Using Regulated Electrical Machines in Small Hydropower Plants Operating in a Power Network

Abstract

Economic factors of operating hydroturbines used in small hydropower plants, including the Francis turbine, Pelton turbine, and axial Kaplan turbine with fixed blades (propeller turbine), are analyzed and compared as a function of the turbine-rotation frequency. It is found that the regulation of the turbine-rotation frequency depending on the changes in consumption of the energy carrier (water flow) improves the efficiency of the propeller turbines by 8–10% and leads to an increase in power production by the hydroaggregate as a whole. For these turbines, an expression describing the capacity (torque) as a function of the rotation frequency is obtained from the propeller characteristic of the turbine by approximating the frequency dependence of the turbine efficiency by a cubic polynomial. Since relative units were used, the obtained expression describes the characteristics of all propeller-type turbines. A mathematical model of an hydroaggregate consisting of a prototypical axial fixed-blade Kaplan hydroturbine coupled with a frequency-controlled synchronous generator with permanent magnets is developed. The study of static and dynamical operation modes of the above-mentioned hydraulic aggregate on the basis of this mathematical model verified the operability of the system and technical solutions used in its design.