Rance Tidal Power Station

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The tidal power plant La Rance (French: Usine marémotrice de la Rance, breton. Stankell vordredan ar Renk ) is a tidal power plant in dam construction at the mouth of the Rance River between Dinard and Saint- Malo in the department of Ille -et -Vilaine in the Brittany in France.

The power plant draws only a small proportion of its power from the flow of the river; the far greater part comes from the tidal currents of the Atlantic, which has a tidal range of more than 8 m at this point.

The power plant supplied in 1967 for the first time power into the grid and was the first commercial tidal power station in the world. With its combined peak output of 240 megawatts, it was for more than 40 years by far the largest power plant of its kind in the world (before the tidal power plant Annapolis, Canada, with only about 20 MW). Only in August 2011, it was replaced by the Korean factory Sihwa -ho as the record holder.

History

Already long before the 20th century there was in Brittany, especially along the Rance tidal mills exploiting the power of the tides to power millstones and other machinery.

The proposal to use the strong tides in the region on a large scale for power generation, was first made ​​in 1921. In 1925 there were in the small town Aber- Wrac'h Landéda at a pilot plant, but which was already shut down again five years later because of financing problems. As of 1943, the Société d' étude pour l' led use Secure the marées ( German: Society for the Study of Use of the Tides) conducted a detailed study on the construction of a tidal power plant on the Rance estuary.

After that, it took nearly 20 more years, until the construction work in 1961 under the leadership of Albert Caquot actually began. Two temporary storage walls made of huge concrete cylinders, a section of the Rance estuary was drained, and in the tub so incurred the current shut-off was built with the power plant from 1963. This continued for three more years until the dam on November 26, 1966 by French President Charles de Gaulle was inaugurated. The following year, 1967, the road has been released over the dam to the crossing and on 4 December 1967, the power plant supplied electricity to the national grid for the first time the EDF one.

For a long time is the power plant as a unique engineering structure is a tourist attraction in itself dar. It attracts about 200,000 visitors.

Technology

The partitioned off by the power plant from the open sea bay of the Rance estuary has an area of ​​about 22 km ² and has a storage volume of about 180 million cubic meters. At maximum tidal flow at any tide 720 million cubic meters of water through the plant, what an average flow of 15,000 m³ / s corresponds to (only Tide currents and the flow of the river not included).

Built for the power plant, a total of about 750 m long shut-off is (from west to east) from a 65 m long and 10 m wide sluice structure for shipping, a 390 m long concrete dam, in which the nacelle for the 24 turbines is integrated, a dam of 175 m length and 115 m wide barrage, consisting of six sections, through which the Tidendurchfluss at the power plant can be regulated over.

The building is driven over the route Departmental No. 168 between Dinard and Saint- Malo crosses in this way the Rance. In the area of the lock a bascule bridge is arranged, which also allows larger ships the passage. Through the lock travel every year about 16,000 ships and boats; across the road at peak times up to 35,000 vehicles per day.

The 24 turbines are Kaplan bulb turbines with horizontal shaft and a rotor diameter of 5.35 m. At a maximum flow rate of 275 m³ / s and a maximum speed of 260 min - 1, each turbine supplies electrical power of up to 10 MW. The wings are rotated by 40 ° in order to adapt to changing requirements: The turbines operate in both flow directions ( ebb and flow ) to generate electricity, but also as pump turbines, so that the power plant can be used as a pumped storage power plant. About 20 % of the time, the system operates in the pumping mode, 60% of the turbine operation. Furthermore, the turbines can also operate in " push mode " to minimize resistance to provide the flow when needed and to empty the reservoir to support the barrier weir quickly and fill. Due to the broad demands a comparatively low efficiency in purchase had to be taken.

The rigidly coupled directly to the turbine generators are three-phase synchronous machine with a voltage of 3.5 kV. The generators are connected in groups of four and dine on three block transformers with a capacity of 80 MVA power to the 225 - kV high-voltage grid (3 x 2 x 4 = 24).

As a protection against the chemical attack of sea water had a complex cathodic protection can be provided which is operated with 1 V voltage and 20 amperes. Had in the entire system - as usual in the sphere of influence of seawater - corrosion-resistant materials are installed and it had to be placed on seals special value.

Ecological impacts / criticism

Although the power plant still lets through a significant tidal current, the ecosystem of the Rance estuary has been significantly changed by the shut-off. The tidal range in the estuary, which was before the construction of the power plant up to 14 m, is now reduced to about 7-8 m and shifted in time.

• The removal of sediment and mud of the Rance to the open sea was so far hindered that there has been a massive silting of the Rance estuary.
• There is no special device to assist fish passage through the power plant dam. Smaller fish and even the most sensitive cuttlefish ( squid) can pass through unharmed, the relatively slowly rotating turbines normally. Only for large species such as seals and porpoises migration between the reservoir and the open sea is impeded.
• The influx of sea water at high tide accrued was reduced so much that the salt content of the water in the Rance estuary decreased markedly. This prevents some saltwater fish such as sand eels and plaice have disappeared. Some fish species whose stocks after the construction temporarily decreased (sea bream, mullet, rays, ... ) have the reservoir has filled up again. On the other hand, some brackish water and freshwater fish have even increased.