Location: Borrowash, Derbyshire
Rating: 15kW and 60kW
Turbines: 1x Ø500mm siphonic ‘Kapeller’, 1x Ø1000mm ‘S’ type propeller
Average available head: 2.5 – 2.7m
Design flow: 0.8m3/s and 3m3/s
Year of commissioning: 2002 and 1995
OVERVIEW
Borrowash is approximately 5 miles east of the city of Derby. The site was established as corn mill in the 11th Century, then converted to a cotton mill in the 19th Century before being demolished in the 1970’s. The scheme utilises water from the River Derwent and has an unusual intake arrangement whereby 12 siphons draw water from the Derwent into the forebay tank. These date from the early 1990’s when Borrowash was a hydropower test site for Coventry Polytechnic.
In 1995, Derwent Hydro installed three 60kW ‘S’ type unregulated propeller turbines. However the intake arrangement proved too much of a constriction to drive all three turbines successfully due to the inefficient nature of the intake siphons. A narrow tail race also constricted the exit flow. As a result, no more than 2 machines could be run at any one time.
Since 2001, 2 of the 3 60kW turbines have been removed and an experimental siphonic turbine installed in their place, developed by Derwent Hydro and IT Power. This machine was designed specifically as a low-cost installation suitable for very small sites, such as the numerous old mills around the UK.
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Existing ‘S’ type turbine (60kW) with generator mounted above |
Siphonic turbine (LHS). Intake siphons (RHS). |
THE DESIGN
The existing works provided the basis of the scheme installed in 1995 and 2002. The forebay with siphon intakes and control hut were all in place. A simple but effective trash rack cleaner was installed - the screen has 45mm bar-spacing and the cleaner operates vertically with hydraulic operation. There is no downstream screen in place, since the Derwent currently has no migratory fish. The site was assessed by the Environment Agency who considered that no significant measures were required with respect to fisheries.
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Intake with hydraulic vertical trash
rack cleaner in foreground
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Speed increasing belt drive on
10kW siphonic turbine
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Variable speed controller (LHS) for the
siphonic unit and grid-connection panel (RHS).
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Siphonic turbine with manual guide vane adjustment providing a ‘Kapeller’ arrangement.
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15kW Siphon turbine:
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The siphonic design allowed the existing infrastructure to be utilised; no major civil works were required.
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The design ensures that the generator is safe from high water levels, a problem that has been encountered at the site.
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A ball valve is used to shut down the system by breaking the siphon action and allowing ingress of air. No sluice gate is required.
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This experimental machine was designed with variable guide-vanes for maximum flexibility during testing. Future machines will have fixed guide vanes.
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The speed increasing drive uses a low-cost ‘polyrib’ belt for durability, reliability and high efficiency.
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The system was installed with a unique ‘variable speed control unit’ allowing the turbine and generator speed to be set at the control panel, while always providing 50Hz generation into the grid. The advantage is that peak power can be tracked according to the available head/flow conditions.
The ‘S’ type turbine:
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The larger turbine uses a 1m diameter runner and fixed guide-vanes. The runner blades can be rotated manually and are adjusted twice per year for low-flow and high-flow seasons.
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The draft tube is an innovative design, incorporating a flap gate to shut down the turbine.
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Although the generator is set relatively high, with a long belt drive, the generator has been vulnerable to flooding in the peak floods of recent years. | 
