9-14 D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUALPHASE DISTANCE APPLIED TO POWER TRANSFORMERS CHAPTER 9: THEORY OF OPERATION9Equations 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 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.9.2.2 ExampleConsider the system shown.Yd5 ABBCCAYd7 ABBCCAYd9 ABBCCAYd11 ABBCCATransformerconnectionLoop Current transformation Voltage transformationI AB_21P13------ 2I B I A– I C–( )= V AB_21P 3V B=I BC_21P13------ 2I C I A– I B–( )= V BC_21P 3V C=I CA_21P13------ 2I A I B– I C–( )= V CA_21P 3V A=I AB_21P13------ I B I C 2I A–+( )= V AB_21P 3V A–=I BC_21P13------ I A I C 2I B–+( )= V BC_21P 3V B–=I CA_21P13------ I A I B 2I C–+( )= V CA_21P 3V C–=I AB_21P13------ 2I C I A– I B–( )= V AB_21P 3V C=I BC_21P13------ 2I A I B– I C–( )= V BC_21P 3V A=I CA_21P13------ 2I B I A– I C–( )= V CA_21P 3V B=I AB_21P13------ I A I C 2I B–+( )= V AB_21P 3V B–=I BC_21P13------ I A I B 2I C–+( )= V BC_21P 3V C–=I CA_21P13------ I B I C 2I A–+( )= V CA_21P 3V A–=3I B– I A I B–
