Power Plant Unit

of a hydroelectric power plant, a complex of hydraulic-engineering structures in a diversion hydroelectric power plant that are directly engaged in the conversion of the potential energy of water to electric energy. The unit consists of (Figure 1) a forebay or storage reservoir, a penstock, a powerhouse, and a short discharge channel (unless this channel is a diversion conduit). The structures of the power plant unit conduct water from the supply diversion structures to the hydroelectric generating units and then remove the water to the drainage diversion structures or river channel. Hydroelectric power plant units can be located at the end, in the middle, or, less frequently, at the beginning of the diversion structures.

Figure 1. Schematic diagram of the power plant unit of a diversion plant: (1) forebay, (2) intake racks, (3) penstock, (4) powerhouse, (5) discharge channel, (H) water head, and (LT) level of tailrace

A forebay in a power plant unit serves to link the nonpressured diversion structures with the penstock; it is used to regulate daily quantities of water supplied by the diversion canal. The storage reservoir, which links the penstock with a pressured (usually tunnel) diversion structure, absorbs undesirable pressure changes in the water supply system brought about by changes in the operating conditions of the hydroelectric power plant. The penstock, which consists either of a row of parallel steel or reinforced-concrete pipes laid on the surface of a steep part of the terrain or of one or several pressured tunnels, conducts water from the fore-bay or storage reservoir to the turbines. The powerhouse of a hydroelectric power plant, which may be built either above or below ground, contains generators, step-up transformers, switchgear, and control panels. Water from the turbines passes through a suction pipe to-the discharge channel and then on to the river channel at the tailrace of the hydroelectric power plant. Hydraulic gates, used during both the operation and repair of the plant, are positioned along the entire water system.