ESTIMATING LOCATIONS OF SHUNT FAULTS ON DISTRIBUTION LINES
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The usual approach for estimating the locations of transmission line shunt faults has been to measure the apparent impedance to the fault from a line terminal and convert the reactive component of the impedance to the line length. Several methods, that use the fundamental frequency voltages and currents measured at one or both line terminals, for estimating the locations of transmission line faults have been proposed in the past. These methods are not suitable for non-homogeneous distribution lines with tapped loads. This thesis presents a technique that estimates the location of a distribution line shunt fault. Intermediate load taps and non-homogeneity of the line are taken into account. Distributed parameter model of the line and voltage dependent load models are used. The loads up to the fault are considered independently and the loads beyond the fault are assumed consolidated at the remote end. The load constants, describing the change in load impedance with voltage, are computed from the pre-fault load voltages and currents. The apparent location of a fault from the line terminal is first estimated by computing the impedance from the fundamental frequency voltage and current phasors, and converting the reactive component of the impedance to line length. The sequence voltages and currents at the nodes up to the fault are calculated and the sequence voltages at the remote end are expressed as a linear function of the distance to the fault. The sequence voltages and currents at the fault are also expressed as functions of the distance to the fault as well as the impedances of loads beyond the fault. An equation for the impedance at the fault is then obtained and its imaginary component is equated to zero. This provides a non-linear equation which is linearized and solved using an iterative approach. Results from computer simulations of single and multi-phase faults on a 25 kV line of the Saskpower system are presented. The results indicate that the proposed technique works well for fault resistances that are of magnitudes comparable to the line impedance.