The temperature and thermally stressed state of the high and medium pressure rotors of the T-250/300-240 district heating steam turbine are calculated, taking into account the concentration of stresses in the neighborhood of the thermal grooves in labyrinth seals. "Critical" zones in the turbine rotors, within which thermal stresses limit the rate of startup, are determined. Some practices for reducing the temperature stresses are suggested.During operation of a turbine it is not possible to monitor directly the level of temperature stresses in the most massive, high-temperature components: the rotors, check valve housings, and cylinders. Two problems arise in this connection: choosing indicators that provide a sufficiently complete and reliable characterization of the thermally stressed state of a turbine, and establishing quantitative relationships between the monitored indicators and the variables which actually determine the operational reliability of a turbine during startup.In order to solve these problems we have to determine which components are "critical elements," within which the temperature stresses determine the rate and duration of startup operations, as well as the zones where the maximum temperature stresses develop within these components.The introduction of a number of structural and engineering measures on the T-250/300-240 turbine, such modernizing the system for heating the flanges and studs, and improving the design of the check valve, have made it possible to reduce the temperature stresses in the stator units under startup conditions. Thus, the high pressure rotor (HPR) and medium pressure rotor (MPR-1) can turn out to be "critical elements."A number of studies of the thermally stressed state of rotors in high-power condensation systems with intermediate steam superheating have been published [1 -6].The computational and experimental studies reported in these papers show that in turbines with intermediate steam superheating, the "critical element" is the MPR. This is because of the large diameter of the medium pressure rotor and the presence of a clearly distinct dummy in the medium pressure rotor of some turbines with a single-flow design for the medium pressure cylinder (MPC), and also because the metal of the medium pressure rotor in the steam inlet zone and front end seal is washed by steam at a rather high temperature (close to the temperature after the intermediate steam superheater). All these features of turbines with intermediate superheating are also characteristic of the T-250/300-240 district heating turbine.On the other hand, in another paper [7], devoted to optimizing the startup regimes for a turbine by modelling its thermally stressed state, the HPR was chosen as the critical element.Thus, in order to identify the "critical elements" of a turbine, in terms of which an optimum startup regime should be established, and also because of the difficulties with experimental investigations of the temperature state of the rotors under operating conditions, we have used the certified...
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