Method and apparatus for steam turbine speed control

A method for controlling steam flow-rate through a steam turbine using a control system comprising a controller for a steam-valve actuator position, a pilot-valve directing hydraulic fluid flow to-and-from a steam-valve actuator, a transmitter sending a signal proportional to a pilot-valve position, an additional controller for the pilot-valve position, and a supplementary controller is for steam-valve actuator velocity, the method comprising:

• (a) sending a position set point from the steam-valve actuator controller to the pilot-valve controller;
• (b) sending a position signal from the pilot-valve transmitter to the pilot-valve controller;
• (c) calculating a position signal within the pilot-valve controller;
• (d) positioning a pilot-valve actuator based upon the pilot-valve position signal;
• (e) calculating a first value proportional to a difference between a steam- valve actuator position and a steam-valve actuator set point as a set point for the actuator velocity controller;
• (f) calculating a second value equal to a first time-derivative of the steam- valve actuator position as a control variable for the actuator velocity controller;
• (g) calculating an additional pilot-valve position signal within the actuator velocity controller based upon the first and second values;
• and
• (h) positioning a pilot-valve actuator based upon the pilot-valve position signal and the additional pilot valve position signal.

An apparatus for controlling steam flow-rate through a steam turbine using a control system comprising a controller for steam-turbine speed to generate a steam-valve actuator set point, a pilot valve directing hydraulic fluid flow to-and-from a steam-valve actuator, a transmitter sending a signal proportional to a steam-valve actuator position, and an additional controller for a pilot-valve position, the apparatus comprising:

• (a) means for calculating a first value proportional to a difference between the steam-valve actuator set point and the steam-valve actuator position;
• (b) means for calculating a second value equal to a first time-derivative of the steam-valve actuator position as a control variable for the pilot-valve controller;
• (c) means for calculating a position signal within the pilot-valve controller based upon the first and second values;
• and
• (d) means for positioning a pilot-valve actuator based upon the position signal of the pilot-valve controller.

An apparatus for controlling steam flow-rate through a steam turbine using a control system comprising a controller for a steam-valve actuator position, a pilot-valve directing hydraulic fluid flow to-and-from a steam-valve actuator, a transmitter sending a signal proportional to a pilot-valve position, and a supplementary controller for steam-valve actuator velocity, the apparatus comprising:

• (a) means for sending a position set point from the steam-valve actuator controller to the pilot-valve controller
• (b) means for sending a position signal from the pilot-valve transmitter to the pilot-valve controller;
• (c) means for calculating a position signal within the pilot-valve controler;
• (d) means for positioning a pilot-valve actuator based upon the pilot-valve position signal;
• (e) means for calculating a first value proportional to a difference between a steam- valve actuator position and a steam-valve actuator set point as a set point for the actuator velocity controller;
• (f) means for calculating a second value equal to a first time-derivative of the steam-valve actuator position as a control variable for the actuator velocity controller;
• (g) means for calculating an additional pilot-valve position signal within the actuator velocity controller based upon the first and second values;
• and
• (h) means for positioning a pilot-valve actuator based upon the pilot-valve position signal and the additional pilot valve position signal.