Turbine Control

The below figure gives a block diagram of power generation control.  On receiving turbine governor demand signals from the Automatic Boiler Control (ABC), the governor is put into operation, and main steam flow changes.  The flow rate of main steam fed to the turbine is converted into generated energy by the turbine generator.

Conventional governor control has been obtained by driving it directly with the turbine according to the control signals.  These signals are amplified by a proportional plus integral controller from the load dispatching values and the deviation signal of generator energy.  To further improve overall control in this case the main steam flow control has been added.  Also the cascaded control method that incorporates the above main steam flow control, has been included as a sub unit of generator energy control.Fig 4.1 gives a block diagram of power generation control.  On receiving turbine governor demand signals from the Automatic Boiler Control (ABC), the governor is put into operation, and main steam flow changes.  The flow rate of main steam fed to the turbine is converted into generated energy by the turbine generator.

Conventional governor control has been obtained by driving it directly with the turbine according to the control signals.  These signals are amplified by a proportional plus integral controller from the load dispatching values and the deviation signal of generator energy.  To further improve overall control in this case the main steam flow control has been added.  Also the cascaded control method that incorporates the above main steam flow control, has been included as a sub unit of generator energy control.

1.       Dispatching Value of Main Steam Flow Rate

The selection of main steam flow rate values in the turbine following mode is different from that of the coordinated control mode.

a)    Coordinated control mode (Not turbine following mode)

The dispatching values of the main steam flow rate are decided by adding advance signals based on the load dispatching values to corrected values of generated energy control.

b)    Turbine following mode

Dispatching values of the main steam flow rate are decided by correcting the program setting point based on the total fuel flow rate of boiler input using the deviation signals of the main steam pressure.

2.    Upper and Lower Limits Using Main Steam Pressure

Stable plant operation cannot be achieved if there is wide variation of main steam pressure, which exceeds the specified value.  Pressure should be immediately restored to its specified value.

Large variation in main steam pressure when operating under coordinated control is caused by a response delay of the boiler.  In order to lessen this variation, main steam pressure must be controlled by the turbine using a turbine governor which provides the most rapid effect on the main steam pressure.

3.   Turbine Governor Control

Main steam flow rate deviation signals are given to the proportional plus integral controller through a deviation limiting circuit for main steam pressure.  Governor opening signals, amplified by the proportional plus integral controller, will send turbine governor control signals after having passed through a manual/auto changing circuit.