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The Analytical Approach to the Temperature Prediction of Steam Turbine Shells Based on the Thermocouple Temperature Measurements at a Few Points

[+] Author Affiliations
Ajit B. Ekbote

John F. Welsh Technology Centre, Bangalore, Karnataka, India

Howard M. Brilliant

GE Energy, Schenectady, NY

Paper No. GT2008-50609, pp. 59-68; 10 pages
doi:10.1115/GT2008-50609
From:
  • ASME Turbo Expo 2008: Power for Land, Sea, and Air
  • Volume 5: Structures and Dynamics, Parts A and B
  • Berlin, Germany, June 9–13, 2008
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4315-4 | eISBN: 0-7918-3824-2
  • Copyright © 2008 by ASME

abstract

The performance and efficiency of a steam turbine does depend upon the clearances during the hot conditions. The reliability and accuracy of the clearance calculations is based upon how good are the temperature predictions of the local zones at the secondary steam leakage path. Especially during the transients of the start-up and shutdown of a turbine, the temperature gradients result in the differential expansions of the shell at the top and bottom. This causes the humping or sagging of the shell. Along with the shell, the stationary parts fixed to the shell, such as diaphragms also move up or down. This increases the probability of interference and rubs. These transient gradients are not, in general, captured in the conventional analyses owing to a plethora of reasons. The methods described in this paper are applicable to any section of a steam turbine, as well as a gas turbine. The authors have considered the double flow low pressure (LP) steam turbine inner casing, for which the field data in terms of the metal temperature measurement was compiled and made available. The LP section of a turbine with bottom condenser has, generally double flow arrangement. The thermocouples put on the geometrically symmetrical points indicated difference in temperature and thus the circumferential variation. The paper describes how a few temperature measurements on the shell using thermocouples can be effectively utilized to calculate the temperature as a boundary condition at all the nodes of the finite element (FE) model by means of shape function interpolation. The results based on this technique give a continuous temperature distribution. The thermocouple based shell temperature measurements in the field are used for the calculations of the temperature at each point and the structural analysis was carried out. The analysis did indicate the sagging & humping of the shell. Plans for future improvements will be presented. Temperature and deflection profiles and transient errors are shown to be representative of observed behavior.

Copyright © 2008 by ASME

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