Study on dynamic response and vibration reduction of medium-speed mills with spring vibration–isolated foundations in thermal power plants

Abstract

Spring vibration–isolated foundations are widely used today to support medium-speed mills in thermal power plants. The vibration of machine body should be considered in the design and vibration evaluation of the foundation of dynamic machine. To investigate the dynamic characteristics and vibration reduction measures used with these foundations, eight mills, including one mill supported by a non-isolated foundation, were tested on site. Vibration safety was evaluated based on the test results. Furthermore, a mill-foundation coupled finite element model was built using ANSYS to analyze modal and harmonic responses. The calculation results were generally in accordance with the test results. Finally, vibration reduction measures were discussed by parametric analysis including the number of isolators and the mass ratio of the foundation to that of the machine. This study shows that the vibration could be effectively reduced by the spring vibration–isolated foundation, particularly for the ground. The vibration displacements of medium-speed mills supported by spring vibration–isolated foundations meet code requirements, but the vibration displacements of the machine body are larger than the code requirements. To achieve good vibration isolation, the maximum horizontal vibration displacement at the top of the foundation is suggested to be 50 µm, and the mass ratio of the foundation to the machine should be 3.0 ± 0.2.