B. K. Gandhi

Effect of transients on Francis turbine runner life: a review

The present electricity market and the injection of power generated using intermittent energy sources have brought instability in the operation of the power grid. This has resulted in frequent load variations, emergency shut-down and restart, total load rejections, and off-design operation of grid connected hydraulic turbines. The present paper reviews the available literature summarizing the effects of transients on Francis turbine investigated experimentally, numerically, and analytically. Transients create both steady and unsteady pressure loading on the runner blade, resulting in cyclic stresses and fatigue development in the runner. These effects shorten the runner life, increase cost of plant operation, and loss of power generation. The reviewed literature has shown that one start–stop cycle can shorten predefined refurbishment time up to 15 hours. Turbine start–stop cannot be avoided, but runner life may be improved by minimizing the unfavourable pressure loading on the blades during transients through strategic movement of guide vanes.

Experimental and Numerical Studies for a High Head Francis Turbine at Several Operating Points

Experimental and numerical studies on a high head model Francis turbine were carried out over the entire range of turbine operation. A complete Hill diagram was constructed and pressure-time measurements were performed at several operating conditions over the entire range of power generation by installing pressure sensors in the rotating and stationary domains of the turbine. Unsteady numerical simulations were performed at five operating conditions using two turbulent models, shear stress transport (SST) k-ω and standard k-e and two advection schemes, high resolution and second order upwind. There was a very small difference (0.85%) between the experimental and numerical hydraulic efficiencies at the best efficiency point (BEP); the maximum difference (14%) between the experimental and numerical efficiencies was found at lower discharge turbine operation. Investigation of both the numerical and experimental pressure-time signals showed that the complex interaction between the rotor and stator caused an output torque oscillation over a particular power generation range. The pressure oscillations that developed due to guide vanes and runner blades interaction propagate up to the trailing edge of the blades. Fourier analysis of the signals revealed the presence of a vortex rope in the draft tube during turbine operation away from the BEP.

Study of the parametric dependence of erosion wear for the parallel flow of solid-liquid mixtures

Abstract The phenomenon of erosion wear due to the cutting action of solid particles in solid–liquid mixture flows has been studied in a slurry pot tester. Special fixtures and design modifications were incorporated in a slurry pot tester in order to ensure that the erosive wear on the wear piece is primarily due to parallel flow of the mixture. Experiments performed at various solid concentrations, particle sizes and velocities, show that the parallel flow wear increases with increase in solid concentration, particle size and velocity. The parametric dependence on velocity is comparatively much stronger as compared to that on either solid concentration or particle size.

Performance Characteristics of Centrifugal Slurry Pumps

The performance of two centrifugal slurry pumps has been reported for three solid materials having different particle size distribution (PSD) in terms of head, capacity, and power characteristics. The results have shown that the values of head and efficiency ratios are not only dependent on solid concentration but are also affected by PSI) of the solids and properties of the slurry. The addition of fine particles in the slurry of coarser material leads to reduction in the additional losses that occur in the pumps due to the presence of solids. It is also observed that with the increase in the pump size, the additional losses due to presence of solids reduce.

Performance Characteristics of Centrifugal Slurry Pump with Multi-Sized Particulate Bottom and Fly Ash Mixtures

The present study reports on the performance characteristics of the centrifugal slurry pump with multi-sized particulate slurry of bottom ash and fly ash mixtures. The performance characteristic of the pump was experimentally evaluated at rotational speed 1450 rpm for bottom ash slurries with and without the addition of fly ash in the concentration range of 10% to 50% (by weight). Addition of fly ash in the bottom ash was varied from 10% to 30% (by weight). The pump total head, overall efficiency, and pump input power at different flow rates were evaluated. The performance characteristics results show that the value of head and the efficiency of the pump depend on the solid concentration. It was also observed that the performance parameter of the pump strongly depends on slurry properties. The addition of fine particles fly ash in the coarser particles of bottom ash slurry, leads to reduce the additional head losses in the pump. The pump performance in terms of head and efficiency improved with addition of fly ash in bottom ash slurry.

Transient Pressure Measurements on a High Head Model Francis Turbine During Emergency Shutdown, Total Load Rejection, and Runaway

The penetration of intermittent wind and solar power to the grid network above manageable limits disrupts electrical power grids. Consequently, hydraulic turbines synchronized to the grid experience total load rejection and are forced to shut down immediately. The turbine runner accelerates to runaway speeds in a few seconds, inducing high-amplitude, unsteady pressure loading on the blades. This sometimes results in a failure of the turbine components. Moreover, the unsteady pressure loading significantly affects the operating life of the turbine runner. Transient measurements were carried out on a scale model of a Francis turbine prototype (specific speed = 0.27) during an emergency shutdown with a transition into total load rejection. A detailed analysis of variables such as the head, discharge, pressure at different locations including the runner blades, shaft torque, and the guide vane angular movements are performed. The maximum amplitudes of the unsteady pressure fluctuations in the turbine were observed under a runaway condition. The amplitudes were 2.1 and 2.6 times that of the pressure loading at the best efficiency point in the vaneless space and runner, respectively. Such high-amplitude, unsteady pressure pulsations can affect the operating life of the turbine.

Experimental investigations of transient pressure variations in a high head model Francis turbine during start-up and shutdown

Penetration of the power generated using wind and solar energy to electrical grid network causing several incidents of the grid tripping, power outage, and frequency drooping. This has increased restart (star-stop) cycles of the hydroelectric turbines significantly since grid connected hydroelectric turbines are widely used to manage critical conditions of the grid. Each cycle induces significant stresses due to unsteady pressure loading on the runner blades. The presented work investigates the pressure loading to a high head (HP = 377 DP = 1.78 m) Francis turbine during start-stop. The measurements were carried out on a scaled model turbine (HM = 12.5 DM = 0.349 m). Total four operating points were considered. At each operating point, three schemes of guide vanes opening and three schemes of guide vanes closing were investigated. The results show that total head variation is up to 9% during start-stop of the turbine. On the runner blade, the maximum pressure amplitudes are about 14 kPa and 16 kPa from the instantaneous mean value of 121 kPa during rapid start-up and shutdown, respectively, which are about 1.5 times larger than that of the slow start-up and shutdown. Moreover, the maximum pressure fluctuations are given at the blade trailing edge.

Experimental Investigation of a High Head Francis Turbine During Spin-No-Load Operation

Water passes freely through a hydraulic turbine in the absence of power requirements or during maintenance of the transmission lines, spillways, or dam. Moreover, the turbine operates under no-load ...

Design and development of variable area orifice meter

The variable area orifice meter indicates the flow rate as a linear displacement of a symmetrical body placed concentrically downstream of an orifice inside a constant area duct. Three shapes of symmetrical body namely, a frustum of cone, frustum of cone with hemispherical base, and frustum of cone with hemispherical base and parabolic apex are used downstream of an orifice to develop a variable area orifice meter. Experiments have been performed at different positions of the symmetrical bodies to evaluate the performance of the variable area orifice meter. The frustum of cone having hemispherical base and parabolic apex gives nearly linear variation of the flow rate with its position for a constant pressure differential.

Vortex Rope Formation in a High Head Model Francis Turbine

Francis turbine working at off-design operating condition experiences high swirling flow at the runner outlet. In the present study, a high head model Francis turbine was experimentally investigate ...