IE50310B1 - A water turbine - Google Patents

Abstract

In a Francis turbine (1), guide vanes (6) are fixed while guide vanes (16a-16f) are movable from a first end position in which the passages defined between the guide vanes are fully closed through a succession of positions in which the passages are opened to a successively greater extent to a second end position in which the passages are fully open. Both the fixed guide vanes (6) and the movable guide vanes (16a-f) have substantially the same cross-sectional profile and have substantially the same dimension in the general direction of water flow through the vanes.

Description

The invention relates to a water turbine, and in particular to a turbine of the Francis type and the guide vanes thereof.

Such turbines normally operate as inward flow turbines, the rotor axis being vertical, but they may also be employed in a cross-flow configuration, in which the axis of the rotor is disposed horizontally.

The power output from a turbine having a rotor with blades of fixed pitch, such as a Francis type turbine, is controllable by varying the volume flow of water passing through the turbine.

The flow of water is generally controlled as it enters the turbine, and in one known method of controlling the volume entering the rotor, the guide vanes of the turbine are fixed and a cylindrical gate is interposable between the guide vanes and the turbine rotor or runner. The volume of water entering the runner is controlled by moving the cylindrical gate so as to obstruct the flow passages between the guide vanes to a greater or lesser extent.

In a second method of controlling the volume of water entering the turbine runner, each of the guide vanes is mounted for pivoting movement about an axis parallel- tothe rotor shaft axis. In a construction which has been used for many years, all of the guide vanes are joined together by a common linkage system, so that each guide .vane will pivot about its axis of pivoting to the same extent, when the linkage system is moved.

Movement of the linkage system thus varies the areas of the flow passages between the vanes, thereby increasing-or reducing -3the amount of water flowing through them and entering the turbine runner.

In order to shut off the flow of water completely, the guide vanes may be pivotable to a position in which they fully obstruct the flow passages, or separate wicket gates may be provided radially outwardly of the pivotable guide vanes.

U.S. Patent Specification No. 2 085 233 describes a speed ring for hydraulic turbines in which movable wicket gates are arranged around the runner in a common annular series with stationary guide vanes, each wicket gate being pivotable to a position in which it closes off the passage between two guide vanes for flow of water therethrough. The construction relates to an axial flow propeller type turbine, and while it reduces the number of moving parts, it has the disadvantage that the dimension of the wicket gates In the general direction of water flow is considerably greater than that of the guide vanes, so that the inner ends of the wicket gates project radially inwardly of the inner ends of the guide vanes in the open position of the wicket gates. Also in their closed positions, the wicket gates are disposed substantially transverse to the general direction of water flow through the guide vanes, which would be disadvantageous for the efficiency of operation at low percentages of gate opening, and require a degree of effort to close.

British Patent Specification No. 446 359 describes a turbine construction in which a set of swivelling vanes is provided radially outwardly of a set of pivotable guide vanes, the set of swivelling vanes being intended to allow isolation of the turbine for inspection or repair. The swivelling vanes comprise an annular series of fixed and movable vanes, the pivotable moving vanes being In this instance substantially shorter in the general direction of water flow than the fixed vanes. Again the movable vanes lie substantially transverse to -45 0 310 the general direction of water flow through tha passageways between the vanes when in their closed positions. This construction also increases the number of moving parts and the complexity of the control mechanism and linkage.

The present invention is directed towards improvements in a Francis turbine in which the volume of water entering the turbine runner is controlled by means of movable guide vanes.

It is an object of the invention to provide a turbine of this type in which the construction will be simplified compared with known constructions and which will be suitable for manual control, if desired.

According to the invention, in a turbine of the Francis type comprising a plurality of guide vanes, some of the guide vanes are fixed while the remainder are movable, passages for flow of water to the turbine runner being defined between adjacent pairs of the guide vanes and the volume of water entering the turbine being controllable by movement of the movable guide vanes to vary the area of flow of the passages defined between the guide vanes, the movable guide vanes being movable from a first end position in which the passages defined between the guide vanes are fully closed through a succession of positions in which the passages are opened to a successively greater extent to a second end position in which the passages are fully open, and both the fixed and the movable guide vanes having substantially the same cross-sectional profile and having substantially the same dimension in the general direction of water flow through the vanes.

Preferably all of the guide vanes, both fixed and movable, are disposed about the turbine runner at substantially the same radial distance and are in substantially the same angular orientation with respect to the runner when the movable guide vanes are in their fully open end position. The guide vanes -5may be disposed in a single annular array and the fixed and movable gude vanes arranged alternately in the annular array so that each movable guide vane has a fixed guide vane on each side of it in the annular array.

In a preferred embodiment, each movable guide vane is mounted for pivoting movement about an axis parallel to the axis of the runner. Preferably each movable guide vane defines an acute angle with each of the adjacent fixed guide vanes when the movable guide vane is in its fully closed end position.

The guide vanes may suitably be fabricated from sheet metal shaped to present the desired contour of the vane surface. The movable guide vanes may additionally comprise a shaft welded to the sheet metal. Extensions of the shafts may be connected to a linkage operable to pivot the movable guide vanes about their axes. A mechanical governor may be connected to the linkage.

The turbine may comprise upper and lower plates to which the fixed guide vanes are welded to form an integral housing structure for the runner.

In a preferred embodiment wherein alternate guide vanes are fixed and movable, a very strong advantageously symmetrical structure is provided 1n which tie bolts between the upper and lower plates are not required. Additionally the turbine can, at least in part, be manufactured by steel fabrication methods. By halving the number of movable guide vanes, the amount of linkage required is also reduced by almost fifty per cent and the effort required to open and close the guide vanes is reduced by a similar proportion. The turbine according to the invention is thus very suitable for control by a mechanical governor. Since the movable guide vanes are always at an acute angle to the fixed guide vanes, the closing effort required to move them against the water pressure is reduced, while excessive turbulence in the flow is avoided. -6The movable guide vanes are designed to guide the water at the correct angle to the runner when in their fully open positions. As the guide vanes are closed, the angle of the water changes so that there is some loss of efficiency at part gate. However, the fixed vanes are always at the correct angle to the runner irrespective of the opening of the movable guide vanes.

The turbine according to the invention may be manufactured at reduced cost and is particularly suitable for use in locations where the flow rate is low and/or tha head small, i.e. for small-scale power generation.

Constructions of turbine according to the invention are hereinafter described by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a section through an embodiment of a turbine according to the invention on the line I-I of Figure 3, the guide vanes being in the fully open position; Figure 2 is similar to Figure 1 but is more or less diagrammatical, the movable guide vanes being shown in various different positions; Figure 3 is a vertical section through the turbine on the line ΠΙ-III of Figure 1 in respect of the portion below the crown plate, and on the line Illa-IIIa of Figure 4 in respect of that portion above the crown plate; Figure 4 is a plan view of the turbine on the line IV-IV of Figure 3; Figure 5 is a section through a turbine according to the invention in a concentric cased construction and incorporating the gate arrangement of Figures 1 and 2; Figure 6 is an end view of the turbine of Figure 5; Figure 7 is an end view of a turbine according to the invention in a spiral cased configuration and incorporating the gate -7arrangement of Figures 1 to 4.

As shown in Figures 1 to 4, the turbine 1 has a rotor 2, which is most suitably a casting, and is mounted on a vertical shaft 3. The rotor turns about its axis within a turbine housing {not shown) in which are arranged a top or crown plate 4 and a bottom plate 5. The plates 4 and 5 are held spaced apart by fixed or stationary guide vanes 6, located between the top and bottom plates and welded to them. The plates 4 and 5 and the fixed guide vanes thus form a strong and rigid integral structure. Because of the welded joints, it is not necessary to secure the plates to each other by means of tie bolts.

The bottom plate 5 is bolted by bolts 5a to a draught tube 7 which is in turn bolted by bolts 7a to rolled steel joists 8 set in concrete 9. The draught tube may Itself also be surrounded by concrete. For clarity the bolts 5a are not shown In Figures 1 and 2. A tailrace is located below the draught tube, but the housing and the arrangement by which water is brought to the turbine and fed into the guide vanes are not shown in any of Figures 1 to 4, again in the interests of clarity, and because they are of conventional design.

As is shown in Figure 3, the top or crown plate 4 is provided with a recess 4a adapted to accommodate the upper edge 2a of the turbine rotor or runner 2, so that water can enter the rotor without impinging against the edge 2a, and shock at entry can thus be avoided. For similar reasons, the upper edge 2b of the lower part 2c of the rotor 2 is widened out under the inner edge 5a of the bottom plate 5, so as to seal under this edge and prevent water from flowing through the turbine without passing through the rotor. In a particular construction of the turbine according to the invention, the rotor 2 is 30 cm (12 Inches) in diameter, and has a dimension in the axial direction of approximately 15 cm (6 inches).

S0310 -8The shaft 3 is supported near its lower end by a bearing 11, which may be a split bearing of plastics material (e.g. Polypenco - Trade Mark). The bearing is housed inside a sleeve 12 to which a capping plate 13 is secured by bolts 13a. The sleeve 12 is mounted on the upper side of the crown plate 4 and is concentric with the axis of the shaft 3.

Near its upper end the shaft 3 is supported by a bearing 14 suitable for combined axial and radial loading. The bearing housing may be secured to rolled steel joists 15 by bolts 15a.

In addition to the fixed or stationary guide vanes 6 welded to the top and bottom plates 4 and 5, movable guide vanes 16a - f are mounted between these plates. Each movable guide vane is mounted for pivoting movement about a shaft 17 passing through the vane. Each shaft 17 is rotatably mounted in the plates 4 and 5, for example in bushes. The vanes are manufactured by a fabrication method from steel plate. A section of plate of appropriate dimensions is bent to the appropriate profile and a shaft 17 is then welded inside each movable vane. The cross-section of the stationary vanes 6 and tha movable vanes 16a - f is identical, as will be clear from Figures 1 and 2, but the stationary vanes are of greater extent in the axial direction than the movable vanes 16a - f, as can be seen in Figure 3, so that the movable vanes, when mounted between the plates 4 and 5, can be pivoted about the shafts 17.

Flow passages are defined between each movable vane and the stationary vanes on either side of it. Thus as each movable vane is pivoted about its shaft 17, it closes off or opens up two flow passages. This can be seen in Figure 2, where each movable vane 16a - f is shown pivoted to a different extent, so that the passages on either side of vane 16a are fully open i.e. the vane 1s in the full gate or fully open position. The passages on either side of the movable vane 16f are fully -9closed off and the vane is in the shut down position. Vanes 16a - 16e, for example, are shown in increasingly closed off configurations. Vane 16b, for example, stands at approximately 752 gate, while vane 16c is at about 502 gate.

It will be seen from Figures 1 and 2 that both the fixed and movable guide vanes are of the same cross-section and have the same dimensions in the general direction of water flow through the vanes. In the fully open condition, all of the guide vanes, both fixed and movable, are disposed about the rotor at the same radial distance, and in the same angular orientation with respect to the rotor. Also the inner ends of the guide vanes are close to the outer edge of the rotor. Thus when the turbine is operated with the guide vanes in the fully open or full gate” configuration, there is minimum clearance between the vanes and the rotor and turbine efficiency is maximised.

This relative disposition of the guide vanes and rotor is of particular importance in the case of a Francis turbine to avoid losses, as far as is practicable, under full gate conditions.

It will also be seen from Figure 2 that when the movable guide vanes are in their closed positions, their orientation 1s still such that their inner ends remain closer to the rotor than do their outer ends. Thus they do not take up a negative inclination with respect to the periphery of the rotor and, in this way, losses due to turbulence as the movable vanes move towards their closed positions are minimised.

It will be appreciated that in practice the vanes would never appear as shown in Figure 2, which is for the purposes of illustration and explanation only. In use, each vane 16a - f would be at the same orientation or extent of pivoting about its shaft 17, i.e. each vane would be in the position shown for vane 16a or that shown for 16b, etc.

X. -10In order to cause the movable vanes to move in this uniform way, the vanes 16a - f are linked together by a mechanical linkage - as shown in Figures 3 and 4. It will be appreciated that this linkage may take many forms and that the arrangement shown is only one such arrangement.

Each shaft 17 extends upwardly through the top plate 4 and is non-rotatably secured to a crank 18. Each crank 18 is pivotably connected to one end of a connecting rod 19 and the other end of the rod 19 is pivotably connected to a lower circular plate portion 20 of a spool member 21. The spool member 21 is concentrically mounted about the sleeve 12 and is supported underneath the lower circular plate portion 20 by a ball bearing 22a. Thus the spool can rotate in either direction about the axis of the shaft 3 within a limited angular extent and can also thus cause the movable vanes 16a f to pivot about their shafts 17 by means of the linkage 18 and 19. As the spool rotates the connecting rods 19 are pulled or pushed and the cranks 18 are pivoted about the axis of the shafts 17. Since the cranks 18 are non-rotatably secured to the vanes 16a - f, the vanes are thus also pivoted. The limits of movement of the spool correspond to shut-down or full gate of the vanes.

At the upper end of the spool 20, two arms 22 extend from the spool, diametrically opposite to each other. The inner ends of these arms are fixedly connected to the spool and their outer ends are pivotably connected to ends of rods 23. The rods 23 extend from the arms 22 to a two-armed rocker lever 24, which is pivoted to the turbine casing at a central point of the lever, while its arms are pivoted to the ends of the rods 23 remote from the arms 22. The respective arms 22 and 24 are approximately parallel to each other and are each disposed substantially at right angles to the respective rod 23 linking them. A shaft 25 extends upwards from the rocker lever 24 and -Ill’s secured to the lever 24 so that rotation of the shaft will cause the lever to rock. The shaft 25 (shown in section in Figure 4) extends upwardly and through a seal in the turbine housing (not illustrated) to an operating mechanism or lever external of the turbine housing, which is not illustrated. The mechanism or lever is thus outside the water filled space.

When the shaft 25 is rotated in one direction, the lever 24 is rocked in a corresponding direction, the rods 23 and arms 22 act to rotate the spool about its axis, and the connecting rods IS connected to the spool and therewith also the cranks 18 connected to the rods 19 are moved so as to move the movable vanes towards full gate. When the lever 25 is rotated in the opposite direction, the vanes 16a - f are moved towards shut-down. The guide vanes are shown in their various different positions by way of illustration only in Figure 2.

The operation of the lever 24 may be purely manual or it may be carried out by means of a governor mechanism, which will present no difficulty to a person familiar with water turbines. When manual operation is employed, and the shaft 25 is rotated by movement of a lever, this lever may be provided with a screw movement to avoid difficulties due to surges during closing movement of the movable vanes. Means may also be provided to retain the manual lever locked in a selected position of adjustment.

Figures 5 and 6 show a turbine according to the invention in a concentric cased construction, water entering the case 51 through inlet 52 and leaving through draught tube 53, after flowing through turbine 54. Shaft 55 is supported at its end by a bearing arrangement 56. The guide vane linkage operating shaft 25 can be seen extending through a seal 57 in the turbine casing 51 to an operating lever 26. -12Details of the guide vane linkage on the turbine 54 are not shown, and also omitted are means for controlling the movement of the lever 26 and locking it to hold the movable guide vanes in a selected guide vane configuration.

Figure 7 shows a turbine according to the invention in a spiral cased configuration. The control arrangements for the movable guide vanes can be seen on the end of the turbine casing.

It will be appreciated that all of the embodiments described are by way of example only, and that the invention extends to other equivalent constructions falling within the scope of the appended claims. In particular, it will be clear that control and operation of the movable guide vanes may be achieved by any of a considerable number of differing means. The turbine according to the invention is of fabricated construction, apart from the cast runner, and is thus simple to manufacture in an economical manner.

Claims (10)

1. A turbine of the Francis type comprising a plurality of guide vanes some of which are fixed while the remainder are movable, passages for flow of water to the turbine runner being defined between adjacent pairs of the guide vanes and the volume of water entering the turbine being controllable by movement of the movable guide vanes to vary the area of flow of the passages defined between the guide vanes, the movable guide vanes being movable from a first end position in which the passages defined between the guide vanes are fully closed through a succession of positions in which the passages are opened to a successively greater extent to a second end position in which the passages are fully open and both the fixed and movable guide vanes having substantially the same cross-sectional profile and having substantially the same dimension in the general direction of water flow through the vanes.

2. A turbine according to claim 1, wherein all of the guide vanes, both fixed and movable, are disposed about the turbine runner at substantially the same radial distance and are in substantially the same angular orientation with respect to the runner when the movable guide vanes are in their fully open end positions.

3. A turbine according to claim 1 or 2, wherein the guide vanes are disposed about the axis of the runner in a single annular array, and the fixed and movable guide vanes are arranged alternately in the annular array, so that each movable guide vane has a fixed guide vane on each side of it in the annular array.

4. A turbine according to claim 3, wherein each movable guide vane is mounted for pivoting movement about an axis parallel to the axis of the runner. -145. A turbine according to claim 3 or 4, wherein each movable guide vane defines an acute angle with each of the adjacent fixed guide vanes when the movable guide vane is in its fully closed position.

5

6. A turbine according to any preceding claim, wherein the guide vanes are fabricated from sheet metal shaped to present the desired contour of the vane surface.

7. A turbine according to claim 6, wherein each of the movable guide vanes comprises a shaft welded to the sheet 10 metal.

8. A turbine according to claim 7, wherein each guide vane shaft comprises an extension connectable to a linkage operable to pivot the movable guide vanes about their pivotal axes.

9. A turbine according to any preceding claim comprising 15 plates to which the fixed guide vanes are welded to form an integral housing structure for the runner.

10. A turbine substantially as herein described with reference to Figures 1 to 4 or Figures 5 and 6 or Figure 7 of the accompanying drawings.