A method is disclosed for improving the operational efficiency of a steam turbine power plant by governing the adjustment of the throttle steam pressure of a steam turbine at a desired power plant output demand value. In the preferred embodiment, the impulse chamber pressure of a high pressure section of the steam turbine is measured as a representation of the steam flow through the steam turbine. At times during the operation of the plant at the desired output demand value, the throttle pressure is perturbed. The impulse chamber pressure is measured before and after the perturbations of the throttle pressure. Because changing thermodynamic conditions may occur possibly as a result of the perturbations and provide an erroneous representation of the steam flow through the turbine, the impulse chamber pressure measurements are compensated for determined measurable thermodynamic conditions in the steam turbine. A compensated change in impulse chamber pressure measurement in a decreasing direction as a result of the direction of perturbation of the steam throttle pressure may indicate that further adjustment in the same direction is beneficial in minimizing the steam flow through the steam turbine at the desired plant output demand value. The throttle steam pressure adjustment may be continually perturbed in the same direction until the compensated change in impulse chamber pressure before and after measurements falls below a predetermined value, whereby the steam flow is considered substantially at a minimum for the desired plant output demand value.
In the operation of a turbine system composed of apparatus (6,12,14,16) for generating steam and a turbine first stage (4) having inlet nozzles connected to be supplied with steam from the steam generating apparatus (6,12,14,16), the steam generating apparatus (6,12,14,16) being composed of a cascade arrangement of a boiler (6) producing steam at a selected pressure which has an assigned lower limit value, a primary superheater section (12), one or more division valves (14) presenting a steam flow passage having a controllable cross-sectional area, and a secondary superheater section (16) connected between the division valves (14) and the inlet nozzles, a method for reducing the output of the system at low load levels comprising: reducing the cross-sectional area of the steam flow passage presented by the division valves (14); and increasing the rate at which heat is supplied to the steam in the secondary superheater section (16) by an amount coordinated with the reduction imparted to the cross-sectional area of the steam flow passage by the reducing step.
A method for improving operational efficiency of a partial-arc steam turbine power plant during power output variations by dynamically adjusting valve point values during turbine operation. Impulse chamber pressure at each of a plurality of valve points is first determined during operation of the steam turbine at constant pressure. For each adjacent pair of valve points, an optimum constant pressure transition point pressure for transitioning from one to the other of the sliding pressure mode and constant pressure mode is then computed. The optimum constant pressure transition point pressure for each pair of valve points is converted to a corresponding percentage of the pressure difference between the adjacent pairs of valve points. The impulse chamber pressure at each valve point is then used to calculate a corresponding impulse chamber pressure for transitioning from the one mode to the other mode based upon the percentage pressure difference. The calculated impulse chamber pressures for transitioning are compared to measured values of impulse chamber pressure and the system force transition from one of the modes to the other mode when the measured value is substantially equal to the calculated transition pressure.
A method for improving operational efficiency of a partial-arc steam turbine power plant during power output variations by dynamically adjusting valve point values during turbine operation. Impulse chamber pressure at each of a plurality of valve points is first determined during operation of the steam turbine at constant pressure. For each adjacent pair of valve points, an optimum constant pressure transition point pressure for transitioning from one to the other of the sliding pressure mode and constant pressure mode is then computed. The optimum constant pressure transition point pressure for each pair of valve points is converted to a corresponding percentage of the pressure difference between the adjacent pairs of valve points. The impulse chamber pressure at each valve point is then used to calculate a corresponding impulse chamber pressure for transitioning from the one mode to the other mode based upon the percentage pressure difference. During the transition, the control valve associated with the transition point and valve point is gradually closed.
A steam pressure rate limiter for a steam turbine system reduces the setting of a steam control valve when a rate of decrease in steam pressure is detected which exceeds a threshold value of rate of decrease. A floor on control of the steam control valve is enforced in order to maintain a predetermined amount of steam flow to the turbine thereby to provide for cooling of the turbine.
