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The St. Margaret’s Bay  Power Plants use the Francis Turbine which can operate with 90% efficiency (see section diagram right)

The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. A casement is needed to contain the water flow. The turbine is located between the high-pressure water source and the low-pressure water exit.

In the case of the Mill lake Power Plant the high water pressure is delivered by the penstocks from Coon & Sandy Lakes & the low pressure exit is into Mill Lake.

For the Tidewater Power Plant the high pressure water is delivered by the penstocks from Mill Lake & the low pressure exit is into St. Margaret’s Bay.

The inlet is spiral shaped. Guide vanes direct the water tangentially to the turbine wheel, known as a runner. This radial flow acts on the runner's vanes, causing the runner to spin. The guide vanes (or wicket gate) may be adjustable to allow efficient turbine operation for a range of water flow conditions.

Turbines, St. Margarets Bay Hydro-electricity Plants, Nova Scotia

spiral case

tops to wicket gates

Shaft driving


Photo taken at Mill Lake Power Plant

Water entry

Direction of flow

Top Of Turbine

Penstock entry

Turbine Isolation Valve


Butterfly valve

Photo taken at Mill Lake Power Plant

Turbine Isolation

When the turbine is shut down for repair or maintenance the large butterfly valve is closed to shut off the water from the penstock.

When the work has been completed on the turbine or generator to re-start the turbine,  the by-pass valve is opened to allow the water pressure on both sides of the butterfly valve to equalise, the main butterfly valve can then be opened.

The wicket gates are then adjusted to optimise to speed of the turbine.