On 22nd March 12 DPA members were given a guided tour of South West Water’s hydro power station at Mary Tavy.

Diagram of the catchment area.

Diagram of the catchment area.

Karl Jones, Asset Manager for the site, was an excellent, informative and enthusiastic guide.   Karl  explained the origins of the power station, which is now 84 years old and has two sets of turbines.   Water is abstracted under licence from leats taken off the River Tavy in varying volumes depending on the amount of water in the river and reaches the power station turbines (which have all been maintained unchanged since installation over 70 years ago) via the Wheal Jewell and Wheal Bennetts reservoirs and pipes with diameters of up to 49 inches.

The turbine hall.

The turbine hall.

The photos show the catchment area, the turbine hall and our guide, Karl Jones chatting with DPA members in the workshop. Altogether a fascinating glimpse into an example of use of one of Dartmoor’s principal natural resources.   The site will be open to the public under the Heritage Open Days scheme in early September – see www.heritageopendays.org.uk – and is well worth a visit.

The workshop.

The workshop.

Technical information

There are two water “plants” at Mary Tavy. No. 1 Plant (commissioned 1932) takes water from the River Tavy via a leat to a 2.5 M gallon reservoir 700 yards from the power station.  This drops 230 feet and provides enough power to drive three Francis turbines.  These, in turn, drive three Crompton Parkinson alternators that produce a total of 710 KW at 415 volts.

No. 2 Plant (commissioned 1937) takes water from Tavy Cleave 1,100 feet above sea level.  This travels along an old mine leat to the 16M gallon Wheal Jewell reservoir.  This water drives three Pelton Wheel turbines which drive three 650 KW English Electric alternators.

The output from both plants is stepped up using transformers to 11,000 volts and is synchronised to the National Grid.  When combined with the nearby Morwellam Power Station, the total power produced is 3.5 Megawatts which is enough to supply a town the size of Tavistock.