ON TORSIONAL OSCILLATIONS OF SHAFT TRAINS OF POWERFUL STEAM TURBINE UNITS UNDER OPERATING CONDITIONS

The problem of massive damageability of low pressure rotors of cogeneration turbines of types T-175 and PT-135 is considered. The hypotheses of crack formation in low-temperature rotors of steam turbines under the action of bending and torsional oscillations are compared. Based on the analysis of a variety of factors, including those of structural and operational nature, it is shown that there are a number of prerequisites that make the second of the hypotheses considered somewhat more preferable. However, the eff ects of torsional oscillations can only be estimated on the basis of the results of experimental studies of dynamic stresses in rotors on real turbine generating units under operating conditions. This required the development and creation of a multichannel control and monitoring system for torsional oscillations of the shaft train of turbine units, its pilot-industrial version implemented on the T-175/210-130 turbine generator unit. Based on the calculations performed out and the analysis of the causes of both the intrinsic and forced torsional oscillations of the shaft train, the requirements were formulated that must be imposed to recording the parameters of torsional oscillations and, what is especially important, for algorithms and software for processing data and presenting the results. It is shown that in most of the published studies only intrinsic torsional oscillations of the shaft trains are given. Typical mistakes are analyzed, and it is shown that the forced oscillations which are multiples of the rotation frequency could not be obtained with the data processing algorithms used, and that conclusions based on such studies are untenable. Moreover, in most cases, using source data not subjected to necessary pre-adjustment prior to using the same in the Fourier transform may cause signifi cant distortion of the analysis results. The methods of measurement, preparation and processing of data suggested in the paper enable to record both intrinsic and forced torsional oscillations of shaft train. The results of studies are presented that have shown that forced torsional oscillations multiple to rotation speed are mostly implemented in the shaft train. Further ways of improving the created system are provided.

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