An Indirect Measurement Methodology to Identify Load Fluctuations on Axial Turbine Runner Blades

Abstract

Smooth integration of intermittent energy sources, such as solar and wind power, into the electrical grid induces new operating conditions of the hydraulic turbine by increasing the off-design operations, start/stops, and load variations. Therefore, hydraulic turbines are subject to unstable flow conditions and unfavorable load fluctuations. Predicting load fluctuations on the runner using indirect measurements can allow for optimized operations of the turbine units, increase turbine refurbishment time intervals, and avoid structural failures in extreme cases. This paper investigates an experimental methodology to assess and predict the flow condition and load fluctuations on a Kaplan turbine runner at several steady-state operations by performing measurements on the shaft in the rotating and stationary frame of references. This unit is instrumented with several transducers such as miniature pressure transducers, strain gages, and proximity probes. The results show that for any propeller curve of a Kaplan turbine, the guide vane opening corresponding to the minimum pressure and strain fluctuations on the runner blade can be obtained by axial, torsion, and bending measurements on the shaft. Torsion measurements on the shaft could support index-testing in Kaplan turbines particularly for updating the cam-curve during the unit operation. Furthermore, a signature of every phenomenon observed on the runner blade signals, e.g., runner frequency, rotating vortex rope components, and rotor-stator interaction, is found in the data obtained from the shaft.

An experimental investigation on the effects of cylindrical rods in a draft tube at part load operation in down-scale turbine

“…The Part-load operation of hydraulic turbines is becoming more common today to regulate the electricity production of intermittent energy sources [1]. The deceleration of swirl inside the draft tube of hydraulic turbines causes vortex breakdown in this operating condition, leading to a rotating vortex rope (RVR).…”

Inner Flow Analysis of Kaplan Turbine under Off-Cam Conditions

“…The results implied that the pressure on the runner blade had a low-frequency fluctuation after opening the guide vane from the fully closed position. Dehkhargani et al [18] also predicted the flow conditions and load fluctuations of a Kaplan turbine runner during several steady-state operations by measuring the shaft in the rotating and static reference systems, and found that the guide vane opening corresponding to the minimum pressure and strain fluctuations on the runner blade could be obtained through axial, torsional and bending measurements. Amiri et al [19] measured the unsteady pressure of the blades and fixed components during load change under off-cam working conditions, and the results revealed that the transition between high load and optimal efficiency point was smooth when the load changed, and there was no rotating vortex rope in the draft tube at the optimal efficiency point.…”