Abstract
This work analyses a two-terminal algorithm designed to locate unsymmetrical faults on 110 kV power transmission lines. The algorithm processes synchronized voltage and current data obtained from both ends of the protected transmission line and calculates the distance of the fault. It is based on decomposing the equivalent circuit into the positive-, negative- and zero-sequence components and finding the point where the output voltages of the right and the left side of the transmission line are equal. Compared to the conventional distance relay locator, the accuracy of this method is higher and less influenced by the fault resistance, the parallel-operated line effect and line asymmetry, as discussed in this work. It is, however, very sensitive to the synchronization accuracy. The mathematical model of the power system was created in the PSCAD (Power Systems Computer Aided Design) environment and the computational algorithm was implemented in Mathematica software.
Highlights
To locate a fault during single-phase faults in a 110 kV line, a fault locator, which is one of the functions of distance protection, is currently used
After the pick up or the trip of the distance protection, a short-circuit loop is determined and the currents and voltages measured in this loop are used for the short-circuit loop reactance and resistance calculation
The computational algorithm used for the fault impedance ZLf determination is based on the solution of the short-circuit loop using the value of the voltage measured at the protection connection point, the current in the forward direction and the current in the backward direction
Summary
To locate a fault during single-phase faults in a 110 kV line, a fault locator, which is one of the functions of distance protection, is currently used. The basic parameters of a protected line are set in the relay and used to compute the fault distance and usually to initiate the locator function as well. A fault loop and its impedance ZLf through the measured phase currents and voltages are determined. The computational algorithm used for the fault impedance ZLf determination is based on the solution of the short-circuit loop using the value of the voltage measured at the protection connection point, the current in the forward direction (to the fault) and the current in the backward direction (back to the point of measurement).
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