New design of tailrace conduits of hydropower plants

1. The new design of the tailrace conduit differs from those used earlier in that the elevations of the top of its roof gradually increase toward the free pool. In this case, depending on the position of the lower pool level, the operating regime of the conduit can be either pressure (at high elevations of the lower pool), or partially pressure and partially free-flow, or free-flow (at low elevations of the lower pool). The geometry of the line of the longitudinal profile of the tunnel ceiling is determined by a calculation based on the condition of no discontinuity of the flow beyond the runner. 2. The new design of the tailrace conduits of hydroelectric stations, pump-storage stations, and pumping stations permits reducing the volumes of works and costs of the structures. Its use is especially advisable under conditions of considerable fluctuations of the lower pool level with lengths of the downstream conduits of about 150–600 m. 3. The use of conduits of a mixed design, in which the initial stretch of the conduit is made with a rising ceiling and the end stretch is free-flow, is possible.