A Comparative Study of the Scale Effect on the S-Shaped Characteristics of a Pump-Turbine Unit

Abstract

S-shaped characteristics in turbine mode are prone to instabilities in associated transient processes. A single value of the speed factor corresponds to multiple values of the discharge factor, having the possibility of changing the operating point among the turbine, turbine brake, and reverse pump modes. Because of this characteristic, the S-shaped curves induce instability in transient processes. Understanding the hydraulic behavior of a turbine on the four-quadrant characteristic is important since it provides detailed performance information through the whole discharge range of the turbine. This study was numerically and experimentally investigated the scale effect on the S-shaped characteristics in the turbine transition region. The four-quadrant characteristic curves (full- and laboratory-scale) in the turbine mode were predicted by numerical simulations. To verify the predicted results, a laboratory-scale experiment was performed in the turbine, turbine brake, and reverse pump modes. Although the full-scale experiment was performed in the normal operating head range, the scale effect can be validated by comparing steady operating points between the two models. Based on the verified results, the internal flow and pressure pulsation characteristics were determined at the operating point in a specific transition region.

Three-Dimensional Numerical Simulation of Pumped Storage Unit No-Load operation with PID control before Grid-Connected

“…Suh J.W. et al [4]combined experimental analysis and CFD simulation to demonstrate the complex internal flow field causing the unstable S-characteristic of pump-turbines at different scales. J.F.…”

Influence Analysis of Runner Inlet Diameter of Hydraulic Turbine in Turbine Mode with Ultra-Low Specific Speed

“…To reduce energy waste, some enterprises use hydraulic turbine devices to recycle and utilize pressure energy [7][8][9]. The hydraulic turbine, as an energy recovery device, is used to achieve the goal of energy recovery by converting the pressure energy of the liquid into the rotating mechanical energy of the turbine runner [10][11][12][13][14]. At present, in the field of high residual pressure fluid recovery, reverse multi-stage pumps are often used as turbines for energy recovery [9,15,16].…”

Investigations on Pressure Fluctuations in the S-Shaped Region of a Pump–Turbine

“…Under different guide vane openings, the unit characteristic curve is S-shaped [9], and the same rotational speed corresponds to multiple discharges, which makes the operating point fluctuate between the turbine condition, the braking, and the reverse pump operating condition. This is the main reason why the power fluctuations occurred in the transient process, and why the grids cannot be connected [10]. When pump-turbines are in the reverse pump operating condition, the rotational speed of the runner continuously increases, which may eventually lead to the failure of the unit [11].…”