1.2.3 Boiler master load controller
In this scheme, the output of the master load controller described in the previous case is used to set the boiler firing rate. The governor speed setpoint is controlled by a boiler pressure error signal, so that the turbine valves increase or decrease steam consumption in a sense to reduce the error.
This responds very satisfactorily to load changes demanded by the operator as the boiler firing rate correction is made first and, subsequently, the rapid response of the turbine can easily control any pressure fluctuations.
However, rapid changes in frequency, particularly the increase arising on load rejection, still produce the necessary governor safety response and abrupt changes in firing which cause large boiler pressure fluctuations.