Le suréquipement des usines hydrauliques

Over-equipment of hydroelectric power stations

Contrôleur Général Adjoint Electricité de France Direction de la Production et du Transport

Abstract

The capacity of the French thermal and hydro-electric parks increased in parallel until the end of 1961, when both had an installed power of 11 000 MW and an annual output of 38 TWh. At the close of 1981, hydropower represented only 19600 MW out of a total installed power of 71 000 MW and provided a little more than one-fourth of the country's requirements, i.e. 72.4 TWh over 264 TWh. However, hydropower has confirmed its role as producing high-grade energy supplementing thermal generation. The cost of the European thermal unit of fuel oil has led EDF to add to the hydro-electric park by over-equipping lake and lock-gate plants which provide the supply-demand system with the advantages stemming from the ability of hydroelectric sets to start up rapidly, to modulate their power without substantial financial cost, to reach equilibrium in exchanges and maintain voltage on the system. Under the programme, commited in 1976, the installation has been completed of such plants as Praguère in the Pyrénées and St. Etienne Cantales on the Cère, a tributary of the Dordogne in the Massif central. The addition of a further set had been provided for in both cases. The 30.8 MW Pelton set installed at Pragnères and commissioned in 1953 has increased maximum power from 160 MW to 185 MW ; at St. Etienne Cantales, a vertical 38.5 MW Francis turbine has been added to the two 27 MW generating sets. New thought has been given to the development of the Truyère and the Dordogne valleys in the Massif Central. The excavation of the weight-dam of Sarrans (height : 100 m) on the Truyère which, already harnessed for a capacity of a 700 MW to generated yearly output of 1.4 TWh, provided an economical solution and allowed a fifth 63.5 MW Francis turbine to be added to the four generating sets of maximum power 114 MW. It was coupled to the system at the beginning of 1981. At Couesque (head : 57 m) further downstream, an additional 60.5 MW set partly fed by an old penstock will be added to the present two 33 MW sets. It will enter into service in 1984. The Dordogne valley has a succession of plants at the foot of dams, supplying total power of 840 MW with a yearly output of 1.6 TWh. The over-equipment of the Aigle (head : 80 m over a 158 h m3 reservoir) started in 1979 and is now being completed. A 133 MW set will increase the maximum power of the plant to 341 MW. It is fed by a galley by-passing the right bank support of the dam. Upstream from the Aigle at Marèges, a request for a concession has been made for the installation of a set identical to that of the Aigle. It would be fed, via a new gallery bypassing the left bank support of the arch-dam, by the reservoir presently exploited by the SNCF to operate a 147 MW power plant. The largest operation is the installation of a 257 MW set at the Ponget plant on the Tarn river. The present plant harnesses the waters of the right bank plateau under a cumulative 460 m head. The intake structures of the present 40 MW sets have been supplemented with a new gallery (a little over 5 km long) and a new confined flow conduit. The plant will start to supply the system in Autumn 1983. It should be noted that the development of the lake-shore and lock plants has allowed an increase in the unit power of plants being renewed. Correspondingly, the St. Guillerme plant will replace the old plants of the Chambon and St. Guillerme and with the two 56 MW Francis turbines will provide additional power of 89 MW to the Romanche river valley. Other projects which would use reversible sets are under study. All these operations can be developed without major consequences for the environment. However, the new intake structures, the operation of merging the new sets and their connection to the discharge structures are all difficult matters. The operator's concern to limit energy losses and not to jeopardize the safety of civil engineering facilities or that of machines in operation necessitates a quest for original approaches. Thus the Sarrans dam was exacavated with an undercutter, an entirely metallic tower was added to the upstream face of the dam for the new Sarrans set and the well shafts at the Aigle, Couesque and Marèges were excavated with a raise drill. The bulkiness of machines has been reduced by the use of a gate-cylinder at Sarrans, St. Etienne Cantales, Aigle (diameter of the gate : 6.24 m) and St. Guillerme. The choices made have also led to reduced civil engineering costs. The energy balance of all these operations is given in the Table below : Development Useful Capacity (reservoir) km 3 Head m Power MW Production GWh Use Factor h Pragnères 74,9 1 154 185 170 920 St-Etienne Cantales 100,6 63 103,5 83 800 Sarrans 255,8 90 177,5 267,5 1 510 Brommat 1,8 260 412 800 1 940 Couesque 19,8 57 124,5 274 2200 L'Aigle 158,4 80 341 500 1470 Marèges 35,2 78 269 343 1 270 Le Pouget 177 461 385 278 720 The total power of these plants, which all contribute to peak-load generation, will be increased by over 660 MW by end 1984. The over-equipment of Marèges, under the new name "Saint-Pierre Marèges" for which the request for a concession is under advisement will increase the figure to approximately 800 MW by end 1986.