Case Study: Excessive Vibration After a Generator Rotor Full Rewind

Abdelhady Mohamed, Machinery Diagnostics Technical Team Leader, Baker Hughes Sherief Mekawey, Machinery Diagnostics Principal Engineer and Technical Leader, Baker Hughes


The Machine Train under discussion consists of a Gas Turbine Frame 9E driving 115MW Generator. The machine is one of 4 crucial simple cycle power plant. In October 2018, the generator rotor was fully rewound followed by a high-speed balancing at OEM certified workshop.
In July 2019, the unit started after an alignment of GT/GEN, and showed an acceptable vibration levels, well below the alarm setpoints on all bearings, however the vibration increased gradually on generator outboard Bearing after three months of operation and reached a level of 10 mm/0-PK at base load of 115MW.
In this situation, OEM team has decided to stop the unit and carried out investigation to find the root cause and rectify the source of the high vibration. Vibration data was collected on all bearings from FSNL (full speed no load) to full load (most important data to define dynamic behavior of the unit specially during loading and thermal stabilization). Excitation system was switched on/off several times at FSNL to check the vibration response on generator bearings.
Furthermore, checked interface between alignment shims and machine foot, likewise, check tightening for any eventual looseness on Generator outboard bearing (including pedestal) and visual inspection of exciter,  etc. but still having high vibration.
In September 2019, OEM Invited Bently Nevada to look into the issue, started the unit and collected vibration/process data. This presentation will discuss the root cause analysis process using different types of data resulting in successfully starting the machine after eliminating the multiple issues found from the RCA (supported by real pictures of the findings).

Bio - Abdelhady Mohamed

Senior Machinery Diagnostics Technical Team Leader within Baker Hughes, Bently Nevada’s MDS team. Certified CAT IV vibration expert with more than 15 years of experience including diagnostics and correction of rotating machinery problems of different types/sizes and applications in different industries, using online and offline diagnostics systems. In addition, to vast experience as the regional training instructor for Bently Nevada in Middle East, Africa, Turkey and Pakistan; teaching our Machinery Diagnostics courses, Systems and Instrumentations courses, in addition to Mobius CAT I, II, III& IV to our internal field engineers and external customers.

Bio - Sherief Mekawey

The Technical Leader of BH-Bently Nevada Machinery Diagnostics Services for Middle East, North Africa and Turkey (MENAT) Region He received Bachelor of Science in Electrical Engineering from Mansura University-Egypt in 1978. Working for Baker Hughes , Bently Nevada for 27 years and has over 35 years of experience in vibration field, including rotating equipment balancing, condition monitoring, vibration analysis, diagnostics and root cause analysis. Published several case studies in Orbit magazine and Turbomachinery symposiums.