Theoretical-empirical model of the steam-water cycle of the power unit

The diagnostics of the energy conversion systems' operation is realised as a result of collecting, processing, evaluating and analysing the measurement signals. The result of the analysis is the determination of the process state. It requires a usage of the thermal processes models. Construction of the analytical model with the auxiliary empirical functions built-in brings satisfying results. The paper presents theoretical-empirical model of the steam-water cycle. Worked out mathematical simulation model contains partial models of the turbine, the regenerative heat exchangers and the condenser. Statistical verification of the model is presented. An analytical modelling with the application of the auxiliary empirical functions admits to obtain the required accuracy with the short computation time, what entails raise of the model usefulness, especially in the operating conditions (Rusinowski et al., 2008). Presented theoretical-empirical model of the steam- water cycle contains the equations as a result of conservation laws and the empirical characteristics describing dependences of the unknown factors on the operating parameters. A mathematical model of the steam-water cycle contains the following partial models: a model of the turbine, models of the regenerative heat exchangers and a model of a condenser. Empirical functions coefficients values are estimated using the least square method on the basis of the special measurements. In order to verify the model, quality evaluation of the prediction is performed. For this purpose statistical factors like a coefficient of determination and estimator of the model's error are used. A model of a cycle A steam-water cycle of an analysed power unit contains 18K370 three-part turbine, low- and high- pressure regeneration system (each involves four heat exchangers), a condenser, a feed water tank and a pump, and an auxiliary turbine. A model of a turbine A worked out model of the turbine contains mass and energy balance equations for high-, medium- and low-pressure parts of the turbine (Szapajko, Rusinowski 2008) taking into account leaks in the valves spindles seals and from the external glands, steam mass flow in the balance piston and inter-body steam mass flow (ABB, Zamech) and the model of the steam expansion line for the individual groups of stages. The course of the steam expansion line for the individual groups of stages is modelled with the utilization of the steam flow capacity equation in form (Perycz, 1992):