System congestion criteria for interconnection of WPP through VSC-HVDC

Abstract

The growth of utilisation of wind power plants (WPP) in power systems placed at long distance of the transmission power system has shown that the best connecting alternatives are by means of high-voltage direct current lines (HVDC) using voltage source converter (VSC) stations. Generally, the bus closest to the WPP and with the highest level of short circuit is selected as the best option to connect the VSC-HVDC link, mainly due to economic criteria. This paper proposes a methodology to select the best connection point in the AC system, taking advantage of the potential increase of transmission capability due to the reactive power controlled at the VSC converter stations; measured as the increment of the loadability margin computed by means of PV curves. Nevertheless, a trade-off between this benefit and the cost of overhead HVDC transmission line as consequence of the length differences among alternatives is required. This trade-off is computed as the cost of the equivalent STATCOM required to get the same loadability margin. Thus, a technical-economical comparison of connection alternatives allows the selection of the best option for connecting the VSC-HVDC line. The methodology has been applied to connect a WPP of 500 MW to the NETS.