Abstract: Arm to solve the problem of field dynamic balancing usually needs to be started many times for multi-span rotor shafting, a whole-machine dynamic balancing method without trial weights for shafting combined with the advantages of influence coefficient and modal shape is developed. According to the shafting structure and running parameters, the rotor dynamic finite element model is built by using rotor dynamics theory and finite element simulation. With the principle of flexible rotor resonance separation, balancing plane number and places of rotors can be determined by using the shafting modes and their orders of shafting unbalance. Unbalance excitation is applied in the balancing weighed place of multi-span rotors respectively. The shafting weighted influence coefficients for balancing speed can be obtained from the vibration response analysis of each measuring points on the shafting, which can replace field dynamic balancing with many times run-up by trial weights. The required shafting balancing weighted of each span rotor can be got by solving balancing vector equations with the least squares method. Finally, a four-rotor and five-bearing shafting experiment rig for simulating 1 000 MW ultra supercritical turbine rotors is taken as an example. The dynamic balancing of four planes at the speed of 2 700 r/min without trial weights is performed by the proposed method. The result shows that it can quality achieve the balancing of flexible shafting with corrective masses at a time with maximum amplitude drop up to percent of 53 for one point, which reduce the balancing times due to blind trial weight, and save balancing cost and period.

Key words: dynamic finite element model, weighted influence coefficient, whole-machine dynamic balancing, without trial weights, multi-span rotor shafting