Régimes transitoires des groupes réversibles Aspects techniques et économiques

¹ Direction des Etudes et Recherches, E.D.F., Clamart
² Région d'Equipement Hydraulique Nord, E.D.F., Plobsheim

Résumé

This report deals with the problems with which the designer of pumped storage schemes with reversible sets is faced when he considers the effect of unsteady machine regimes on the project. The various factors which enter into scheme design are briefly reviewed. These are : (a) The characteristic times of the conduits (examples of which are given in Figure 1) and the economic gains which result from concentrating the supply ducts. (b) The very important problem of shutting of the flow through the turbines. The sequence of operating regimes is briefly described (these may include temporary flow inversion). It is shown that shutting down quickly in two short periods may often be preferable since this puts a limit on excess pressures attained and also avoids secondary phenomena. The effect of machine moment of inertia and of the surge tank selected is discussed in the light of scheme site characteristics. (c) Unsteady regimes arising from loss of driving torque in pumpwise operation are examined, together with several purely accidental regimes. For instance, Figure 8 shows initiation of water hammer arising out of very rapid guide-vane closure. The example shown in Figure 9 presents the results of an economic optimization study in terms of the unsteady regimes obtained and the important variables (run-up time of reversible power set and supply ducting). Here the overpressures were calculated by a simple method, wave celerities being infinite. Figure 10 justifies this approximation. For more accurate calculation of the excess pressures and speeds to be considered in projects and project guarantees, a more comprehensive method should be used. Electricité de France has written a computer programme to determine these unsteady regimes. A brief description of the programme is given in the appendix, together with a list of the simplifying assumptions. The programme permits calculation of flows, pressures and unit speeds at any moment and at any point in a hydraulic system comprised of basins, feed conduits, turbine-pumps with speed governors, surge tanks etc., for all kinds of system structure. The solution is obtained by applying a difference scheme to the Alliévi equations.