Balancing large turbine-generator rotors

SINCE turbine-generator rotors are highly stressed structures that combine materials of widely varying properties, unbalance may be caused by geometrical errors, non-homogeneity of materials, or distortion under the speed and temperature of operating conditions. The purpose of balancing is to offset these imperfections by adjustment of the rotor mass distribution so as to secure a rotor which will run so smoothly that only small periodic forces will be transmitted to the supporting bearings and foundation.