The impact of grid connnection of large-scale wind farms on the transmission grid in the south of Sweden

In this report, the static and dynamic impact on the transmission grid in the south of Sweden has been studied when connecting two large wind farms. The two wind farms are Lillgrund, 150 MW, and Krieger’s Flak, 640 MW. The study has been performed using the software Power System Simulator for Engineers, PSS/E. The static study shows no problem with voltage level or losses. However, during low load situations, the 135 kV lines between Trelleborg and Sege risk becoming overloaded. This problem must be addressed before both wind farms are allowed to be connected to the system.Dynamically, the implementation of a dynamic model for Baltic Cable is vital for the study. The cable has dynamic effects, like commutation failure in the converter station in Kruseberg, that need to be modelled. The simulations show a need to install an SVC if wind turbines equipped with ordinary fixed speed induction generators are used. Simulations with General Electric’s dynamic model for its 3.6 MW wind turbine show that there is no need to install an SVC in order for the voltage to re-establish. However, no comparison with actual data has been made so the correctness of the model can not be checked. The simulations also show a low impact on the system when disconnecting both wind farms simultaneously. Finally, no problems with rotor angle stability have been found