Vertical Pump Motor Synchronous Vibration Case Study
A 4160V, 3600 RPM motor on an existing vertical pump suffered a major failure attributed to a lightning strike. After repair vibration levels were well above shutdown with the motor running at above 1 inch/second. Several inspections and re-assemblies were made with the same results. During each assembly the rotor was low speed balanced and the assembled motor was balanced on a steel surface and rubber surface to less than 0.1 inch/second. Further investigation of the vibration was pursued through the use of impact testing and finite element analysis. This testing and analysis revealed the existence of a natural frequency near running speed. Finite element analysis was used to make modifications to detune the system; however vibration levels did not change significantly. Final solution of the vibration problem consisted of two plane balancing the motor on the pump head indicating that the standard shop approach to balancing the motor was ineffective. This paper discusses potential causes of the problem and makes recommendations for identifying and correcting the problem.
Case Study 3
Bezugl, John (2008). Vertical Pump Motor Synchronous Vibration Case Study. Texas A&M University. Turbomachinery Laboratories. Available electronically from