Systematic Approach to Resolve 2-Pole Vibration Issue for IEEE 841

In recent times, industry has seen significant vibration issues for two pole motors when tested in field and more specifically in petrochemical industry where we need to meet stringent IEEE 841 (Standard, IEEE, 841: IEEE Standard for Petroleum and Chemical Industry. IEEE, 2021) vibration limits leading to increased costs associated with rework and warranty, thereby causing further delay to end customer’s project timelines and costs. Traditional methods to resolve 2P vibration issues involved trial and error methods, which is time consuming, non-validated simulation models with high test to design error, and unstructured approach to reduce vibrations. Hence, we need a structured root cause analysis and modified and validated mathematical models to simulate and estimate the system natural frequencies to understand system resonance issues and predict vibration amplitudes before testing, thereby reducing the issue resolution time and costs. This chapter highlights the systematic approach to understand and find root cause analysis to resolve the high vibrations caused due to twice line frequency vibrations in 2-pole induction motor on rigid base. Developed simulation models to estimate natural frequencies using modal analysis and to predict vibration amplitudes at 2F using harmonic analysis and validated with test results to reduce the simulation errors to less than +/− 5%. Lessons learnt from modified FEA boundary conditions, motor component and assembly-level interactions, sensitivity analysis due to bolt types, torque, rigid and flexible bases, soft foot, bearing and rotor system, structural stiffness, etc. helped to refine simulation model for better prediction of motor natural frequency using harmonic analysis to estimate the vibration amplitudes. In addition, for a similar phenomenon in 2-pole medium voltage motors with fabricated rotors where rotor axial/radial ducts are extensively used for cooling and reducing some weight, vibration amplitudes at 2F due to magnetic asymmetry could be observed. These rotor ducts can lead to false positive rotor duct fault, produced for healthy motors, which is an ongoing problem in the industry. There is no practical solution to avoid this unnecessary maintenance cost. In this paper, developed approach was adopted for predicting natural frequencies and vibration amplitudes for 2-pole medium voltage induction motors having NEMA 580 frame size and ducted rotor construction and then validated with test results. Sensitivity analysis due to ducted rotor construction and stack stiffness helped in understanding influence of rotor ducts over vibration amplitudes. Refined mathematical models helped significantly to resolve considerable vibration issues for 2P motors on rigid base.