CHAPTER 10: THEORY OF OPERATION FAULT LOCATORL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 10-5310The faulted segment can be found by recognizing that the sum of the voltage drops around a loop through the unfaultedsegments is zero. The residual voltage phasors are computed for each loop. The loop with the lowest residual voltagecontains the two unfaulted segments. Therefore, the differences between each pair of estimates is calculated as follows:Eq. 10-53The faulted segment is selected as follows:Eq. 10-54whereEq. 10-55A similar set of equations is applied to determine whether the fault is between the tap and the local terminal or betweenthe tap and remote terminal 1.Next, having all the data prepared, the following universal equation is used to calculate the fault location:Eq. 10-56For this equation, two-terminal applications, the following equalities hold:Eq. 10-57For two-terminal applications, the distance is reported from the local relay. In three-terminal applications, the distance isreported from the terminal of a given line segment.Phase rotation must be the same at all line terminals for correct operation of the multi-ended fault locator.
