Abstract: Residual unbalanced moment is a key index to evaluate the build quality of turbine runners. In the runner static balance system based on the stress bar method, the unbalanced moment calculated using the balance equation often deviates significantly from the real counterweight moment, which affects the calculation of the real residual unbalanced moment. Through analysis of the balance state of a real balance system, this paper first points out the bending deformation of the stress bar’s surveying rod will cause its bending moment to deviate from the real unbalanced moment of the runner. Then, considering engineering application cases, we examine the preconditions of concentrated deformation and small deformation, and derive a formula to correct the difference between the stress bar bending moment and the real unbalanced moment of the runner for the case of the stress bar with its fixed end lower or higher than the runner centroid. Finally, a case study proves our correction formula can reduce calculation errors effectively and help improve the build quality and key performance of turbine runners.

Key words: turbine runner, static balance, stress bar, unbalanced moment calculation, correction formula