10-52 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUALFAULT LOCATOR CHAPTER 10: THEORY OF OPERATION10The following composite signals in (in per-unit values) are obtained from the base equation (first equation shown), takinginto account system phase rotation, CT nominal values, and VT nominal values and connections as set under the phase VTbank of the first 87L source.Eq. 10-47whereILOC(A, B, C) is the phasor of the local current, for phases A, B, and CILOC(X) is the phasor of the local composite (mixed) currentIREM1(A, B, C) is the phasor of the first remote current, for phases A, B, and CV LOC(A, B, C) is the phasor of local A, B, and C voltagesV LOC(X) is the phasor of the local composite voltageComposite currents are calculated locally at each terminal locally. Composite voltage is continuously transmitted toremote terminals, where upon receipt it is labeled as V REM1(X) for channel 1 and VREM2(X) for channel 2. The transmittedcomposite voltage signal is supervised by a VT fuse fail condition of the first source of 87L function. During VT fuse failconditions, transmitted voltage is substituted with zero, signaling to remote peers that multi-ended fault location shouldbe inhibited.The impedance for fault location calculation (in per-unit values) is calculated as follows:Eq. 10-48Consequently, the positive-sequence line secondary impedance entered under in the fault locator menu yields followingsignals used for calculation. For two-terminal applications, we have:Eq. 10-49For three-terminal applications, we have:Eq. 10-50For two-terminal applications, fault calculations can be executed directly using the signals above. For three-terminalapplications, it is first necessary to define the faulted line segment. This is done by estimating the tap voltage as seen fromall three line terminals.Eq. 10-51The fault current is calculated as follows:Eq. 10-52
