Steam turbine speed is not to the first approximation a function of the inlet pressure. The turbine speed is set by the grid frequency and is a statement in your problem.

YOu must be attempting to find some other parameter.

dprice,
first of all thanks for your replay and the second things that our turbine is a pump driven and we want to make on-line washe for the last couple of stages by de-superheating the steam inlet temperaure.
But since the turbine shaft speed function with the energy input to the turbine we warred that test will reduce turbine RPM and steam inlet governor become out of control and at the end it will decrease the pump header pressure.
so detrmine turbine shaft RPM Vs energy inlet needed prior to do the test.
regars,

Hello

The amount of energy which is consumed in the turbine depends on the turbine RPM, Tourque applied to the turbine's shaft in addition to turbine's efficiency, so if you change inlet pressure this will lead to a change in input power, assuming that the turbine efficiency and toruque applied on the shaft are constant the the turbine RPM will be less.

thanks

Khaled

Would not the speed of such an auxiliary drive steam turbine  be a function of the load it is driving, and probably also the inertia of the rotating shaft system, all balanced by its governor control as set by demand control signal?

In the last two months you have probably tried it, but carefully controlled test, keeping inlet steam superheated, by a margin of say 25degC, would tell.  if you can measure stage outlet conditions, you may be able to find changes in pressure ratios or enthalpy drop efficiency that will changed when blades have been washed.