【正文】 of the offshore wind farm is implemented in the dynamic simulation tool PSS/E and consists of 80 wind turbines of 2MW power capacity each, see . Each wind turbine is simulated by a physical windmill model consisting of : 1. the induction generator model with representation of the stator transients, 2. the windmill shaft system model, 3. the aerodynamic model of the wind turbine, 4. the pitch control system given by the control logic and the blade servo. For putation of wind turbine aerodynamics there are used airfoil data for a 2 MW pitch windmill equipped with an induction generator. Each wind turbine is via its KV/30KV connected to the wind farm internal work. The internal work is anised in eight rows with 10 wind turbines in each row. Within the rows, the wind turbines are connected through the 30 KV sea cables. The distance between two wind turbines in the same row is 500 m and the distance between two rows is 850 m. The rows are through the 30 KV sea cables connected to the offshore platform with 30 KV/132 KV transformer and, then, through the 132 KV sea/underground cable to the connection point in the transmission system onland. There is chosen an acconnection of the offshore wind farm to the transmission work. An irregular wind distribution over the wind farm area there is assumed since the wind turbines are shadowing each other for ining wind. The efficiency of the wind farm is 93%at the given wind distribution and the power production pattern is shown in . Furthermore, the windmill induction generators have a little different short circuit capacities viewed from their terminals into the internal work and this is why the wind turbine initial setpoints are different. 4 The short circuit capacity from the wind farm connection point into the transmission work is 1800 MVA. In all the simulating examples, the failure event is a short circuit fault in the transmission system of 150 ms of duration. When the fault is cleared, the faulted line is tripped and the short circuit capacity is reduced to 1000MVA. Only the line tripping and, then, reducing of the short circuit capacity to 1000MVA does not lead to voltage instability. This ensures that possible voltage instability is only the result of the short circuit fault with the following windmill overspeeding. 4. Dynamic reactive pensation In this work, the dynamic reactive pensation of the large offshore wind farm is a SVC of the capacity that will be necessary for maintaining the shortterm voltage stability. The model of the SVC is as in Ref. 5 5． When operating as stall windmills Blade angle control is primarily used for optimization of the wind turbine mechanical power with respect to ining wind and hence, this control ability is not necessarily available at failure events in external power system with respect maintaining the shortterm voltage stability. This implies that the pitch or active stall wind turbines may operate as conventional (passive)stall wind turbines, by the same way as windmills onland, with the exception that they may not be disconnected. As the basis case with respect to the offshore wind turbine data, the rotor winding resistance upRR . ? , the generator inertia sHG ? ,the mill inertia sHM ? , 6 and the shaft stiffness radelupK ./..? ,see Appendix A. If no dynamic reactive pensation is applied, a short circuit fault and a posefault line tripping will result in voltage instability, see . The windmills will be, then , tripped by the protective relays and power reserves of approx. 150 MW shall be found immediately. For voltage reestablishing after the short circuit fault, it will be necessary to use 100 MVAr of dynamic reactive pensation. The simulated curves for the voltages and speeds are given in . It is noticed that the wind turbine dynamic properties such as the voltage, the generator speed etc, show a fluctuating behaviour in the windmill drivetrain sy