Modeling and Simulation of Transient Fault Response at Lillgrund Wind Farm when Subjected to Faults in the Connecting 130 kV Grid

The purpose of this thesis was to investigate what type of faults in the connecting grid should be dimensioning for future wind farms. An investigation of over and under voltages at the main transformer and the turbines inside Lillgrund wind farm was the main goal. The results will be used in the planning stage of future wind farms when performing insulation coordination and determining the protection settings. A model of the Lillgrund wind farm and a part of the connecting 130 kV grid were built in PSCAD/EMTDC. The farm consists of 48 Siemens SWT-2.3-93 2.3 MW wind turbines with full power converters. The turbines were modeled as controllable current sources providing a constant active power output up to the current limit of 1.4 pu. The transmission lines and cables were modeled as frequency dependent (phase) models. The load flows and bus voltages were verified towards a PSS/E model and the transient response was verifed towards measuring data from two faults, a line to line fault in the vicinity of Barseback (BBK) and a single line-to-ground fault close to Bunkeflo(BFO) substation. For the simulation, three phase to ground, single line to ground and line to line faults were applied at different locations in the connecting grid and the phase to ground voltages at different buses in the connecting grid and at turbines were studied. These faults were applied for different cofigurations of the farm. For single line to ground faults, the highest over voltage on a turbine was 1.22 pu (32.87 kV) due to clearing of a fault at BFO (the PCC). For line to line faults, the highest over voltage on a turbine was 1.59 pu (42.83 kV) at the beginning of a fault at KGE one bus away from BFO. Both these cases were when all radials were connected and the turbines ran at full power. The highest over voltage observed at Lillgrund was 1.65 pu (44.45 kV). This over voltage was caused by a three phase to ground fault applied at KGE and occurred at the beginning of the fault and when all radials were connected and the turbines ran in idle operation. For all simulated configurations, the highest over voltage occurred at the turbine located at the end of the longest radial. The highest over voltages on the main transformer were 1.56 pu (42.03 kV) on the low voltage side and caused by a three-phase fault at KGE and 1.17 pu (131.9 kV) on the high voltage side from a phase-to-phase fault at BFO. The most severe voltage dip occurred on turbine E-02 with 0.014 pu (0.38 kV) remaining voltage and was caused by a three phase to ground fault at BFO. This occurred when only that radial was connected. The amount of power generated and radials connected affected the maximum over and under voltage levels. Lower power generation resulted in higher over voltages and more severe voltage dips at the turbines. Fewer radials resulted in lower over voltages and less severe voltage dips.