Analysis of the Power Fluctuations Caused by the Unstable Flow in the Trifurcation of Multi-Turbine Diversion Systems with Common Penstock in Hydropower Units

Abstract

Stable operation is a challenge for hydropower stations with multi-turbine hydraulic coupled division systems with a common penstock. In this paper, the serious power fluctuations in a power station with such a division system are analyzed. The fluctuations occur in many conditions without any movement of the regulating system. The mathematical analysis illustrates that pressure fluctuation is responsible for power fluctuations. The computational fluid dynamics (CFD) method provided by ANSYS is used to study the flow pattern in penstocks. The vortex caused by the irrational structure of trifurcation is the reason for pressure fluctuations. Several methods are proposed to optimize the flow stability and three cases are simulated based on these measures. The calculation results of three cases prove the effectiveness of these measures. The measure of setting the new guide plate is finally conducted, and the output power fluctuations vanish. The flow calculation plays a role in the analysis and optimization of the hydraulic system of the hydropower unit. Some rules are summarized from the cases and are helpful in the design of trifurcation in a division system with a common penstock.

CFD simulations of hydraulic short-circuits in junctions, application to the Grand’Maison power plant

“…This junction, if not well designed, can lead to discharge unbalanced between the three penstocks. In [14], the authors considered a trifurcation with a spherical shape and they reported an amplitude of the discharge variation of approximately 30 m 3 s −1 in two of the three penstocks, leading to power fluctuations larger than 10 MW. Thanks to CFD simulations, the authors showed that the diameter of spherical trifurcation is responsible of the flow instabilities.…”

Design and dynamic control of integrated synergetic controller for single penstock two-machine hydropower system

“…But the model is still not refined enough. [23] focuses on controlling the power of multiple turbines with common pressure pipes by optimizing the flow stability.…”

Stability Analysis of Different Regulation Modes of Hydropower Units

“…Many causes can result in frequency oscillations, Energies 2021, 14,1933 2 of 19 such as the induction generator effect, turbine damping, the inertia ratio, proportionalintegral-derivative (PID) controller parameters, and the feed-forward controllers [11][12][13][14][15]. Hydraulic fluctuation is also a common cause of unstable regulation and operation in transient processes [16][17][18]. The proportion of hydropower in energy sources also affects the stability of a system [19].…”