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Energies 2016, 9(8), 620; doi:10.3390/en9080620

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

1
School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
2
Waterpower Laboratory, Norwegian University of Science and Technology, Trondheim 7491, Norway
3
State Key Laboratory of Hydro-Power Equipment, Harbin Institute of Large Electrical Machinery, Harbin 150040, China
*
Author to whom correspondence should be addressed.
Academic Editor: Enrico Sciubba
Received: 15 April 2016 / Revised: 25 June 2016 / Accepted: 29 July 2016 / Published: 5 August 2016
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Abstract

The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum. View Full-Text
Keywords: pump turbine; hump characteristic; hysteresis characteristic; experimental investigation pump turbine; hump characteristic; hysteresis characteristic; experimental investigation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Li, D.; Wang, H.; Chen, J.; Nielsen, T.K.; Qin, D.; Wei, X. Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model. Energies 2016, 9, 620.

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