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Thor – a New Design of Overhead Transmission Line Towers

Schmidt, Mark Kokborg / Nielsen, Mogens G. / Endahl, Brian / Steenholt‐Eliasson, Karl Emil

In these years Denmark puts a significant effort into reducing the CO2‐emission. Consequently, a more flexible and strong electricity transmission grid is needed to be able to transmit the power from the offshore wind farms to the consumers. Furthermore, the grid must be able to reach the international markets.

Therefore, a new detailed design of a series of overhead line (OHL) towers have been carried out. The contemporary design has been prepared by the engineers, Ramboll, together with architects, Dissing+Weitling, for the Danish transmission system operator (TSO), Energinet, and the main purpose is to have an aesthetic OHL acceptable to the public together with a cost‐efficient series of towers.

The towers are designed as lattice structures. All the traditional lattice OHL towers are constructed using angle bars, while the new design is constructed of circular tubes for all lattice members. This design gives a more open appearance of the tower that is not as massive as the resent designed OHL towers with a shaft of monopoles. The tubes have multiple advantages compared to angle bars: smaller width, lower wind resistance, higher buckling capacity and wider profile opportunities.

The traditional angle bar towers are prepared as almost fully bolted structures with no welding. However, even though the members are bolted together welding must be done on lattice towers of circular tubes, and new connections have been developed; also, to meet the aesthetic requirements.

This paper introduces the new transmission line design with focus on the tower structure and the special aesthetic designed connections.