Right and Left-Hand Natural Modes of Industrial Rotating Machines. Model Study

Abstract

The rotors of rotating machines are guided by links. The matrixes representing links are, in general, not symmetrical. Right and left-hand natural modes differ. Left-hand modes are particularly used to define modal unbalances.

The high pressure rotor of a turbine generator of 1000 MW at 1500 rpm of a nuclear plant is here being studied. Three models are described; their first flexural natural pulsation, while on fixed supports, is equal to 1116 rpm, close to the first critical speed. The structure of the first two models is that of a De Laval-Jeffcott rotor, the third rotor concords with a high pressure rotor. For each of the models, two kinds of bearings have been teamed : cylindrical and 3 lobes.

Natural pulsations as well as right and left-hand modes are determined by literal formulas for the first model, by special software for the other two. Comparisons are set up between amplitudes and the phases of the right and left-hand natural modes; the differences are related to the assymetries of impedance matrixes.

The quality of the first two models, in reference to the concordant model, is shown through the comparison between the natural modes.