TPi March 2014

Cadair Idris: A Flexible Approach to Penstock Specification

Hafod y Llan hydro The 640kW Hafod y Llan scheme will permanently add to the uses that Snowdon has been put to over the years and careful planning, design and project management meant that the installation was effectively disguised within the rugged landscape before it was even completed. But this well-camouflaged scheme hides an extraordinary feat of engineering: once fully operational, the hydro-electric plant will play a key role in delivering the National Trust’s ‘Fit for the Future’ initiative to invest in renewable energy, with a generating capacity equivalent to the power requirements of all the Trust’s properties in Wales. Constructing such a significant scheme within such a challenging landscape has been no simple undertaking, and doing so while delivering the National Trust’s remit to conserve and protect the environment has added to the project’s complexities. However, that environmental responsibility was central to Hydropower Services’ design for the scheme, and local contractor GHJ Civil Engineering & Construction leveraged its local and hydro scheme knowledge to manage the project’s logistical and environmental challenges. Specifying the penstock The Hafod y Llan scheme will extract water from the Afon Cwm Llan river at the head of the valley, which will be fed through a 1km black PE100 penstock, supplied by PE pipe specialist T he rocky mountainsides of Snowdonia have been a Mecca for walkers and the quarrying industry for generations and, amidst the tourists, farming has provided the bedrock of the Snowdonia National Park’s rural communities. Some areas of the terrain are too rugged even for hardy Welsh sheep, however, but the landscape continues to deliver new opportunities for jobs, commerce and essential commodities… this time in the shape of hydroelectric power. The Snowdownia National Park has been the location for two new hydroelectric power stations over the past year, both of which have involved the installation of a PE penstock in the mountainside supplied by GPS PE Pipe Systems, to carry the water to the turbine at the base of the mountain.

GPS PE Pipe Systems. At the foot of the penstock, GHJ has constructed a power house designed to look like a typical Snowdonia out house. Here the rapid flow of water will enter the turbine, generating electricity before being returned to the river downstream without any effect on the water quality. PE pipe was chosen for the penstock installation thanks to its flexibility, which has allowed the contractor to bend and shape the pipe to the contours of the landscape, routing the penstock as close as possible to the river. The use of PE has also enabled the design team to match the wall thickness (SDR) of the pipe to the required water pressure at differing points along the route, providing cost and raw material savings. The only exception to this is the final section of penstock where the water enters the turbine at very high pressure, and the wall thickness that would have been needed for PE pipe made ductile iron a cheaper alternative. Explains Alan Jones from GHJ, “Using PE pipe made the installation less invasive on the landscape because the pipe’s flexibility enables the penstock route to stay true to the contours of the hillside. Using PE also made the installation more cost effective because it required less excavation and gave us some leeway for small diversions around clumps of heavy rock. Indeed, the ductile iron’s maximum bend tolerance of two degrees meant that we had to painstakingly cut through rock to lay the final section of pipe at the base of the penstock and the increased excavation time and costs involved in this demonstrate the balancing act between material costs and installation requirements on projects like this.”

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March 2014 Tube ProducTs InTernaTIonal