Steam Turbine Overspeed Control and Behavior During System Disturbances

System disturbances involving partial load rejection may cause turbine overspeed control action. To provide information necessary to evaluate power plant transients during such disturbances, this tutorial paper reviews the typical normal overspeed control functions on GE reheat steam turbines with either Electro-Hydraulic Control or Mechanical-Hydraulic Control. Normal overspeed control is related to speed control and the overspeed trip. The characteristic behavior of normal overspeed control is shown for full load rejections and a representative partial load rejection. Enhancement of power plant partial load rejection capability by considering combined turbine-boiler dynamic behavior is discussed.