Planning network reinforcements with Dynamic Line Ratings for overhead transmission lines

Recent years have seen an increase in wind energy penetration on to the Northern Ireland (NI) transmission network to meet renewable energy targets. It is predicted that by 2020 40% of NI energy will come from the wind resource, which is concentrated in the North and West of the province. However, most of the demand for electricity is in the east where the country is most densely populated. In the near future this will create a strain on the transmission network connecting the West to the East of the province. Weather-based Dynamic Line Ratings (DLR) for overhead lines (OHLs) provides a short-term solution to up-rating the critical lines in the network while waiting for system extension, which can take years in planning and construction. Overhead lines connected to wind farms are particularly suited for DLR. The load on the line is dependent on the output of the wind farm. The higher the wind speed, the higher the load. However, increased wind speed across the lines also increases the cooling of the line and hence increases its rating. The DLR system keeps track of the change in line rating as the weather conditions change. Building on previous work this paper describes case studies at three HOkV lines on which Northern Ireland Electricity (NIE) have successfully installed DLR equipment. The paper examines how restringing certain sections of overhead lines with higher temperature conductor in conjunction with DLR implementation allows a greater increase in ampacity of the line than DLR alone. By modelling predicted wind generation and using historical weather data it is possible to predict the future impact on the electricity network. The paper outlines studies performed under worst case contingencies and predicted system loading under expected wind and thermal generation for summer 2011.