Modelling and optimization of simultaneous AC-DC transmission to enhance power transfer capacity of the existing transmission lines

With ever-growing population, the demand of electric power is also increasing day by day. To meet this increasing demand, the power transferred should also increase. However, the existing EHV transmission lines cannot be loaded up to their thermal limits because of the considerations of their transient stability. To address this issue simultaneous power transfer scheme came into existence. With this scheme it is possible to load the transmission lines close to their thermal limits, thus increasing the power transfer capacity of the line. This is done by the transferring AC power with DC current superimposed on it. A double circuit line is converted into composite AC-DC line which will be used for simultaneous AC-DC transmission. In this work, simple mathematical model of composite line is developed and analysed to track down the conditions for maximum power transfer. Developed mathematical approach is also compared with the existing graphical method for calculating maximum power transfer. The results obtained from mathematical model are found to be in close proximity to those obtained by graphical analysis.