Rotor for a steam turbine, steam turbine, power plant and method for mounting blades in a rotor for a steam turbine

Abstract

The present disclosure relates to a rotor (2), a steam turbine, a power plant and a method (10) for mounting rotor blades in a circumferential female rotor groove (6) of a rotor (2) for a steam turbine. A method (10) comprises inserting (11) a plurality of first blades (9) and inserting (12) second blades (20) in the female rotor groove (6), and inserting (13) a set of closure blades (22, 23, 24). A middle closure blade (24) is coupled to two side closure blades (22, 23) with respective male-female couplings. Shims (28) are arranged around the closure group (22, 23, 24), closing circumferential spaces.

Description

ROTOR FOR A STEAM TURBINE, STEAM TURBINE, POWER PLANT AND METHOD FOR MOUNTING BLADES IN A ROTOR FOR A STEAM TURBINETECHNICAL FIELD

[0001] The present disclosure relates to a rotor having closure blades in a blade stage. Especially, to a drum rotor for a reaction steam turbine. The present disclosure further relates to a method for mounting rotor blades in rotors (blading and re-blading of a rotor stage), and also to steam turbines and various types of power plants including said rotors.BACKGROUND

[0002] Steam turbines are rotary mechanical devices that generate mechanical energy from steam that flows through the turbine. For example, electrical power may be generated by coupling the steam turbine to an electrical generator. A steam turbine includes a rotor which includes a shaft and a plurality of blades arranged in rows. The rotor blades may be referred to as moving blades. The rotor is supported by bearings and is housed in a casing, e.g. a cylinder-shaped casing. The size of steam turbines can vary and can range from industrial size turbines to the largest half-speed steam turbines.

[0003] There are different types of steam turbines which are divided by how steam interacts with blades. The main types are reaction and impulse steam turbines.

[0004] The rows of blades may be connected to the rotor shaft in different manners. In an impulse turbine, or disc-type rotor, the rotor is comprised of a plurality of discs, which are either integral or connected to the shaft. The discs are spaced along the longitudinal direction of the shaft and the blades are mounted to the radially outward portions of the discs. The blade roots associated with impulse turbines can vary in attachment method and can be of either an internal or external form. In a drum-type rotor, the blades are mounted on a drum, e.g. a cylindrical or conical drum. In drum-type rotors, the roots of the moving blades may be of varying shapes, but are typically of external form and inserted into slots or female rotor grooves on the rotor drum. A T-Shaped root inserted into a rotor with a groove that mirrors the blade root form is a common example. The art depicted in this disclosure utilizes this basic configuration.

[0005] Drum-type rotors are typically used in reaction steam turbines, whereas impulse steam turbines commonly use disc-type rotors.

[0006] Stator nozzles comprise a plurality of blades attached to the casing and spaced along a circumferential direction of the casing. A pair of a row of nozzles and a subsequent row of moving blades is usually referred to as a stage of a steam turbine. A steam turbine is typically comprised of a plurality of stages.

[0007] During operation of the steam turbine, the nozzles have a fixed position. They direct the flow of steam between a preceding row of moving blades and the next row of moving blades. The shaft to which the moving blades are attached therefore turns. And the shaft may for example turn a generator for producing electric power.

[0008] The dimensions and shape of the moving blades are relevant for their efficiency, reliability and lifespan. Both the moving blades and the nozzles may generally have an airfoilshaped cross-section and may comprise a leading edge, a trailing edge, a pressure side and a suction side. A cross-section usually changes along a length (i.e. the radial height) of a blade for optimizing an interaction of the blade with the steam and for increasing efficiency. Blades are therefore usually twisted. Blade shapes may also change from one stage to the next, since the thermodynamic conditions (temperature, speed, pressure etc.) will generally be different from one stage to the next.

[0009] A moving blade, i.e. a rotor blade, generally is comprised of two or three portions: a root, an airfoil, and, optionally, a cover portion. The cover portion may be an attachment or may be integral to the blade design. When integral, this is referred to as a shroud. The shroud may extend along a circumferential direction of the row of moving blades. The shrouds of neighboring moving blades may be loosely connected for stabilizing the moving blades and for providing harmonic control. A moving blade which does not include a shroud at its tip may be referred to as non-shrouded moving blade or a free tip moving blade. Rotor blades having a shroud substantially mid-span (i.e. substantially half way along a length of the blade) are also known.

[0010] As mentioned before, a root portion of a blade for a rotor drum may have a T-Shaped root. Another possible shape can be one with a round cross-section. This root portion may be inserted in a circumferential slot of the drum which defines a rotor groove. The blades can be inserted in the slot and then rotated around the longitudinal axis of the moving blade for securing the blade to the drum. Subsequent blades may be introduced in this manner so as to fill a rotor groove in the rotor to create a row of blades.

[0011] A challenge with this method of mounting the turbine rotor blades relates to the last blade or the last few blades to be introduced into the slot. In some examples, a closure blade, i.e. the blade which is to close the last remaining circumferential gap, may have a different root portion such that it may be radially introduced into the slot. Additional securing means are then usually required. Fasteners such as grub screws may be used. However, using these fasteners require perforating the rotor drum for creating a receiving cavity for the fasteners. This weakens the rotor and decreases its lifetime.

[0012] Another known solution is the use of an admission slot or opening in the rotor groove (also called sometimes a rotor groove or a blade-retaining groove), such that rotor blades may be radially introduced in rotor openings for securing their roots in place. However, this also weakens the rotor. Additionally, machining of admission slots in the rotor is time-consuming and also creates a safety risk for operators. This time-consuming machining prolongs mounting of blades, which is not desired as it extends a power outage. The safety risk comes from the weight of the rotor which has to be managed during the whole process involving said machining.

[0013] Other solutions include complicated and time-consuming mechanisms, and shims are usually added for filling the gaps. The shims are evenly distributed across the row of moving blades to maintain integrity of the rotor. The even distribution is also to balance the weight of the rotor during rotation. A shim is a thin piece of material, typically metallic, which helps to adjust the position of the moving blades in the slot of the rotor. Shims are not desired for many reasons. They may be liberated during operation of a steam turbine leading to a need for servicing. Shims also contribute to much longer and more complex mounting of blades as during mounting, shims are used in different sizes.

[0014] The present disclosure therefore provides methods, rotors, steam turbines, and power plants which can mitigate or eliminate one or more of the above-mentioned disadvantages. In particular but not limited to, methods, rotors, steam turbines, and power plants are limiting the usage of shims, ensure fast mounting of blades, avoid weakening of rotors and risks associated with machining of rotors.SUMMARY

[0015] The presented summary is provided for a better understanding of aspects of the invention. It should not be constructed as limiting or exhaustive. All aspects of the invention can be used with any designs of airfoils which means that all aspects of the invention have a wide application in steam turbines.

[0016] In an aspect of the present disclosure, a rotor for a steam turbine comprising a female rotor groove extending along a circumferential direction of the rotor is provided. That rotor groove as it is known forms part of a blade stage. A set of blades placed in that rotor groove forms what is called a row of blades. The rotor comprises a plurality of first blades and each blade of the plurality of first blades comprises a first root portion. The rotor also comprises four, six or more second blades and each second blade comprises a second root portion. Additionally, the rotor comprises a set of three closure blades consisting of a first side closure blade, a second side closure blade, and a middle closure blade that is placed between the first side closure blade and the second side closure blade. The set of closure blades is for closing a row of moving blades on the rotor. In other words, the set of closure blades keeps all blades within a row of the rotor in place, and without the set of closure blades, the moving blades would move and ultimately start to fall out of the rotor. Each of the first side and the second side closure blades comprises a third root portion and the middle closure blade includes a fourth root portion.

[0017] Each root portion of the blade from the group consisting of the plurality of first blades, the first and second side closure blades, and the four, six or more second blades includes a male root part adapted to the female rotor groove for retaining that blade in the female rotor groove. The rotor further comprises a first male-female coupling for retaining the middle closure blade by the first side closure blade, and a second male-female coupling for retaining the middle closure blade by the second side closure blade. In other words, the middle closure blade is retained by the first male-female coupling with the first side closure blade, and by the second male-female coupling with the second side closure blade. This means that all blades except of the middle closure blade are attached to the rotor by couplings between the male root parts of the blades and the female rotor groove.

[0018] Attaching blades to a rotor and retaining blades in the rotor are terms known in the field of turbine engineering. Those terms include a connection between a blade and a rotor which is suitable for operating a turbine including said rotor. Different operating conditions can be implemented and the invention can be applied to all of them.

[0019] The width in the circumferential direction of the first root portion is larger than the width in the circumferential direction of the second root portion to create spaces, and said spaces are filled with shims.

[0020] Changing the relationship between the size of the first root portion and the size of the second root portion as described above together with the described above configuration of the set of closure blades allows to limit the number of shims significantly. In particular to the number of the second blades. The number of second blades is four, six or can be more, forexample, 10, 20. Knowing that there can be around 110 blades in a given female rotor groove, decreasing the number of shims from 110 to 20, 10, six or four offers a significant advantage in terms of eliminating of a risk of shim liberation. The rotors comprising the configuration as described above can have blades mounted significantly faster when compared to configurations having more shims. That allows to use the rotor much faster and so it shortens any outage caused by the need of mounting blades. This is because those different configurations require multiple installation and removal of shims during mounting of blades. This is needed due to geometrical interactions between the blades during mounting. This aspect by omitting the need for using shims of different sizes and multiple installation and removal of shims has further advantage in terms of how precisely and therefore how durable the rotor is bladed for the first time or re-bladed when upgraded or serviced. It should be noted that the rotor does not require to have any admission slots and so the rotor is more durable when bladed or re-bladed with this aspect of the invention.

[0021] In examples, the second blades are distributed between the set of closure blades and the plurality of the first blades. This example allows for faster mounting blades which is relevant for any provision of upgraded blades or serving of rotors. It also facilitates the inspection of the rotor. This particular configuration and its benefits cannot be drawn from the common practices in the field as typically blades are evenly distributed across the female rotor groove. A more improved example requires that the second blades are distributed between the first side closure blade and the plurality of the first blades, and between the second side closure blade and the plurality of the first blades. Even a more improved example has the number of the second blades equally distributed between the first side closure blade and the plurality of the first blades, and between the second side closure blade and the plurality of the first blades.

[0022] In examples, at least one of the first male-female coupling and the second malefemale coupling includes or consists of a protrusion and a recess. The recess can be of any suitable shape that matches the protrusion to create the corresponding male-female coupling. The same applies to the protrusion. The coupling can be realized mainly or only by a geometrical matching. It can also be supported with an additional welding. Welding however is not required.

[0023] In some examples, the middle closure blade includes two protrusions used for retaining that blade in the female rotor groove. Two or more protrusions or even other suitable shapes can be used to realize male-female couplings. Multiple male-female couplings can be used which include, for example, two or more protrusions in one blade and two or more recesses in the other or a mixture of protrusions and recesses in one blade and acorresponding mixture of protrusions and recesses in the other blade. Protrusions can be in the form of protruding stripes or bars. Various types of male-female couplings can be implemented in a single blade or in a pair of blades coupled by said male-female couplings.

[0024] In more detailed examples, the first male-female coupling includes or consists of a first protrusion in the first side closure blade and a first recess in the middle closure blade. In these or other examples, the second male-female coupling includes or consists of a second protrusion in the second side closure blade and a second recess in the middle closure blade. Placing one or both of recesses in the middle closure blade creates more durable closure for all the blades. The reason is a decreasing of mass of the middle closure blade which experiences less tension when compared to heavier middle closure blades having one or two protrusions. Less tension means that the middle closure blade is less prone or even prohibited from liberation from one or both male-female couplings.

[0025] In examples, each said shim is adjacent to at least one of the second blades. This means that each shim is adjacent to the corresponding second blade. This offers further and substantive increase in speed of mounting blades and also in terms of improving inspection of rotors. In more detailed examples, only a single shim is used to fill each space and each said single shim is adjacent to at least one of the second blades. Said single shim can be composed of two half-shims. This example offers better performance in terms of tempo of assembly and in terms of accuracy of assembly. The reason is that using a single shim for filing the space not just allows to by-pass frequent change of shim size during assembly, which weighs on accuracy and rate of assembly, but also provides a decreased chance for shim liberation. This indicates that this example offers in addition to the previous example, a higher durability. In examples, each root portion of the blade from the group consisting of the plurality of first blades, the first and second side closure blades, and the four, six or more second blades includes a male root part that has a conical, round or other cross-sectional shape that allows the blade to be inserted radially and rotated in the female rotor grove. The preferred shape of a male root part is a T-shape cross-section as it combines ease of manufacturing with durability of retaining of blades.

[0026] In examples, the steam turbine is a reaction steam turbine. The rotor is a drum rotor. The drum rotor is particularly difficult to operate due to geometrical hindrances. That means that mounting, and in particular closing, of blades used for impulse turbines cannot be implemented with ease on reaction turbines. An advantage of the invention is that it can be used on reaction turbines as it is able to work with geometrical hindrance that is present on the reaction turbines. It should be noted that the invention is compatible with impulse turbines.

[0027] Another aspect of the invention relates to a steam turbine including a rotor asdescribed in this description. In examples, the steam turbine is a reaction steam turbine or the rotor is a drum rotor or both the steam turbine is a reaction steam turbine and the rotor is a drum rotor. The term “drum rotor” includes drum-type rotors and drum-style rotors.

[0028] The rotor and the steam turbine as described in this description are applicable to any type of power plant as well as to industrial application. In a further aspect, a fossil, renewable-energy, waste-to-energy, combined-cycle or nuclear powerplant comprises the steam turbine or the rotor as described herein.

[0029] Another aspect includes a method for mounting blades in a rotor for a steam turbine. The rotor comprises a female rotor groove extending along a circumferential direction of the rotor. The method comprises mounting a plurality of first blades by radially inserting a first root portion of each blade of the plurality of first blades into the female rotor groove and subsequently rotating the first root portion. This results in retaining each said blade by an interaction between a male root part with the female rotor groove. The method further comprises mounting four, six or more second blades by radially inserting a second root portion of each of the second blades into the female rotor groove and subsequently rotating the second root portion. This results in retaining each said blade by an interaction between a male root part with the female rotor groove. The method further comprises radially inserting third root portions of a first side closure blade and of a second side closure blade into the female rotor groove and subsequently rotating them, and subsequently radially inserting a fourth root portion of a middle closure blade into the female rotor groove between the third root portions of the first side closure blade and of the second side closure blade to retain the middle closure blade in the female rotor groove by a first male-female coupling with the first side closure blade and by a second male-female coupling with the second side closure blade.

[0030] Each root portion of the blades from the group consisting of the plurality of first blades, the first and second side closure blades, and the four, six or more second blades includes a male root part adapted to the female rotor groove for retaining that blade in the female rotor groove.

[0031] In this aspect, the width in the circumferential direction of the first root portion is larger than the width in the circumferential direction of the second root portion to create spaces in the number equal to the number of the second blades, said spaces being located next to each of the second blades. Those spaces are needed as otherwise the blades cannot be mounted in the female rotor groove. At the same time, those spaces have to be secured with shims. Thus, the method comprises also inserting shims in each said space for completing mounting of blades in the female rotor groove. Preferably, a single shim is used for each said space. More preferable, each said single shim is composed of two half-shims.

[0032] With the methods and rotors herein provided, machining openings in the rotor drum for securing the rotor blades to the rotor drum may be avoided. These openings weaken the rotor drum and can reduce its lifetime. Also, the use of fasteners such as grub screws may be avoided. A faster, safer and simplified installation of the rotor blades may be achieved. Also, the rotor may be more durable.

[0033] Elements of the aspects and examples can be combined together in any number and order to form new aspects and examples which are within the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 schematically illustrates an example of a portion of rotor blade for a steam turbine mounted in a rotor.

[0035] Figure 2 shows a flow chart of a method for mounting blades in a female rotor groove of a rotor for a steam turbine.

[0036] Figure 3 schematically illustrates an example of a portion of a female rotor groove of a rotor for a steam turbine with rotor blades arranged in the female rotor groove.

[0037] Figure 4 schematically illustrates an example of a closure set of rotor blades.DETAILED DESCRIPTION OF EXAMPLES

[0038] Reference now will be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation only, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0039] A schematic example of a portion of rotor blade for a steam turbine is shown in figure 1 . The rotor blade 1 is generally comprised of three portions: a root or root portion 36, an airfoil portion 3, and an optional shroud area portion 29. The root portion 36 serves for connecting the rotor blade 1 to a rotor drum or disc. The airfoil portion 3 is the aerodynamic portion that is configured to interact with the steam that passes by. The interaction results in a force thatcontributes to turning the blade. In this particular example, the rotor blade 1 comprises a shroud portion 29 arranged at the tip of the blade. The shroud or tip portion 29 of the rotor blade 1 rotates close to the stator casing when the rotor of the steam turbine rotates.

[0040] The rotor blade 1 comprises a platform 5 upon which the airfoil portion 3 is arranged. The platform 5 may also be called “shoulder” and may be positioned on top of the rim 8 of the rotor. Generally, this area prevents rotation of the root of the blade, along its axis, within the rotor.

[0041] The root portion 36 may include a male root part including a radial shank 46, an axially forward extending flange 26A, and an axially rearward extending flange 26B. The root portion may be radially inserted, and subsequently rotated. The male root part thereby fits in the female rotor groove in the rotor 2, and the root portion is radially retained in the female rotor groove by the flanges 26A and 26B. The female rotor groove conforming to blade root portion 36 may be provided in a rotor drum. Arrow 4 schematically indicates an axial direction of the rotor.

[0042] In an aspect of the disclosure, a method 10 for mounting blades in a rotor 2 for a steam turbine is provided. The steam turbine may be a reaction steam turbine. The rotor may be a drum rotor. The rotor comprises a female rotor groove extending along a circumferential direction of the rotor. The flow chart of figure 2 illustrates an example of such a method 10.

[0043] The method comprises, at block 11 , mounting a plurality of first blades 1 by radially inserting a first root portion 36 of each blade of the plurality of first blades into the female rotor groove and subsequently rotating the first root portion.

[0044] A rotor drum is rotatable around its longitudinal axis. The rotor drum may comprise a plurality of circumferential female rotor grooves spaced along the axial direction of the rotor drum in which rotor blades, specifically a root portion 36 of the blades 1 , can be inserted. The plurality of circumferential female rotor grooves is arranged at different longitudinal positions of the rotor drum.

[0045] The blade 1 of the example of figure 1 may be inserted, i.e. radially introduced, in a female rotor groove of the rotor drum and then turned. After turning of the blade 1 , a top portion of the root 36 such as a platform or shoulder 5 may rest on top and / or sides of the rim 8 of the rotor drum in which the slot is provided. The blade 1 can therefore be slid along the slot in the circumferential direction for arranging it in a desired position.

[0046] Additional blades 1 can be arranged in the female rotor groove of the rotor drum in this manner until a large portion of the female rotor groove has been populated with the blades.

[0047] Figure 3 schematically illustrates an example of a portion of a female rotor groove 6 of a rotor drum 7 for a steam turbine with rotor blades 1 arranged therein. In this figure, the shoulders 5 of the roots 36 of the blades 1 rest on top of rim 8 in which the matching root portion 36 is provided.

[0048] Method 10 further comprises, at block 12, mounting four, six or more second blades by radially inserting a second root portion of each of the second blades into the female rotor groove 6 and subsequently rotating the second root portion.

[0049] In the example of figure 3, a plurality of first blades 9 and a plurality of second blades 20 are provided. The first blades 9 may account for the majority of the rotor blades that are arranged in the female rotor groove 6. After they have been inserted and are radially retained in the female rotor groove 6, a circumferential gap may remain between the first blades arranged at the ends of the group of first blades 9. I.e., the plurality of first blades 9 may be arranged in the female rotor groove and form a shape of an open ring. The second blades 20 may be inserted and retained in the circumferential gap between the ends of the “open ring” of first blades 9.

[0050] The first blades 9 and the second blades 20 may have a different width. Specifically, the second blades 20 may have a smaller width than a width of the first blades 9. A width 21 of a blade may be measured along the circumferential direction of the female rotor groove (when the blade 9, 20 is arranged and locked therein), and therefore along the circumferential direction of the rotor drum 7. Specifically, a width 21 of the shoulder or platform 5 may be regarded as the width 21 of the blade.

[0051] In general, the first blades 9 may be arranged in the female rotor groove 6 first, and the second blades 20 may be arranged afterwards. The second blades 20 may be movable, e.g. slidable, along the circumferential direction of the female rotor groove.

[0052] Method 10 further comprises, at block 13, radially inserting third root portions of a first side closure blade 22 and of a second side closure blade 23 into the female rotor groove 6 and subsequently rotating them, and radially inserting a fourth root portion of a middle closure blade 24 into the female rotor groove 6 between the third root portions of the first side closure blade 22 and of the second side closure blade 23 to retain the middle closure blade 24 in the female rotor groove 6 by a first male-female coupling with the first side closure blade 22 and by a second male-female coupling with the second side closure blade 23.

[0053] Each root portion of the blade from the group consisting of the plurality of first blades9, the first 22 and second 23 side closure blades, and the four, six or more second blades 20includes a male root part adapted to the female rotor groove 6 for retaining that blade in the female rotor groove 6.

[0054] First 22 and second 23 side closure blades are thus inserted and retained in the radial direction by rotating them around themselves, and then a middle closure blade 24 is radially inserted between the two side closure blades 22, 23. The middle closure blade 24 is the blade 24 that is mounted last. The circumferential female rotor groove has been almost entirely filled with the previously installed blades 9, 20. The middle closure blade 24 is radially inserted between the side blades 22, 23, but it is not turned or rotated around its longitudinal axis because there is no sufficient space.

[0055] Once the second blades 20 and the closure blades 22, 23, 24 have been arranged in the female rotor groove 6, the number of second blades 20 mounted between the first side closure blade 22 and the plurality of the first blades 9, and between the second side closure blade 23 and the plurality of the first blades 9, may be equal. The second blades 20 may be mounted on both sides of the set formed by the closure blades 22, 23, 24.

[0056] The closure blades 22, 23, 24, which may form a closure set, may comprise root portions with recesses and / or protrusions extending in the circumferential direction when arranged in the female rotor groove 6, which will be further illustrated with reference to the example of figure 4.

[0057] In some examples, the blades 22, 23, 24 of the closure set and the first blades 9 may have the same width. This may help to provide symmetry along the circumference of the rotor.

[0058] Figure 4 schematically illustrates an example of a closure set of rotor blades. Similarly to figures 1 and 3, arrow 4 indicates the circumferential direction of the female rotor groove. When the side closure blades 22, 23 have been inserted in the female rotor groove and rotated, their shoulders 5 rest on top of the rim 8 in this example, see also figure 3. The roots 36 of the side closure blades 22, 23 and the middle closure blade 24 are configured to provide a male-female coupling between them, specifically in the circumferential direction 4 of the female rotor groove. The side closure blades 22, 23 can therefore sandwich the middle closure blade 24 and help to retain it in the female rotor groove.

[0059] As previously explained, the first 9 and second 20 blades, see figure 3, may be retained in the radial direction when inserting them in the female rotor groove 6 and rotating them around their longitudinal axes. The same is applicable to the side closure blades 22, 23. In other words, the roots 36 of these blades 9, 20, 22, 23 may comprise flanges 26 for securing the blades 9, 20, 22, 23 in the radial direction, see figure 4. When the blades 9, 20, 22, 23have been inserted and rotated, the flanges 26 may protrude in the axial or longitudinal direction of the rotor drum. The protrusions and / or recesses of the side blades 23 may protrude in the circumferential direction.

[0060] As the root 36 of the middle closure blade 24 is not to be rotated around itself due to the lack of space, but rather sandwiched by the side closure blades 22, 23, the middle closure blade 24 lacks such flanges 26. In some examples, the first male-female coupling includes or consists of a first protrusion in the first side closure blade and a first recess in the middle closure blade. In these examples, the second male-female coupling may include or consist of a second protrusion in the second side closure blade and a second recess in the middle closure blade.

[0061] In the example of figure 4, circumferential root end portions of the middle blade 24 comprise recesses 25. The circumferential root end portions of the side closure blades 22, 23 configured to face the middle closure blade 24 therefore comprise protrusions 27. The protrusions 27 of the side closure blades 22, 23 and the recesses 25 of the middle closure blade 24 may provide a male-female coupling between the side closure blades 22, 23 and the middle closure blade 24.

[0062] Other configurations of protrusions 27 and recesses 25 are possible. For example, the middle closure blade 24 may comprise two protrusions, or a recess on one side and a protrusion on the other. A middle closure blade 24 with two recesses 25 minimizes its weight. This may reduce the stress in the connection with the side closure blades 22, 23, and therefore the risk of the middle closure blade 24 undesirably disengaging and leaving the female rotor groove during operation.

[0063] In this example, the middle closure blade includes one recess on a side surface of the root portion. It should be clear that other male-female couplings may be provided, e.g. more than one protrusion on a side surface, or both a protrusion and a recess on a side surface (with the corresponding counterparts on the neighboring blade).

[0064] The side surfaces of the root end portions of the side closure blades 22, 23 which face away from the middle closure blade 24 may lack protrusions and recesses. For example, the corresponding circumferential end surfaces of the side closure blades 22, 23 may be flat.

[0065] Returning to method 10, the width 21 (see e.g. figure 3) in the circumferential direction of the first root portion is larger than the width in the circumferential direction of the second root portion to create a number of spaces equal to the number of second blades 20, said spaces being located next to each of the second blades 20. Method 10 further comprises,at block 14, inserting a shim 28 in each said space for completing the mounting of blades in the female rotor groove 6.

[0066] Shims 28 are therefore inserted for totally closing the circumferential gap and for securing the middle closure blade 24 between the side closure blades 22, 23. Inserting the shims 28 may provide for an effective male-female coupling between the root portions 36 of the two side closure blades 23 and the middle closure blade 24, for example as the protrusions are forced to engage the recesses on the closure blades. A male-female coupling may alternatively or additionally be provided before the shims 28 are inserted. For example, the first 22 and second 23 side closure blades and the middle closure blade 24 may be moved along the female rotor groove of the rotor drum for joining these blades 22, 23, 24 before the shims 28 are inserted.

[0067] Each said space may be adjacent to at least one of the second blades 20. For example, a space may be provided adjacent each second blade 20 such that a shim 28 is inserted in each space.

[0068] The shims 28 may particularly be arranged with the second blades 20, for example between the second blades 20 and optionally between a second blade 20 and a side blade 23 of the closure set. A number of second blades 20 and a number of shims 28 may be the same. A pitch, i.e. a center-to-center distance (along the circumferential direction 4), of two adjacent first blades 9 may be the same. A pitch of the first blades may be higher than the pitch of the second blades.

[0069] Reducing a width 21 of the second blades 20 with respect to the first blades 9, see figure 3, may help to reduce a number of shims 28 used. Inserting shims 28 is time consuming and therefore this allows for a simpler and faster closing of the circumferential gap.

[0070] The use of the closure blades 22, 23, 24, specifically due to the male-female coupling connections, also helps to reduce a number of shims 28 required. Using less shims 28 reduces the risk of shim liberation during operation of the steam turbine.

[0071] In some examples, the plurality of shims comprises less than 10 shims, specifically 8 shims or less. For example, 6 shims or 4 shims may be used. As previously mentioned, using less shims facilitates and speeds up the installation of the rotor blades in the female rotor groove of a rotor, and reduces the risk of shims becoming dislodged in operation.

[0072] Each root portion of the blade from the group consisting of the plurality of first blades 9, the first 22 and second 23 side closure blades, and the four, six or more second blades 20 may include a male root part that is T-shaped.

[0073] In a further aspect of the disclosure, a rotor 2 for a steam turbine is provided. With reference to the examples of figures 3 and 4, the rotor comprises a female rotor groove 6 extending along a circumferential direction 4 of the rotor. The rotor further comprises a plurality of first blades 9, each blade of the plurality of first blades 9 comprising a first root portion. The rotor further comprises four, six or more second blades 20, each second blade 20 comprising a second root portion.

[0074] The rotor further comprises a set of three closure blades 22, 23, 24 consisting of a first side closure blade 22, a second side closure blade 23, and a middle closure blade 24 between the first side closure blade 22 and the second side closure blade 23. Each of the first side closure blade 22 and the second side closure blades 23 comprises a third root portion, and the middle closure blade 24 includes a fourth root portion.

[0075] A first male-female coupling for retaining the middle closure blade 24 by the first side closure blade 22, and a second male-female coupling for retaining the middle closure blade 24 by the second side closure blade 23 are provided.

[0076] Each root portion of the blade from the group consisting of the plurality of first blades 9, the first 22 and second 23 side closure blades, and the four, six or more second blades 20 includes a male root part adapted to the female rotor groove 6 for retaining that blade in the female rotor groove 6.

[0077] A width 21 of the first root portion in the circumferential direction of the rotor is larger than a width of the third root portion in the circumferential direction of the rotor to create spaces. The rotor further comprises shims 28 filling the spaces. A number of spaces may be equal to the number of the second blades 20.

[0078] The first male-female coupling may include or consist of a first protrusion 27 in the first side closure blade 22 and a first recess 25 in the middle closure blade 24. The second male-female coupling may include or consists of a second protrusion 27 in the second side closure blade 23 and a second recess 25 in the middle closure blade 24, see figure 4.

[0079] The second blades 20 may be distributed between the set of closure blades 22, 23, 24 and the plurality of first blades 9. Specifically, the second blades 20 may be distributed between the first side closure blade 22 and the plurality of the first blades 9, and between the second side closure blade 23 and the plurality of the first blades 9. And the number of the second blades 20 distributed between the first side closure blade 22 and the plurality of the first blades 9, and between the second side closure blade 23 and the plurality of the first blades 9, may be equal.

[0080] A number of second blades 20 may be four or six in some examples. For example, three second blades 20 may be arranged at a side of the set of closure blades 22, 23, 24, and the three other second blades 20 may be arranged at the opposite side of the set of closure blades.

[0081] Each said shim 28 may be adjacent to at least one of the second blades 20. For example, the second blades 20 and the shims 28 may be positioned in shim-second blade pairs.

[0082] Each root portion of the blade from the group consisting of the plurality of first blades 9, the first 22 and second 23 side closure blades, and the four, six or more second blades 20 may include a male root part that is T-shaped.

[0083] The rotor may be a drum rotor, and the steam turbine may be a reaction steam turbine.

[0084] The blades 9, 20, 22, 23, 24 of this rotor may specifically be mounted as explained with respect to the method 10 of the previous aspect. Details and explanations with respect to method 10 and figures 1 - 4 may be applicable to this aspect, and vice versa. As previously mentioned, the root portions 36 of the blades 9 of the first group, the blades 20 of the second group and the two side blades 22, 23 may be T-shaped shaped in some examples.

[0085] A rotor blade may in some examples further include a cover portion or shroud 29 at its tip, see figures 3 and 4. The shroud 29 may extend along a circumferential direction of the rotor. The shrouds of neighboring rotor blades may be loosely connected for stabilizing the rotor blades. The shrouds of the first blades 9, the second blades 20 and the closure blades 22, 23, 24 may extend a same amount in the circumferential direction.

[0086] In a further aspect of the disclosure, a steam turbine comprising the rotor of the previous aspect, i.e. a rotor with a circumferential female rotor groove and rotor blades arranged in the female rotor groove as described throughout this disclosure, is provided. In some examples, the steam turbine may be a reaction steam turbine and the rotor is a drum rotor.

[0087] In a further aspect of the disclosure, a fossil, renewable-energy, waste-to-energy, combined-cycle or nuclear powerplant comprising a steam turbine as described herein or a rotor as described herein is provided.

[0088] This written description uses examples to disclose a teaching, including the preferred embodiments, and also to enable any person skilled in the art to put the teaching into practice, including making and using any devices or systems and performing anyincorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Elements from the various embodiments, aspects and examples described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments, aspects and examples in accordance with principles of this application which are part of the disclosure. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Claims

CLAIMS1 . A rotor (2) for a steam turbine comprising a female rotor groove (6) extending along a circumferential direction (4) of the rotor (2), the rotor (2) comprising: a plurality of first blades (9), each blade (9) of the plurality of first blades (9) comprising a first root portion (36); four, six or more second blades (20), each second blade (20) comprising a second root portion (36); and a set of three closure blades (22, 23, 24) consisting of a first side closure blade (22), a second side closure blade (23), and a middle closure blade (24) between the first side closure blade (22) and the second side closure blade (23), wherein each of the first side (22) and the second side (23) closure blades comprises a third root portion (36), and wherein the middle closure blade (24) includes a fourth root portion; a first male-female coupling for retaining the middle closure blade (24) by the first side closure blade (22), and a second male-female coupling for retaining the middle closure blade (24) by the second side closure blade (23); and wherein each root portion (36) of the blades from the group consisting of the plurality of first blades (9), the first (22) and second (23) side closure blades, and the four, six or more second blades (20) includes a male root part (46, 26, 26A, 26B) adapted to the female rotor groove (6) for retaining that blade in the female rotor groove (6), and wherein a width (21) of the first root portion (36) in the circumferential direction (4) of the rotor (2) is larger than a width (21) of the second root portion (36) in the circumferential direction (4) of the rotor (2) to create spaces, and the rotor (2) further comprising shims (28) filling the spaces.

2. The rotor of claim 1 , wherein a number of second blades (20) is four or six.

3. The rotor of claim 1 or claim 2, wherein the second blades (20) are distributed between the set of closure blades (22, 23, 24) and the plurality of the first blades (9).

4. The rotor of claim 3, wherein the second blades (20) are distributed between the first side closure blade (22) and the plurality of the first blades (9), and between the second side closure blade (23) and the plurality of the first blades (9).

5. The rotor of claim 4, wherein the number of the second blades (20) distributed between the first side closure blade (22) and the plurality of the first blades (9), and between the second side closure blade (23) and the plurality of the first blades (9), is equal.

6. The rotor of any of claims 1 - 5, wherein the first male-female coupling includes or consists of a first protrusion (27) in the first side closure blade (22) and a first recess (25) in the middle closure blade (24).

7. The rotor of any of claims 1 - 6, wherein the second male-female coupling includes or consists of a second protrusion (27) in the second side closure blade (23) and a second recess (25) in the middle closure blade (24).

8. The rotor of any of claims 1 - 7, wherein each of said shims (28) is adjacent to at least one of the second blades (20) and / or each of said shims (28) is composed of two half-shims.

9. The rotor of any of claims 1 - 8, wherein the steam turbine is a reaction steam turbine.

10. The rotor of any of claims 1 - 9, wherein the rotor (2) is a drum rotor.11 . The rotor of any of claims 1 - 10, wherein each root portion (26) of the blade from the group consisting of the plurality of first blades (9), the first (22) and second (23) side closure blades, and the four, six or more second blades (20) includes a male root part (46, 26, 26A, 26B) that is T-shaped.

12. The rotor of any of claims 1 - 11 , wherein a number of spaces is equal to the number of the second blades (20), and each space is filled with a single shim (28).

13. A steam turbine comprising the rotor (2) of any of claims 1 - 12.

14. The steam turbine of claim 13, wherein the steam turbine is a reaction steam turbine and the rotor (2) is a drum rotor.

15. A fossil, renewable-energy, waste-to-energy, combined-cycle or nuclear powerplant comprising the steam turbine as claimed in any of claims 13 - 14 or the rotor (2) as claimed in any of claims 1 - 12.

16. A method (10) for mounting blades in a rotor (2) for a steam turbine, the rotor (2) comprising a female rotor groove (6) extending along a circumferential direction (4) of the rotor (2), the method (10) comprising: mounting (11) a plurality of first blades (9) by radially inserting a first root portion (36) of each blade (9) of the plurality of first blades (9) into the female rotor groove (6) and subsequently rotating the first root portion (36); mounting (12) four, six or more second blades (20) by radially inserting a second root portion (36) of each of the second blades (20) into the female rotor groove (6) and subsequently rotating the second root portion (36); radially inserting (13) third root portions (36) of a first side closure blade (22) and of a second side closure blade (23) into the female rotor groove (6) and subsequently rotating them; and radially inserting a fourth root portion of a middle closure blade (24) into the female rotor groove (6) between the third root portions (36) of the first side closure blade (22) and of the second side closure blade (23) to retain the middle closure blade (24) in the female rotor groove (6) by a first male-female coupling with the first side closure blade (22) and by a second male-female coupling with the second side closure blade (23); and wherein a width (21) in the circumferential direction (4) of the first root portion (36) is larger than a width (21) in the circumferential direction (4) of the third root portion (36) to create spaces located next to each of the second blades (20); and inserting (14) a shim (28) in each said space for completing the mounting of blades in the female rotor groove (6); and wherein each root portion (36) of the blades from the group consisting of the plurality of first blades (9), the first (22) and second (23) side closure blades, and the four, six or more second blades (20) includes a male root part (46, 26, 26A, 26B) adapted to the female rotor groove (6) for retaining that blade in the female rotor groove (6).

17. The method of claim 16, wherein a number of the second blades (20) mounted between the first side closure blade (22) and the plurality of the first blades (9), and between the second side closure blade (23) and the plurality of the first blades (9) is equal.

18. The method of claim 17, wherein the second blades (20) are mounted on both sides of the closure blades (22, 23, 24).

19. The method of any of claims 16 - 18, wherein the first male-female coupling includes or consists of a first protrusion (27) in the first side closure blade (22) and a first recess (25) in the middle closure blade (24).

20. The method of any of claims 16 - 19, wherein the second male-female coupling includes or consists of a second protrusion (27) in the second side closure blade (23) and a second recess (25) in the middle closure blade (24).21 . The method of any of claims 16 - 20, wherein a number of shims (28) is the same as a number of the second blades (20).

22. The method of any of claims 16 - 21 , wherein the steam turbine is a reaction steam turbine.

23. The method of any of claims 16 - 22, wherein the rotor (2) is a drum rotor.

24. The method of any of claims 16 - 23, wherein each root portion (36) of the blade from the group consisting of the plurality of first blades (9), the first (22) and second (23) side closure blades, and the four, six or more second blades (20) includes a male root part (46, 26, 26A, 26B) that is T-shaped.

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