Patent Description:
In the field of converting hydraulic energy into electrical energy, the use of axial flow turbines is known. Such an axial flow turbine includes a runner which is movable about an axis, and which is rigidly connected to a drive shaft. The runner comprises a hub and a multitude of blades connected to the hub. In the case of a so-called propeller type turbine the blades are fixedly connected to the hub. In the case of a so-called Kaplan type turbine the blades are pivot-mounted to the hub. A facility for converting hydraulic energy into electrical energy using an axial flow turbine includes a so-called inner head cover which is located adjacent to the hub and surrounds the drive shaft. Usually within the inner head cover a shaft seal and at least one bearing are located.

In the field of converting hydraulic energy into electrical energy, it is known that discharging gas into the water flow path in the region of the runner offers many benefits e.g., avoidance of cavitation, reduction of vibrations, improvement of efficiency at low water flow and increase of dissolved oxygen in the water passing the turbine. Of course, to achieve the later mentioned benefit the gas being discharged must contain oxygen. In prior art several ways for discharging gas into the water passing the runner of a facility for converting hydraulic energy into electrical energy have been proposed. For example, <CIT> discloses feeding air via hollow coupling bolts (see Fig. <NUM>) or a hollow drive shaft into the hub of an axial flow turbine (see Fig. <NUM>). <CIT> discloses means for discharging air into the water passing the runner comprising channels arranged in the inner head cover structure, which open into an annular chamber, which is in communication with the inlet-side flow space of the runner through bores. The annular chamber also communicates through holes with an annular space in the runner hub, from which channels open out into the water flow space at various points on the runner hub. <CIT> shows a further example of a facility for converting hydraulic energy into electrical energy.

Equipping an existing facility for converting hydraulic energy into electrical energy with the means for discharging gas into the water passing the runner known from prior art while refurbishing the facility involves the exchange or modification of many parts of the facility.

It is the intention of the invention to disclose an alternative method of equipping an existing facility for converting hydraulic energy into electrical energy with means for discharging gas into the water passing the runner while refurbishing the facility. Thanks to the invention only a very small amount of effort has to be spent for exchange or modification of parts during refurbishing the facility.

The task is solved according to the invention by an embodiment according to the independent claims. Further advantageous embodiments of the present invention can be found in the dependent claims.

In the following, the invention is explained with reference to figures. The figures show in detail:.

<FIG> displays a facility for converting hydraulic energy into electrical energy in a very schematic way. The facility comprises an upper and a lower reservoir of water, a turbine and a generator connected to the turbine. Of course, the reservoirs can be part of a body of flowing water as a river. In this case the river upstream of the turbine is the upper reservoir and the river downstream of the turbine is the lower reservoir. The turbine comprises a runner of the axial flow type moveable around an axis. Water flowing from the upper reservoir to the lower reservoir passes the turbine and causes the runner to rotate around its axis and the connected generator to generate electricity. The facility comprises a water passage and the water flows through the water passage and the runner is located within the water passage.

<FIG> displays a part of a turbine with a runner of the axial flow type before refurbishment. The runner comprises a hub, which is designated by <NUM>, and several blades connected to the hub <NUM>. In <FIG> is only one of the blades shown and designated by <NUM>. In the case of a so-called propeller type turbine the blades are fixedly connected to the hub. In the case of a so-called Kaplan type turbine the blades are pivot-mounted to the hub. The runner is connected to a drive shaft, which is designated by <NUM>. The turbine comprises an inner head cover which is located adjacent to the hub <NUM> and surrounds the drive shaft <NUM>. The inner head cover is designated by <NUM>.

Hub <NUM>, blades <NUM> and drive shaft <NUM> belong to the rotatable part of the axial flow turbine whereas the inner head cover <NUM> belongs to the non-rotatable part of the axial flow turbine.

The axial flow type runner shown in <FIG> is a propeller type runner and the blades <NUM> are fixedly connected to the hub <NUM>. Other axial flow type runners (Kaplan type runners) have blades <NUM>, which are pivot-mounted to the hub <NUM>. In this case the hub <NUM> is bulkier than a comparable propeller type hub <NUM> since it has to contain the means for pivoting the blades <NUM>. Usually, the remaining inner space of a hub <NUM> of a Kaplan type runner is filled with oil or water.

<FIG> displays the part of a turbine shown in <FIG> after refurbishment according to a first embodiment of the present invention. The refurbished turbine comprises a first cover plate, which is designated by <NUM> and which is connected to the inner head cover <NUM>, and a second cover plate, which is designated by <NUM> and which is connected to the hub <NUM>. Both cover plates <NUM> and <NUM> are surrounding the axis of rotation of the runner, but for the sake of convenience <FIG> shows only the right part of the cover plates <NUM> and <NUM> respectively. Cover plates <NUM> and <NUM> meet at a seal, which is designated by <NUM>. Since the first cover plate <NUM> is a non-rotatable part of the turbine and cover plate <NUM> is a rotatable part of the turbine the seal <NUM> is a so-called rotatable seal.

In the arrangement shown in <FIG> a part of the outer surface of the head cover <NUM>, a part of the outer surface of the hub <NUM>, the inner surface of the first cover plate <NUM> and the inner surface of the second cover plate <NUM> are confining an annular shaped space, which is located outside of the original turbine and within the original water passage.

The refurbished turbine comprises a first opening located at the inner head cover <NUM> leading from the inside of the inner head cover <NUM> to the annular shaped space. The first opening is designated by <NUM>. The refurbished turbine can comprise more than one first opening <NUM>. The refurbished turbine comprises a second opening located at the hub <NUM> leading from the annular shaped space into the inside of the hub <NUM>. The second opening is designated by <NUM>. The second opening <NUM> is located near the top of the hub <NUM>. The refurbished turbine can comprise more than one second opening <NUM>. The refurbished turbine comprises a third opening, which is located at the runner and is designated by <NUM>. The third opening can be located at various parts of the runner. In any case the third opening <NUM> is configured to allow gas flowing from inside of the runner into the water passage surrounding the runner. In the embodiment according to <FIG> the third opening <NUM> is located at the bottom of the hub. The third opening <NUM> could be located at any suited part of the hub, e.g., in the region between the blades <NUM>. The refurbished turbine can comprise more than one third opening <NUM>.

The arrangement according to <FIG> enables the refurbished turbine to discharge gas into the water passage. <FIG> shows the flow path of the discharged gas whereas the flow path is indicated by the arrows. The gas enters the first opening <NUM> from inside the inner head cover <NUM>. Through the first opening <NUM> it enters the annular shaped space and flows towards the second opening <NUM> through which it enters the hub <NUM>. Then it passes the hub <NUM> and is discharged into the water passage via the third opening <NUM>. The rotatable seal <NUM> mitigates water infiltration from the surrounding water passage.

It is clear, that the gas has to be delivered to the inside of the inner head cover <NUM> before it can flow in the described manner. How this is achieved strongly depends on the detailed structure of the existing facility. In most cases the gas can be delivered into the inner head cover <NUM> by providing additional pipes and by using existing compartments inside the facility. The gas can be delivered using a compressor or just by the influence of atmospheric pressure.

<FIG> displays a refurbished turbine according to another embodiment of the present invention. The third opening <NUM> is located according to this embodiment at the trailing edge of at least one of the blades <NUM>. The gas is flowing to the third opening <NUM> through a gas passage inside the corresponding blade <NUM>, which is designated by <NUM>. The gas enters from inside the hub <NUM> into the gas passage <NUM> by passing an inlet aperture, which is designated by <NUM>. Alternatively, the third opening <NUM> can be located at the radial periphery of the blade <NUM>. Discharging gas at this position can mitigate cavitation and vibration.

<FIG> displays a refurbished turbine according to another embodiment of the present invention. In addition to the embodiment according to <FIG> the embodiment according to <FIG> comprises a boundary plate, which is designated by <NUM> and is located within the hub <NUM>. The boundary plate <NUM> separates the gas flow passage within the hub <NUM> from the remaining space inside the hub <NUM>. This can be useful in case the original hub <NUM> was filled with oil or water. In the refurbished hub the remaining space inside the hub <NUM> can again be filled with oil or water and the gas flow through the separated passage is not hindered by the oil or water. Alternatively, the separated gas flow passage inside the hub can be located completely in the hub shell. In this case the complete inside of the refurbished hub can again be filled with oil or water. The later alternative embodiment is especially useful for Kaplan type runners because the space inside the hub is very limited. Another alternative way to separate the gas flow passage within the hub can be achieved using one or more pipes within the hub connecting a second opening <NUM> with a corresponding third opening <NUM> or with a corresponding air inlet aperture <NUM>. Note that a separated gas flow passage inside the hub can also be applied in case that the third opening is located at the bottom of the hub <NUM>.

<FIG> displays a refurbished turbine according to another embodiment of the present invention. The difference to <FIG> is, that the third opening <NUM> is not located at the bottom of the hub <NUM> but located at the side of the hub <NUM> between the blades <NUM>.

<FIG> displays a refurbished turbine according to another embodiment of the present invention. The displayed embodiment comprises two third openings <NUM>, which are located at the suction side of a blade <NUM>.

<FIG> displays a refurbished turbine according to another embodiment of the present invention. The displayed embodiment comprises a third opening <NUM>, which is located at the periphery of a blade <NUM> near the leading edge of the blade <NUM>. The opening is located at the suction side of the blade <NUM>.

<FIG> displays a refurbished turbine according to another embodiment of the present invention. The displayed embodiment comprises a third opening <NUM>, which is located at the periphery of a blade <NUM> near the trailing edge of the blade <NUM>. The opening is located at the suction side of the blade <NUM>.

Alternatively, the third opening <NUM> in the embodiments according to <FIG> and <FIG> could be located directly at the tip of the blade <NUM>. In this case the discharged gas would enter the water passage in the space between the blade and the boundary of the water passage.

The somewhat edged shape of the first and second cover plate <NUM> and <NUM> shown in the <FIG> is just for the sake of simplicity. Of course, the contours especially at the outside of the cover plates <NUM> and <NUM> can be shaped smoother so that the adjacent water flow is not or just minimally disturbed. Also, the radial width of the annular space can be much smaller as shown in the <FIG>.

The method of refurbishing a facility for converting hydraulic energy into electrical energy according to the present invention comprises at least the following steps:.

whereas the first cover plate <NUM> and the second cover plate <NUM> are surrounding the axis of rotation of the runner, and a part of the outer surface of the head cover <NUM>, a part of the outer surface of the hub <NUM>, the inner surface of the first cover plate <NUM> and the inner surface of the second cover plate <NUM> are confining an annular shaped space in order to allow gas to flow from inside the inner head cover <NUM> through the first opening <NUM>, the annular shaped space and the second opening <NUM> and to be discharged through the third opening <NUM> into the water passage of the facility during operation of the refurbished facility.

The cover plates <NUM> and <NUM> can be connected to the mentioned parts by welding or bolting. The cover plates <NUM> and <NUM> can be formed as an integral part. In this case the runner or the runner blades must be dismounted during refurbishment. The cover plates <NUM> and <NUM> can alternatively consist of several segments which can be connected by welding or bolting. Depending on the runner geometry the second cover plate <NUM> may comprise recess clearances for the runner blades. In the case of a Kaplan type runner the recess clearances must allow pivoting of the blades.

For the embodiments according to <FIG>, <FIG> the method of refurbishing comprises the following additional steps:.

whereas the third opening <NUM> is located at the trailing edge or the radial periphery of the blade <NUM> (or other locations of the blade <NUM> mentioned before) comprising the gas passage <NUM> and the gas passage <NUM> extends between the inlet aperture <NUM> and the third opening <NUM> in order to allow the gas discharging through the third opening <NUM> into the water passage to flow through the gas passage <NUM> by passing the inlet aperture <NUM>.

The gas flow passage <NUM> can be machined into an existing blade <NUM> by machining a shallow groove in the blade <NUM> and providing an overlying cover plate (compare <FIG> in <CIT>). The cover plate can by welded or bolted to the existing blade <NUM>.

For the embodiments mentioned in connection with <FIG> the method of refurbishing comprises the following additional steps:.

Claim 1:
A method of refurbishing a facility for converting hydraulic energy into electrical energy, this refurbished facility comprising:
- a water passage,
- a turbine with a runner of the axial flow type located within the water passage and moveable around an axis and belonging to a rotatable part of the turbine and comprising a hub (<NUM>) and several blades (<NUM>) connected to the hub (<NUM>),
- a drive shaft (<NUM>) connected to the runner,
- an inner head cover (<NUM>) located adjacent to the hub (<NUM>) and surrounding the drive shaft (<NUM>) and belonging to the non-rotatable part of the turbine;
this method being characterized in that it includes the following steps:
- Providing a first cover plate (<NUM>),
- Providing a second cover plate (<NUM>),
- Providing a first opening (<NUM>) located at the inner head cover (<NUM>),
- Providing a second opening (<NUM>) located at the hub (<NUM>),
- Providing a third opening (<NUM>) located at the runner,
- Connecting the first cover plate (<NUM>) to the inner head cover (<NUM>),
- Connecting the second cover plate (<NUM>) to the hub (<NUM>),
whereas the first cover plate (<NUM>) and the second cover plate (<NUM>) are surrounding the axis, and a part of the outer surface of the inner head cover (<NUM>), a part of the outer surface of the hub (<NUM>), the inner surface of the first cover plate (<NUM>) and the inner surface of the second cover plate (<NUM>) are confining an annular shaped space in order to allow a gas to flow from inside the inner head cover (<NUM>) through the first opening (<NUM>), the annular shaped space and the second opening (<NUM>) and to be discharged through the third opening (<NUM>) into the water passage during operation of the refurbished facility.