Methodologies to assess the interaction of network, environment and territory in planning transmission lines

The development of the Italian extra high voltage grid may greatly benefit from methodologies aimed at comparing the different technological options in the frame of the reference environmental conditions. Indeed, a harmonic growth of the grid requires tools for the evaluation of the social performance of new investments, in terms of economic efficiency, environmental impact and technical capabilities. The paper deals with such topics with reference to the following technical options: overhead lines (OHL), cables with XLPE insulation (CL), HVDC interconnections, Gas Insulated Lines (GIL). The goal of the contribution is to select and define proper tools for the comparison of these technologies from an overall social-environmental perspective. Several performance indicators have been selected. The technical ones are related to power losses (losses in the lines and in the interconnection stations for HVDC), voltage drops, capability curves, effects of shunt reactive compensation for XLPE cables. The economic indicators take into consideration the installation costs, the cost for operation and maintenance (including the monetary value of active power losses), cost for the interconnection of the line with the existing grid and those for dismantling at the end of the life of the lines. More difficult is the evaluation of environmental and land impacts, for which there are indicators strictly related to the type of technology considered and others that are needed to properly “describe” the territory. Indicators of the first type are referred to the magnetic field, land occupation and right of way requirements, the presence of compensation equipments [m2/Mvar], acoustic and electromagnetic pollution, visual impact, disamenities and impacts during construction. In addition to the aforementioned approach, and with a view to include in the overall analysis other environmental aspects, such as the constraints linked to the territory directly involved in a given transmission and/or interconnection link, a GIS (Geographical Information System)-based methodology and tool have been developed. By the GIS it has been possible to produce thematic digital maps of the whole Italian territory for each indicator and for each index. These digital maps classify the Italian territory in terms of environmental and land quality in the present situation. As a last step, a methodology has been defined to quantitatively measure the environmental impact of new power lines. Environmental impact in a single parcel is defined as a three-dimensional vector, each element of which is the calculated decrease of each index in the parcel. Thus, for a set of proposed new power line configurations it is possible to calculate the space-distributed impacts. Dedicated maps can be obtained, showing the situation without and with the proposed lines, in order to highlight the differences inside each parcel of the study area. Since three environmental aspects are investigated for a variety of sites, the comparison of the various configuration alternatives is intrinsically multidimensional. Therefore, multicriteria methods must be used to draw a final assessment.