Experimental study of a Francis turbine under variable-speed and discharge conditions. (April 2018)

• Record Type: Journal Article
• Authors: Trivedi, Chirag; Agnalt, Einar; Dahlhaug, Ole Gunnar
• Is Part Of: Renewable energy. Volume 119(2018)
• Page Start: 447
• Page End: 458
• Publication Date: 2018-04
• Subjects: Hydropower -- Turbine -- Francis-99 -- Pressure -- Load variation -- Variable-speed; Renewable energy sources -- Periodicals; Power resources -- Periodicals; Énergies renouvelables -- Périodiques; Ressources énergétiques -- Périodiques; 333.794
• DOI: 10.1016/j.renene.2017.12.040
• Languages: English
• ISSNs: 0960-1481

Abstract

Abstract: This work investigates the unsteady pressure fluctuations in a hydraulic turbine that are observed during steep ramping. Although hydraulic turbines are expected to operate seamlessly during steep ramping, the resulting pressure amplitudes are so significant that they take a toll on a machine's operating life. Objective of the present study is to investigate time-dependent pressure amplitudes in the vaneless space, runner and draft tube during power ramping-up and -down under variable-speed configuration. Novelty is to vary both discharge and rotational speed of a runner. The measurements are performed on a high-head model Francis turbine. The investigations revealed that amplitudes of characteristics frequencies, especially rotor-stator interaction, are small during steep ramping however, at the end of transient cycle, the amplitudes quickly increased 30-fold. During steep ramping, blade passing frequency was appeared in the runner, which is uncommon phenomenon in high-head Francis turbines. Strong reflection of pressure waves towards runner from vaneless space (guide vane walls) may be one of the causes for the appearance of blade passing frequency in the runner. Highlights: Unsteady pressure measurements were conducted in a high head Francis turbine. The maximum pressure amplitudes were obtained in the vaneless space and the runner. Inertia of the rotating masses can be important to stabilize the power grid. Torque is function of both, the rate of guide vane movement and the runner speed. At the end of transient cycle, the pressure amplitudes quickly increased 30-fold.