Modern wind turbines (WTs) are mostly connected to the medium-voltage or high-voltage grids of a grid operator. The grid integration must therefore possess important properties in order to make safe operation of the grid possible and to maintain the voltage quality of the public grid. This chapter deals with the important properties of public electrical grids, the possibilities of influencing the grid by means of operating media such as WTs, and the conditions under which WTs can even be connected to the public electrical grid. The end of the chapter deals with grid integration of WTs that have an effect on future developments such as Supergrids and smartgrids.
10.1 Energy Supply Grids in Overview
This section will deal with the basics of power transmission. The advantages and disadvantages of the different grid structures and the use of different voltage levels are described.
Because of current heat losses, which depend upon the square of the current, and because of the voltage changes dependent on the current (voltage decrease or voltage increase), there is also a rise of the required grid voltage generally with the distance and the power to be transmitted. The grid impedance rises with increasing distance or length of the grid; with constant power to be transmitted, the current is reduced by the selection of a higher voltage level. The flow of load set in the electrical power supply grid, made up of active and reactive ...