Analysis of earth faults in a wind farm integrated into the electric power system

Abstract

The aim of this paper is to investigate the processes of earth faults occurrence in a wind farm network, integrated into the electric power system. The wind power farm is realized with squirrel-cage induction generators (SCIG). Each generator has a 0.69/21kV step-up transformer. The connection of the wind power farm to the electric power system is implemented through a step-up substation with a single 21/115kV transformer. The star center of the transformer 21kV winding is grounded by means of a 40 ohm resistor. A synthesized in MatLab/Simulink computer model investigates the processes of earth faults occurrence in the medium-voltage (MV) network of the wind farm. Results have been obtained, concerning the influence of the earth fault location on the transient voltages and currents at both rated torque of the generators and no-operating generators. When there is an earth fault in one of the lines, the voltages and currents of the MV network are asymmetrical and higher harmonics of the currents and voltages are generated. A harmonic analysis of the current and voltage results has been made and the total harmonic distortion (THD) has been determined for several characteristic points of the wind farm network. The parameters of voltage contamination of the power system with higher harmonics in case of an earth fault occurrence in the wind power substation have been determined. It has been found that the earth faults in the MV network of the wind farm generate voltages and currents contamination of the power system with higher harmonics.