Patent ID: 8131485
Filing Date: 2012-03-06
Classification: G01R

Abstract:
1. A method using models of faults and fault loops for symmetrical components and different types of faults in a fault locator for locating a fault in electric power lines of a transmission or a distribution system, in which division of the transmission or distribution system line into sections is used and a hypothetical location of the fault is assumed in at least one of these sections, said system having a predetermined number of terminal stations, said method comprising: measuring current for a fault condition and a pre-fault condition in all of said predetermined number of terminal stations of the system, measuring the line phase voltage for fault and pre-fault conditions in one of said predetermined number of terminal stations of the system, calculating in said fault locator symmetrical components of the measured current and voltage signals and the total fault current in the assumed hypothetical location of the fault, assuming in said fault locator a first hypothetical location of the fault is located in a section of the electric power line between the beginning of the line and a first tap point, a second hypothetical location of the fault is located in a section of the electric power line between the end of the line and a last tap point of a branch of the electric power line, and a consecutive hypothetical location of a fault which is located in the branch, calculating in said fault locator the distance from the beginning of the line to the fault located between the beginning of the line and the first tap point, the distance from the end of the line to the fault located between the end of the line and the last tap point of the branch of the line, the distance from the end of the line to the fault located in the branch, calculating in said fault locator resistances for each of said faults, selecting in said fault locator the actual location of a fault first by comparing the numerical values concerning the previously determined distances and rejecting the results whose numerical values are negative or bigger than one (1) in relative units and then by analyzing the values of the calculated fault resistances for said faults and rejecting those results of the calculations for which the value of fault resistance is negative, and if it is found that only one numerical value concerning the distance is contained in the numerical interval between zero and one in relative units and the value of calculated fault resistance for the distance to the fault point is positive or equal to zero, then these results are final and they indicate the actual distance to the fault point and the value of fault resistance in the fault point, determining in said fault locator, impedance modules or impedances of equivalent source systems for the negative sequence component for phase-to-ground faults, phase-to-phase faults, and double phase-to-ground faults or for the incremental positive sequence component for three-phase faults when if, after the selection of the actual fault point it turns out that at least two numerical values concerning the previously calculated distances are contained within the numerical interval from zero to one in relative units and the values of the calculated fault resistances for these fault points are positive or equal to zero, and assuming that the fault occurred in a definite section, and during the impedance determination it is additionally checked whether the calculated values of the impedance of equivalent source systems are contained in the first quadrant of the Cartesian co-ordinate system for the complex plane and the previously calculated distances to fault locations are rejected for which impedance values are not contained in the first quadrant of the system, and if it turns out that only one value of the impedance of the equivalent source system concerning distance is contained in the first quadrant of the system, then the result of the calculation of the distance to the fault location, for the impedance, is considered to be final and said fault locator has found the location of the fault.