Renewable Energy Technology - MJ2411 Lecture Series on Hydropower Large-scale Hydropower Series 2.2 Babak Rezapoor [email protected] Photo: Courtesy of Kvaerner 1 Water Turbines Impulse Turbines: Pelton Cross flow A pelton wheel has one or more free jets A cross-flow turbine is drum-shaped and discharging water into an aerated space uses an elongated, rectangular-section and impinging on the buckets of a runner. nozzle directed against curved vanes on a cylindrically shaped runner. Source: hydroroues.fr Walchensee Power Station P=124 MW, H=200 m Source: Wikipedia 2 Water Turbines Reaction Turbines: Francis turbine Kaplan turbine Propeller turbine Deriaz turbine Bulb turbine Pump turbine (reversible reaction-type turbines ) 3 Water Turbines Francis turbine Francis turbine is the most widely used type of turbine for large-scale hydropower Source: Fluid Mechanics, John F. Douglas, Janusz Maria Gasiorek 4 Water Turbines Francis turbine The water is accelerated in the guide vane passages and given a definite tangential velocity component as it Source: Courtesy of Alstom Power enters to the runner. 5 Water Turbines Francis turbine θ: Guide vane angle Absolute velocity v1 has two components: radial direction (velocity of flow), vf1 tangential direction, vw1 Energy output is maximum when there is no tangential flow at exit. This means a radial flow at entrance to the draft tube or in other word, no whirl component at outlet. FOR: Frame Of Reference Absolute FOR (r) Relative FOR 6, AREST Course Water Turbines Francis turbine Source: Boving KMW Turbine 7 Water Turbines Francis turbine Source: Boving KMW Turbine 61,5 MW guide apparatus, Indonesia Source: Boving KMW Turbine 469 MW runner, Sweden 8 Water Turbines Francis turbine Source: Boving KMW Turbine 9 Water Turbines Kaplan turbine Axial flow turbines with variable pitch blades are known as Kaplan turbines. With rotating blades, very wide range of high efficiency may be achieved. The efficiencies of Kaplan turbines are between 90 and 93 percent. The hub contains a mechanism, called Combinator, which enables the blade tilt to be changed automatically with respect to opening of the guide vane (variable-pitch blades), thus altering the stagger angle to meet the fluid tangentially. Source: Courtesy of Karlstads Mekaniska Werkstad 10 Water Turbines Kaplan turbine Source: Boving KMW Turbine 11 Water Turbines Kaplan turbine Source: Courtesy of Boving KMW Turbine 12 Water Turbines Kaplan turbine Source: Boving KMW Turbine 13 Water Turbines Kaplan turbine The angle between the chord line and the turbine axial direction is the stagger angle. It is also known as the setting angle or rotor angel. SourceThe Design of High-Efficiency Turbomachinery, J.D. Gordon Wilson 14 Water Turbines Kaplan turbine The ability to change both runner and guide vane angles simultaneously enables to achieve maximum efficiency under varying flow conditions. Effects of rotor and guide vane angle adjustments on turbine efficiency Source: Incompressible Flow Turbomachines, G.F. Round, 2004 15 Water Turbines Propeller turbine The propeller turbine is a fixed-blade type turbine developed by Victor Kaplan and was first produced in early 1900s. The propeller is the axial-flow turbine. Propeller turbines are suitable for very large volume flows and low heads only few meters (1.5 to 15 meter). The turbine with fixed blades has a bit higher peak efficiency (0.2 to 0.5%) than a Kaplan turbine. But fixed blades result in a rapid fall of efficiency under part-load conditions. Source: NPTEL, http://nptel.ac.in 16 Water Turbines Deriaz turbine The Deriaz turbine is a mixed-flow radial turbine with adjustable runner blades. It is a hybrid machine having the characteristics of a Francis and a Kaplan turbine. Deriaz design is similar to a Kaplan turbine but with inclined blades to make it more suitable for higher heads. It can be used for reversible pump- Source: Mhylab, mhylab.com turbine 17 Water Turbines Typical efficiency curves for different types of hydropower turbines Source: Vinogg and Elstad, 2003 18 Water Turbines Bulb turbine The bulb turbine was developed in the mid 1900s and used for the lowest heads. It has a propeller type turbine runner and components enclosed in a bulb. The entire generator is mounted inside the water passageway as an integral unit with the turbine. Bulb turbines can be used for low heads and large heads discharge variations and therefore, these turbines replaced the Kaplan turbines for heads normally below 25m. Source: visualdictionaryonline.com 19 Water Turbines Pump turbine (reversible reaction-type turbines ) A pump turbine is both a pump and turbine in one device. The runner is designed to also work in reverse mode as a turbine. In pumped-storage plants, Pump turbines transfer water to a high storage reservoir during off-peak hours. The stored water can then be used for hydroelectric power generation to cover temporary peaks in demand. Source: Courtesy of Alstom Power 20 Water Turbines Pump turbine (reversible reaction-type turbines ) Source: Boving KMW Turbine 21 Water Turbines Pump turbine (reversible reaction-type turbines ) Source:Turbiner og turbinregulering, Elfrlaget 22 Turbine Selection In general, impulse turbines are used Turbinen type Head range (m) for high head sites, and reaction Propeller 3 – 75 turbines are used for low head sites Kaplan 20 – 50 Francis 30 – 600 Pelton 50 – 1500 Bulb 0,5 – 30 23 Turbine Selection Turbine Selection Chart By turbine selection chart, a turbine can be selected based on the head and the flow rate (flow rate is specified on the X axis, while the net head is set on Y axis) Source: Courtesy of Sulzer Hydro Ltd. 24 Turbine Selection Specific Speed The comparison of turbines with different design is achieved by the use of their specific speed, sometimes referred as the type number. The specific speed of a turbine characterizes the turbine's shape in a way that it is not related to its size but to its geometrical design. Dimensionless groups of variables Dimensional analysis is a tool to understand the properties of physical quantities independent of the units used to measure them. 25 Turbine Selection Dimensionless groups of variables Head and power coefficients, Ψ and P, are both functions of the flow coefficient Φ The functional relationship between Ψ , P and 훷 are determinable by experiment (Nowadays CFD as well) and constitutes a set of performance characteristics that represent the whole family of geometrically similar turbines. 26 Water Turbines Specific Speed Specific speed for turbines can be expressed by eliminating turbine size (D) from the ratio of power and head coefficients. (dimensionless) Since specific speed is obtained from dimensionless coefficients, it is also dimensionless provided a consistent system of units, such as SI unit is used. It is common practice to omit g and ρ from the equations and write the specific speed as ns in non-dimensional form as: (dimensional) It is then essential to state the units used for all the relevant quantities! ns in the above classification is based on rotational speed (N) in rpm, power (P) in kw and head (H) in meter. 27 Water Turbines Specific Speed The specific speed of a turbine can also be defined as the speed of an ideal, geometrically similar turbine, which yields one unit of power for one unit of head. The specific speed of a turbine is given by the manufacturer (along with other ratings) and always refers to the point of maximum efficiency. With the aid of specific number the various types of turbines may be classified and compared together as shown in the next picture. 28 Water Turbines Specific Speed Impulse turbines 0 < Ns < 45, high-head, low-flow rate Radial-flow turbines/Francis-type 75 < Ns < 380, medium-head, medium-high flow rate Axial-flow, propeller/Kaplan-type 380 < Ns, low-head, low-medium flow rate In general low specific speed machines correspond to low volume flow rates and high heads, whereas high specific speed machines correspond to high volume flow rates and low heads. Source: Wikipedia 29 Water Turbines Turbine Selection Chart Based on Specific Speed Source: ? 30.