Study of transmission capacity calculation method under high voltage security constraint

The integration to weak power grid of large scale wind farm will decrease the margin of voltage stability and increase the difficulty of voltage control. The grid actual operation exposes a new characteristic that the wind turbines trip off since low voltage firstly and high voltage secondly. Based on the power characteristics of wind turbine under LVRT, this paper explains that the root cause of high voltage after grid fault is that wind turbines´ active power cannot recover together with voltage synchronously. According to the network structure characteristics of wind power collection area, a network equivalent method for wind power collection area is proposed, which is suitable for the analysis of voltage changing. The relationship between the PCC´s voltage rise and the power drop is deduced under the constant power characteristics of wind turbines. A kind of transmission capacity calculation method under high voltage constraint is also proposed. Finally based on actual system, the validity of this method is proved through the comparison of numerical calculation and simulation.