Research and Solutions to Minimize Frontal Area Overheating of Hydro Generator Stator with Vertical Axis

About ten hydroelectric power plants realized from 1970 to 1990 in Romania are confronted with stator overheating. The developed mathematical model analyzes the voltage stability based on modal analysis of the Jacobian matrix, identifying the hazardous modes of variation between voltage and flow rate, correlated with the characteristics of the analyzed generators and their response to these variations. Vulnerable elements in the system for inductive and capacitive modes of operation are identified. In these conditions, hydro generators cannot attend the secondary voltage control, not even for a frequency power dependency control. The elaborated mathematical model was tested at the hydroelectric power plants Gilceag, Mariselu, and Susag with similar functioning conditions. The necessary conditions for stator ventilation and variation of flow hydrodynamic parameters during the operation were established. The theoretical model was tested with an experimental method applied separately for the thermal and ventilation conditions. Some results obtained during the measurements are illustrated and correlated with the theoretical results. The model was tested to prevent the onset instability of voltage drops and accelerated overheating. Finally, some solutions to minimize the stators overheating based on local conditions are recommended.