Effects of Governor Characteristics on Turbo-Generator Shaft Torsionals

Some of the torsional modes of oscillation of turbine-generator multimass shaft systems can be destabilized through the control action of high speed electrohydraulic turbine governing systems. This form of destabilization surfaced during the commissioning of one of Ontario Hydro´s 665 MVA nuclear units. The causes of the problem were identified by measurements taken during the commissioning process and a detailed study of the control system. Conclusions reached as to the causes were supported by computer modelling. More accurate valve linearization circuits and filtering of shaft torsional components in the governor speed signal resolved the problem. A recommendation is made for direct monitoring of shaft torsional components, at least during the commissioning process.