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Resonance problems in vertical hydropower unit after turbine upgrade
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
2008 (English)In: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Conference paper (Refereed)
Abstract [en]

In 2005 a vertical 42 MW hydropower unit was upgraded in Sweden. The upgrade included the fitting of a new turbine guide bearing, a modified runner, a modified turbine regulator and a new brushless exciter. One of the requirements was that the dynamic behaviour of the machine should not be affected. In spite of the requirements, resonance problems became apparent after the hydropower unit was re-commissioned. Measurements from the re-ommissioning showed poor alignment of the shaft system and shape deviations in the generator. The exchange of the turbine guide bearing from a sleeve bearing to a block bearing also caused changes in the machines dynamic behaviour. Measurements on the unit were conducted at normal operation and resonance. These show that at normal operation, the machine has dominant frequencies at the nominal speed and at twice the nominal speed. When the machine goes into resonance, the dominant frequencies increase to approx. 2.4 times the nominal speed.The machine will undergo a major overhaul in ten years. The objective is to find a solution of the resonance problem that is both inexpensive and possible to implement. The conclusion was drawn that the low damped eigenmode at 2.4 times the nominal speed had been excited and caused the machine to go into resonance. The unit's dynamic sensitivity to different bearing settings was investigated numerically and with tests on site, i.e. bearing clearances were varied. The calculated result was verified against measured resonance frequencies. Agreement between the estimated and measured result was good. Other possible measures to rectify the resonance problems were also analyzed numerically. The effect of making the surrounding structures more rigid, the installation of additional guide bearings, making the shaft system more rigid, etc. were examined. A temporary solution, used for the last six months, is to operate the machine with larger bearing clearances on all bearings. Increased bearing clearance of the turbine guide bearing cause increased damping of the natural frequency at 2.4 times the nominal speed. No problems related to resonance have occurred at the hydropower unit during the last six months.

Place, publisher, year, edition, pages
Foz do Iguassu, 2008.
Research subject
Solid Mechanics
URN: urn:nbn:se:ltu:diva-28206Local ID: 1ecc0220-b00e-11dd-b677-000ea68e967bISBN: 978-85-60858-13-1 (PDF)OAI: diva2:1001401
IAHR Symposium on Hydraulic Machinery and Systems : 27/10/2008 - 31/10/2008
Godkänd; 2008; Bibliografisk uppgift: CD-ROM; 20081111 (ysko)Available from: 2016-09-30 Created: 2016-09-30Bibliographically approved

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Nässelqvist, MattiasGustavsson, RolfAidanpää, Jan-Olov
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