1.2.2   Turbine master load controller with boiler on pressure control


To overcome the previous point about non-linear droop characteristics, a separate load/frequency controller is built having the features shown in Fig 2.5. For any operating frequency, depending on the characteristics, there will be a demanded load determined by this characteristic which is compared with the measured electrical load in the master load controller.

schematic of a simple load/frequency controller

The resulting error signal provides the input to the governor speed setpoint, which changes the load on the turbine to reduce the error. This form of slow-acting integral error correction gives accurate droop characteristics or control to a fixed load (infinite droop), if selected. The master load controller may be included as part of the governing system or may be provided separately in a unit control scheme. Apart from providing accurate linear droop characteristics, the performance of this scheme is very similar to the scheme described in the previous subsection.


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