Cost of controls for small hydroelectric plants or river systems. Final report

The general control principles for low-head hydro installations and, in particular, differences with conventional hydro plants are emphasized. Treating the flow-release mechanism through the turbine as a simple adjustable orifice, two models were derived to depict the dynamic behavior of a dam of arbitrary geometrical shape. Two specific trapezoidal structural examples were used to characterize the difference in behavior of low-head and conventional hydroelectric dam sites. As almost all low-head plants would require the use of a propellor-type turbine, the study was restricted to the analysis of both the theoretical and empirical behavior of Kaplan-type turbines. Flow control is accomplished in such cases by either adjustable wicket gates, adjustable propellor blade angle, or both. Small hydro plants operate essentially by two modes. For Mode I, the flow release rate is automatically adjusted to match the inflow rate, thus maintaining a constant head. Mode II operation requires a considerably more sophisticated controller to maintain a constant power setting at reasonably high efficiency. Very tight control of both head and flow rate is required and, except for cases where very stable inflow rates are guaranteed, it is possible that a microcomputer would be required to perform this function. In comparing the fullymore » automated on site control vs remote control alternatives, no clear picture emerges on a mere cost basis. In all the discussions the use of conventional turbine-related equipment was assumed with the exception of shaft-speed transducers where the use of optical shaft encoders is strongly recommended. It is the authors' opinion that hydraulic servo motors cannot be economically or reliably replaced as wicket-gate and propellor-blade-angle controllers, even in small turbines. A complete linerarized per unit dynamic model was developed to depict the behavior of a hydroelectric plant.« less