In this paper, a procedure is presented to determine the unbalance distribution in a multi-mass flexible rotor system without requiring that trial weights be placed upon the shaft to first determine the influence coefficient matrix of the various balance planes. A modified Nyquist plotting procedure is presented to generate a polar plot of proximity probe measurements for determination of the 90-deg phase shift position of the modal eccentricity. By knowing the rotor modal mass and mode shape, a modal balancing distribution can be calculated. This relationship provides a quick procedure in estimating a first mode balance correction weight in both magnitude and angular location. An application is presented for a steam turbine during the startup of a hydrogen gas compression train. Higher order modal unbalance corrections are shown to be calculable in a similar manner.

This content is only available via PDF.