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Cruachan Hydroelectric Scheme
Ben Cruachan, above Lochawe, Argyll and Bute, Scotland, UK
associated engineer
Sir Edward McColl
James Williamson & Partners
date  1959 - 1965
era  Modern  |  category  Power Generation  |  reference  NN079280
Cruachan is the world’s first high-level reversible pumped storage scheme for generating hydroelectricity. The power station is located deep inside a mountain, where tropical plants flourish in the warm humid and well-lit conditions.
The mountains that encircle the power station reservoir have their highest point at Ben Cruachan (1,126m). Some 220,000 cubic metres of rock were excavated to make the cavern housing the generating station 1km below ground. The cavern is accessed by a tunnel 7.3m wide and 4m high.
The turbine hall is 91.5m long, 23.5m wide and 38m high, and has an adjacent transformer hall. Although there is a control building, nowadays the station’s operations are controlled remotely from Cathcart near Glasgow.
There are four 100MW Francis reversible pump turbines in the cavern. Cruachan’s maximum output is 440MW — enough to power 225,000 homes. It can achieve full power from shut down in two minutes, or 30 seconds if compressed air is used to start the turbine blades spinning first.
On a generating cycle, water from the reservoir exits through two flow control gates. These lead to two tunnels some 400m long and inclined at 55 degrees to the horizontal. The tunnels end at 2.7m diameter steel-lined penstocks with flow valves. Water flows through the valves to the turbines. The spinning turbine blades transfer their rotational motion to the generators and produce electricity.
After passing through the turbines the water enters a surge chamber, designed to protect the system from any sudden influxes. From there, it enters the tail race — a chamber 7m in diameter and more than 900m long. Water from the tail race is discharged into Loch Awe.
The whole process is reversed for a pumping cycle. Water is pumped uphill from Loch Awe to the reservoir during periods of low energy demand (such as at night), to cope with peak demand later.
The power station can operate continuously for 22 hours before the water in the reservoir is used. It has to maintain a 12 hour emergency supply in reserve. At full power, the turbines can pump at 167 cubic metres per second and generate at 200 cubic metres per second.
The reservoir is bounded to the south west by a buttressed concrete gravity dam (NN080281) 316m long, sited 390m up the mountain side. Its catchment area covers 2,300 hectares, and a network of 19 tunnels divert water from surrounding streams into the catchment.
Environmental restrictions on the dam design meant that all its operational equipment is hidden inside the dam wall, giving the structure a clean line.
Transformers step up the voltage from 16kV to 275kV. A transmission line carries power from the top of the cable shaft, in front of the dam, 8km east to Dalmally sub-station and on to Windyhills near Glasgow. The cable shaft has 1,420 steps, making it the tallest in Britain.
Construction was completed in 1965 and the scheme was opened officially by HM Queen Elizabeth II on 15th October 1965, with two of the generating units operational and the other two in service by 1967.
Sadly, the scheme’s designer Sir Edward McColl died before it opened. Cruachan was owned and operated originally by the North of Scotland Hydro Electric Board, but was transferred to Scottish Power in 1990.
The visitor centre is open to the public from February until mid December. It was refurbished recently, and reopened on 26th June 2009. Cruachan is cited as one of the best post-war monuments of Scottish architecture.
Man contractors: William Tawse, Edmund Nuttall
Turbine and generator supply: Sulzer Escher Wyss, Boving, GEC
Research: ECPK

Cruachan Hydroelectric Scheme