National Grid UK
From Wikipedia, the free encyclopedia
The National Grid is the high-voltage electric power transmission network in Great Britain, connecting power stations 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 northern France (HVDC Cross-Channel), Northern Ireland (HVDC Moyle), and the Isle 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 now National Grid plc. In Scotland the grid is owned by Scottish Power and Scottish and Southern Energy Group. These groups also operated the systems until April 1, 2005, when National Grid plc took control of day-to-day operations, though the network is still owned by the Scottish companies.
Contents |
[edit] History
The principles of three-phase high-voltage electrical power distribution were established by Nikola Tesla, working for Westinghouse in the United States, at the end of the 19th century. Charles Merz, of the Merz & McLellan consulting partnership, was the first to use this system in the United Kingdom, at his Neptune Bank power station near Newcastle upon Tyne which opened in 1901[1] and by 1912 developed into the largest integrated power system in Europe.[2] 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.[3] The 1926 Act created the Central 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, but by 1938 the grid was operating as a national system. The grid was nationalised by the Electricity Act 1947, which also created the British 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 to West Burton, to become the "Supergrid".
[edit] Standing Reserve and Frequency Response
Main article: Reserve service
[edit] Grid description
[edit] Network size
The following figures are taken from the 2005 seven-year statement (SYS) at [1].
- Demand (2005/6): 63 GW (approx.) (81.39% of Capacity)
- Capacity (2005/6): 77.4 GW
- Number of large power stations: 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 km
[edit] Losses
Figures are again from the 2005 SYS.
- Joule heating in cables: 857.8 MW
- Fixed losses: 266 MW (consists of corona and iron 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%. [2].
[edit] 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. [3]
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. [4]
[edit] Typical conductor currents
From [5].
- 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 A
[edit] Control of the Grid
- Main article: How the UK National Grid is presently controlled.
[edit] Transmission costs
[edit] Triad Demand
Triad Demand is measured as the average demand on the system over three half hours between November and February (inclusive) in a financial year. These three half hours comprise the half hour of system demand peak and the two other half hours of highest system demand which are separated from system demand peak and each other by at least ten days.
These half hours of peak demand are usually referred to as Triads
In April of each year, each licensed electricity supplier (Centrica, BGB etc) is charged a charge for the peak load it imposed on the grid during those three half hours of the previous winter. Exact charges vary depending on the distance from the centre of the network, but in the South West it is £21,000/MW for 1 year, or £7k/MW for each of the three half hours, for convenience assuming they were identical, (which is unlikely however they will be close). The average for the whole country is about £15,000/MW per year.
If averaged over all power supplied in the UK in one year then this is currently around 0.2p/kWh. This is calculated by taking the total annual triad charges, which are say £15/MW/ year x 50 GW = £750m and dividing it by the total number of units sold – say 3.6 ×10exp11 kWh = 0.2p/kWh.
This is the sole money with National Grid Transco uses to recover its costs and these charges are commonly also known as TnUOS - Transmission Use of System charges. (Note this is for high voltage long distance transmission and the lower voltage distribution is charged separately).
[edit] Cost per kWh of Transmission
If the total number of units delivered by the UK generating system in a year, are divided into the total TNUOS or TRIAD receipts, then one gets the surprisingly low figure of around 0.2p/kWh. This is calculated by taking the total annual Triad charges, which are say £15,000/MW/ year x 50,000 MW = £750m/y and divide it by the total number of units sold – say 3.6 ×10exp11 kWh.
- For present National Grid charges for transmission see:
- http://www.nationalgrid.com/uk/Electricity/Charges/usefulinfo/
- http://www.nationalgrid.com/NR/rdonlyres/E5B27828-6705-4F21-9B4B-0A998D7AFA5C/5849/FinalTariffs2006_2007.xls
[edit] Impact of renewables
[edit] See also
- How the UK National Grid is presently controlled
- Energy use and conservation in the United Kingdom
- UK topics
[edit] References
- ^ Dr Marc Rands (29th September, 2005). Kelvin to Weir, and on to GB SYS 2005. Royal Society of Edinburgh.
- ^ Survey of Belford 1995. North Northumberland Online.
- ^ Lighting by electricity. The National Trust.
- UK Electricity Networks: The nature of UK electricity transmission and distribution networks in an intermittent renewable and embedded electricity generation future by Scott Butler
- The electricity supply industry and the Central Electricity Generating Board, UK Competition Commission Report 1987
- Map of UK power stations and national grid
[edit] External links
- The Transmission System from National Grid's Seven Year Statement