- National Grid (UK)
The National Grid is the high-voltage
electric power transmission network inGreat Britain , connectingpower station s and major substations and ensuring that electricity generated anywhere in Great Britain can be used to satisfy demand elsewhere. There are also undersea interconnections to northernFrance (HVDC Cross-Channel ),Northern Ireland (HVDC Moyle ), and theIsle of Man (Isle of Man to England Interconnector ).On the breakup of the Central Electricity Generating Board in 1990, the ownership and operation of the National Grid in England and Wales passed to
National Grid Company plc , later to become National Grid Transco and nowNational Grid plc . InScotland the grid is owned byScottish Power andScottish and Southern Energy Group . These groups also operated the systems untilApril 1 2005 , when National Grid plc took control of day-to-day operations, though the network is still owned by the Scottish companies.History
At the end of the 19th century,
Nikola Tesla established the principles ofthree-phase high-voltageelectrical power distribution while he was working for Westinghouse in theUnited States . The first to use this system in theUnited Kingdom wasCharles Merz , of theMerz & McLellan consulting partnership, at hisNeptune Bank Power Station nearNewcastle upon Tyne . This opened in 1901, [cite web
url=http://www.royalsoced.org.uk/enquiries/energy/evidence/ShawA1.pdf
title=Kelvin to Weir, and on to GB SYS 2005
date=29 September, 2005
author=Mr Alan Shaw
publisher=Royal Society of Edinburgh] and by 1912 had developed into the largest integrated power system in Europe. [cite web
url=http://www.nnouk.com/survey/survey-utilities.shtml
title=Survey of Belford 1995
publisher=North Northumberland Online] The rest of the country, however, continued to use a patchwork of small supply networks.In 1925 the British government asked Lord Weir, a Glaswegian industrialist, to solve the problem of Britain's inefficient and fragmented electricity supply industry. Weir consulted Merz, and the result was the "Electricity (Supply) Act 1926", which recommended that a 'national gridiron' supply system be created. [cite web
url=http://www.nationaltrust.org.uk/main/w-chl/w-places_collections/w-collections-main/w-collections-highlights/w-collections-lighting-electricity.html
title=Lighting by electricity
publisher=The National Trust] The 1926 Act created theCentral Electricity Board , which set up the UK's first synchronised, nationwide AC grid, running at 132 kV, 50 Hz. It began operating in 1933 as a series of regional grids with auxiliary interconnections for emergency use. Following the unauthorised but successful short term paralleling of all regional grid, in 1937 (approx) by the nighttime engineers, by 1938 the grid was operating as a national system. The grid was nationalised by the "Electricity Act 1947", which also created theBritish Electricity Authority .In 1949 the British Electricity Authority decided to upgrade the grid by adding 275 kV links. From 1965, the grid was partly upgraded to 400 kV, beginning with a 150-mile (241 km) line from
Sundon toWest Burton , to become the "Supergrid".Grid description
National Grid currently has three main offices it uses to provide 24hr care and assistance for the whole country, these are in Gloucester, Hinckley and Northampton. These sites are operational 24hrs a day providing an emergency service to the entire United Kingdom.
Network size
The following figures are taken from the 2005 seven-year statement (SYS) [ [http://www.nationalgrid.com/uk/library/documents/sys05/default.asp?sNode=SYS&action=&Exp=Y National Grid] ]
* Maximum Demand (2005/6): 63 GW (approx.) (81.39% of Capacity)
* Capacity (2005/6): 79.9 GW (or 80 GW per 2008 seven-year statement [ [http://www.nationalgrid.com/uk/Electricity/SYS/current//electricitycapacity.html Energy Information Administration - International Electricity Installed Capacity Data ] ] )
* Number of largepower station s: 181
* Length of 400 kV grid: 11,500 circuit km
* Length of 275 kV grid: 9,800 circuit km
* Length of 132 kV (or lower) grid; 5,250 circuit kmLosses
Figures are again from the 2005 SYS.
*Joule heating in cables: 857.8 MW
* Fixed losses: 266 MW "(consists of corona andiron losses; can be 100 MW higher in adverse weather)"
* Substation transformer heating losses: 142.4 MW
* Generator transformer heating losses: 157.3 MW
* Total losses: 1423.5 MW (2.29% of peak demand)Although losses in the national grid are low, there are significant further losses in onward
electricity distribution to the consumer, causing a total distribution loss of about 7.7%. [ [http://www.iea.org/Textbase/stats/electricityoecd.asp?oecd=United+Kingdom&SubmitB=Submit&COUNTRY_LONG_NAME=United%20Kingdom Electricity Stats] ] However losses differ significantly for customers connected at different voltages; connected at high voltage the total losses are about 2.6%, at medium voltage 6.4% and at low voltage 12.2%. [ [http://www.chpa.co.uk/news/reports_pubs/Time%20to%20Take%20a%20Fresh%20Look%20at%20CHP%20October%202005.pdf Time to Take a Fresh Look at CHP...] , Simon Minett, Director, DELTA Energy and Environment, October 2005]Power flow
There is an average power flow of about 8 GW from the north of the UK, particularly northern England, to the south of the UK across the grid. This flow is anticipated to grow to about 9 GW by 2011. [ [http://www.nationalgrid.com/uk/library/documents/sys05/default.asp?action=mnch7_6.htm&Node=SYS&Snode=7_6&Exp=Y#Overview_Of_Main_Power_Flows_At_Peak Overview of Main Power Flows at Peak] ]
Because of the power loss associated with this north to south flow, the effectiveness and efficiency of new generation capacity is significantly affected by its location. For example new generating capacity on the south coast has 11% greater effectiveness due to reducing transmission system power losses compared to new generating capacity in north England. [ [http://www.nationalgrid.com/uk/library/documents/sys05/dddownloaddisplay.asp?sp=sys_Table7_5 Table 7.5 - Effectiveness of Marginal Generation due to Transmission Losses] ]
Typical conductor currents [ [http://www.emfs.info/what_TermTuto.asp A basic introduction to electricity, EMFs and the terminology used] ]
* 400 kV, 700 MW circuit: 1 kA
* 132 kV, 70 MW circuit: 300 A
* 11 kV, 3 MW circuit: May 150 A
* 400 V, 150 kW final distribution circuit: 200 Atanding Reserve and Frequency Response
National Grid is responsible for contracting short term generating provision to cover demand prediction errors and sudden failures at power stations. This covers a few hours of operation giving time for market contracts to be established to cover longer term balancing.
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