CHAPTER 6: ACTUAL VALUES METERINGC70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL 6-136For 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 setting defines aparticular AC signal source to be used as the reference.The relay first determines if any “Phase VT” bank is indicated in the source. If it is, voltage channel VA of that bank is usedas the angle reference. Otherwise, the relay determines if any “Aux VT” bank is indicated; if it is, the auxiliary voltagechannel of that bank is used as the angle reference. If neither of the two conditions is satisfied, then two more steps of thishierarchical procedure to determine the reference signal include “Phase CT” bank and “Ground CT” bank.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. The figure illustrates this.Figure 6-3: UR phase angle measurement convention6.4.1.3 UR convention for measuring symmetrical componentsThe URs calculate voltage symmetrical components for the power system phase A line-to-neutral voltage, andsymmetrical components of the currents for the power system phase A current. Owing to the above definition, phaseangle relations between the symmetrical currents and voltages stay the same irrespective of the connection of instrumenttransformers. This is important for setting directional protection elements that use symmetrical voltages.For display and oscillography purposes the phase angles of symmetrical components are referenced to a commonreference as described in the previous sub-section.WYE-connected instrument transformersThe above equations apply to currents as well.• ABC phase rotation: • ACB phase rotation:
