Theoretical Analysis On Heat Expansion Of Steam Turbine Casing And Its Application

The friction between dynamic and stationary parts of steam turbine unit is an important factor that restricts the fast start up and safe operation of turbine. If expansion at different stages of turbine casing and rotor can be calculated accurately, the cleft between dynamic and stationary parts can be monitored online. It is useful to speed up start up of the unit and it helps improve the security of the unit operation.As a result of the complexity of turbine casing shape , it used to estimate the axial expansion according to the ratio between weight and area of turbine. Those kinds of methods are complex but the result is not very precise. Off-line analysis using finite element software is used to reflect heat expansion of turbine casing precisely. So far, it has not been reported that mathematical simulation is used to analyze the connection between temperature change and axial deformation based on heat transfer and heat deformation theory. In this paper a proximate method is invented to calculate heat expansion of turbine casing, which makes it possible to monitor the cleft between dynamic and stationary part of turbine precisely.To estimate heat expansion of turbine casing, this paper presents a new method to calculate temperature distribution of flat when initial temperature distribution is available and environmental temperature is constantly changing, which is based on classic transient heat conduction. Based on different geometrical shape the casing is divided into several parts, heat expansion of which is calculated respectively. Expansion reference temperature (ERT) is defined to describe the capability of each part. A good coincidence comparing the theoretical result calculated according to the new method presented in this paper with finite element calculation can be observed.A system of monitoring stage expansion is designed to put the theory into practice. So it can be tested by practice. Through combination with thermodynamic and rotor model, a online monitoring system is formulated to calculate expansion difference of the unit. After a period of trial operation it proved to be satisfactory. So the theory is correct and valuable.In the paper a new concept, visual thermal analysis ,is created to solve the problem that finite element analysis is complex and can't be transplanted easily. In other words the analysis process is intuitivism and simple to the most degree so long as precision of the analysis can be assured.So called visual thermal analysis means that users can set up an entity by linking different models which are established based the parameters input by users. And boundary conditions are added to the entity. After the calculation the final result is displayed in form of diagram and table. Based on the theory above a software package is designed to calculate casing temperature field, thermal stress and thermal expansion. The interface of the software is friendly. It is easy to operate and the result of the analysis is accurate...