The open thermodynamic systems of the whole steam turbine and the low pressure(LP)cylinderLP regenerative heater were established.By building up the simultaneous equations of these two systems

the common cold end loss of the condenser was reduced and the energy that the enthalpy rise of feedwater pump brought to the feedwater was calculated.Thus

the shaft power of the feedwater pump and the actual inner power of the auxiliary turbine can be obtained.So the pump efficiency and the relative internal efficiency of the small turbine can be online monitored.Application of this method on a 660 MW unit shows that

this method had the capability of real time collecting data and monitoring performance changes of the turbine driven feed pump set.