Clywedog Reservoir was constructed close to the small Welsh town of Llanidloes between 1963 and 1967. The 50 million cubic metre capacity reservoir is primarily used to regulate the flow of the Severn River.
Which originates in the region and is the longest river in the United Kingdom. The reservoir covers an area of around 2.5 km² and is up to 80 metres deep in places. It also considerably reduces the risk of flooding along the riverbanks. A further benefit of the Clywedog Reservoir lies in its capacity to generate hydroelectric power. Up until half a year ago electricity was only generated by two Francis turbines. In November 2016, these two machines were complemented by an additional turbine installed at the foot of the dam. The additional unit is a Kaplan syphon turbine made by the Austrian hydropower allrounders at GUGLER Water Turbines GmbH. Several months of sophisticated advance planning made it possible to complete structural implementation before the end of the year – of what, in terms of organisational issues, was a very challenging project.
The River Severn is the longest flowing body of water in the UK at a length of 354 km. Its source is located close to Llanidloes, a small town in the Cambrian Mountains in central Wales, at an altitude of 610 m above sea level. From source-to-sea the river flows through several English counties before the estuary ultimately meets the Atlantic Ocean at the opening of the Bristol channel. Note: Due to the extreme height difference of 15 m between high and low tides at the mouth of the Severn Estuary the British government had once planned to build an immense tidal power station. However, a negative viability study ensured the project was rejected. In the 1960s Clywedog Reservoir was installed near the source of the Severn to improve the regulation of the river.
The 50 million cubic metre reservoir was created during the construction of a dam wall on one of the tributaries ‘Afon Clywedog’, and plays an important role in protecting the regions lower down from flooding. The area surrounding Clywedog Reservoir is also a popular attraction for tourists and trekkers, and even sailors indulge in their favourite pastime on its waters. The potential energy stored in the reservoir is also exploited by a hydropower generating plant. In order to extract even greater potential from the water, the local operators – Severn Trent Water Limited – decided to install an additional turbine. GUGLER Water Turbines GmbH supplies systems all around the globe and was success in bidding for the contract to supply the entire electromechanical and water control infrastructure for the new hydroelectrics project. The Austrian company has built and installed several turbine systems for international customers in Chile, South Korea and all over Europe, and this was the first order to have been awarded by a client in the United Kingdom.
NEW OUTDOOR POWER PLANT
GUGLER’s responsible project manager, Thomas Danner, explains: “One stipulation made by the customer was that no structural adaptions should be made to the dam while installing the additional turbine. Furthermore, the controls for the new hydroelectric infrastructure had to be integrated into the control technology installed for the older turbines.” Another condition was that every part of the new system would need to be placed outside the dam. According to Mr. Danner, the key advantage of this was the elimination of the necessity and associated costs of installing structural concrete.
KAPLAN SYPHON TURBINE
The system was installed right at the foot of the 72 m-high dam wall where there is an equalising basin with a total drop distance of almost 5.5 m. The new turbine is able to utilise the remaining water from the existing water power infrastructure. Below the dam, the water running through the turbine is then processed a second time. “The conditions set down for a project in this location meant the ideal solution had to be a double regulated Kaplan syphon turbine. The installation of this type of turbine does not require any extra structural concrete and it was comparatively affordable and easy to use the water storage basin for the generation of electricity” said Danner.
TURBINE STARTED VIA VACUUM PUMP
One distinctive feature of the Kaplan syphon turbine at the new Clywedog power plant is that a vacuum pump is required to start it. Water is drawn up a short pipeline from the equalising basin via the pump and arrives at a 4-blade rotor with a diameter of 645mm. After completing the start-up procedure, the turbine can operate normally without the vacuum pump. The turbine receives a standard flow volume of 2.2 m³/s. In optimum water flow conditions the vertical-axis-mounted machine can produce up to 100 kW. A Schorch asynchronous generator is coupled directly with the turbine shaft to serve as an energy transformer. All of the electricity this plant generates is fed into the municipal power grid.
OPTIMALLY INTEGRATED CONTROLS
The modern technology built into the system ensures that energy production at the new power plant is fully automated. All of the new electronics, control and guidance technology at the plant was also provided by GUGLER. The challenge for the project manager, Mr. Danner in terms of control technology was to integrate the ultra-modern command technology into the control system used for the existing turbines: “We had to adapt our proven automation solution to suit the older control system. The knock-on benefit for those running and maintaining the plant is that each of the access terminals uses identically structured control visualisation.”
INSTALLED IN JUST A FEW WEEKS
The turbine constructors were also subject to strict customer in terms of the selection of electrical and electronic components. Since safety legislation and norms in the UK are very strict as regards electrical technology, it was a considerable challenge to acquire the necessary components. Thomas Danner explained the general challenge posed by the comprehensive organisational tasks ahead of the actual structural implementation thus: “In principle, we had to bring the specific requirements of three different groups under one roof: the operators, the planning agency, ANF Consulting Ltd, and the construction contractors J.N. Bentley Ltd. The difficulties were exacerbated by the relatively remote location of Clywedog Reservoir. The transportation of immensely heavy power plant equipment to its final destination was a challenge in itself.”
INSTALLATION AND SUBSEQUENT G59 INSPECTION PASSED WITH DISTINCTION
Ultimately, the complexity of organisational activity ahead of implementation paid off in the smooth running and rapid completion of the installation phase in November 2016. Local installation engineers working under the supervision of GUGLER specialists managed to finish the entire installation within the time limit of four weeks set by the dam operators. Rapid installation enabled the plant to be subjected to the so-called G59 test in mid-December. The G59 test is an inspection carried out by UK grid operators on plants producing electricity fed into the public grid. The test pays particular attention to safety aspects with a precise inspection of all electronic components. As expected, it was completed successfully.As a result, normal operation of the new power plant started up at the beginning of 2017. As the G59 test was successfully completed before the end of the year it ensured eligibility for subsidised electricity rates. The plant operators expect the new turbine to produce an additional annual power output of around 430,000 kWh.