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Identification of reactive power provision boundaries of a distribution grid with DFIGs to a transmission grid

Development of the distribution grids brings also new challenges. With efficient exploitation of all the available resources in the grid, many related problems can be solved. The problem addressed in this paper is becoming more and more common in the practice. There is a need to control reactive power exchange between the grids of different voltage levels. This need becomes more pronounced with increasing penetration of distributed generation and cables in the system. But, the cause of the problem can be also a part of its solution. This paper shows that it is possible to control the reactive power exchange to a noticeable extent using the distributed generation located in the grid and the on-load tap changers. The results have been obtained from the analysis of a representative model of Swedish distribution network with installed DFIG wind turbines. While not going deeper into the control strategies, the reactive power boundaries of the system are identified. Critical elements are found for different case scenarios. Solutions on adjustment of reactive power capabilities of the grid are proposed.