The 380kV Thames Crossing

The 380kV Thames Crossing. An overhead powerline crossing of the River Thames between Dartford and West Thurrock. Its towers are the tallest electricity pylons in the UK. Two 190-metre tall lattice towers either side of the Thames. The span width is 1372 metres, the minimum height of the conductors over the river is 76 metres. Each tower is equipped with three crossbars and is capable of carrying two circuits for 380 kV three-phase AC. Check out The Gorge - Flash Bristow's website for a bit more detail. 

Three-phase electric power systems are used for high and extra-high voltage AC transmission lines (50 kV and above). The towers must be designed to carry three (or multiples of three) conductors. The towers are usually steel lattices or trusses (wooden structures are used in Germany and Scandinavia in some cases) and the insulators are either glass or porcelain discs or composite Insulators using Silicone Rubber or EPDM rubber material assembled in strings or long rod whose length is dependent on the line voltage and environmental conditions. One or two earth conductors (or "ground conductors") for lightning protection are often mounted at the top of each tower.