GE Multilin L90 Line Current Differential System 9-539 THEORY OF OPERATION 9.6 FAULT LOCATOR9• Relay 1: 0.38781 pu 0.26811°• Relay 2: 0.30072 pu – 12.468°• Relay 3: 0.37827 pu 8.9388°Since they have a common per-unit base, the composite voltages are used at all locations. The currents are ratio matchedusing the tap settings.For example, the composite current at relay 1 is 1.3839 pu of its local CT; that is, 1.3839 × 1200 A = 1.6607 kA. When cal-culated at relay 2 from the data sent from relay 1 to relay 2, this value is 1.6607 kA / 1000 A = 1.6607 pu of the relay 2 CT.This is due to the procedure of applying tap settings to the received phase currents before calculating the composite signal.As a result, the three relays work with the following signals.The line impedances entered in secondary ohms are recalculated as follows (refer to the previous sub-section for equa-tions).Using the data in the previous two tables, the tap voltages are calculated as follows (refer to the previous sub-section forequations).From the above table, it is already visible that:• Looking from relay 1 there is no fault between the tap and the local terminal and between the tap and remote 2 termi-nal. Therefore, the fault must be between the remote 1 terminal = relay 2 and the tap.• Looking from relay 2 there is no fault between the tap and the remote 1 terminal, and between the tap and remote 2terminal. Therefore, the fault must be between the local terminal = relay 2 and the tap.• Looking from relay 3 there is no fault between the tap and the remote 1 terminal, and between the tap and the local ter-minal. Therefore, the fault must be between the remote 2 terminal = relay 2 and the tap.Note that the correct value of the tap voltage is equal for all three relays. This is expected since the per-unit base for thecomposite voltages is equal for all three relays.The three relays calculate the differences as follows (refer to the previous sub-section for equations).Table 9–37: COMPOSITE SIGNALS AT ALL THREE RELAYSVALUE RELAY 1 RELAY 2 RELAY 3VLOC(X) 0.38781 pu 0.26811° 0.30072 pu –12.468° 0.37827 pu 8.9388°VREM1(X) 0.30072 pu –12.468° 0.38781 pu 0.26811° 0.38781 pu 0.26811°VREM2(X) 0.37827 pu 8.9388° 0.37827 pu 8.9388° 0.30072 pu –12.468°I LOC(X) 1.3839 pu –84.504° 5.4844 pu –85.236° 1.2775 pu –56.917°I REM1(X) 4.5704 pu –85.236° 1.6607 pu –84.504° 1.0379 pu –84.504°I REM2(X) 1.7033 pu –56.917° 2.0439 pu –56.917° 3.4278 pu –85.236°Table 9–38: PER-UNIT LINE IMPEDANCEVALUE RELAY 1 RELAY 2 RELAY 3Local to tap 0.088509 pu 80.5° 0.12644 pu 80.5° 0.092735 pu 80.5°Remote 1 to tap 0.15174 pu 80.5° 0.073754 pu 80.5° 0.11801 pu 80.5°Remote 2 to tap 0.069551 pu 80.5° 0.057957 pu 80.5° 0.20232 pu 80.5°Table 9–39: CALCULATED TAP VOLTAGES USING TERMINAL DATAVALUE RELAY 1 RELAY 2 RELAY 3VT(LOC) 0.26581 pu 2.2352° 0.39755 pu –178.9° 0.26535 pu 2.4583°VT(REM1) 0.39758 pu –178.9° 0.26582 pu 2.2351° 0.26581 pu 2.2352°VT(REM2) 0.26535 pu 2.4583° 0.26535 pu 2.4587° 0.39758 pu –178.9°
