Mitigation of Resonance Problem in Turbine Generator Housings at Captive Power Plant

Abstract

In a power plant, the Turbine and Generator are among the most critical assets in the power plant. Any high vibration behaviour during their operation or commissioning can raise serious unexpected failure and potential operational risks. Resonance is very typical condition in equipment which causes catastrophic failure of the equipment. A chronic high-vibration issue was observed at the Generator Front Bearing (BRG-4) of Turbine Generator Detailed vibration analysis, including spectrum analysis, shaft orbit plots, phase analysis, and structural bump tests, identified the presence of a resonance condition, this condition effects in turbine and generator as Excessive vibrations, Fatigue and structure damage, Bearing and shaft misalignment and also reduces equipment’s operational life. Root cause investigation revealed a minor gap between the stator bolts and the concrete foundation, which compromised stiffness and enabled structural resonance. To mitigate the issue, epoxy grouting using Monopal liquid was strategically applied at identified antinode locations. The grouting significantly improved structural stiffness and damping, thereby shifting the system\'s natural frequency away from the forcing frequency. Post-rectification measurements demonstrated a drastic reduction in vibration amplitude at BRG-4—from 30.91 mm/s to 7.95 mm/s, bringing the system back within safe operating limits. Other turbine section vibrations also normalized. This case effectively demonstrates how resonance-induced vibration can be addressed through structural modification and damping enhancement using epoxy grouting techniques.

Introduction

The Hindalco Mahan plant operates a 6×150 MW captive power plant to ensure uninterrupted power for its smelter operations. One of the critical issues faced in the turbine-generator (TG) system was high vibration at bearing no. 4 (generator front bearing), with a recorded peak amplitude of 30.91 mm/s—well into the critical zone per ISO 10816 standards.

Problem Diagnosis:

• Excessive vibration was traced to resonance, a condition where the system’s natural frequency matches the external excitation frequency.

• 1X frequency was dominant in the vibration spectrum, typically associated with issues like unbalance, misalignment, or looseness.

• Phase analysis showed a 90° phase shift, confirming resonance.

• A bump test (impulse hammer test) revealed that the natural frequency of the structure coincided with the generator’s operating frequency.

• Structural looseness due to a gap between stator bolt and concrete was the root cause, creating a weak point and amplifying vibration.

Solution Implemented:

• Epoxy grouting (using Monopal liquid) was applied at two identified antinode points on the structure.

  • Epoxy improved stiffness and damping, shifted the system’s natural frequency, and reduced vibrational energy.

  • Approximately 100 litres of epoxy were used.

  • A 72-hour curing period was maintained before restarting the machine.

Results:

• Post-epoxy grouting, vibration at the generator front bearing dropped significantly and returned to the normal operational range.

• The overall health of the equipment improved from critical to satisfactory, resolving structural cracks and preventing further damage.

Key Technical Insights:

• Resonance in mechanical systems can result in severe damage if undiagnosed.

• Phase analysis and bump testing are effective tools for identifying resonance issues.

• Epoxy grouting is a reliable method to modify natural frequency and improve system damping.

• Proper diagnosis and strategic corrective actions can greatly enhance equipment reliability and operational safety.

Conclusion

The persistent high vibration issue at the generator front bearing (BRG-4) in Unit-2 of the Hindalco Mahan captive power plant was identified to be a result of a resonance condition. Detailed vibration spectrum, phase, and bump test analyses confirmed that the natural frequency of the generator structure matched its forcing frequency, amplifying the vibration to a critical level of 30.91 mm/s (as per ISO 10816 standards). Through root cause analysis, it was discovered that a minor structural gap between the stator bolts and the concrete foundation was enabling resonance. Epoxy grouting using monopal liquid at identified antinode points significantly enhanced the stiffness and damping characteristics of the foundation, effectively shifting the natural frequency and mitigating the resonance effect. Post-rectification results demonstrated a substantial drop in vibration levels at the generator front bearing—from 30.91 mm/s to 7.95 mm/s—bringing it within acceptable limits. This case study underscores the importance of accurate vibration diagnostics, resonance identification, and the effectiveness of structural enhancement using epoxy grouting in improving machine reliability and preventing catastrophic failure.

References

[1] Vance, John M. Machinery vibration and rotordynamics / John Vance, Brian Murphy, Fouad Zeidan.p. cm. [2] BHEL turbine generator civil base GA and sectional drawing. [3] Mobius VCAT-III vibration analysis literature. [4] NASA conference publication 3344 on Rotor dynamics problems in high performance machinery 1996. [5] Vibration standards ISO10816 and ISO7919, ISO 20816-3:2022. [6] Vibration standards ASTM E756.

Copyright

Copyright © 2025 Sushil Sharma. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.