During routine vibration analysis of a combined cycle, slight increases in synchronous vibration were detected during the run-up of a synchronous electric generator. Initially, these were attributed to minor mechanical balancing changes near a critical speed, but over time, it became clear the vibrations only occurred during run-ups, not rundown, ruling out rotor unbalance as the cause.

As vibrations increased and alarm levels were exceeded, similar issues were observed in other generators. Evidence pointed to electromagnetic issues, and after testing various theories, the owner determined that winding short circuits caused asymmetrical magnetic forces during run-ups. An electric rotor repair confirmed this diagnosis, as vibrations returned to normal afterward.

This case highlights the impact of electrical problems even when generators aren’t at base load and emphasizes the importance of owners maintaining a technical perspective, as OEM recommendations may not always be accurate.

Mechanical Engineer with a Master’s degree in Industrial Maintenance and Diagnostic Techniques, and a Master’s degree in Energy Engineering. He is Certified as Vibration Analyst Cat IV since 2011 and has over 20 years of international experience in Diagnostics and personnel training. Additionally, he has participated in Root Cause Analysis in collaboration with machinery manufacturers and in the definition of procedures for the Diagnosis of Critical Machinery.