Power Transmission is the movement of electricity from a power station or generating site through a transmission network to a grid supply point. This is to ensure the geographical distribution of electrical power to meet demand across the U.K.
A single electricity system operator (ESO) who is National Grid Electricity System Operator is responsible for ensuring the stable and secure operation of the national electricity transmission system in the U.K.
Transmission system operators (TSO) are responsible for developing, operating and maintaining these high voltage systems within their onshore transmission areas. These are National Grid Electricity Transmission plc for England and Wales, Scottish Power Transmission Limited for southern Scotland and Scottish Hydro Electric Transmission plc for northern Scotland and the Scottish islands groups.
The power transmission network transmits electricity over long distances at extra high voltages (EHV), normally at 400kV, 275kV or 132kV to reduce energy losses on overhead or underground transmission networks using high voltage alternating current (HVAC). High voltage direct current (HVDC) technology is used for greater efficiency over very long distances and is typical in offshore transmission on renewable energy and interconnector projects.
Fossil fuel power station burn natural resources like coal and gas to produce heat which are used to turn water into steam which turns a turbine to enable a generator to produce electricity. The bulk of electricity in the U.K is generated by burning fossil fuels utilising where possible the natural resources of the U.K supplemented by imports to fill the availability of fossil fuels. It is estimated 40% of all electricity generated is produced from gas and 8% from coal but these numbers reduce each year as power stations are decommissioned.
Overhead Power Transmission
The transmission network in the U.K is predominately made up of overhead transmission lines which are carried using a network of steel and wooden electricity pylons. They are normally used in open country and rural areas over long distances and are a more cost effective solution than underground networks with a longer life span which are easier to install and maintain.
Underground Power Transmission
The underground transmission network in the U.K is primarily situated in heavily urbanised areas, where offshore transmission networks come onto land or its environmentally challenging to cross land in greenfield areas. There are an increasing number of projects to replace existing overhead transmission lines with underground networks to address to aesthetic impact on the countryside.
Offshore Power Transmission
The offshore transmission network in U.K territorial waters which predominantly uses HVDC technology is used on the exit cables of an onshore wind farms which are now sold to an offshore transmission operators (OFTO) to own and maintain. There are also now an increasing number of interconnector projects which are large HVDC offshore transmission networks installed between the U.K an many European countries.