STRONG WEIR SEGMENT ENSURES SAFETY OF POWER STATION ON THE LINTH

Autor: Roland Gruber , 03.10.2016

Work on the new hydroelectric power station on the river Linth is nearing completion at Hätzingen in the Swiss canton of Glarus. Operated by the Trümpi family, ...

... the new plant is going to utilise a hitherto free-flowing part of the Linth River, generating electricity sufficient to supply some 1,600 homes. To be able to manage the considerable bed load pressure and at the same time fulfil elevated flood protection requirements, the new Linth weir was equipped with an 18.5 m weir segment. The steel hydraulics construction element is crucial for the successful operation of the power plant and was designed, manufactured and mounted by the specialists from Braun Maschinenfabrik in Upper Austria.

Since last year, construction work has been going on again on the Linth River. Hefti Hätzingen AG, a company owned by building contractor and experienced hydropower plant operator Fritz Trümpi, has built a new weir system below the Legler power station. Starting this autumn, when the new plant is scheduled to commence operations, the weir will catch 20 m3/sec. What is special about this installation is that the headrace channel leading to the Hefti Hätzingen power station below will now get a bypass in the shape of a penstock. The old weir at the lower plant will be redesigned and equipped with a new fish pass. Its weir gate will be open most of the time. The power house of the new Rufi power plant is built at the so-called “Rufi Runse“, so electricity can be generated from a hitherto unutilised stretch of the Linth River. After driving the turbines, the works water stream will be split. Part of it will be led back into the river while another portion will go on to the old Hefti Hätzingen power plant. In an average production year, the new power station will facilitate generating a total of about 4.8 GWh of clean electricity. The concept has been educed by the renowned planning office Jackcontrol AG, which was responsible for the planning and the site management.

SEALING DEVICE FROM AUSTRIA
The sealing device added to the new weir construction plays a significant role in the flood management of the new power station. To ensure a reliable flood discharge while at the same time managing the enormous bed load pressure, the operator decided in favour of in tegrating a weir segment. Hefti Hätzingen fell back on the tried and tested steel hydraulic construction solutions from the Upper Austrian manufacturer Braun Maschinenfabrik for this. The specialist for high-quality steel hydraulic constructions is well-known beyond the Austrian borders. Its innovative mechanical components and steel construction parts can be found in hydroelectric power stations around the globe.

WEIR OPENING WITH NO ENERGY SUPPLIED
Flood waters can reach a height of three meters, so the new Linth weir for the Rufi power plant required a sealing device capable of creating an opening as tall as 3.3 m. The solution for this is a segment weir 18.5 m wide and 2.0 m high that is opened via two 18.5 ton counterweights. The engineers from Braun Maschinenfabrik designed the system such that this function can be performed by two hydraulic cylinders even if the counterweights are detached or missing. During normal operations, they serve for closing. This means that the two cylinders hydraulically overcome the pulling force of the counterweights. They were dimensioned generously, so each of the cylinders can move the entire weir all by itself. The maximum forces exerted by the 220 mm diameter cylinders are 350 kN for lifting and 200 kN for lowering and keeping down the weir segment. What is special about the system designed by Braun Maschinenfabrik is mainly that – owing to its two counterweights – the segment can be lifted under full water pressure and sediment load entirely without any energy supplied from outside. In the event of a controller breakdown, the segment will be lifted to its top position. Lifting speed is limited by purpose-designed blinds in the hydraulic lines.

A MILESTONE ACHIEVED
Not only he weir segment but the entire steel hydraulic construction equipment has been supplied by the Austrian specialists. Among other things, this includes a bottom outlet protection sluice, three intake gates for the diversion channel, sand trap flushing sluices and a sluice gate for the fish pass. The sluices for the bottom outlet and the diversion channel have already been installed; installation of the segment was completed this March. There are no more obstacles left to overcome before feeding back the Linth River to its original bed, from which it had been diverted since September 2015 for construction work. An important milestone along the path towards completion of the new Rufi hydroelectric power plant has been passed. The new small hydroelectric station is expected to commence operations this autumn, generating clean electricity sufficient to supply about 1,600 homes and further improving the CO2 balance of the Glarus province.

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This March, a powerful weir segment was installed at the new Linth weir.

photo credits: Braun

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The new weir segment has a width of 18.5 m and opens entirely without any external power.

photo credits: Braun

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Hoisting the segment body weighing 20 tons to its bearings requires expertise, experience and precision.

photo credits: Braun