With an extremely demanding construction project in the Swiss Alps - at about 1 mile above sea level - the heart of a gigantic project is being constructed deep inside the mountain: the underground cavern for a new pumping station, which will increase the present power of 280 NW to 1,480 NW. With an extreme incline of 45 degrees and a height difference of approximately 600 ft, conveyor systems in a substation transport 500 tons of excavated material per hour, around the clock.
The conveyor belts are driven by NORD industrial gear units. In the context of the extension project "Linthal 2015" a new, underground pumping station will pump water from the existing Limmerboden reservoir at an altitude of 1.1 miles to the1,968 ft higher Muttsee in order to power the turbines to generate electricity. This project is being constructed by the Kraftwerke Linth-Limmern AG. In contrast to purely hydroelectric power stations, pumped storage power stations not only have an upper, but also an additional lower reservoir. When power is generated, water from the upper reservoir flows into the pressure system. The water drives turbines, which in turn power the motor generator. The electrical power which is produced is fed into the grid. After leaving the turbine, the water flows into the lower reservoir. If too much electricity is produced, the water can be pumped back from the reservoir into the higher altitude lake, from where it can be used later to generate electricity. Pumped storage power stations can therefore store energy in the form of water in reservoirs. Pumped storage is a well established method of compensating for fluctuations of supply and demand in the grid network in an environmentally friendly and economic manner.
The "Linthal 2015" project includes 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 317 million ft³ to 882 million ft³. The existing compensating reservoir is also being expanded accordingly. Construction work on Switzerland's largest hydroelectric project is being carried out at considerably different altitudes and inside of the mountain. The compensation reservoir at an altitude of about 2,600 ft is the lowest point. 0.6 miles above this is the upper Limmernboden reservoir with a capacity of 3,249 million ft³.
At an altitude of about 1.0 miles and some 1,968 ft inside the mountain, the heart of this gigantic expansion project is being created with huge excavated chambers for the four groups of machinery with an output of 1,000 MW in the new Limmern pumped storage power station. The underground station consists of a 492 ft long, 98 ft wide machinery chamber with a maximum height of 174 ft, as well as a separate transformer vault which is about 426 ft long, 66 ft wide and 82 ft 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 is now complete. The excavation of the rock was carried out continuously,- 24/7 in 3-shift operation. The chambers were excavated downwards. Every day about 28,000 ft³ of rock were removed from the mountain and in total almost 86 million ft³ were excavated from both chambers. NORD industrial gear units were used in the conveyor systems which are located in the central area of the "Linthal 2015" construction project. Two "S-conveyors" conveyed 500 t of material per hour over a distance of about 853 feet with an extreme incline of 45 degrees and a height difference of around 590 ft. The excavated material was then conveyed down to a crushing plant. This conveyor belt was driven by a NORD industrial gear unit with brake control, which simultaneously generated electricity. On the second conveyor belt, the crushed material was conveyed up to the gravel plant, where it was stored until it was needed for further processing as construction aggregate for the dams or as concrete for walls and ceilings.
This conveyor belt was driven by two NORD industrial gear units, which were located on the left and the right of the conveyor belt and were connected by a common shaft. With a protection class of IP55, these industrial gear units each have a drive power of 335 hp. The speed of the conveyor belt is 7.2 ft/s.