Vibration activity evaluation of double-span rotor at rundown caused by its initial curvature and residual unbalance

Abstract

The work is dedicated to the study of vibration activity of double-span rotor of turbine unit (TU) consisting of a high-pressure rotor and a rotor of medium-low pressure rotor combined with it (HPR—MLPR system) at the lowest critical rotational frequencies at rundown. When using the design model of the system, it was assumed that the rotors were installed on anisotropic elastic-damper supports, tied among themselves by a rigid clutch, and having the initial curvature (nonremovable initial deflection) and the residual unbalances in both spans. Two types of bearings were considered–elliptical and six-shoe segmental bearings. It was believed that the initial deflection during operation or as a result of noncompliance of start-up conditions initially gets only HPR and the axis shape of unloaded HPR is known and it is a flat curve. The resultant curve of nonremovable deflection of the HPR–MLPR system occurring after installing the shafting into the bearings was also considered flat and located in the same plane as the initial deflection of HPR. The cases of additional presence with the rotors of concentrated residual unbalances in the middle of each span are considered. The case of availability with both rotors of the shafting antisymmetric point unbalances on each of the spans was not considered in this work. The values of each of the factors of vibration activity (of the initial deflection of HPR and residual unbalances of both rotors) were chosen to be equal to the maximum permissible established by the active in the practice of TU operation limitations on the maximum values of the initial deflection of thermally unstable rotor and its residual unbalances. The influence of location of residual unbalances in relation to the initial deflection curve of HPR–MLPR system on the total amplitudes of transient vibrations caused by both excitation factors in the reference points of the system at TU rundown was investigated. It was established that, at the unfavorable relations between directions of curvature of the rotors of HPR–MLPR system and their residual unbalances with segmental bearings, touching in the diaphragm seals in the middle of HPR span is possible.