Maentwrog power station was built by the North Wales Power Company and supplied electricity to North Wales, Deeside and Cheshire. It exploits the water resources of the

Snowdonia Snowdonia or Eryri (), is a mountainous region in northwestern Wales and a national park of in area. It was the first to be designated of the three national parks in Wales, in 1951. Name and extent It was a commonly held belief that the nam ...

mountains, using water turbines to drive electricity alternators. The 24MW station has been owned by several organisations; since 2004 it has been owned by the

Nuclear Decommissioning Authority The Nuclear Decommissioning Authority (NDA) is a non-departmental public body of the Department for Business, Energy and Industrial Strategy, formed by the Energy Act 2004. It evolved from the Coal and Nuclear Liabilities Unit of the Department o ...

. It generates an annual electricity output of 60.6GWh.

History

Maentwrog

hydro-electric Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...

power station was first commissioned in October 1928 by the North Wales Power Company Limited. The company also owned

Dolgarrog Dolgarrog is a village and community (Wales), community in Conwy County Borough, in Wales, situated between Llanrwst and Conwy, very close to the Conwy River. The village is well known for its industrial history since the 18th century a ...

and

Cwm Dyli Cwm Dyli is the location of a hydro-electric power station on the southern flank of the Snowdon range in North Wales. At the time it was built, it was the largest hydro-electric power station in the United Kingdom. It is Britain's oldest power st ...

power stations. The new station was financed by the issue of £1.7million of

debenture In corporate finance, a debenture is a medium- to long-term debt instrument used by large companies to borrow money, at a fixed rate of interest. The legal term "debenture" originally referred to a document that either creates a debt or acknowl ...

stock in 1924. The architectural design of the power house was by

Sir Alexander Gibb ''Sir'' is a formal honorific address in English for men, derived from Sire in the High Middle Ages. Both are derived from the old French "Sieur" (Lord), brought to England by the French-speaking Normans, and which now exist in French only as ...

and Partners. To power the station a new reservoir was built at

Trawsfynydd Trawsfynydd (; Welsh for "across hemountain") is a linear village in Gwynedd, Wales, near Llyn Trawsfynydd reservoir, and adjacent to the A470 north of Bronaber and Dolgellau and 10 km (6 miles) south of Blaenau Ffestiniog. The total com ...

, formed by the construction of four dams. The main dam on the

Afon Prysor The River Dwyryd ( cy, Afon Dwyryd, meaning a river of two fords) is a river in Gwynedd, Wales which flows principally westwards; draining to the sea into Tremadog Bay, south of Porthmadog. Geography The Dwyryd rises in the hills to the north of ...

was Britain's first large

arch dam An arch dam is a concrete dam that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, causing the arch to straighten slightly and strengthen ...

. The other three cut off dams were Gyfynys, Hendre Mur and Trawsfynydd. In 1925, members of the North Wales and South Cheshire Joint Electricity Authority visited the dam at Maentwrog, then under construction. They reported that they were "greatly impressed with the magnitude of the work and with the expeditious way in which this great work is being carried out". The reservoir is above the power station. It has an area of and can hold 33million cubic metres of water. Water flows to the power station through a diameter low pressure pipeline and two tunnels, plus a diameter high pressure line. The working head of water is . The station initially had a capacity of 18MW, but this was increased in 1934 to 24MW by an additional 6MW generator set fed by a diameter high pressure pipeline. By 1925, the transmission lines of the North Wales and South Cheshire Joint Electricity Authority to which the North Wales Power Company was connected extended from

Pwllheli Pwllheli () is a market town and community of the Llŷn Peninsula ( cy, Penrhyn Llŷn) in Gwynedd, north-western Wales. It had a population of 4,076 in 2011 of whom a large proportion, 81%, are Welsh language, Welsh speaking. Pwllheli is the pl ...

Runcorn Runcorn is an industrial town and cargo port in the Borough of Halton in Cheshire, England. Its population in 2011 was 61,789. The town is in the southeast of the Liverpool City Region, with Liverpool to the northwest across the River Mersey. ...

and to the borders of Staffordshire, and served an area of . The operation of the stations was dependant on rainfall. In the year 1935/6, the North Wales Power Company noted that rainfall was well above average, with of rain at Cwm Dyli. As a result the company's three stations (Maentwrog, Cwm Dyli and Dolgarrog) were able to generate a total of 93,199.950

MWh A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...

of electricity. In 1960, the catchment area of the reservoir was increased by , which included the construction of 8 miles (12.9 km) of leets or open channels. The operation of the

Trawsfynydd nuclear power station Trawsfynydd nuclear power station ( cy, Atomfa Trawsfynydd) is a decommissioned Magnox nuclear power station situated in Snowdonia National Park in Gwynedd, Wales. The plant, which became operational in 1965, was the only nuclear power station in ...

from 1965 to 1991, using the reservoir for cooling water, restricted the height of water available for hydro-electricity. In 1988, construction work began on a replacement dam downstream of the original arch dam. The S-shaped dam is long and high, it contains of concrete.

Owners

Maentwrog power station has been owned by the following organisations, through nationalisation, reorganisation and privatisation of the electricity industry. * North Wales Power Company Limited (1926–48) *

British Electricity Authority The British Electricity Authority (BEA) was established as the central British electricity authority in 1948 under the nationalisation of Great Britain's electricity supply industry enacted by the Electricity Act 1947. The BEA was responsible for ...

(1948–55), nationalisation 1948 *

Central Electricity Authority The Central Electricity Authority (CEA) was a body that managed and operated the electricity supply industry in England and Wales between 1 April 1955 and 31 December 1957. The CEA replaced the earlier British Electricity Authority (BEA) as a r ...

(1955–57) *

Central Electricity Generating Board The Central Electricity Generating Board (CEGB) was responsible for electricity generation, transmission and bulk sales in England and Wales from 1958 until privatisation of the electricity industry in the 1990s. It was established on 1 Januar ...

(1958–90) *

Nuclear Electric Nuclear Electric was a nuclear power generation company in the United Kingdom. It was formed in 1990 as part of the privatisation process of the UK Electricity Supply Industry. In 1996, it was amalgamated into a new company – British Energy, ...

(1990–2004), privatisation 1990 *

(2004–present). Maentwrog power station was vested in Nuclear Electric when the British electricity supply industry was privatised in 1990. From 2004 the Nuclear Decommissioning Authority (NDA) assumed ownership although operations are devolved to NDA site licence company

Magnox Ltd Magnox Ltd is a nuclear decommissioning Site Licence Company (SLC) under the Nuclear Decommissioning Authority (NDA), a government body set up specifically to deal with the nuclear legacy under the Energy Act 2004. In September 2019, it became a ...

Plant and equipment

The original generating plant comprised four 6MW Boving-English Electric 6.6kV generating sets. The alternator exciters are directly coupled, 40kW, 110V. There were English Electric and Ferranti

step up transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's c ...

s, from 6.6kV to 20, 33, and 66kV. The original plant was removed in 1989-92 and new plant with a generating capacity of 30MW (2 × 1MW) was installed.

Operations

Operating data for the period 1935–92 was:''CEGB Statistical Yearbook'' 1972 to 1986 Central Electricity Generating Board The station output, in MWh, is shown graphically:The station is currently (2020) operated by

. on behalf of the Nuclear Decommissioning Authority.

References

{{Reflist

External links