Patent Description:
The general structure of a Kaplan turbine <NUM> is illustrated on <FIG>; it comprises a runner <NUM> that is secured at a first end of a rotating shaft <NUM> centered on a vertical axis Z1 and configured to rotate around said axis in operating conditions. It further comprises a hub <NUM> equipped with a series of movable or adjustable runner blades <NUM>. Coupling flanges <NUM> connect each a runner blade <NUM> to the hub <NUM>, so that the blades are adjustable. The runner <NUM> is housed in the upper part of a draft tube <NUM> that is designed for evacuating water downstream and for increasing the efficiency of turbine <NUM>. A volute <NUM> is arranged around the runner <NUM> and is fed with water. Indeed, the volute <NUM> is usually connected to a non-represented penstock that extends from a non-represented upstream reservoir. As a result, water outbursts in the volute <NUM> with a high potential energy. Water flows afterwards between the blades <NUM> of runner <NUM>, thereby inducing the runner <NUM> to rotate. The flow rate of water circulating around the runner <NUM> is regulated by the blades themselves and also by means of guide vanes <NUM> that are disposed in a circular pattern within the distributor. The guide vanes <NUM> are each pivotable around an axis parallel to axis Z1 to reduce or increase the flow rate of water entering the turbine <NUM>.

A generator rotor <NUM> is connected at a second end of the shaft <NUM>, which is opposed to the first end thereof in the longitudinal direction of the shaft <NUM>, that is along axis Z1. The rotor <NUM> is disposed coaxially within a stator <NUM> of a generator <NUM>.

Another embodiment, to which the invention also applies, is shown on <FIG>: the shaft is arranged horizontally and the turbine <NUM> (or bulb turbine) comprises components identical or similar to those of <FIG> and which bear the same reference numbers. The blades <NUM> are attached to the hub <NUM> and are part of the bulb unit <NUM>. The installation of <FIG> further includes a concrete structure <NUM> that delimits a horizontal channel C1 of circulation of water. The bulb <NUM> is disposed within the channel C1 and is adapted to rotate around a horizontal rotation axis X6 under the action of a forced water flow F coming from a non-represented reservoir. The bulb <NUM> includes a bulb casing <NUM> that is supported within channel C1 by a bulb hanger <NUM> and stay vanes <NUM>. The runner <NUM> is coupled to a non-represented generator which is disposed within the bulb casing <NUM> and which delivers an alternative voltage to a non-represented electricity power grid.

In this application, the expression "Kaplan turbine" will refer to a turbine provided with a Kaplan runner, whatever the direction of its shaft. Alternatively, it will be referred to a turbine with a Kaplan runner.

The moving parts of such turbines are usually lubricated with grease or oil.

For this reason, most Kaplan runner hubs are designed to be filled with oil, but we see more and more environmental pressures requesting oil free runners.

Oil free runners are known in the art, for example from <CIT>: they are designed with self-lubricated bushing operating in a hub filled with water instead of oil. But this design is plagued with limitations and problems. The life expectancy of self-lubricated bushings and blade's mechanisms components of the runner hub in water are much shorter than bronze bushings in oil due to corrosion, even when stainless steel is used.

In water-filled solution, a corrosion inhibitor is sometime used to prevent/limit the corrosion inside the runner, but due to environmental constraints this kind of chemical products is less and less accepted and for most of self-lubricated bushings the wear and friction are still negatively impacted by water.

An air-filled hub can be implemented instead of a water-filled hub, but this type of runner is known to provide a humid environment which is also unfavorable for the life of the runner and prone to heavy detrimental rusting effects. This detrimental effect is even present if the air-filled hub is maintained at a positive pressure, due to condensation and to potential minor water leaks inside the hub.

An air-filled design without air exchange is made by several manufacturers: the oil inside the runner is replaced by air and the blade bronze bushings are replaced by self-lubricated material; the air is not changed in operation and accumulating water is usually drained during maintenance. But all water leakages coming from the blade seals and other localization create an environment which is highly corrosive. After a while the runner may be running with some mixture of humid air and liquid water inside it. Even if the water is drained automatically or during rare periodic maintenance, the corrosive environment is still present because the humid atmosphere remains. Document <CIT> discloses a Kaplan turbine comprising means for supplying air to the turbine hub.

There is therefore a need for a new system and a new method to operate and/or to lubricate a Kaplan turbine.

The invention first concerns a turbine comprising a shaft, a runner, or a Kaplan runner, which comprises a number of blades and a hub, located at the end of the shaft and supporting the blades, said turbine further comprising :.

Dry air is air with a dew point low enough to ensure no condensation inside the hub and able to remove or absorb humidity from the hub.

Preferably, the dryer, or the means for generating dry air, should be able to generate dry air having a dew point lower than <NUM>, for example at or around -<NUM> or preferably at or around -<NUM>, or at around -<NUM> or at around -<NUM>. The lower the dew point, the more moisture could be extracted from the runner hub. Preferably the dew point is at least <NUM> lower than the water temperature.

The dryer (or the means for generating dry air) can be selected based on its dew point and air flow rate. A dew point at least <NUM> lower than the water temperature provides a good capacity for efficient moisture removal, assuming a complete hub air exchange in a reduced time, for example in no more than <NUM> minutes.

Thus, according to the invention a hub of a turbine, preferably comprising a Kaplan turbine, can be swept with dry air, eliminating at least part of, and preferably all, the water and humidity present in the turbine.

According to the invention, the interior of the runner hub is maintained dry and without humidity or condensation, for example originating from any leak, by circulating dry air inside the runner hub. This dry air is capable to eliminate water entering the hub from water leaks and will prevent condensation which eliminates any potential corrosion issue and optimizes the expected life of the runner components.

A turbine according to the invention may comprise means, for example one or more sensor(s), to monitor or measure the humidity of said flow of air evacuated out of said turbine. Thus, an air outlet can allow the monitoring of the air condition inside the runner hub.

A turbine according to the invention may further comprise an outlet chamber or tank to collect at least part of said flow of air evacuated out of said turbine. The humidity of the air of said flow of air can be monitored by one or more sensor(s) in said chamber. Said outlet chamber can for example at least partly surround said shaft.

In a turbine according to the invention:.

In a turbine according to the invention, said means for supplying the turbine with a flow of said dry air can comprise means for varying the flow or the frequency of said flow of dry air; for example it comprises means for regulating or to control said flow and/or the frequency of said flow of dry air, for example on the basis of an ambient air humidity degree and/or of water temperature and/or rate of humidity of said flow of air evacuated out of said turbine.

The invention also concerns a shaft for a turbine, for example according to the present invention as described above and in this application, comprising :.

The invention also concerns a method for operating a turbine as described above or in this application.

The invention also concerns a method for operating a turbine, for example a Kaplan runner and/or as described above and/or in this application, comprising:.

Dry air may be generated from atmospheric air.

The invention concerns in particular a method for operating a turbine comprising a shaft, a Kaplan runner having a number of blades and a hub, located at the end of the shaft and bearing the blades, said method comprising :.

In a method according to the invention, the dry air should preferably have a dew point lower than <NUM>, for example at or around -<NUM> or preferably at or around -<NUM>, or at or around -<NUM> or at or around -<NUM>. The lower the dew point, the more moisture can be extracted from the runner hub. Preferably the dew point is at least <NUM> lower than the water temperature. This provides a good capacity for efficient moisture removal, assuming a complete hub air exchange in a reduced time, for example in no more than <NUM> minutes.

A humidity rate of said flow of air which is evacuated out of said turbine can be measured. Said flow and/or the frequency of said flow of dry air may be continuous or variable and/or adjusted depending on said humidity rate; the dry air flow may be for example regulated or controlled, for example on the basis of an ambient air humidity degree and/or of water temperature and/or rate of humidity of said flow of air evacuated out of said turbine.

In a method according to the invention, the hub of the turbine can be filled with dry air.

A turbine, or a turbine comprising a Kaplan runner, according to the invention or implemented in a method according to the invention can be of the horizontal type or of the vertical type or can be operated at any angle between horizontal and vertical.

An example of a Kaplan turbine, or a turbine comprising a Kaplan runner, comprising a dry air supply system according to the invention is illustrated on <FIG>, on which the same reference numbers designate the same elements as discussed above in connection with <FIG> and <FIG>.

On this figure a dry air generating system <NUM> is connected to a circuit <NUM> in order to inject a flow <NUM> of dry air into the turbine, for example into a duct <NUM> formed in the rotating shaft <NUM> and extending down to the hub <NUM>, in particular in order to keep the interior of the runner hub dry.

Said system <NUM> generates dry air from atmospheric or outside air. It may comprise a tank or accumulator <NUM> (see <FIG>) for buffering said dry air. In addition to a dryer <NUM>, it can further comprise a filter <NUM> and/or a compressor. This dry air may be compressed, for example at a pressure sufficient to provide the said air flow. For a given pressure, the corresponding dry air flow can be calculated or obtained.

For example, for a Kaplan runner operating in water, for example water of a cold Nordic river, which has a temperature close to zero degree Celsius in winter, the upper limit for the dry air dew point should be zero degree Celsius. This would allow to avoid condensation inside the runner hub even when water is almost down to <NUM>. Furthermore, to remove moisture already present into the hub, the dry air should have a lower dew point than <NUM>: a dew point around -<NUM> or preferably -<NUM>, or - <NUM> or -<NUM> could be selected to allow some capacity to remove some moisture already present into the runner hub. The lower the dew point, the more moisture could be extracted from the runner hub.

The dryer (or the means for generating dry air) can be selected based on its dew point and air flow rate. The inventors have observed that a dew point at least <NUM> lower than the water temperature provides a good capacity for efficient moisture removal, assuming a complete hub air exchange in no more than <NUM> minutes. An example of dryer which can be implemented is a desiccant air dryer, for example a D2 modular desiccant dryer of Nano Purification Solutions, Inc, see for example www. <NUM>-<NUM>-<NUM>, Issue <NUM>, Series <NUM>. It can be a compressed air dryer using the pressure swing adsorption principle of drying compressed air, utilizing two identical columns each containing a hygroscopic desiccant bed. Other dryers can be used.

The humidity level or rate of this dry air can be measured to make sure condensation will not occur and/or to be able to drag some humidity from the runner hub, preferably even under the most adverse temperature conditions which is the coldest possible hub temperature when the runner is in operation, at rest or even during maintenance when runner can be exposed to ambient air temperature. In other words, this air has a dew point low enough to ensure no condensation is formed inside the hub and able to remove or absorb humidity from the hub.

The circuit <NUM> may comprise one or more regulating valve(s) <NUM> in order to regulate or to stop the flow <NUM> of dry air circulating in direction of the duct <NUM>. Said one or more valve(s) can be controlled by a control system of the unit, for example a computer or a processor (not represented on the figure), for example based on an information or a signal from a humidity sensor as explained below. An example of such a control system is illustrated on <FIG>.

In particular, the flow <NUM> of dry air can be supplied to the Kaplan runner through the shaft <NUM>, and more particularly through the duct <NUM> extending along said shaft. As illustrated on <FIG>, the air <NUM> then circulates in the hub <NUM> where it is mixed with air already present therein and then evacuated through a return or evacuation duct <NUM> which may also be formed in the shaft <NUM> and flows outside the shaft through an air outlet <NUM>. Alternatively, said return or evacuation duct <NUM> could be located outside said shaft; preferably it is against the shaft or fixed to the shaft, thereby rotating with it. For example an air outlet tank <NUM> is connected to said air outlet <NUM> and can comprise means, for example a sensor, to monitor the air condition, in particular the humidity, inside the runner and particularly inside the hub <NUM>. The flow <NUM> of dry air can be regulated based on an information from said means or sensor about the humidity rate inside the hub.

A turbine of the Kaplan type is composed of different parts which are assembled together. Water can leak from the outside of the runner hub <NUM> into the runner hub in particular at the interfaces between the blades and their seals or where sealing flanges are present, at the runner cone for example. The flow of dry air which is circulated as explained above therefore becomes laden with humidity as it flows through the hub <NUM>. The air at outlet <NUM> can therefore be moisty air. Thus, the measurement of the humidity level or rate in the air at air outlet <NUM> is an indication of possible leaks in the turbine. This measurement of the humidity level or rate can be compared with a reference value or with the humidity level or rate of the flow <NUM> of dry air injected into the inlet duct <NUM>. In other words, the air that flows through the runner can be tracked and/or analysed to check the humidity inside the runner and to detect the presence of any leakage. For example, as illustrated on <FIG>, a chamber or tank <NUM> can be located at the outlet <NUM> and collect air which has flowed through the runner as explained above, such chamber or tank being provided with humidity sensor and/or a float (not represented on <FIG>). It is also possible to exhaust the moisty air directly inside the river without circulating back to the chamber or tank <NUM>. In this case for example a bluetooth sensor can be located in the runner cone. The above explanation, given in connection with a Kaplan turbine with a vertical shaft, also apply to a Kaplan turbine with a horizontal shaft or for a Kaplan turbine at any angle.

<FIG> is a more detailed example of a horizontal Kaplan turbine implementing the invention and showing details of the air flow in the hub <NUM>. A flow of dry air <NUM> is injected into the runner through horizontal duct <NUM>, then into the hub <NUM> and is swept through areas <NUM>, <NUM>' of the hub possibly containing water or humidity resulting from water leaking from outside the hub into the runner. References <NUM> (blade seals), 20A (cone flange), 20B (hub filling port), 20C (at cone closing plate) are examples of various locations where water can leak into the runner. Similar locations are found in a vertical Kaplan turbine. As it travels through the hub, the dry air can thus be progressively laden with humidity or moisture. It may flow through parts of the runner located at, or closer to, the zone <NUM> of largest diameter. References 21A and 21B designate bushings.

<FIG> and <FIG> are other embodiments of a vertical Kaplan runner implementing the invention and showing details of the air flow through or into the hub <NUM>. The same references as in <FIG> designate the same elements and reference is made for these elements to the above description. Here the dry air may flow through parts of the runner. The duct <NUM> is preferably positioned so that it may capture air at locations where water may accumulate during operation (<FIG>) and/or when the machine is stopped (<FIG>).

The inlet <NUM>' to duct <NUM> (the drain) may be located at the bottom of the hub, as shown on <FIG>; this will depend on the operation of the machine and where the water should actually accumulate.

As shown on <FIG>, the inlet to duct <NUM> (the drain) may be located at the largest diameter of the runner, because when the machine rotates, water is going to flow to this area due to centrifugal forces.

In any of the embodiments given in this application, the inlet duct <NUM> may have a first section at least partly located in the shaft and a second section comprising a plurality of distributing ducts 16a, 16b (see for example on <FIG>), for example at least two ducts 16a, ,16b connected to the first section and extending from said first section laterally or at an angle with respect to the direction of said shaft. Said distributing ducts 16a, 16b can distribute dry air at locations which are offset from the vertical axis of the runner.

<FIG> is a more detailed example of a vertical and/or horizontal Kaplan implementing the invention and showing details of the air flow through or into the hub <NUM> and the moisty air exhaust inside the water passage. The same references as in the preceding figures designate the same air inlet elements and reference is made for these elements to the above description. Here the dry air may flow through various parts of the runner. A moisty air exhaust <NUM> can be positioned to exhaust the moisty air directly to the water passage.

<FIG> shows a detail of the shaft <NUM> of an embodiment of the invention comprising both the inner duct <NUM> to introduce a flow <NUM> of dry air and the lateral duct <NUM> through which the moisture laden air <NUM> is evacuated. Air <NUM> can then be evacuated through the rotating outlet <NUM> and then possibly to a chamber or tank <NUM> which is fixed and located close to, or around, the shaft <NUM> with labyrinths <NUM> which can be fixed on the shaft in order to maintain a tight gap between the rotating parts (the shaft) and the static part (the tank <NUM>, which is preferably fixed on static parts, and is for example centred around the shaft, without contact between the tank and the shaft). Thus the shaft, comprising the inlet and the outlet ducts <NUM>, <NUM>, is rotating while the exit tank <NUM> is preferably fixed with respect to the shaft, while being located close to or around it. The air can then be evacuated from the tank <NUM> through an outlet duct <NUM> to the atmosphere. The reference <NUM> designates at least one humidity sensor and/or a water level indicator (indicating a water level in said tank <NUM>); it can provide an information about the humidity and/or water level in the tank <NUM>, thus giving a measurement of, or an information about, the humidity level in the hub <NUM>, and therefore an information about possible leaks of water from outside the turbine into the hub. The information about the degree or rate of humidity can be provided to a controller which can be programmed to regulate the volume and /or the frequency of the inlet air flow <NUM> and/or some maintenance plan based on said information. Alternatively, even without controller, this information can be used to plan maintenance of the system, for example the replacement of one or more seal(s).

<FIG> shows an example of a dry air generating system <NUM> together with the air supply system <NUM> which can be implemented in the frame of the present invention. In this embodiment one or more filter(s) <NUM>, a dryer(s) <NUM> and a compressor feed a tank <NUM> with dry air. The pressure inside the tank <NUM> can be measured with a pressure gauge <NUM> and controlled by pressure sensor <NUM>. The system may comprise a pressure limit or relief valve <NUM> to protect the tank.

Dry air <NUM> can be supplied from the tank <NUM> to a Kaplan turbine through supply system <NUM> which for example comprises one or more valve(s).

An example of a control system for a system according to the invention is illustrated on <FIG>. It comprises a processor or a computer <NUM> configured or programed so as to implement a process according to the invention, in particular in order:.

Alternatively, or in addition, said processor or computer <NUM> can be configured or programed so as to implement a process according to the invention, in particular in order to control:.

For example said processor or a computer <NUM> implements a computer program comprising instructions for implementing a method according to the invention.

The device of <FIG> can be controlled by said processor or a computer <NUM>.

The invention allows all elements of the runner, in particular the bushing(s) and/or bearing(s) and/or the blade mechanism to operate in dry air. The invention avoids any environmental risk associated with any liquid in the runner : there can be no leakage of any kind into the water of the river, since no oil or water inhibitor or antibacterial additive is used.

Claim 1:
A turbine (<NUM>) comprising :
- a shaft (<NUM>);
- a Kaplan runner which comprises a number of blades (<NUM>) and a hub (<NUM>), located at the end of the shaft and bearing the blades,
- means (<NUM>) for generating dry air;
- means (<NUM>, <NUM>) for supplying the turbine with a flow (<NUM>) of said dry air;
- means (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for evacuating a flow (<NUM>) of air out of said turbine after said flow of dry air has flowed at least through the hub (<NUM>).