Western Hydro's aim is to develop small-scale (50-1000 kW) hydroelectric
schemes with the minimum effect on the environment. Schemes developed
and being developed in Cornwall rely on the abstraction and reintroduction
after use of river flow in excess of that necessary (as governed by
the Environment Agency) to maintain the normal function of the river
and its aquatic environment. In most cases, the introduction of an
additional waterway in the form of a leat system actually increases
the biodiversity and alleviates flood damage to the river. Where possible
and particularly in sensitive sites, pipelines and powerhouses are
buried to minimise the visual impact of the schemes.
Example:
Western Hydro Ltd
Trelubbas Power Plant, Cober Valley, Cornwall
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Buried Powerhouse to reduce visual impact and noise
Installed Capacity: 220
kW grid connected
Qmax: 0.7 m3/sec
Gross head: 43 m
|
The Trelubbas hydroelectric scheme
is situated on the River Cober between Coverack Bridges and Lowertown
where the river drops off the edge of the granite intrusion to the
east of Coverack Bridges. The impermeable granite plateau forms a
large catchment area for the Cober River (25 sq. km at Trelubbas intake)
and contains natural underground reservoirs together with peat type
moorland soils that help to even the flow. A stone weir at Coverack
bridges diverts excess flow through a fish screen and into a leat
system 800 metres in length around the edge of the steep valley to
a penstock drum screen at the end of the leat. A steel 710 mm diameter
buried steel penstock pipe runs down the valley slope to a buried
powerhouse 43 metres below the level of the leat. River flow at the
Trelubbas intake regularly exceeds 4 cumecs with an average winter
time flow well in excess of 1 cumec. A maximum excess flow (Qmax)
of 0.7 cumecs is permitted by the Environment Agency to be diverted
from the river into the scheme.
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Cink Crossflow
Turbine |
In the powerhouse the penstock
pipe is fed into a Cink crossflow turbine operating at 750 rpm and
driving a Newage 400 kVA synchronous alternator. Mains connection
is governed by a GP Electronics Mainscon system supplying the grid
at 415 volts in 3 phases. A buried cable transports the power to a
350 kVA transformer at the top of the valley where the power is transformed
to 11 kV for introduction to the local grid lines in the area. The
power plant is fully automated and able to govern itself as the flow
rates vary using level sensing at the penstock screen to control the
valve gear on the turbine. Remote sensing and control of the plant
can also be achieved using Dexdyne's Netrix equipment which includes
data logging and analysis accessed with a programmed laptop from anywhere
in the world via a phone link.
After passing through the turbine, the water is fed back to the river
through a tail race pipe immediately downstream of the powerhouse
so that the river is only depleted for a short section approximately
1 km in length. The power produced by the scheme is presently purchased
by London Electricity through a 3 year term contract to supply.
