Modified WLS three-phase state estimation formulation for fault analysis considering measurement and parameter errors
The realities in the power systems such as asymmetrical faults, asymmetric lines, bad data, and inherent errors in the measurements and the error in the impedance of the line are effective factors on the accuracy of fault location algorithms for transmission lines. In this paper, a comprehensive scheme based on the three-phase state estimation formulation is proposed for fault analysis including detection of fault occurrence, discrimination of faulty line and fault location, and identification of fault type and the phases contributed in the fault. For this purpose, the weighted least square (WLS) state estimation is partly modified by adding three-phase voltage phasors at the fault point to the state variables and considering the distance between the fault point from two ends of the faulty line as suspicious parameters. The optimization problem is also modified by adding two constraints regarding to zero-injection (ZI) buses and parameter errors. In addition, a solution algorithm is proposed to encounter bad data of measurements and parameter errors. The scheme uses fault phasor quantities to determine the correct values of all suspicious parameters and accurate fault location. The scheme has been applied to several test systems such as the IEEE 118-bus test system. Studying different fault scenarios including different cases of the quantities and parameter error demonstrate the acceptable performance of the proposed scheme.
Authors: Alireza Ghaedi and Mohammad Esmail Hamedani Golshan