Governing of Steam Turbines

Governing of steam turbines is to control the speed of turbines irrespective of load. Following are the methods of governing:

• Throttle governing.
• Nozzle control governing.
• By-pass governing.

In throttle governing system, pressure of steam entering the turbine is reduced at part loads. It is used in only small turbines due to available heat loss in irreversible throttling process. In nozzle governing system, a number of nozzles (4–12) are used with individual poppet valve and according to load requirement steam is supplied to these nozzles through the valves. All nozzles may be in operation at full load and some nozzle may be idle at part load. In by-pass governing system, some part of the steam is passed through first stage and rest of steam passed through second stage of the turbine. This is used in high pressure turbines where use of nozzle governing is not possible.