Analysis of shaft torsional phenomena in governing large steam turbine generators with non-linear valve stroking

The paper focuses on how shaft torsional problems can be initiated in some situations by fast action of steam control valves. It demonstrates that sha ft flexibility can exert a significant influence on steam turbine-generator response following severe supply system disturbances, particularly for lar ge machines where the turbine has nonlinear valve stroking and fast valving . The effect can be minimised by careful location of the speed sensor on th e turbine shaft and by filtering to reduce speed input or acceleration sign als due to troublesome low-frequency torsional vibrations to an insignifica nt level. Digital implementation of steam-turbine control systems is described. Respo nse for a range of control philosophies where digital control procedures ar e used are given. Two large machines where digital speed sensing and filter ing techniques in steam valve control are implemented are examined.