AbstractA mathematical model to simulate the dynamical behaviour of a drum-boiler turbine group is developed.The particular flexibility in its application is the most relevant characteristic of the model. In fact it is possible to simulate the dynamic behaviour of any drum- boiler and high-intermediate low pressure turbine by decomposing the general plant into subsystems connected with standard interfaces.The dynamic behaviour of each of these blocks is described in mathematical terms by considering them as open lumped parameter systems.Governing laws of fluid dynamics, of heat transfer and equations of state are written taking into account the changes in characteristics of fluid flow versus the two state variables, density and pressure,by linearized equations, around steady state operating conditions. The results of the simulation in open loop of dynamic behaviour of a 170 MW plant are presented too.