONE 1 REST:0.000 A 0.0°827845A1.CDRUR phase anglereference0 o-45 o-90 o-135 o-270 o-225 o-180 o-315 opositiveangledirectionNOTE
