Application of Torsional Vibration Measurement to Shaft Crack Monitoring in Power Plants

The primary goal of the this project was to demonstrate the feasibility of detecting changes in shaft natural frequencies such as those associated with a shaft crack on rotating machinery in electric power generation plants using non-contact, non-intrusive measurement methods. During the operation of power plant equipment, torsional natural frequencies are excited by turbulence, friction, and other random forces. This paper primarily addresses the results of field application of non-intrusive torsional vibration sensing to a hydro station and to large induced-draft ID fan motors. Testing reaffirmed the potential of this method for diagnostics and prognostics of shafting systems. The first few shaft natural frequencies were visible, and, for the hydro station, correlated well with finite element results finite element results are not available for the ID fan motors. In addition, several issues related to the development of the non- intrusive transducer were revealed.