Selection of the parameters of hydraulic turbines when reconstructing operating hydroelectric stations

Abstract

At present about 25% of hydroelectric stations of the country with a total installed capacity of 8900 MW have been operating for more than 30 years, and 37% of the hydrostations with a total capacity of more than 12,000 MW have been operating for more than 20 years and, consequently, the equipment of these stations is also approaching the end of their standard service life [1].The following characteristics are typical for hydrostations where problems of the reconstruction and reequipping of the units are urgent: the majority of hydrostations are equipped with adjustable-blade turbines, the operating regimes of which on the complete performance curve nl'---Ql' are far from the optimal efficiency with respect to the reduced discharge; at a number of hydrostations the installed capacity of the turbines has been increased by 10-25% in comparison with the design due to boosting the operating regime of the turbines; the statistical distribution of the use of the capacity of a turbine--generator unit N u has shifted in recent years toward high loads in comparison with the design.As a result of boosting the operating regimes of the turbines and changing the operating regimes of the hydrostations, the use of the energy of the stream has worsened, since the weighted average efficiency with respect to generation was 5-10% below the maximum possible for the give type of turbines.Along with a decrease of the efficiency of using the stream and a shift of the operation of the turbines into the zone of lower efficiency values and increased dynamic loads, a tendency toward a decrease of the reliability of the units is observed: an increase of the rate of failure of the blades, an increase of the rate of destruction of the turbine bearings, intensification of cavitation of the waterway of the units, etc. [2, 3].An increase of the efficiency and reliability of the hydropower equipment with a service life exceeding the standard will inevitably require its replacement. The need for replacement is dictated not only by physical wear of the main elements of the units but also by the circumstance that they have become obsolete relative to modem types of turbines, as well as by the changed requirements imposed on hydrostations on the part of the power systems.Problems related to the reconstruction and reequipping of turbines are best solved within the framework of large-scale reconstruction of the hydrostations. This direction should become the main one in the 12th Five-Year Plan and should take over from modernization of individual components of the equipment, which was carried out to provide standard operating readiness of the hydrostations. For the successful solution of problems of replacing turbines during reconstruction and reequipping it is necessary: to evaluate the efficiency of using the stream by the existing turbine equipment under the established operating conditions and for the selected parameters (rotational speed n and diameter of the turbine runner D1); to determine the optimal requirements imposed on the parameters of th...