Abstract
At present, hydropower plants play an important role because of their flexibility in the generation of electricity. Today, the required operating range of turbine units is expected to extend to deep part load. At part load the draft tube vortex rope is generated and, in some cases, can produce large pressure pulsations limiting the operation of the turbine. The draft tube vortex rope has been much studied.In this paper, the effects of the part load behavior on the hydraulic system in existing power plants has been studied. Different hydropower units with Francis turbines has been selected for this purpose. All of them present strong vibrations in penstocks and other machine components at part load. Vibrations, pressure fluctuations and other parameters were measured in different positions of the turbine, the draft tube and the penstock. Signals were acquired during transients and for several operating loads. The signals in time and frequency domain and other signal treatments for these cases are shown.
Highlights
Years ago, the turbines used to operate around the best efficiency point and avoiding part load and overload operation
Because this vortex is generated at the exit of the runner where the pressure is at the minimum, the pressure inside the vortex rope can reach the vapor pressure, and cavitation appears which may induce pressure fluctuations that propagate in the whole hydraulic system [5,6]
3.1.Hydropower 1 Vibrations in penstock between 6 and 8 maximum power (MW) related with vortex rope frequency were detected
Summary
The turbines used to operate around the best efficiency point and avoiding part load and overload operation. When the turbine is operating at off-design conditions, the flow leaving the runner has a rotating component and forms a vortex Because this vortex is generated at the exit of the runner where the pressure is at the minimum, the pressure inside the vortex rope can reach the vapor pressure, and cavitation appears which may induce pressure fluctuations that propagate in the whole hydraulic system [5,6]. The interaction between this excitation source and the system in case of resonance may lead to high-pressure fluctuation, power swing and large level of vibrations [7,8,9,10]. A case where the resonance produced large machine vibrations is discussed
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