Model-based initial residual unbalance identification for rotating machines in one and two planes using an iterative inverse approach

To achieve acceptable dynamical behavior for large rotating machines operating at subcritical speeds, the balancing quality check at the planned service speed in the installation location is often demanded for machines such as turbo-generators or high-speed machines. While most studies investigate the balancing quality at critical speeds, only a few studies have investigated this aspect using numerical methods at operational speed. This study proposes a novel, model-based method for inversely estimating initial residual unbalance in one and two planes after initial grade balancing for large flexible rotors operating at the service speeds. The method utilizes vibration measurements from two planes in any single direction, combined with a finite element model of the rotor to inversely determine the residual unbalance in one and two planes. This method can be practically used to determine the initial and residual unbalance after the balancing process, and further it can be used for condition-based monitoring of the unbalance state of the rotor.