National Grid (UK)

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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 1 Grid description 1.1 Network size 1.2 Losses 1.3 Typical conductor currents 1.4 Conductor codes 2 History 3 References 4 External links

Grid description

Network size

The following figures are taken from the 2005 seven-year statement (SYS) at [1].

• Demand (2005/6): 63 GW (approx.)
• 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

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)

Typical conductor currents

From [2].

• 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

Conductor codes

The National Grid's conductors are standardised by BS 215 (Part 2) 1970 (equivalent to IEC 60209), and the various types are given code names. All aluminium conductors are ACSR (aluminium conductor, steel-reinforced).

UK code	Conductor material	Core size(mm2)	No strands	Strand size	Insulation material	Nom OD(mm)	Weight (kg/km)	Breaking load (kN)	R at 20°C(Ω/km)
1 GOPHER	Aluminium	25.00	6	2.36	None	7.08	106	9.60	1.0930
2 WEASEL	Aluminium	30.00	6	2.59	None	7.77	128	11.40	0.9077
3 FERRET	Aluminium	40.00	6	3.00	None	9.00	172	15.20	0.6766
4 RABBIT	Aluminium	50.00	6	3.35	None	10.05	214	18.40	0.5426
5 HORSE	Aluminium	70.00	12	2.79	None	13.95	538	61.20	0.3936
6 DOG	Aluminium	100.00	6	4.72	None	14.15	394	32.70	0.2733
7 WOLF	Aluminium	150.00	30	2.59	None	18.13	726	69.20	0.1828
DINGO									0.1815
8 LYNX	Aluminium	175.00	30	2.79	None	19.53	842	79.80	0.1576
CARACAL									0.1563
9 PANTHER	Aluminium	200.00	30	3.00	None	21.00	974	92.20	0.1363
JAGUAR									0.1367
91 ZEBRA	Aluminium	400.00	54	3.18	None	28.62	1621	131.90	0.0674

From [3], [4].

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 [5] and by 1912 developed into the largest integrated power system in Europe [6]. 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 [7].

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".

References

• 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

External links

• The Transmission System from National Grid's Seven Year Statement