Reduction of the visual impact of overhead transmission line systems through utilisation of line surge arresters as lightning protection

The main reason for the increasing public resistance to overhead transmission line systems in Denmark is the impact on the environment with emphasis on the visual aspect. Therefore the Danish Transmission System Operator Energinet.dk is currently carrying out a research project, in cooperation with the Technical University of Denmark, on how to lessen the visual impact of 400 kV overhead line transmission systems. In this paper omission of shield wires combined with installation of a suitable number of line surge arresters is investigated as a possible alternative to transmission lines equipped with shielding wires thereby reducing tower height, allowing more compact designs of towers thus minimizing the visual environment impact of the lines. Omission of shield wires in the system and instead utilizing a larger number of surge arresters in the (upper) phases of an overhead line without reduction in line performance and lightning protection of the nearest substations requires thorough modelling of the new line including all electrical parameters necessary for performance evaluation under all conditions. In this paper, explicit use of line surge arresters as lightning protection on the line will be investigated by transient simulations on a 400 kV line with either shield wires or line surge arresters. These simulations will also be used to estimate number and location of the line surge arresters in the line to ensure a satisfactory performance of the line when omitting shield wires in the tower top. The simulation model will consist of a line section modelled in PSCAD/EMTDC as a distributed frequency dependent parameter line. Based on results from numerical simulations it is shown that line surge arresters can be used instead of shield wires however this has consequences with respect to the performance of the line and the required protection level in substations. The use of line surge arresters gives the possibility to decrease the height of towers thereby improving the visual impression of the overhead line transmission systems. However the usage of line surge arresters will, dependent upon line surge arrester placement, result in a denser visual impression of the tower top. The results will be discussed in particular with respect to possible future tower top geometries.