CHAPTER 10: THEORY OF OPERATION PHASE DISTANCE APPLIED TO POWER TRANSFORMERSL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 10-3510Equations from the “Current Transformation” and “Voltage Transformation” columns are used to derive inputs to the three(AB, BC, and CA) phase distance elements. For example, if the CTs are located at the delta side of the Delta-Wye 11transformer, and a given zone is set to look through the transformer into the system connected to the Wye winding, the CTlocation setting for that zone is set to Dy11 and the relay uses instead of a traditional I A - I B for the AB phasedistance element.The current supervision pickup setting applies to the currents specified in the “Current Transformation” columns.A distance zone originates at the location of the VTs (regardless of the location of the CTs). For information on settings seethe Application of Settings chapter.10.4.2 ExampleConsider the system shown.Figure 10-13: Sample system configurationNormally, in order to respond to the fault shown in the figure, a distance relay is applied at the relaying point X. The tableoutlines the relay input signals at this location.Table 10-10: Relay input signals at location XInput Primary SecondaryVA 100.4 kV ∠–7.32° 38.25 V ∠–7.32°
