Simulation of the dynamic behaviour of steam turbines with Modelica

Abstract

Steam turbine technology is one of the leading technologies used in electricity production since more than one hundred years. In recent time requirements for steam turbines have been changing slowly. Steam turbines are not longer used in power plants with high operation times and a high full load share only, but are also implemented in combined cycle power plants or solar thermal power plants. This type of plants requires good dynamic behavior of the steam turbine due to fast and frequent start ups and daily cycling. To optimize the performance of this kind of power plants and their components it is necessary to simulate and analyze their dynamic behavior. Therefore, a general model approach for steam turbines within Modelica has been developed. This model approach is based on a general model, which can be adjusted to the necessary model depth as described in this paper. Steam turbines in a solar thermal power plant with direct steam generation must fulfill special requirements regarding their dynamic behavior. Hence, this model is applied as an example to explain the behavior of an industrial steam turbine used in such plants. Furthermore, this paper shows first results of simulations with turbine models. To validate the model, the results are compared with results from the Siemens internal steady state calculation tool. Since results stay within the estimated accuracy, the model approach can be used for further calculations. The dynamic behavior of the turbine is analyzed by using typical solar irradiance disturbances. This analysis shows that no critical operation points occur within the turbine.