GE Multilin D30 Line Distance Relay 8-138 THEORY OF OPERATION 8.2 PHASE DISTANCE APPLIED TO POWER TRANSFORMERS8Equations 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 11 trans-former, and a given zone is set to look through the transformer into the system connected to the Wye winding, the CT loca-tion setting for that zone shall be set to Dy11 and the relay would use instead of a traditional for the ABphase distance 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 more information on set-tings please refer to Chapter 9: Application of Settings.8.2.2 EXAMPLEConsider the system shown below:Figure 8–5: SAMPLE SYSTEM CONFIGURATIONNormally, in order to respond to the fault shown in the figure, a distance relay shall be applied at the relaying point X. Therelay input signals at this location are shown in the following table.If installed at the location X, the relay would use the following input signals for its phase AB distance element:V = VAB = 77.402 kV ∠57.5° primary or 29.49 V ∠57.5° secondaryI = I A – I B = 2.576 kA ∠–27.6° primary or 42.93 A ∠–27.6° secondaryAnd consequently it would see an apparent impedance of:Zapp = V / I = 30.05 Ω ∠85° primary or 0.687 Ω ∠85° secondaryINPUT PRIMARY SECONDARYVA 100.4 kV ∠–7.32° 38.25 V ∠–7.32°VB 97.23 kV ∠–53.4° 37.04 V ∠–53.4°VC 181.8 kV ∠–150.0° 69.26 V ∠–150.0°IA 1.288 kA ∠–27.6° 21.47 A ∠–27.6°IB 1.288 kA ∠152.4° 21.47 A ∠152.4°IC 0 03I B– I A I B–837727A2.CDRABwye, 330 lag°0.688 85°Ω∠2.57Ω∠88.4°150 MVA, 10%13.8kV/315kVZ = 30.11 85°L Ω∠VT = 315kV/120VCT = 300:5VT = 13.8kV/120VCT = 8000:5deltaH X
