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  • 1.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, Rolf K.
    Vattenfall, VRD.
    Lundström, Niklas L. P.
    Umeå university.
    Karlsson, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Calleecharan, Yogeshwarsing
    Nässelqvist, Mattias
    Karlberg, Magnus
    Lundin, Urban
    Uppsala University.
    Developments in rotor dynamical modeling of hydropower units2009In: Proceedings of the IUTAM Symposium on Emerging Trends in Rotor Dynamics: held in New Delhi, India, March 23 - March 26, 2009 / [ed] Kshitij Gupta, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2009Conference paper (Refereed)
  • 2.
    Nässelqvist, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation and characterization of rotordynamic properties for hydropower units2009Licentiate thesis, comprehensive summary (Other academic)
  • 3.
    Nässelqvist, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation and characterization of rotordynamic properties for vertical machines2012Doctoral thesis, comprehensive summary (Other academic)
  • 4.
    Nässelqvist, Mattias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, R.
    Vattenfall Power Consultant AB Mechanical and Process Engineering, Kyrkogatan 4, Gävle.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Bearing load measurement in a hydropower unit using strain gauges installed inside pivot pin2012In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 52, no 4, p. 361-369Article in journal (Refereed)
    Abstract [en]

    To determine a machine's mechanical condition it is of importance to know the radial bearing forces in the machine. Radial forces are caused by magnetic pull forces in the generator, clamped shafts, mass unbalance and flow properties around the turbine. Measuring the shaft displacement in the bearing or the bearing housing acceleration is not sufficient for status determination of a vertical hydropower unit. It is the magnitude and frequencies of the radial forces in combination with structure properties which give information as to whether a measured value is harmful or not. This paper presents an alternative method for measurement of radial bearing load in a hydropower unit. The method presented in this paper is based on strain measurements on pivot pins. The pivot pins are placed behind the bearing pad and the radial loads acting on the pad propagate through the pivot pin. New pivot pins were purchased and equipped with strain gauges. The new pivot pins were calibrated and a transfer function between applied load and measured output voltage was identified for each pivot pin. After calibration the pivot pins were installed in a vertical hydropower unit. Measurements were performed for several different operating modes of the hydropower unit. To verify that the measured load levels were of right order of magnitude, the radial bearing loads were calculated from numerical simulations of bearing properties and shaft eccentricity measurements. The two methods for determining bearing load showed almost the same results. This indicates that either method can be used to determine bearing load

  • 5. Nässelqvist, Mattias
    et al.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Case study of resonance phenomena in a vertial hydropower unit2008In: ISROMAC-12: the Twelfth International Symposium on Transport Phenomena and Dynamics of Rotating Machinery ; Honolulu, Hawaii, February 17 - 22, 2008, Pacific Center of Thermal-Fluids Engineering, Honolulu, 2008Conference paper (Refereed)
    Abstract [en]

    In 2005 a vertical 42 MW hydropower unit was upgraded in Sweden. One of the requirements was that the dynamic behaviour of the machine should not be affected. Resonance problems became apparent after the hydropower unit was re-commissioned and, in order to remedy this, new measurements and calculations were undertaken. While measuring, the machine went into resonance twice. During normal operation the shaft displacement showed high amplitudes at a frequency of twice the machine's nominal speed. At resonance the displacement amplitude increased and a dominant frequency occurred at ~2.4x nominal speed. To explain the reason for the resonances, new rotor dynamic calculations were performed using non-isotropic bearing and bracket properties. This model showed good correlation between calculated and measured values for the lowest eigenfrequencies. Probable explanations for the resonance are shape deviation in the generator, misalignment of the shaft and low damping of some critical eigenfrequencies close to twice the nominal speed.

  • 6. Nässelqvist, Mattias
    et al.
    Gustavsson, Rolf
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Resonance problems in vertical hydropower unit after turbine upgrade2008In: 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.

  • 7.
    Nässelqvist, Mattias
    et al.
    Hydro Power, ÅF, 80320 Gävle.
    Gustavsson, Rolf K.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Experimental and numerical simulation of unbalance response in vertical test rig with tilting-pad bearings2014In: International Journal of Rotating Machinery, ISSN 1023-621X, E-ISSN 1542-3034, Vol. 2014, article id 309767Article in journal (Refereed)
    Abstract [en]

    In vertically oriented machines with journal bearing, there are no predefined static radial loads, such as dead weight for horizontal rotor. Most of the commercial software is designed to calculate rotordynamic and bearing properties based on machines with a horizontally oriented rotor; that is, the bearing properties are calculated at a static eccentricity. For tilting-pad bearings, there are no existing analytical expressions for bearing parameters and the bearing parameters are dependent on eccentricity and load angle. The objective of this paper is to present a simplified method to perform numerical simulations on vertical rotors including bearing parameters. Instead of recalculating the bearing parameters in each time step polynomials are used to represent the bearing parameters for present eccentricities and load angles. Numerical results are compared with results from tests performed in a test rig. The test rig consists of two guide bearings and a midspan rotor. The guide bearings are 4-pad tilting-pad bearings. Shaft displacement and strains in the bearing bracket are measured to determine the test rig's properties. The comparison between measurements and simulated results shows small deviations in absolute displacement and load levels, which can be expected due to difficulties in calculating exact bearing parameters.

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