a better solution was sought. Consideration was given to 400 kV and 500 kV schemes: both gave a sufficient margin for future expansion. The decision in favour of a 400 kV system was made for two main reasons. Firstly the majority of the 275 kV lines could be uprated to 400 kV, and secondly it was envisaged that operation at 400 kV could begin in 1965 compared with 1968 for a 500 kV scheme. Design work was started and in order to meet the programme for 1965 it was necessary for the contract engineering for the first projects to run concurrently with the design. One of these projects was the West Burton 400 kV Indoor Substation, the first section of which was commissioned in June 1965. From 1965, the grid was partly upgraded to 400 kV, beginning with a line from Sundon to West Burton, to become the Supergrid. In the 2010 issue of the code that governs the National Grid, the Grid Code, the Supergrid is defined as those parts of the British electricity transmission system that are connected at voltages in excess of 200 kV. The 2.2 GW undersea Western HVDC Link from Scotland to North Wales was built in 2013–2018. This was the first major non-alternating current grid link within Great Britain, although interconnectors to foreign grids already used HVDC. In 2021 a new non-lattice design of electricity pylon, the T-pylon, was built near East Huntspill, Somerset for the new 35 mile Hinkley Point C to Avonmouth connection. Characteristics of the grid The contiguous synchronous grid covers England (including the Isle of Wight), Scotland (including some of the Scottish islands such as Orkney, Skye and the Western Isles which have limited connectivity), Wales, and the Isle of Man. Network size The following figures are taken from the 2005 Seven Year Statement. Maximum demand (2005/6): 63 GW (approx.) (81.39% of capacity) Minimum demand (2020 May): 15.3 GW Annual electrical energy used in the UK is around Capacity (2005/6): 79.9 GW (or 80 GW per the 2008 Seven Year Statement) Number of large power stations connected to it: 181 Length of 400 kV grid: 11,500 km (circuit) Length of 275 kV grid: 9,800 km (circuit) Length of 132 kV (or lower) grid; 5,250 km (circuit) Total generating capacity is supplied roughly equally by renewable, gas fired, nuclear, coal fired power stations. Annual energy transmitted in the UK grid is