Fast line three phase reclosing practice on Brazilian grid and its impact on thermal generation plant shaft

Three phase reclosing of transmission lines is being an operation practice of Brazilian electric utilities. As the Brazilian power system was almost entirely composed by hydro plants, the impacts of three-phase reclosing on the machine-turbine shaft were not of main concern. With the first large thermal unities, this practice has to be revised. Abrupt variations of generator electrical torque, due system switching may lead to excitation of torsional oscillations of machine shaft. These are low damped oscillation of subsynchronous frequencies typically within the range 10-50 Hz. Three phase faults close to machine terminal constitute two severe abrupt changes on electrical torque, caused by fault application and fault removal. This work presents an analysis of shaft torque duty of Termobahia plant caused by tripolar reclosing in its vicinity. The paper discusses the difficulty of obtaining shaft data from manufacturer, modeling aspects and presents results and alternatives to attenuate the problem.