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.
Highlights
Due to dramatic increase in renewable energy source use, pumped storage power plants to balance the fluctuations of the electric grid have seen rapid development
Energy coefficients analysis reveals the hump characteristic and associated hysteresis phenomenon is a result of the Euler momentum and hydraulic losses
In the first hump region far away from BEP the hysteresis characteristic mainly results from the difference of the hydraulic losses, while the second one might arise from the combined effect of Euler momentum and hydraulic losses
Summary
Due to dramatic increase in renewable energy source use, pumped storage power plants to balance the fluctuations of the electric grid have seen rapid development. One occurs in the head-discharge curve under the high head and low discharge operating conditions in pump mode, which is well known as the hump characteristic. 1515mm, due to the vibration of the water water pressure caused by the hump instability instability characteristic, the operating point jumps to point D This process will delay the start‐up start-up of the pump‐turbine pump-turbine in in pump pump mode. In 2012, Ran et al [11] confirmed this phenomenon exists in a low specific speed pump-turbine The same year, they [12] conducted simulations to predict this phenomenon. For the pump-turbine investigated in this research, the hump region under 19 mm GVO investigate why this phenomenon occurs. Detailed analysis of time and frequency characteristics was performed to analyze the type of unsteady sources
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