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MDA Technologies 5/2014

MDA Technologies 5/2014

Heavy-duty work for

Heavy-duty work for industrial gear units in the Alps In an extremely demanding construction project in the Swiss Alps, at an altitude of around 1,700 m and almost 600 m inside the mountain, large chambers have been being excavated to form the new expanded underground center of a pumped storage hydroelectric power station. With an extreme incline of 45 degrees and a height difference of approximately 180 m, conveyor systems in a sub-station transported 500 tons of excavated material per hour, around the clock, using conveyor belts that were driven by industrial gear units. The expansion project “Linthal 2015” is Switzerland’s largest hydroelectric undertaking. The overall output of the existing power plants will be increased from 480 MW to 1,480 MW. A new underground pumping station will pump water from a reservoir at an altitude of 1,860 m above sea level into a reservoir lake about 600 m higher up. The pumped storage power station will use this elevation difference to produce hydroelectric power on demand. The builder is Kraftwerke Linth-Limmern AG, a member of Axpo Holding AG. The power requirements of a national electricity grid are subject to large fluctuations over the course of a single day. Power consumption is at a minimum at night and typically peaks at midday and in the evening. In Switzerland, electric power is mainly supplied by nuclear and river-based hydroelectric power stations. Biomass and conventional thermal power stations also make a contribution. In contrast to nuclear and river-based plants, pumped storage hydroelectric power stations can rapidly respond to changes in demand. The opti- mum interplay between these various types of power generation technologies ensures that a reliable and economic power supply is maintained around the clock. Pumped storage stations meet peak demand Unlike regular hydropower plants, pumped storage stations cannot just generate energy at peak times; they can also convert excess power, which is available during periods of low demand, into valuable peak-time energy. The demand for peak energy is continuously increasing throughout the entire European grid network. An important reason for this is the massive development of wind energy plants in the coastal regions of the European Union. This factor results in an increase in the so-called stochastic energy, which depends on random wind conditions and therefore cannot be reliably planned. Excess wind power generated in off-peak times can be used to pump water back into the reservoirs of pumped storage power stations. If there is no wind during the day, pumped storage power stations can then cover the power defi- 22 MDA Technologies 5/2014

Drive technologies cit. A further reason for the increasing demand for peak energy is the opening of the electricity market. As consumers can purchase power from any supplier in a free market, power distribution networks must increasingly be regulated by system services, which ensure a reliable supply. While regular hydropower plants have only an upstream reservoir, pumped storage plants have an additional lower reservoir. Power is generated when water flows from the upper reservoir into the pressure system. The water drives turbines, which in turn power the motor generator. The electrical power which is produced there is fed into the grid. After leaving the turbine, the water flows into the lower reservoir. At peak times, water can be pumped back from the reservoir into the higher altitude lake using excess power from the grid in order to generate hydroelectric power again at a later time. Thus, pumped storage power stations can store energy in the form of water in reservoirs. Pumped storage is a well-established method of compensating fluctuating supply and demand in the grid network in an eco-friendly and economic manner. The scope of the “Linthal 2015” project included excavation and construction work for the underground central station of the pumped storage power station and the tunnel system for the water that provides the power. Construction of a new heavyweight dam for the higher lake will increase its storage volume from the present 9 to 25 million m³. The existing compensating reservoir is also being expanded. Construction work has been carried out at different altitudes and for the most part inside the mountain. The compensation reservoir is the lowest point at an altitude of about 800 m. The Limmernboden reservoir with a capacity of 92 million m³ is located one thousand meters further up. At an altitude of about 1,700 m and some 600 m into mountain, the heart of this gigantic expansion project has been created: huge excavated chambers house four groups of machinery for the new 1,000 MW pumped storage plant. The underground station consists of a 150 m long, 30 m wide machinery chamber with a maximum height of 53 m and a separate transformer vault which is about 130 m long, 20 m wide, and 25 m high. This central station creates the link between the two lakes via a system of upper and lower water delivery tunnels, parallel pressure shafts, and other service tunnels. The excavation work for the two chambers has recently been completed. The work proceeded rapidly in an intensive 24/7, 3-shift operation. The chambers were excavated from top to bottom. Every day, about 800 m³ of rock were removed – in total 2,445,000 m³ from both chambers. Drive systems for conveyors The conveyor system used for the “Linthal 2015” construction project was driven by industrial gear units from Nord Drivesystems. Two “S-conveyors” each transported 500 tons of material per hour over a distance of about 260 m with an extreme incline of 45 degrees and a height difference of around 180 m. The excavated material was conveyed down to a crushing plant. This conveyor belt was driven by a Nord industrial gear unit with brake control, which also generated electricity. On a second conveyor 01 02 03 04 01 and 02 A Nord SK 12407 geared motor was used to drive the lower conveyor belt 03 Nord manufactures modular industrial gear units for output torques up to more than 242,000 Nm with a one-piece UNICASE housing 04 The upper conveyor belt moved downwards and the lower conveyor belt moved upwards MDA Technologies 5/2014 23

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