Electrical limiting Factors for Wind Energy Installations in Weak Grids

In this paper the electrical limiting factors for installation of wind turbines have been used to determine which types of power quality problems that will dominate when wind turbines are installed in weak grids. The main limiting factors are static voltage level influence, the flicker emission, and of course, the capacity of the line. The investigation is based on field measurements on a fixed-speed wind turbine and on a semi-variable-speed wind park. It is found that the limiting factor from the power quality point of view is the flicker emissions if one fixed-speed wind turbine is installed. If three or more turbines are installed it is the static voltage variations or the line capacity that sets the limit. It is found that the X/R-ratio of the grid plays a significant influence on the installation possibility, and a ratio of 1.3-2.8 is the most favourable, depending on the short circuit ratio. For variable-speed wind turbines it is the static voltage change and the line capacity that are the limiting factors