New Drivers in electric power transmission. The connections to the transmission grid

The introduction of a competitive framework in the electricity industry poses new challenges to transmission system operators charged with connecting new independent power plants to the existing extra high voltage grid. Assuring fast and reliable connections respecting the environment is a crucial task requiring sometimes innovative solutions. The paper looks at the available options for the connection of power plants to the existing extra high voltage transmission grid taking into account investment, operation and maintenance and environmental costs, identifying the best solution as a function of the land value. Three different technical solutions are compared: • overhead lines, • cable lines; • gas insulated lines. Overhead lines are the traditional technology with few innovative solutions. High voltage cables made a breakthrough with the introduction of XLPE insulation reducing dramatically the losses and improving the life duration of dielectric. Gas Insulated Lines (GIL), even if rely on a technology that dates back in the seventies and eighties when most of the related patents were deposited in Europe and the USA, show brilliant performances when the reduction of electromagnetic field has to be achieved. While overhead lines have a low investment cost, cables and GIL can eliminate the visual impact. In addition, GIL can almost avoid the presence of electromagnetic field above threshold of 0.5 or even 0.2 T, as required by a recent legislation in Italy, making feasible connections otherwise unlikely for environmental reasons. The paper makes a detailed technical and economic assessment of these different technologies looking at the best social solution in different conditions, showing with great detail that the best solution has to be found in every specific case. An analytical methodology to find the least cost technology for the connection of new power stations is also presented.