The dynamic behavior at part load has been a major problem for low head and medium head Francis turbines. Vortex rope (draft tube swirl), caused due to the flow instabilities in the draft tube under off-design part load operating conditions, create low frequency pressure pulsations at a frequency of 0.2 to 0.4 times the rotational frequency of the runner. High amplitude vibrations due to resonance can occur in case these pulsations coincide with the natural frequency of a hydraulic, mechanical, or structural component. This study presents the results of the vibration analysis done using the online vibration monitoring & diagnosis system installed on 2 x 100 MW Francis turbines in a hydroelectric power plant located in south east of Turkey which involve high overall vibrations exceeding the alarm limits at partial loads. Orbit and FFT spectrum plots are obtained from relative shaft vibration measurements performed using eddy-current displacement sensors wired to a real-time multichannel vibration analyzer. Measurement results at the turbine guide bearing revealed the vortex rope phenomenon between 40% and 65% loads.
Emre Orhon was born in İstanbul, Turkey, in 1978. He received the B.E. degree in mechanical engineering and the M.Sc. degree in machine dynamics, vibration & acoustics from İstanbul Technical University, in 1999 and 2009, respectively. From the same university he also received the M.A. degree in musical composition from Center for Advanced Studies in Music, in 2002. He holds Vibration Analyst Cat-II certificate. Since 2000, he has been with Pro-Plan Ltd., Istanbul, Turkey, where he is currently working as a senior engineer on condition monitoring & vibration analysis. He worked as a project manager in online vibration monitoring system installation projects in various power plants and conducted many lectures on machine vibration diagnostics in Turkey.