Theoretical and experimental research on turbo-generator shaft alignment using strain gauge method

Abstract

Shaft alignment is a key factor for the safe and reliable operation of a turbine unit. This paper presents an approach to estimate the turbo-generator shaft alignment using strain gauge technique with two measuring sections nearby each coupling. The change of shaft bending moment is linearly proportional to the change of bearing elevation and reaction force. So the bearing load distribution can be identified from the strain values and bending moments which are measured using strain gauge. The transfer matrix method is used to calculate the detailed shaft alignment data including deflection, slopes, bearing reaction forces, influence coefficients, sag/gap values. Experiments were carried out on a test rig with 3 rotors, 2 couplings and 6 bearings. It was shown that the strain gauge identification results agree well with the results using the jack-up method. The maximum relative error of each bearing loads is almost 8.7%. The sag/gap values using the strain gauge method are close to those using the laser alignment method. The maximum relative error is less than 7.5%. Results also show that the strain gauge method is sensitive to possible disturbances in the bearing elevation. In the end, strain gauge alignment technique with two measuring sections nearby each coupling was applied on the shaft alignment estimation of a 600 MW turbine unit successfully. The bearing loads and shaft deflection were obtained accurately.