Method for detecting fatigue damage of hydraulic unit and hydraulic unit thereof

Abstract

The invention relates to a method for detecting fatigue damage of a hydraulic unit and to a hydraulic unit thereof. The invention relates to a method for detecting fatigue experienced at at least one specific location of a hydraulic unit (10), the method being characterized in that the fatigue experienced at at least one specific location is detected by at least one fatigue indicator (F), the at least one fatigue indicator being arranged for remote interrogation via a line or via a wireless connection.

Description

Technical Field

[0001] The present invention relates to a method for detecting fatigue damage of a hydraulic unit. In particular, the present invention relates to a method for detecting fatigue damage of a hydraulic unit implementing a fatigue indicator arranged to be remotely interrogated.

[0002] The invention also relates to a hydraulic unit provided with a fatigue indicator arranged to be interrogated remotely. Background Art

[0003] When, for example, a water flow drives the runner of a hydraulic machine to rotate, the runner must withstand mechanical stresses whose magnitude is particularly high at specific locations known as "hot spots", notably at the corners of the runner blades.

[0004] The cumulative effect of this mechanical stress produces fatigue, which can eventually trigger crack initiation and propagation ( Figure 1 ).

[0005] The breaking and / or release of parts of the runner due to the occurrence of cracks may cause significant damage to the hydraulic press and cause the hydraulic press to stop operating.

[0006] The influence is not limited to the runner, but other elements of the hydraulic unit, such as shafting, wicket gates or pipes, are also subject to significant mechanical strains / stresses.

[0007] Therefore, it is crucial to be able to estimate the fatigue and associated remaining life of these components of the hydraulic unit.

[0008] Mechanical strain measurement campaigns are often performed for this purpose.

[0009] For example, in the case of a rotating wheel, the mechanical strain measurement activity typically involves positioning a gauge (notably a strain gauge), particularly in the vicinity of a hot spot, and analyzing the data collected by the gauge in order to infer the mechanical stress experienced at the hot spot location.

[0010] However, this approach is not satisfactory.

[0011] In practice, analysis of the data usually requires the establishment of a fluid dynamics model of the hydraulic unit, which is cumbersome to implement.

[0012] Furthermore, this series of events and the measurement activity caused the hydraulic turbine under test to stop operating, so that the hydraulic turbine could not be used for production. In other words, the measurement activity caused a shortfall for the operator.

[0013] Furthermore, the meter H needs to be located in very close proximity to specific locations (and notably, hot spots) that are not easily accessible. In particular, the meter H requires a wired connection. For example, Figure 2 As depicted in , the meter H is mounted on the suction side, pressure side, leading edge or trailing edge of the blade B.

[0014] Additionally, depending on the duration of the mechanical strain measurement campaign, a very limited range of operating conditions can be tested.

[0015] Finally, the cost for performing such measurement activities is quite high.

[0016] The object of the present invention is therefore to propose a method for detecting fatigue damage of a hydraulic unit which is less cumbersome than the known prior art methods.

[0017] The invention also aims to provide a method for detecting fatigue damage of a hydraulic unit, in which method the fall-off of the fatigue indicator can be prevented. Summary of the invention

[0018] The aforementioned purpose is at least partially achieved by a method for detecting fatigue experienced at at least one specific position of a hydraulic unit, the method being characterized in that the fatigue experienced at at least one specific position is detected by at least one fatigue indicator, which is arranged for remote query via a line or via a wireless connection.

[0019] According to one embodiment, at least one fatigue indicator is calibrated such that they are sensitive to fatigue experienced at at least one specific location, optionally at least the specific location being a location known as a hotspot, where the experienced fatigue corresponds to a local maximum.

[0020] According to one embodiment, at least one fatigue indicator is located remote from at least one specific location.

[0021] According to one embodiment, at least one fatigue indicator is located on a dry surface of the hydraulic unit.

[0022] According to one embodiment, at least one fatigue indicator is located on the water surface of the hydraulic unit.

[0023] According to one embodiment, the hydraulic unit includes at least one component selected from among a hydraulic machine, a water or air circuit and a valve or a rotary electric machine, and wherein the at least one specific position is located on at least one of the at least one component.

[0024] According to one embodiment, the hydraulic unit comprises a hydraulic machine provided with a wheel arranged to rotate about a rotation axis once the unit is in operation, the specific position being on the wheel.

[0025] According to one embodiment, the runner includes blades, each of the blades having two opposite sides, respectively a pressure side and a suction side, and extending from an outer surface of a hollow hub, the pressure side and the suction side of the blade, the hollow hub further including an inner surface opposite to the outer surface, and a fatigue indicator is located on the inner surface of the hollow hub so that when the runner is triggered to rotate, the fatigue indicator is isolated from turbulence that may occur between the blades.

[0026] According to one embodiment, at least one fatigue indicator, upon detecting fatigue above a predetermined fatigue threshold, converts said fatigue into a change in a physical parameter, optionally the physical parameter being a resistance or a count of accumulated strain.

[0027] According to one embodiment, at least one fatigue indicator comprises a plate having a top surface on which the crack gauge is located.

[0028] According to one embodiment, the plate comprises a pre-initiated crack designed to propagate beneath the crack gauge once a predetermined fatigue threshold is reached, the pre-initiated crack optionally being guided in a groove formed on a bottom surface of the plate opposite to the top surface and extending along a first direction.

[0029] According to one embodiment, the crack gauge comprises a resistor made of wires arranged on the top surface perpendicular to the first direction and designed to break selectively, advantageously successively, depending on the magnitude of fatigue causing the propagation of the pre-initiated crack, optionally arranged in order of increasing length along the first direction.

[0030] According to one embodiment, at least one fatigue indicator comprises a central section connecting two side sections, the central section being designed to break once a predetermined fatigue threshold is reached, optionally the two side sections having a flat shape.

[0031] According to one embodiment, the method further comprises collecting the changes in the physical parameters by a data acquisition system via a wireless connection, optionally the operating conditions of the hydraulic unit are collected by the data acquisition system.

[0032] The invention also relates to a hydraulic unit comprising at least one fatigue indicator arranged for remote interrogation via a line or via a wireless connection and sensitive to fatigue experienced at at least one specific location of the hydraulic unit.

[0033] According to one embodiment, at least one fatigue indicator is calibrated such that they are sensitive to fatigue experienced at at least one specific location, optionally at least the specific location being a location known as a hotspot, where the experienced fatigue corresponds to a local maximum.

[0034] According to one embodiment, at least one fatigue indicator is located remote from at least one specific location.

[0035] According to one embodiment, at least one fatigue indicator is located on a dry surface of the hydraulic unit.

[0036] According to one embodiment, at least one fatigue indicator is located on the water surface of the hydraulic unit.

[0037] According to one embodiment, the hydraulic unit comprises a hydraulic machine provided with a wheel arranged to rotate about a rotation axis once the unit is in operation, the specific position being on the wheel.

[0038] According to one embodiment, the runner includes blades, each of the blades having two opposite sides, respectively a pressure side and a suction side, and extending from an outer surface of a hollow hub, the pressure side and the suction side of the blade, the hollow hub further including an inner surface opposite to the outer surface, and a fatigue indicator is located on the inner surface of the hollow hub so that when the runner is triggered to rotate, the fatigue indicator is isolated from turbulence that may occur between the blades.

[0039] According to one embodiment, at least one fatigue indicator, upon detecting fatigue above a predetermined fatigue threshold, converts said fatigue into a change in a physical parameter, optionally the physical parameter being a resistance or a count of accumulated strain.

[0040] According to one embodiment, at least one fatigue indicator comprises a plate having a top surface on which the crack gauge is located.

[0041] According to one embodiment, the plate comprises a pre-initiated crack designed to propagate beneath the crack gauge once a predetermined fatigue threshold is reached, the pre-initiated crack optionally being guided in a groove formed on a bottom surface of the plate opposite to the top surface and extending along a first direction.

[0042] According to one embodiment, the crack gauge comprises a resistor made of wires arranged on the top surface perpendicular to the first direction and designed to break selectively, optionally continuously, depending on the magnitude of fatigue causing the propagation of the pre-initiated crack, optionally the wires being arranged in order of increasing length along the first direction.

[0043] According to one embodiment, at least one fatigue indicator comprises a central section connecting two side sections, the central section being designed to break once a predetermined fatigue threshold is reached, optionally the two side sections having a flat shape.

[0044] According to one embodiment, the method further comprises collecting the changes in the physical parameters by a data acquisition system via a wireless connection, optionally the operating conditions of the hydraulic unit are collected by the data acquisition system.

[0045] Technical solution 1. A method for detecting fatigue experienced at at least one specific position of a hydraulic unit, the method being characterized in that the fatigue experienced at the at least one specific position is detected by at least one fatigue indicator (F), and the at least one fatigue indicator is arranged for remote query via a line or via a wireless connection.

[0046] Technical Solution 2. The method according to Technical Solution 1 is characterized in that the at least one fatigue indicator is calibrated so that they are sensitive to the fatigue experienced at the at least one specific position, optionally, wherein the at least specific position is a position called a hot spot, where the fatigue experienced corresponds to a local maximum.

[0047] Technical Solution 3. The method according to Technical Solution 1 or 2 is characterized in that the at least one fatigue indicator (F) is positioned away from the at least one specific position.

[0048] Technical Solution 4. The method according to any one of Technical Solutions 1 to 3 is characterized in that the at least one fatigue indicator is located on a dry surface of the hydraulic unit.

[0049] Technical Solution 5. The method according to any one of Technical Solutions 1 to 3 is characterized in that the at least one fatigue indicator is located on the water surface of the hydraulic unit.

[0050] Technical Solution 6. A method according to any one of Technical Solutions 1 to 5, characterized in that the hydraulic unit includes at least one component selected from a hydraulic press, a water or air circuit and a valve or a rotating motor, and wherein the at least one specific position is located on at least one of the at least one components.

[0051] Technical Solution 7. The method according to any one of Technical Solutions 1 to 5 is characterized in that the hydraulic unit includes a hydraulic machine provided with a rotating wheel, the rotating wheel is arranged to rotate around a rotation axis once the unit is in operation, and the specific position is on the rotating wheel.

[0052] Technical Solution 8. The method according to Technical Solution 7 is characterized in that the impeller includes blades (43), each of which has two opposite sides respectively referred to as the pressure side and the suction side, and extends from the outer surface (44a) of the hollow hub (44), the pressure side and the suction side of the blade forming a section of the hydraulic surface, the hollow hub further includes an inner surface (44b) opposite to the outer surface (44a), and the fatigue indicator is located on the inner surface of the hollow hub, so that when the hydraulic unit is in operation, the fatigue indicator is isolated from the water flow or air flow circulating through the hydraulic channel.

[0053] Technical Solution 9. The method according to any one of Technical Solutions 1 to 8 is characterized in that when the at least one fatigue indicator detects fatigue above a predetermined fatigue threshold, the fatigue is converted into a change in a physical parameter, optionally wherein the physical parameter is resistance or a count of accumulated strain or stress.

[0054] Technical Solution 10. The method according to Technical Solution 9 is characterized in that the at least one fatigue indicator includes a plate having a top surface, and the crack gauge is located on the top surface.

[0055] Technical Solution 11. The method according to Technical Solution 10 is characterized in that the plate includes a pre-initiated crack, which is designed to extend below the crack gauge once the predetermined fatigue threshold is reached, optionally wherein the pre-initiated crack is guided in a groove formed on the bottom surface of the plate opposite to the top surface and extends along a first direction.

[0056] Technical Solution 12. The method according to Technical Solution 11 is characterized in that the crack meter includes a resistor made of a wire, which is arranged on the top surface perpendicular to the first direction and is designed to break selectively and optionally continuously depending on the magnitude of the fatigue causing the extension of the pre-initiated crack, optionally, wherein the wire is arranged in order of increasing length along the first direction.

[0057] Technical Solution 13. The method according to Technical Solution 9 is characterized in that the at least one fatigue indicator includes a central segment connecting two side segments, and the central segment is designed to break once the predetermined fatigue threshold is reached, optionally, wherein the two side segments have a flat shape.

[0058] Technical Solution 14. The method according to any one of Technical Solutions 9 to 13 is characterized in that the method further includes collecting the changes in the physical parameters by a data acquisition system via a wireless connection, optionally wherein the operating conditions of the hydraulic unit are collected by the data acquisition system.

[0059] Technical solution 15. A hydraulic unit comprising at least one fatigue indicator, which is arranged for remote query via a line or via a wireless connection and is sensitive to fatigue experienced at at least one specific position of the hydraulic unit. Optionally, the at least one fatigue indicator (F) is positioned away from the at least one specific position. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Further characteristics and advantages will emerge from the following description of an embodiment of a method for detecting fatigue damage of a hydraulic unit according to the invention, given by way of non-limiting example with reference to the accompanying drawings, in which:

[0061] - Figure 1 Indicates a crack on the corner of the blade of the runner (area marked with "A");

[0062] - Figure 2 is a photograph showing a strain gauge mounted on the suction side of a blade of a runner;

[0063] - Figure 3 A hydraulic unit is shown in perspective, in particular, the hydraulic unit comprises a Francis hydraulic turbine and a synchronous generator;

[0064] - Figure 4a Based on the cross-sectional view Figure 3 Schematic representation of a hydraulic turbine, in particular, a runner provided with a fatigue indicator located on the inner surface of a hollow hub;

[0065] - Figure 4b Based on the cross-sectional view Figure 3 Another schematic representation of a hydraulic turbine of, in particular, a runner provided with a fatigue indicator located on the inner surface of a hollow hub;

[0066] - Figure 4c is a schematic representation of a Pelton wheel, in particular, the wheel is provided with a fatigue indicator;

[0067] - Figure 5 is a perspective view of the Francis runner blades, with the gray levels associated with the magnitude of the local stress experienced by the blades as water flows through the runner;

[0068] - Figure 6 is a perspective view of a plate of a fatigue indicator according to the invention, showing a pre-initiated crack in a groove on the bottom surface of the plate;

[0069] - Figure 7 is a plan view of a crack gauge from Kyowa implemented in a first embodiment of the present invention;

[0070] - Figure 8 is a plan view of a fatigue indicator implemented in a second embodiment of the present invention. DETAILED DESCRIPTION

[0071] The invention relates to a method for detecting fatigue damage of a hydraulic unit.

[0072] The term "fatigue" refers to the weakening of a material caused by repeatedly applied loads. Fatigue is a progressive and localized structural damage that occurs when a material is subjected to cyclic loading. In particular, fatigue occurs when a material is subjected to repeated loading and unloading. If the load is above a predetermined threshold, microscopic cracks will begin to form.

[0073] In particular, in the present invention, fatigue is detected using a fatigue detector which is arranged for remote interrogation, for example via a line or via a wireless connection.

[0074] As a very specific example, a fatigue detector may be implemented for detecting fatigue experienced on surfaces known as hydraulic surfaces, which delimit hydraulic channels of a hydraulic unit.

[0075] In the context of the present invention, the term "hydraulic channel" refers to a channel defined by hydraulic surfaces, which are surfaces on which the water flow exerts a force when the hydraulic unit is operated in water mode. Hydraulic channels also include pipes through which the water flows, such as penstocks.

[0076] It is also understood that when operating in the water-in mode, the water-in surface of the hydraulic unit is not limited to the hydraulic surface. In particular, the hydraulic unit also includes other surfaces referred to as protected surfaces. The so-called protected surface may be a surface that is wetted by part of the water flow having a flow rate lower than the flow rate in the hydraulic channel, such as the inner surface of the hub. Alternatively, the so-called protected surface may be a surface that remains dry, such as on the outer surface of the pressure pipe.

[0077] According to the invention, the hydraulic unit comprises a hydraulic machine and the water or air circuits (pressure pipes) and valves (ball valves or butterfly valves) necessary for its operation. The hydraulic machine may comprise a hydraulic turbine mechanically coupled to a rotating electrical machine. The rotating electrical machine may be a synchronous or asynchronous generator or a motor-generator.

[0078] In a particular embodiment, the method may be implemented for detecting fatigue damage of a hydraulic machine of a hydraulic unit, and in particular detecting fatigue damage of a runner of the hydraulic machine.

[0079] The hydraulic machine can be used in turbine mode for generating electricity and / or in pump mode for pumping water and / or in condenser mode.

[0080] Furthermore, fatigue indicators allow, depending on their sensitivity, to detect at an early stage the appearance of cracks in specific locations, for example locations far from the area where said fatigue indicators are located. It is thus possible to plan inspection or maintenance operations of the hydraulic unit depending on fatigue damage.

[0081] In particular, the method according to the invention may advantageously be performed for monitoring fatigue of a runner, and more particularly of a blade, before failure and / or cracking occurs.

[0082] Alternatively, the method according to the invention can also be advantageously performed for monitoring fatigue damage of components of a generator. As a very specific example, the fatigue indicator according to the invention is implemented for monitoring fatigue damage of a rotor spider. In particular, the fatigue indicator is placed on the rotor spider, for example, before its commissioning. Thus, according to the invention, the monitoring of fatigue damage of components that are difficult to access, such as a rotor spider, is made easier compared to known prior art processes. The invention provides the benefit that fatigue damage can be assessed remotely.

[0083] It will be appreciated that the invention is not limited to these specific examples and that the method may be applied to detecting fatigue damage in any component of a hydraulic unit.

[0084] The invention will now be described in the context of turbine mode. However, given his general knowledge and the following description, the skilled person may generalize the invention to other operating modes of the hydraulic machine, and in particular to pump mode and condenser mode.

[0085] Figure 3 The general architecture of a hydraulic unit 10 according to the invention is depicted.

[0086] The hydraulic unit 10 comprises a generator 20 connected to the electrical grid. The generator may comprise a synchronous generator, an asynchronous generator, a motor generator.

[0087] It is understood, without necessarily going into detail, that the generator comprises a rotor arranged to rotate inside a stator, the windings of which are connected to the grid.

[0088] The hydraulic unit 10 further comprises a hydraulic turbine 30 provided with a runner 40 mechanically coupled to the rotor of the synchronous generator 20 via a shafting 60 extending along the axis of rotation XX′.

[0089] When in use, water flow through the runner and in particular through the hydraulic passage drives the runner in rotation.

[0090] By "hydraulic channel" is meant the flow channel through which water flows to apply the force required to trigger the rotation of the rotor.

[0091] In particular, the hydraulic channel is defined by a hydraulic surface, which is a surface on which the water flow exerts a force when the water flow drives the runner to rotate. The hydraulic channel also includes a conduit through which the water flow flows.

[0092] Inside the runner, hydraulic channels are defined by the surfaces of the runner 40 that are directly exposed to hydraulic disturbances originating from the flow of the water current.

[0093] The rotor 40 further comprises at least one fatigue indicator F.

[0094] The at least one fatigue indicator F can be queried remotely via wire or via a wireless connection.

[0095] By "fatigue indicator" is meant an indicator that is sensitive to the stress cycles (i.e. fatigue) experienced by the device to which it is connected (e.g. a rotor). In particular, when the hydraulic unit accumulates repeated loads above a given threshold at a specific location, the fatigue indicator irreversibly changes its structure. Notably, and as a non-limiting example, the structural change of the fatigue indicator involves the breaking of the connection, which translates into a change in the resistivity of said indicator.

[0096] The at least one fatigue indicator may be located on a wet surface or a dry surface.

[0097] In particular, at least one fatigue indicator F is calibrated such that it is sensitive to fatigue experienced in at least one specific location.

[0098] The term “sensitive” means that the fatigue indicator can detect damage.

[0099] For example, at least certain locations are locations known as hot spots where the fatigue experienced corresponds to a local maximum.

[0100] The so-called "local maximum" means that there is a region including a specific location such that the mechanical stress at the specific location is higher than the mechanical stress at any other location in the region.

[0101] Optionally, at least one fatigue indicator F may be located remote from at least one specific location.

[0102] Therefore, it is possible to remotely detect fatigue at a specific location that is not conveniently accessible.

[0103] For example, at least one fatigue indicator F may be located on at least one area located away from the hydraulic channel, which area is referred to as a protected area ( Figure 4a and Figure 4b ).

[0104] By "located away from the hydraulic channel" is meant a fatigue indicator that is not exposed to and does not disturb the water flow through the hydraulic channel when the hydraulic machine is in operation. In other words, the fatigue indicator is in an area away from the hydraulic surface, referred to as a protected area.

[0105] The inventors have noticed that the cumulative effect of repeated loads affects the runner as a whole. In particular, the load effect on the runner, whatever the location considered, depends on the operating conditions and mechanical characteristics of the runner. More precisely, the accumulated strain or stress at a specific location of the runner can be inferred from the knowledge of the accumulated strain or stress at any other location, taking into account the operating conditions and mechanical characteristics.

[0106] Thus, a fatigue indicator located on a region provides an indication of accumulated strain or stress at other locations of the runner as well as at specific locations such as a hydraulic surface of the runner.

[0107] Notably, certain locations are locations known as hot spots where the mechanical stresses experienced correspond to local maxima when the wheel is rotating.

[0108] in this regard, Figure 5 is a perspective view of the Francis runner blades. The gray levels are associated with the local stresses experienced by the blades as water flows through the runner. Figure 5 It can be noted that the stress experienced by the blade in the corner (location A) at the intersection of the trailing edge 43a and the hollow hub 44 is quite high relative to the rest of the blade.

[0109] The fatigue indicator may be calibrated to detect damage at a specific location of the rotor when fatigue at said specific location is above a given fatigue damage threshold.

[0110] The method may comprise implementing a plurality of fatigue indicators F which are calibrated to detect different damage magnitudes.

[0111] According to this configuration, it is possible to assess the magnitude of damage experienced by the rotor.

[0112] The implementation of the aforementioned concepts is not limited to runners, but can be extended to other elements of the hydraulic unit and, notably, to shafting, valves, guide vanes, pipes, generators, for example.

[0113] The calibration of the fatigue indicator may be based on numerical simulations. In particular, the numerical simulations may involve computational fluid dynamics for calculating the pressure loads on the runner, and finite element analysis of the stresses resulting from said pressure loads.

[0114] In this regard, a person skilled in the art is referred to the document [1] cited at the end of the description.

[0115] Alternatively, calibration of the fatigue indicator may be performed during a learning phase or in a reduced-scale model of the wheel.

[0116] By "reduced scale model" is meant a laboratory hydraulic press and its size or footprint is advantageously reduced relative to a hydraulic press.

[0117] A supplementary calibration may be performed based on the material and geometry of the fatigue indicator to determine the propagation velocity within the fatigue indicator.

[0118] For example, the runner is a Francis runner comprising blades 43 each having two opposite sides, respectively referred to as the pressure side and the suction side, and extending from an outer surface 44a of a hollow hub 44 having, for example, a conical shape ( Figure 4a and Figure 4b ).

[0119] The blades 43 can be further fixed to the periphery of the runner by means of a peripheral shield 47 ( Figure 4a and Figure 4b ).

[0120] The hub further includes an inner surface 44b opposite the outer surface 44a.

[0121] The hydraulic passages of the Francis wheel are bounded by the pressure and suction sides of the blades and by the outer surface of the hollow hub 44 .

[0122] According to this configuration, the fatigue indicator may be located on the inner surface 44b of the hollow hub 44 opposite the outer surface so that the indicator is isolated from the water circulating through the hydraulic passage when the hydraulic machine is in operation. For example, the fatigue indicator may be glued, welded or mechanically fixed to the inner surface ( Figure 4a and Figure 4b ).

[0123] exist Figure 4c In another example illustrated in , the wheel is a Pelton wheel.

[0124] When damage above a predetermined damage threshold is detected, the fatigue indicator converts said damage into a change in a physical parameter. According to one example, the physical parameter is electrical resistance.

[0125] Alternatively, the physical parameter is a count of accumulated strain or stress or load. In this respect, the fatigue indicator may be provided with a processor configured to perform the count of strain or load.

[0126] Advantageously, each fatigue indicator comprises a plate 50 having a top surface 51 on which a crack gauge G1 is located ( Figure 6 ).

[0127] In particular, the plate 50 may include a pre-initiated crack 53 designed to propagate beneath the crack gauge G1 once a predetermined fatigue threshold is reached.

[0128] The formation of pre-initiated cracks enhances the sensitivity of the fatigue indicator to stress build-up (or fatigue) and thus makes it possible to predict the occurrence of cracks at specific locations at a very early stage.

[0129] The sensitivity of the fatigue indicator can be further enhanced by suspending the plate of the fatigue indicator on two bases.

[0130] It is therefore possible to plan inspection and maintenance of components of the hydraulic unit before a major failure occurs and thus extend the life of the components.

[0131] By "lifetime" is meant the time before failure occurs on a rotor under specific operating conditions.

[0132] Advantageously, the pre-initiated crack is guided in a groove formed on the bottom face of the plate, opposite the top face, and extends along the first direction Z.

[0133] according to Figure 7 In the first embodiment of the invention illustrated in FIG. 1 , the crack gauge G1 may include a resistor made of a wire CW1 arranged on the top surface perpendicular to the first direction Z and designed to be selectively broken depending on the magnitude of fatigue damage causing the propagation of a pre-initiated crack. In other words, the number of broken wires depends on the magnitude of damage detected in a specific location.

[0134] Advantageously, the wires CW1 are arranged in order of increasing length along the first direction.

[0135] according to Figure 8 In the second embodiment of the invention illustrated in FIG. 1 , each fatigue indicator F may include a central section CS connecting two side sections LS1 and LS2, for example having a flat shape. The central section is a weak zone in which the stresses experienced by the fatigue indicator accumulate. In particular, as described in document [2] cited at the end of the description, the central section is designed to break once a predetermined fatigue threshold is reached.

[0136] Whatever the embodiment considered, the method may comprise collecting the variation of the physical parameter by means of a data acquisition system connected to at least one fatigue indicator via a wired or wireless connection.

[0137] In particular, the lines may be passed along the shafting of the hydraulic unit. Optionally, the lines are housed in grooves formed along the shafting.

[0138] In particular, the lines may be passed along the shafting 60 of the hydraulic unit ( FIG. 4 ).

[0139] Optionally, the wiring is received in grooves formed along the shafting.

[0140] Alternatively, the shafting 60 is a hollow shaft, inside which the lines pass.

[0141] A coupling flange at one end of the shafting 60, for example having a disc shape, can ensure that the shafting is fixed to the rotor. In particular, a line can pass along a groove formed on the coupling flange for connecting at least one fatigue indicator.

[0142] The hydraulic unit may also comprise measuring devices for measuring parameters like torque fluctuations experienced by the shafting, bearing vibrations and shafting displacements or hydraulic pressure pulsations.

[0143] These parameters define the operating conditions that directly influence the life of the rotor and can therefore be transmitted to a data acquisition system via wire or via a wireless connection.

[0144] The mounted fatigue indicator, when located on the protected area, does not interfere with the water flow driving the rotor in rotation, so that the fatigue indicator is prevented from falling off.

[0145] Therefore, the fatigue indicator may be permanently mounted on the rotor.

[0146] A dewatering / refilling sequence of events is no longer necessary, so that the costs associated with fatigue detection of the hydraulic turbine according to the invention are limited compared to the methods known from the prior art.

[0147] The invention also relates to a hydraulic unit comprising at least one fatigue indicator arranged for remote interrogation via a line or via a wireless connection and sensitive to fatigue experienced at at least one specific location of the hydraulic unit.

[0148] Optionally, at least one fatigue indicator F is located remote from at least one specific location.

[0149] References

[0150] [1] Pierre-Yves LOWYS et al., “Hydro plant operating range extension transverse approach for increasing turbine flexibility”, Hydrovision International 2014, Track H: Technical paper.

[0151] [2] EP 0 032 101.

Claims

1. A method for detecting fatigue experienced at at least one specific location of a hydraulic unit, said method being characterized in that said fatigue experienced at said at least one specific location is detected by at least one fatigue indicator (F), said at least one fatigue indicator being arranged for remote interrogation via a line or via a wireless connection; in, The hydraulic unit comprises a hydraulic machine provided with a rotating wheel, the rotating wheel being arranged to rotate about a rotation axis once the hydraulic unit is in operation, the at least one specific position being on the rotating wheel; wherein said at least one fatigue indicator (F) is located away from said at least one specific position; The runner comprises blades (43), each of which has two opposite sides, respectively referred to as the pressure side and the suction side, and extends from an outer surface (44a) of a hollow hub (44), the pressure side and the suction side of the blade forming a section of a hydraulic surface, the hollow hub further comprising an inner surface (44b) opposite to the outer surface (44a), the at least one fatigue indicator being located on the inner surface of the hollow hub so that when the hydraulic unit is in operation, the at least one fatigue indicator is isolated from a water flow or an air flow circulating through the hydraulic channel.

2. The method according to claim 1, characterized in that Said at least one fatigue indicator is calibrated such that it is sensitive to said fatigue experienced at said at least one specific location.

3. The method according to claim 1, characterized in that The at least one fatigue indicator is located on a dry surface of the hydraulic unit.

4. The method according to claim 1, characterized in that: The hydraulic unit includes at least one member selected from among a hydraulic machine, a water or air circuit, and a valve or a rotary electric machine, and wherein the at least one specific position is located on at least one of the at least one member.

5. The method according to claim 1, characterized in that The at least one fatigue indicator, upon detecting fatigue above a predetermined fatigue threshold, converts the fatigue into a change in a physical parameter.

6. The method according to claim 5, characterized in that The at least one fatigue indicator includes a plate having a top surface with a crack gauge located on the top surface.

7. The method according to claim 6, characterized in that The plate includes a pre-initiated crack designed to propagate beneath the crack gauge once the predetermined fatigue threshold is reached.

8. The method according to claim 7, characterized in that The crack gauge includes a resistor made of a wire arranged on the top surface perpendicular to the first direction and designed to selectively break depending on the magnitude of the fatigue causing the propagation of the pre-initiated crack.

9. The method according to claim 5, characterized in that The at least one fatigue indicator comprises a central section connecting two side sections, the central section being designed to break once the predetermined fatigue threshold is reached.

10. The method according to any one of claims 5 to 9, characterized in that The method further includes collecting, by a data acquisition system via a wireless connection, the change in the physical parameter.

11. The method according to claim 2, characterized in that The at least one specific location is a location known as a hot spot, where the fatigue experienced corresponds to a local maximum.

12. The method according to claim 5, characterized in that The physical parameter is electrical resistance or a count of accumulated strain or stress.

13. The method according to claim 7, characterized in that The pre-initiated crack is guided in a groove formed on a bottom surface of the plate opposite to the top surface, and extends along a first direction.

14. The method according to claim 8, characterized in that The conductive lines are arranged in order of increasing length along the first direction.

15. The method according to claim 8, characterized in that The wires are broken continuously.

16. The method according to claim 9, characterized in that The two side sections have a flat shape.

17. The method according to claim 10, characterized in that The operating conditions of the hydraulic unit are collected by the data acquisition system.

18. A hydraulic unit comprising at least one fatigue indicator arranged for remote interrogation via wire or via a wireless connection and sensitive to fatigue experienced at at least one specific location of the hydraulic unit; in, The hydraulic unit comprises a hydraulic machine provided with a rotating wheel, the rotating wheel being arranged to rotate about a rotation axis once the hydraulic unit is in operation, the at least one specific position being on the rotating wheel; wherein said at least one fatigue indicator (F) is located away from said at least one specific position; The runner comprises blades (43), each of which has two opposite sides, respectively referred to as the pressure side and the suction side, and extends from an outer surface (44a) of a hollow hub (44), the pressure side and the suction side of the blade forming a section of a hydraulic surface, the hollow hub further comprising an inner surface (44b) opposite to the outer surface (44a), the at least one fatigue indicator being located on the inner surface of the hollow hub so that when the hydraulic unit is in operation, the at least one fatigue indicator is isolated from a water flow or an air flow circulating through the hydraulic channel.

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