REMOVABLE BLADE TIPS FOR A KAPLAN TURBINE

Abstract

 The invention concerns a Kaplan turbine (100) comprising:
- a runner, which comprises a number of blades (16) and a hub (114), located at the end of a shaft (126) and supporting the blades,
- a curved or S shaped discharge ring (200), having a discharge ring throat,
- wherein each of said blades having a removable blade tip (138), so that the outside diameter of the runner is larger than said discharge ring throat diameter (D) when the blade tips are mounted on the blades, but smaller (d₂) than said discharge ring throat diameter (D) when the blade tips are removed from the blades.

Description

TECHNICAL FIELD AND PRIOR ART

[0001] The invention concerns turbines equipped with Kaplan runners.

[0002] The general structure of a Kaplan turbine 100 is illustrated on figure 1; it comprises a runner 112 that is secured at a first end of a rotating shaft 126 centered on a vertical axis Z1 and configured to rotate around said axis in operating conditions. It further comprises a hub 114 equipped with a series of movable or adjustable runner blades 116. Coupling flanges 118 connect each a runner blade 116 to the hub 114, so that the blades are adjustable. The runner 112 is housed in the upper part of a draft tube 200, also known as the discharge ring 202. The latter is designed for evacuating water downstream and for increasing the efficiency of turbine 100. A spiral case 122 is arranged around the runner 112 and is fed with water. Indeed, the spiral case 122 is usually connected to a non-represented penstock that extends from a non-represented upstream reservoir. As a result, water outbursts in the spiral case 122 with a high potential energy. Water flows afterwards between the blades 116 of runner 112, thereby inducing the runner 112 to rotate. The flow rate of water circulating around the runner 112 is regulated by the blades themselves and also by means of guide vanes 124 that are disposed in a circular pattern within the distributor. The guide vanes 124 are each pivotable around an axis parallel to axis Z1 to reduce or increase the flow rate of water entering the turbine 100.

[0003] A generator rotor 132 is connected to the end of the shaft 126 opposite to the runner 112. These parts all rotate along axis Z1. The rotor 132 is disposed coaxially within a stator 134 of a generator 130.

[0004] Figure 2A which shows in detail the interface between the tip of a blade 116 and the concrete wall of the discharge ring 202. Fish trapping often occurs in areas like area I.

[0005] To solve this problem, it is required that discharge rings have 3 curves, successively convex 204, concave 206 and convex 204' as illustrated on figure 2B. This results in a diameter D = 2.R (also called "discharge ring throat diameter") available for the introduction of the blades being smaller than the diameter d₁ = 2.r₁ of the blades themselves.

[0006] For maintenance purposes, the double curvature therefore prevents any runner disassembly. In other words, it is impossible to remove the runner for any maintenance purpose because of the double curvature.

[0007] For this reason, discharge ring inserts 210 are sometimes used as illustrated on figure 2C: they are maintained against the concrete structure forming the discharge ring 202 and can be removed therefrom to allow removal of the runner; but this means that the design of a discharge ring is complex, since it must include inserts 210 having a specific S shape adapted to the discharge ring, and securing means 214 to maintain the inserts against the concrete wall. Furthermore, discharge ring inserts 210 are heavy and cumbersome.

[0008] There is therefore a need for a new structure of a Kaplan turbine provided with a curved or S shaped discharge ring.

[0009] There is also a need for a new method of assembling the blades of a Kaplan turbine provided with a curved or S shaped discharge ring.

[0010] There is also a need for a new method of refurbishing a Kaplan turbine provided with a curved or S shaped discharge ring, for example when the discharge ring is not provided with removable inserts.

SUMMARY OF THE INVENTION

[0011] 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, a curved or S shaped discharge ring, having a discharge ring throat diameter, each of said blades having a removable blade tip, so that the outside diameter of the runner is larger than said discharge ring throat diameter when the blade tips are mounted on the blades, but smaller than said discharge ring throat diameter when the blade tips are removed from the blades.

[0012] The curved or S shaped discharge ring can have one or more discharge ring insert(s).

[0013] Thus, according to the invention the runner can be removed from the discharge ring without having to remove the discharge ring insert(s).

[0014] According to the invention, the blade tips are attached to the blades by securing means, for example bolts and/or solder joints.

[0015] Each of said blades and its removable blade tip can be made of the same material, for example steel.

[0016] The invention also concerns a method for removing the runner of a Kaplan turbine according to the invention from its discharge ring, said method comprising

• removing the tips from the blades;
• then removing the runner from the discharge ring.

[0017] The invention also concerns a method for installing the runner of a Kaplan turbine according to the invention in its discharge ring, said method comprising :

• moving the runner into the discharge ring, the blades not being provided with the tips;
• then mounting the tips on the blades.

[0018] The invention also concerns a method of refurbishing an existing Kaplan turbine having :

• a runner, which comprises a number of blades and a hub, located at the end of a shaft and supporting the blades,
• a curved or S shaped discharge ring, having a discharge ring throat diameter,

said method comprising changing said blades to blades having a removable blade tip, so that the outside diameter of the runner is larger than said a discharge ring throat diameter (D) when the blade tips are mounted on the blades, but smaller (d₂) than said discharge ring throat diameter (D) of the ring inlet when the blade tips are removed from the blades.

[0019] In any method according to the invention, the discharge ring can comprise one or more removable discharge ring inserts, which can be removed before removing the runner from the discharge ring or moving the runner into the discharge ring.

[0020] A method according to the invention may further comprise:

• securing said removable blade tip to each of said blades when the runner is in the discharge ring, with help of securing means, for example bolts and/or solder joints;
• or securing said removable blade tip from each of said blades when the runner is in the discharge ring, by removing said securing means, for example said bolts and/or said solder joints.

[0021] In any method according to the invention, each of said blades and its removable blade tip can be made of the same material, for example made of steel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 

• figure 1 shows an example of a known vertical Kaplan turbine;
• figure 2A shows a blade of a known Kaplan turbine and illustrates the problem of the fish trapping;
• figure 2B shows a blade of a Kaplan turbine in a discharge ring provided with a discharge ring insert;
• figure 3 shows a blade of a Kaplan turbine according to the invention provided with a blade tip;
• figures 4A - 4C show different securing means for a blade and its blade tip according to the invention;
• figure 5A shows a vertical turbine according to the invention;
• figures 5B shows a vertical turbine according to the invention, the shaft, the hub and the blades being removed from the discharge ring.

DETAILLED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0023] An example of a blade for Kaplan turbine according to the invention is illustrated on figure 3, on which the same reference numbers designate the same elements as discussed above in connection with figures 1 and 2A-2C.

[0024] On this figure a blade 116 is formed of two parts, one main part 136, extending from the hub, and a removable extension 138, provided to the end of the main part. Both the removable extension 138 and the main part 136 are preferably made of the same material, for example steel. For fluid flow reasons, a small gap remains between the end of the wall of the discharge ring and the removable extension 138 turned to the wall.

[0025] The extension 138 can be fixed to the main part by bolts 140, 142 (at thicker sections) and/or by soldering 148 (at thinner sections) as illustrated on figures 4A-4C. Bolts 140, 142 can be high strength bolts, bolts 140 in thicker sections being adapted to sustain bending forces, while bolts 142 in thinner sections being adapted to sustain shear forces. The portions which are welded, in particular those with full penetration welds (as on figure 4C), sustain both bending and shear forces.

[0026] As shown on figure 5A, the diameter d₂ of the main part 136 (without removable extension 138) is less than the discharge ring throat diameter (D) (which is the diameter of the upper inlet of the discharge ring), so that the blades and the hub 114 can be removed (see figure 5B, arrow 150) together from the discharge ring after the extensions 138 are removed from all blades (figure 5B), even if the discharge ring has no insert 210. If the discharge ring has an insert 210 (which can be in several sections), this can also be removed, but this step generates extra costs and time and is no longer needed if blades according to the invention are implemented.

[0027] The invention also provides a new way of assembling and/or disassembling Kaplan runner blades implementing removable blade tips 138.

[0028] The tips 138 of the runner blades can be manufactured separately from the rest of the blade. Both parts can then assembled, for example with bolted joints (figures 4A and 4B) at thicker sections and welds (figure 4C) at thinner sections.

[0029] The invention also provides a new way of refurbishing existing Kaplan turbines: blades according to the invention, implementing removable blade tips 138, can be installed, in particular on those turbines not comprising discharge ring inserts.

[0030] Blade tips 138 according to the invention can be mounted on the blades and/or demounted therefrom at any step of their machining, and before and/or after the blades are installed on a turbine. They can also be demounted from the blades before installing the runner on site, in the discharge ring 200 and/or before removing the runner from the discharge ring 200.

[0031] For example, the blade tips 138 can be mounted on the blades and/or demounted therefrom during their machining, for example in a factory.

[0032] A detailed fabrication process is now disclosed.

[0033] The blades are machined, for example implementing a 5-axis machining of both the blades and their tips 138.

[0034] The tips 138 can be temporarily mounted on the blades (as shown on figures 4A - 4C) this step possibly including 5-axis dowelling, and/or threading and/or weld preparations. They can be fastened to the blade with dowels and/or patch bolts and/or temporary welds.

[0035] Finishing step of tips can be performed and repeated as needed.

[0036] The blades, including their tips 138, can then be assembled to the runner.

[0037] A vertical lathe machining of the outer diameter of the tip can be performed once they are assembled on the runner.

[0038] A checking step can be performed to check for the runner-blade homology.

[0039] The tips 138 can be disassembled from the blades.

[0040] The runner blades and their tips can then be shipped to the turbine site.

[0041] Onsite, but outside of the turbine pit, the following steps can be performed.

[0042] The blades (without their tips 138) are assembled to the hub 114 (but not to the blades).

[0043] The runner is prepared for tower assembly, the tower assembly being the assembly of the turbine shaft 126, the intermediate headcover (the part under the reference number 126, on each side of the rotation symbol) and the runner.

[0044] The tips 138 are temporarily attached to the tower assembly (but not to the end of the blades).

[0045] Inside of the pit:
The non-removable double-spherical discharge ring 200 is installed.

[0046] The tower assembly is lowered (see figure 5B, arrow 152) including the runner, but without the tips being mounted to the blades.

[0047] The tips 138 are then fastened to the blade with dowels and/or patch bolts and/or permanent welds (as shown on figures 4A - 4C).

[0048] A checking step can be performed to check for the runner-blade homology.

[0049] To remove the tower assembly:

• welds and/or patch bolts and/or dowels of the tips are removed;
• the tips can be temporarily attached to the tower assembly;
• the tower assembly is removed (figure 5B, arrow 150).

[0050] The invention provides in particular the following advantages:

• it eliminates the need for a removable discharge ring insert;
• it eliminates the risk of the discharge ring insert being stuck at disassembly;
• it does not require any head cover modifications and allows to keep the existing head cover as is;
• installation of blade tip 138 can be done off any project critical path;
• it allows a longer fatigue life :
  Removable blade section at blade tip allows for longer fatigue life (vs section at blade heel which was also considered as alternative to the DR inserts)
• it allows an easier maintenance, since the mass, respectively the volume, of the blade tip 138 is much less than the mass, respectively the volume, of a discharge ring.

[0051] Preliminary calculations (finite elements) show that there is no contact separation except for a very small region with 0.03 mm gap in bolted joints. Stress on bolted and welded joints is therefore manageable.

Claims

1. A Kaplan turbine (100) comprising:

- a runner (112), which comprises a number of blades (116, 136) and a hub (114), located at the end of a shaft (126) and supporting the blades,

- a curved or S shaped discharge ring (202, 204, 204', 206) having a discharge ring throat diameter (D),

- wherein each of said blades has a removable blade tip (138), so that the outside diameter of the runner is larger than said discharge ring throat diameter (D) when the blade tips (138) are mounted on the blades (136), but smaller (d₂) than said discharge ring throat diameter (D) when the blade tips are removed from the blades.

2. A turbine according to claim 1, further comprising one or more removable discharge ring inserts (210).

3. A turbine according to any of claims 1 to 2, further comprising securing means (140, 142, 148) to attach each of said blade tips to a blade.

4. A turbine according to any of claims 1 to 3, each of said blades and its removable blade tip (138) being made of the same material.

5. A turbine according to any of claims 1 to 4, each of said blades and its removable blade tip (138) being made of steel.

6. A method for removing the runner of a Kaplan turbine according to any of claims 1 to 5, from its discharge ring, said method comprising :

- removing the tips (138) from the blades (136);

- then removing (150) the runner from the discharge ring.

7. A method for installing the runner of a Kaplan turbine according to any of claims 1 to 5 in its discharge ring, said method comprising :

- moving the runner into the discharge ring (152), the blades (136) not being provided with the tips (138);

- then mounting the tips (138) on the blades (136).

8. A method of refurbishing a Kaplan turbine having

- a runner (112), which comprises a number of blades (116, 136) and a hub (114), located at the end of a shaft (126) and supporting the blades,

- a curved or S shaped discharge ring (200, 204, 204', 206) having a discharge ring throat diameter (D),

said method comprising changing said blades to blades (136) having a removable blade tip (138), so that the outside diameter of the runner is larger than said discharge ring throat diameter (D) when the blade tips are mounted on the blades, but smaller (d₂) than said discharge ring throat diameter (D) when the blade tips are removed from the blades.

9. A method according to claim 8, said discharge ring comprising one or more removable discharge ring inserts (210).

10. A method according to claim 8 or 9, further comprising securing said removable blade tip (138) to each of said blades when the runner is in the discharge ring.

11. A method according to any of claims 8 to 10, each of said blades and its removable blade tip (138) being made of the same material, for example made of steel.

Drawing