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COMPACT VERTICAL AXIAL TURBINE “SAXO” J. Gale, E. Höfler, A. Bergant Abstract: The paper enlightens some of the most important design, hydraulic, ecologic and economic advantages of the compact vertical axial turbine called the Saxo turbine. Special attention is drawn on description of the Saxo turbine, its main differences comparing to tubular and Kaplan turbines and some unique solutions applied during development. The comparison is supported with model tests, experiences on prototypes and theoretical and numerical investigations of the flow field in entire water passage. As Saxo turbine is rarely installed in practice, the paper aims to draw attention on this turbine design and to awaken professional discussion.

1 Introduction The name Saxo turbine is relatively unknown and is in use for tubular S-shape axial unit with vertical shaft. The name "Saxo" most probably originates from Canada where turbines of this type are relatively common. During the last decade, the Saxo turbines have became a very well recognized product with over 30 commissioned units in North American market by Litostroj Power only (see Table 1). As these turbines became popular in North American market due to its compact and ecologic design, simplified civil works, robustness and versatility, this is surprisingly not true for the European market where the Saxo turbines are still somehow overlooked. It looks like that European investors prefer and trust in more conventional turbine types i.e. Kaplan turbines and tubular turbines, instead of alternative Saxo turbines. The situation is surprising for us, as we know that Saxo turbines incorporate so many obvious advantages. To overcome this gap, this paper in sections that follows, gives some basics on Saxo type turbines.

2 General turbine description The Saxo turbine is a double regulated vertical axial turbine with construction, which is similar to the tubular turbines (bulb/pit) in section between inlet elbow and semiaxial distributor (conical guide vanes), while in the section between the runner and the turbine outflow, it is similar to conventional Kaplan turbines (see Fig. 1). At first look, the turbine is similar to the Kaplan turbine, however without spiral casing and with conical distributor instead of cylindrical. Due to their compact construction, the Saxo turbines are appropriate for the net heads ranging from several meters up to more than 30 m and discharges from 6 up to 85 m3/s as shown in Fig. 2, which shows typical operational ranges of tubular, Kaplan and Saxo turbines. The turbine output power range spans from 0,5 MW up to 20 MW. Therefore, the Saxo turbine is suitable for covering both operating ranges of Kaplan and tubular turbines. Fig. 2 16th Intern. Seminar on Hydropower Plants – TU Wien 2010

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shows also application range of the typical Saxo type turbine in more detail with an indication of the runner reference diameter D and the number of runner blades zrb.

Fig. 1. Typical cross section through the Saxo turbine (water passage system).

HPP Project Sainte-Anne, Canada Jean Guerin, Canada Pouvoir Riverin, Canada Sainte-Anne II, Canada McDougall, Canada Magpie, Canada Chute Allard, Canada Rapides-des-Coeurs, Canada Vernon, USA Hound Chute, Canada Lower Sturgeon, Canada Sandy Falls, Canada Chute Garneau, Canada Pont Arnaud, Canada

Hn [m] 24 24 28 24 16,5 20,5 17,83 22,69 10,97 9,87 12,45 9,05 10,26 15,68

Q 3 [m /s] 25 27,85 8 25 28 70 66 66 50,97 53,6 63,2 66,7 57,2 56,2

P n No.of Year of Owner -1 [MW] [min ] units supply 5,38 300 1 1996 Axor Group, Inc. 5,78 300 1 1997 Axor Group, Inc. 2,01 600 1 1999 Algonquin Power Fund, Inc. 5,38 300 1 2002 Société d’Énergie RSA 4,18 257,14 1 2002 RSP Hydro Inc. 12,95 225 3 2006 Hydromega GP, Inc. 10,57 200 6 2007 Hydro Quebec 13,62 225 6 2007 Hydro Quebec 5,08 144 4 2007 Transcanada Hydro NE, Inc. 4,71 163,64 2 2010 Ontario Power Generation 7,02 180 2 2010 Ontario Power Generation 5,27 180 1 2010 Ontario Power Generation 5,32 180 1 2010 Ville de Saguenay 8 200 1 2010 Ville de Saguenay

Table 1: Litostroj Power's list of commissioned units in North America with basic parameters.

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100

LEGEND D = Reference diameter zrb = No. of runner blades

KAPLAN D < 3,1 m

D = 3,1 m

D > 3,1 m

Head H [m]

zrb = 6

zrb = 5 10

zrb = 4

SAXO

TUBULAR (BULB) 1

1

10

100

1000

3

Discharge Q [m /s]

Fig. 2. Typical application range of Kaplan, tubular and Saxo turbines.

Our experiences show that investors of hydropower plants prefer to choose Kaplan turbines primarily because of their advantages during operation (reliability, maintenance, etc. ), and the possibilities to easily install generators with large rotating masses. On the other hand, the investors prefer tubular turbines because of simplified civil works and hydraulics. The Saxo turbine, due to its compact design, comprises even better operational and maintenance characteristics than Kaplan turbines and have better hydro-energetic design than tubular turbines. The Saxo units have fewer problems with handling and installation of the equipment due to smaller components, which allow the use of smaller powerhouse crane, consequently less bulky powerhouse structure and quicker installation of factory pre-assembled components (see Fig. 3). From the point of view of civil works, the Saxo turbines have a significant advantage over classical Kaplan turbines.

3 Turbine main components Figure 1 shows typical cross section through powerhouse and water passage with inlet conduit, the Saxo turbine, draft tube and an independently placed generator. Instead of a spiral casing like for Kaplan turbines, there is a compact elbow with deflector vanes, which predetermines the flow downstream to the stay and guide vanes and the runner. Water is lead to the inlet elbow through a horizontal or an inclined penstock. Inlet elbows are rather uncommon at standard turbine configurations; however, compact elbows with guide vanes have been profoundly experimentally investigated. With the correct configuration of the guide vanes, they produce a very small coefficient of local losses (Idelchik, 1986) and yield uniform flow field downstream the elbow. The shape of the penstock and elbow depends solely on the head water level relative to the runner axis. For example, see Fig. 4 for alternative solutions of the intake elbow. 16th Intern. Seminar on Hydropower Plants – TU Wien 2010

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Fig. 3. HPP Pouvoir Riverin: The factory-preassembled part that includes inlet elbow, stay vanes and guide vanes with regulating mechanism is ready for concreting.

Vertical shaft alignment for the torque transmission from the runner through the generator is fed throughout the elbow. The sealing of the shaft at the top of turbine elbow is quite simple while at the waterside the sealing is not necessary. System of lubricating-sealing water was carefully considered (filtering, keeping pressure i.e., discharge, etc.) because the inflow of the unclean water from the turbine passage must be prevented also when the turbine is not in operation. This problem has been successfully solved by using a closed system of lubricating-sealing water. Downstream the intake elbow are located stay vanes and conical guide vanes (distributor). The guide vanes are used to adjust discharge and to enable bestefficiency operation (on-cam) by directing water to the runner blades. The guide vanes acts as a swirl generator whose advantage is that it generates slightly forced vortex flow due to which the velocity field ahead of the runner blades becomes uniform. However, the guide vanes also partially obstruct the flow, especially at partial openings. The runner is assembled of four to six blades, which can be regulated. Below the runner, there is a relatively short conical diffuser (less civil works) with an elbow and the square-sectioned draft tube. The design of the Saxo type turbine is very rigid and the turbine shaft is vertical. That enables very good characteristics during operation. The generator, which serves as a flywheel as well, can be attached directly to the inlet elbow for smaller sized units, whereas for larger sized units the generator is normally attached to the concrete block surrounding the inlet elbow. The generator can be driven directly by the turbine shaft or with an aid of rotation speed multiplicator. Bottom bearing of the generator is at the same time the second guide bearing of the turbine while thrust (axial) bearing of the generator takes loading of turbine as well.

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Fig. 4. Alternative solutions for the intake elbow; left: high head turbine, middle: medium head turbine, and right: low head turbine.

One of very important advantages of the Saxo turbine design from the point of view of ecology is application of the water lubricated and cooled turbine guide bearing near the turbine runner. The material of the bearing liner is moulded polymer PTFE (commercially named Teflon) with additives or sintered metal based on bronze. The choice of such bearing is avoiding the use of oil or grease and it simplifies the maintenance in a great extent.

Fig. 5. Hydraulic power unit.

Besides the Hydraulic power unit (see HPU in Fig. 5), the auxiliary systems of the Saxo turbine are limited to the system for preparation of cooling, lubrication and sealing water and relatively simple drainage system. The system for water preparation can serve for cooling of the generator bearings if necessary. The generator requires lubricating system for oil bearing as well. The HPU is optimally minimized, which is achieved by increasing the hydraulic pressure up to 150 bars for the runner and distributor mechanisms and installation of hydraulic piston pump. Auxiliary systems are located near the turbine itself. The oil distributor is a device of hydraulic system that is necessary for setting the angle of runner blades. In the oil 16th Intern. Seminar on Hydropower Plants – TU Wien 2010

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distributor the oil under high pressure flows from the static tubes to the rotating tubes which are installed inside the hollow generator & turbine shaft. In Saxo turbine it is possible to install the oil distributor at the top of the generator (Fig. 1) at the free end of the shaft. This is the best choice from the point of view of inspection, control and maintaining.

4 Civil works and plant erection The civil works with Saxo turbine are considerably simplified comparing to the Kaplan turbines (see Fig. 6). The Saxo units are typically smaller than their Kaplan competitors for the same head/discharge conditions. The overall width of the powerhouse is about 5 to 30% smaller. Due to the fact that the Saxo units are typically smaller, more Saxo units have to be incorporated into the power station. The size of the Saxo units means up to 40% shallower dig-out than for classic Kaplan units and adequately shorter length of the powerhouse. Significant savings regarding the civil works are also accomplished due to absence of the spiral case at the Saxo turbine.

Fig. 6. Comparison of typical civil works dimensions for Saxo turbine (top) and for Kaplan turbine (bottom).

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The erection of the Saxo turbine is in comparison with the erection of classical Kaplan turbine simplified. The draft tube elbow can be made of concrete or steel. In latter case the draft tube elbow is placed by mobile crane. Afterwards the powerhouse is finished and powerhouse crane put into operation. The single part inlet elbow is placed by powerhouse crane, centered, anchored, and concreted. Figure 3 shows an example of smaller unit where factory preassembled stay ring and distributor assembly are assembled together with the inlet elbow. For larger units, the preassembled stay ring and distributor assembly are lifted to the inlet elbow from bottom floor. The erection of the turbine shaft is similar to that of the Kaplan type turbine, but the runner is attached to the shaft with the aid of a shear ring rather than classic flange. The runner is lifted to the shaft from bottom floor as well. Erection of the runner casing and the dismantling flange follows. At the same time, the generator and other equipment can be erected. The time needed for erection of two Saxo units is up to 50% shorter than the time needed to erect one Kaplan unit.

5 Theoretical and numerical investigations The theoretical (Höfler et. al, 1997) and numerical (Gale, 2009) investigations have been mainly focused on design and validation of the hydraulic shape of the guide vanes and the runner blades, and to the water passage region between them. Firstly, the streamline curvature method (SCM) has been applied for designing a new runner blade row, considering the real apparatus and a real shape of guide vanes (Fig. 7). The second step was evaluation and analysis of the flow field by using CFD tools for viscous flow analysis. The considered water flow passage in CFD analyses started several meters before the inlet elbow (stable boundary condition) and ended with extension after draft tube exit; whole turbine was considered at once. The analysis has been performed for different guide vane openings and different runner blades positions and as a result a 3D turbine efficiency charts were made. Cavitation occurrence was thoroughly investigated as well (see Figs. 8 and 9). The hydraulic design and the CFD results have been successfully validated by model tests (Djelić et al., 2006).

Fig. 7 Distribution of the surface pressure coefficient predicted by SCM method during optimization of runner blades of the Saxo turbine.

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Fig. 8.: CFD analysis results - streamlines through stay vanes, guide vanes and five bladed runner.

Fig. 9.: CFD analysis results - Left: relative pressure distribution on rotating and non-rotating walls around the runner. Right: cavitation appearance in four bladed runner of Saxo turbine

6 Conclusions The short analysis of design and hydraulic characteristics of the Saxo turbine undoubtedly shows some advantages of the turbines of this type compared to tubular and Kaplan turbines for a quite wide range of operating conditions. The vertical axial tubular unit in S-configuration has been especially developed as a low cost turbine. Its configuration ensures high performance and reliability, light erection, minimized civil works, easy maintenance and long lifetime. The Saxo type turbine has been optimized, standardized, and adopted for small and medium hydro power plants for net heads up to 30 meters, flows up to 85 m3/s, and rated output up to 20 MW. The Saxo turbine is suitable for new projects as well as for refurbishment of Kaplan unit power plants or low and even medium head Francis unit power plants. The core of

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the units is factory pre-assembled and tested. The cost-effective Saxo type units are a very good choice overall offering quickest return of investment. The use of water-lubricated guide bearing in combination with the ecologic water filled runner significantly reduces chances for contamination of the river water with oil or grease. Finally, the concept of the Saxo turbine is a fish friendly, which means that water passage itself protects fish population in front of pressure shock and the relatively small runner in diameter and low rotating speed further reduces posibility of fish strike in comparison to a Kaplan and tubular turbines. Acknowlegment The authors wish to thank ARRS (Slovenian Research Agency) for their generous support of research on hydraulic characteristics of Saxo turbines.

Notation The following symbols are used in this paper: Cp = pressure coefficient; D = runner diameter; Hn = net head; Q = discharge; P = turbine output; zrb = number of runner blades. References [1] [2]

[3]

[4]

I. E. Idelchik, Handbook of Hydraulic Resistance, 2nd Ed. Hemisphere Publishing Corporation (1986). E.Höfler, N. Jelić, T. Kolšek, Numerical flow analysis in Saxo turbine by using different methods, Proceedings of the International Conference on Hydropower into the Next Century, Portorož (1997) 173 - 184. J. Gale, Numerical analysis of flow in the model turbine TS4 having LitC runner blade (in Slovene); Project E5/KP-10-06, Internal Report No.: Por10261, Litostroj Power (2009). V. Djelić, V. Vujanič, I. Kern, M. Krušec, R.R. Stopar, Z. Peršin, Saxo turbine TS5-SX3 – Tests of model turbine for Rapides-des-Coeurs HP, Chute-Allard HP and Magpie HP (in Slovene); Report No.: 2858, Turboinstitut (2006).

Author(s) Dr. Janez Gale Litostroj Power d.o.o. Research and Development Litostrojska 50, SI-1000, Ljubljana, Slovenia Phone: +386 1 5824 302, FAX: +386 1 5824 174 16th Intern. Seminar on Hydropower Plants – TU Wien 2010

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Email: [email protected] Short CV: Janez Gale has finished Faculty for Civil Engineering (University of Ljubljana) in 2001. He took special lessons on engineering of hydraulic buildings. In 2002 he started with postgraduate study of Nuclear engineering at Faculty for Mathematics and Physics (University of Ljubljana). He defended his doctoral thesis in June 2008. The title of the thesis was Fluid-Structure Interaction for simulations of fast transients in piping systems. Since 2008 he is employed by Litostroj Power d.o.o.. Dr. Gale is an active researcher and project leader in number of national and international research projects.

Edvard Höfler Litostroj Power d.o.o. Research and Development, Retired Litostrojska 50, SI-1000, Ljubljana, Slovenia Phone: +386 1 5824 302, FAX: +386 1 5824 174 Email: [email protected] Short CV: Edvard Höfler acquired his BSc in Mechanical Engineering in 1971 at the Faculty of Mechanical Engineering of the University of Ljubljana, Slovenia. Starting 1970, he was employed at the Department of Aerodynamics of the Turboinsititute, Ljubljana. He worked as Research Engineer on developing and testing radial and axial fans as well as on experimental investigations of pumps and water turbines. From 1994 to retirement in 2008 he was employed in Litostroj, Ljubljana. As Project Engineer, he worked on design of water turbines and related equipment. Currently he is a post-graduate student at the University of Ljubljana, Slovenia. Dr. Anton Bergant Litostroj Power d.o.o. Research and Development Litostrojska 50, SI-1000, Ljubljana, Slovenia Phone: +386 1 5824 284, FAX: +386 1 5824 174 Email: [email protected] Short CV: Anton Bergant graduated in Mechanical Engineering from the University of Ljubljana, Slovenia in 1981. He has been employed with Litostroj Industries since 1980, except from October 1989 to January 1993 when he was employed as research officer with the University of Adelaide, Australia. He defended his Doctoral Thesis at the Faculty of Mechanical Engineering, University of Ljubljana in 1993. The topic of his thesis was Transient cavitating flow in piping systems. He is currently employed full-time with company Litostroj Power d.o.o., Ljubljana and part-time with Faculty of Mechanical Engineering, Ljubljana. He is head of Research and Development Department at Litostroj Power. In 2009 he was appointed as Associate Professor for Fluid Mechanics at the University of Ljubljana.

16th Intern. Seminar on Hydropower Plants – TU Wien 2010