The most important problems encountered in power plants are related to cold start-up, hot start-up, daily and seasonal variation in load. These problems are specially critical for high power units above 525°C and 10.5 MN/m2. As a result of higher thermal capacity of the thicker components in larger power units, the temperature gradient and thermal stresses assumed much higher values. It is, therefore, particularly important during transient operation conditions to know the temperature distribution and thermal stresses of rotors. One of the most common concerns is how fast can a turbine be started without significant damage. If the turbine is loaded very rapidly, high temperature gradient and excessive thermal stresses can easily damage the machine.

A concept was developed whereby an on-line computer was used to control the start-up and load variation operations of the turbine. The feasibility of such concept depends upon the knowledge of the instantaneous temperature distribution and thermal stresses of the turbine rotors. This paper presents a 2-D mathematical model of the transient temperature distribution as well as thermal stresses of the rotor. The mathematical model was simulated in the computer and ADI method was used for the solution of the governing equations. Discussions will be made of the procedure of coupling this mathematical model with on-line computer for optimum control of start-up and load variation schedule.

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