This paper presents a new method for the computation of fault location in two-and three-terminal high voltage lines. The method is based on digital computation of the three-phase current and voltage 60/50 Hz phasors at the line terminals. The method is independent of fault type and insensitive to source impedance variation or fault resistance. Furthermore, it considers the synchronization errors in sampling the current and voltage waveforms at the different line terminals. The method can be used on-line following the operation of digital relays or off-line using data transferred to a central processor &om digital transient recording apparatus. The paper starts with a twotefininal line to explain the principles and then presents the technique for a three-terminal line. The proposed technique was first tested using data obtained from a steady state fault analysis program to evaluate the convergence, observability and uniqueness of the solution. The technique was then tested using Em-generated transient data The test results show the high accuracy of the proposed technique. Lines INTRODUCIIONThe development of digital fault location techniques for transmission lines has been a subject of interest to researchers and power enginems tor the last decade. An accurate fault location technique is of special importance in improving postfault analysis for line inspection and routine maintenance. A fault location technique can be implemented as part of a digital distance relay, a stand-alone device, or an independent algorithm using data obtained by digital fault recorders for post-fault analysis. Many of the algorithms assume data to be available at one. terminal of the line. In this case, the apparent impedance and the prefault currents can be used to compute the fault location t1-41. Infeed currents and fault resistances are sources of errors in these fault location algorithms. Different approaches were implemented to reduce the effect of fault resistance. One approach considered the fault current flowing in the fault resistance for single-line-to-ground fault cases to be proportional to the zero-sequence current at the relay [2]. Therefore, the apparent impedance is considered to be 91 W 167-7 PURD by the IEEE Power System Relaying Committee of the IEEE Power Engineering Society for presentation at the IEEE/PES 1991 Winter Meeting, New York, New York, February -3, 1991. September 1, 1990; made available for printing December 18, 1990. A paper recommended and approved Manuscript submitted *M. W. L. Peterson is presently with err anti International control^ Corporation where Vr is the relay voltage signal Iris the relay current signal I, is the zero-sequence current at the relay D is the distance to the fault. RI and Xi are the line resistance and reactance per mile RF is the unknown fault resistanceUsing the real and imaginq components of equation (1) leads to two equations in two unknowns (D and RF). The equations are then solved for D. In case of interphase faults (bc fault for example), the current flowing in the fault ...

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