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Site Records

Subterranea Scotia

Invergarry Power Station

St. Fillans Power Station sign

OS Grid Ref: NH 31916 013025
Date opened: 1957
Date closed : Operational

Invergarry, on the shores of Loch Oich in the Great Glen, is the lower stage of the Garry development - its catchment includes the discharge from the upper stage, at Quoich.

Completed in 1956, it's a relatively small station with a single 20MW generator, and a gross head of 174ft. It is an interesting example of a semi-underground construction - it has walls and a roof, but the walls are very low on three sides of the structure, and the fourth side is reached by a short curving 'cutting' through the rock, which descends steeply and provides road access. Everything inside the station, from the top of the generator on down, is below ground level.

From the dam, water is led to the power station by a low-pressure tunnel, 14,000ft long, and horseshoe in section, with an equivalent diameter of 16' 6". There is one sidestream intake on the way - the Aldernaig burn is captured and the water brought into the low-pressure tunnel via an intake tunnel 500ft long, and sloping down at 1 in 3.

The low-pressure tunnel terminates at the base of the surge chamber, which is of the differential type, and is 112ft high by 60ft in diameter. From the base of the surge chamber, the water falls down a vertical high-pressure shaft, 90ft deep by 16ft in diameter. From the base of the shaft, the short remaining distance to the power station is covered by a high-pressure tunnel 340ft long, followed by a steel penstock tunnel 460ft long, to the main inlet valve.

Inside the station, the machinery consists of a single vertical Kaplan turbine and generator unit. The head is high for this type of machine - the initial design of the station called for two smaller Francis units - and a large relief valve is provided, discharging into the short tailrace tunnel.

Invergarry was totally refurbished in 2003, which provided an opportunity to see parts of the system that are not normally visible.

There are 38 images of Invergarry in the archives, and drilldown to high-resolution pictures is available; click on virtually any picture, and a high-resolution version will open in a new window.

Looking down the access road to Invergarry power station:

Invergarry Power Station

Photo: Invergarry Power Station
Photo by: Mike Ross

Invergarry dam, hidden away in a pretty gorge:

Invergarry Dam

Photo: Invergarry Dam
Photo by: Mike Ross

An archive view of Invergarry immediately after completion, taken from Loch Oich, looking at the tailrace outfall:

Invergarry Power Station

Photo: Invergarry Power Station
Photo by: Mike Ross

This drawing shows the whole scheme. It's a clickable imagemap; click on any of the pink-highlighted areas to bring up the relevant webpage:

The Invergarry scheme - cross-section

Illustration: The Invergarry scheme - cross-section
Illustration by: Scanned by Mike Ross, from Water Power, June 1959

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Last updated 6th February 2006
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