Experimental Modal Analysis (EMA) is an extremely useful Root Cause Analysis & Defect Elimination (RCA&DE) technique, which helps CBM practitioners in solving many Plant problems by identifying natural frequencies, damping coefficients, and mode shapes of the vibrating machine trains or mechanical structures.
When it is known that the excitation force coincides with one of the natural frequencies found in the modal analysis, the structure or machine foundation could be redesigned or modified to shift the natural frequency away from the excitation frequency. Structural elements can be added in order to increase the stiffness of the structure or mass can be increased or decreased. Other approach could include increasing the damping of the structure by changing the material or adding viscoelastic material to the surface of the structure.
During one of the site investigations, EMA was carried out on the GTG #2B Generator at one of the power plants in Oman, to assess the condition and behaviour of end winding vibrations which had a history of fractures of the bar insulation, banding cracking related failures. The operational condition and stresses on the end winding may loosen the ties & blocks and may cause the windings to vibrate. The natural frequencies of end winding should not be equal to the system natural frequency or operational frequency (95-110 Hz) of the generator, which may cause high amplitude due to resonance, increasing stresses on the machine.
This presentation highlights the EMA basics and applications, Turbo Generator design details, Generator End Windings modal test methodology, instrumentation used, test results pre and post repairs with discussion on the test results.
Praveen an Industry Thought Leader, is presently leading the Reliability Engineering & Asset Management (REAM) business at Special Oilfield Services Co. LLC, Oman. He is an experienced professional with 22+ years of rich experience in Condition Monitoring & Reliability Industry with Vibration Analyst Cat III, ARP-A Certifications from Mobius Institute®, Australia, CMRP certification from SMRP, US Ultrasound Level I from UE Systems Inc. and life member of Council of Vibration Specialists (CVS), executive member of ISA and a trained CRE. He helps Industry and Industrial Plants adopt an effective and efficient RCM program and optimum CBM strategies.
He has spoken in National and International Conferences in India, Asia and Middle East, has published more than 20 technical papers and is a recognized Mobius Training Instructor for Vibration Analysis and Asset Reliability Trainings.