EP4695536A1

EP4695536A1 - Shaft sealing assembly and corresponding methods of sealing of casings of synchronous condensers, electric generators and their flywheels

Info

Publication number: EP4695536A1
Application number: EP23730768.1A
Authority: EP
Inventors: Wolfgang Walter; Olaf Dierker; Pierre-Yves David
Original assignee: Ge Vernova Technology GmbH
Current assignee: Ge Vernova Technology GmbH
Priority date: 2023-06-02
Filing date: 2023-06-02
Publication date: 2026-02-18
Also published as: WO2024245569A1

Abstract

The present disclosure relates to shaft sealing assemblies (2) for sealing a casing (5) of a rotating machine (1) that includes electric generators, short circuit generators, synchronous condenser and flywheels thereof. The present disclosure further relates to methods for sealing of a casing (5) of a rotating machine (1). A shaft sealing assembly (2) comprises a shaft seal gland (8) configured to be arranged around the rotatable shaft (3), a flexible sleeve (7) configured to flexibly connect the shaft seal gland (8) to the casing (5) and to create a seal between the shaft seal gland (8) and the casing (5) for maintaining pressure conditions within the casing (5), and a fixation element (6) configured to fix the shaft seal gland (8) to the bearing block (4) thereby avoiding or preventing relative displacement of the shaft seal gland (8) and the bearing block (4).

Description

SHAFT SEALING ASSEMBLY AND CORRESPONDING METHODS OF SEALING OF CASINGS OF SYNCHRONOUS CONDENSERS, ELECTRIC GENERATORS AND THEIR FLYWHEELS

TECHNICAL FIELD

[0001] The present disclosure relates to shaft sealing assemblies for synchronous condensers, electric generators for turbines and flywheels for electric generators, and more particularly relates to synchronous condensers, electric generators and flywheels configured to operate at a substantial overpressure or at a substantial vacuum. The present disclosure further relates to methods for mounting a shaft sealing assembly around a shaft of a synchronous condenser, flywheel or electric generator.

BACKGROUND

[0002] A rotating component, for example, a rotating shaft for an electric generator or for a synchronous condenser, is housed at least in part in a casing, e.g. a cylinder-shaped casing. Bearings arranged in bearing blocks support the rotating shaft. Typically, on both sides of the casing. Bearing blocks may also be referred to as bearing pedestals, plummer blocks or pillow blocks.

[0003] Seals are provided to maintain conditions within the casing by closing the gap between the casing and the rotatable shaft. Seals can allow to keep a desired pressure level inside the casing. Seals can also help to avoid the leakage of fluid or gas, for example, cooling air and other cooling gas to the outside of the casing and to prevent the entrance of e.g. outside air into the casing. A suitable pressure inside the casing may be kept by providing one or more seals on the shaft, between the bearings blocks and the casing.

[0004] A low pressure or vacuum inside the casing may sometimes be desired. Rotor drag and friction may be reduced inside the casing, which may help to increase efficiency and to avoid an excessive increase of rotor temperature. This may be particularly applicable to a flywheel casing, e.g. when a flywheel is coupled to a shaft of a synchronous condenser or of an electric generator. Vacuum may be applied inside the flywheel casing. One or more seals can be arranged on the flywheel shaft to seal a flywheel casing and may allow to maintain vacuum (or any desired suitable pressure) within the casing. Another application, in addition to the flywheel casing, can be made in synchronous condensers and electric generators as such in order to reduce friction and windage losses in them.

[0005] Throughout the present disclosure, a vacuum may be interpreted as a pressure that is at a level that is lower than atmospheric pressure. In particular, significantly lower (typically 0.1 bar absolute). Accordingly, overpressure may be interpreted as a pressure that is at a level that is higher than atmospheric pressure. In particular, significantly higher (typically up to 1 bar gauge).

[0006] A bearing block may rotatably support a shaft of an electric generator or of a synchronous condenser flywheel. A seal gland comprising at least one seal may be provided between a casing and the rotatable shaft, sealing a space between the casing and the rotatable shaft. Sealing a space herein means sealing the casing in order to prevent or decrease losing overpressure or vacuum within the casing. However, due to differing thermal expansion, e.g. between the casing and the bearing block (bearing pedestal), or other causes, the seal gland may be subjected to relative displacement between the rotating and stationary components. The risk of rubbing and seal wear may increase in such a situation. Also, the pressure differential between casing and seal and ambient conditions may cause varying forces which can lead to slipping and/or failure of components. Ultimately, losing overpressure or vacuum within the casing can lead to tangible losses in electrical power generated by and in cooperation with the rotating machine.

[0007] The present disclosure provides effective and durable shaft sealing assemblies for synchronous condensers, electric generators and their flywheels.

SUMMARY

[0008] In an aspect of the present disclosure, a shaft sealing assembly for sealing a casing of a rotating machine is provided. The rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser. The electric generator can also be, but is not limited to, a short-circuit generator. The casing includes a rotatable shaft. The rotating machine is configured to work under pressure conditions within the casing: the pressure conditions are selected from a substantial overpressure and a substantial vacuum. In this aspect, the shaft sealing assembly is configured to be mounted on (e.g., arranged around) the rotatable shaft and between the casing and a bearing block that supports the rotatable shaft. The shaft sealing assembly comprises: a shaft seal gland configured to be arranged around the rotatable shaft, a flexible sleeve configured to flexibly connect the shaft seal gland to the casing and to create a seal between the shaft seal gland and the casing for maintaining pressure conditions within the casing, and a fixation element configured to fix the shaft seal gland to the bearing block thereby avoiding or decreasing relative displacement between the shaft seal gland and the bearing block.

[0009] Decreasing relative displacement between the shaft seal gland and the bearing block ensures that relative displacement between the shaft seal gland and the rotatable shaft is limited or prevented. This relative displacement is responsible for failure of the shaft seal gland. Thus, limiting or even preventing it ensures longer lifetime for the shaft seal gland and for the shaft sealing assembly.

[0010] It is known that relative displacement can originate, for example, from differences in thermal expansion that can occur both in transient and in stationary conditions. The fixation element ensures that the risk of rubbing and wearing of shaft sealing assembly is decreased by reducing this relative displacement. Avoiding of relative displacement is more beneficial as it minimizes the risk of rubbing and wearing of the shaft sealing assembly. In embodiments, the fixation element preferably rigidly fixes the shaft seal gland to the bearing block. In other embodiments, the fixation element resiliently fixes i.e. in a spring-like manner, which is not preferred, the shaft seal gland to the bearing block. The fixation element can have many forms. It should be noted that implementing the fixation element as described above allows to decrease the clearances between the rotating shaft and the shaft seal thereby improving sealing of the casing. This has a positive impact on efficiency of the rotating machine. It is worth noting an additional benefit of this fixation element (especially for examples where the fixation element includes arms), i.e., it does not require disengagement of the rotating shaft to be installed or serviced, i.e., removal of the rotating shaft. It follows that unlike other solutions that require time and effort to disengage the rotating shaft, this can be installed faster, easier and safer as well as can be serviced faster, easier and safer.

[0011] It should be noted that the fixation element is configured to fix the shaft seal gland to the bearing block if the fixation element is configured to fix said gland to a part of the bearing block or to any extension, ring, arm or combinations thereof mounted or connected to the bearing block. All those parts, extensions, rings, arms or combinations thereof are considered to be part of the bearing block since they are attached to it. Also, they are not affecting the mode of operation of the shaft sealing assembly. The same with the flexible sleeve configured to flexibly connect the shaft seal gland to the casing, i.e., the flexible sleeve is configured to flexibly connect the shaft seal gland to the casing if it is configured to flexible connect the shaft seal gland to an extension, arm, disk, element and combinations thereof of the casing. This is because all those parts, extensions, arms, disks, elements and combinations thereof are attached to the casing. Additionally, they are not affecting the mode of operation of the shaft sealing assembly. In examples, the fixation element has two or more parts that create it.

[0012] As described above, the flexible sleeve flexibly connects the shaft seal gland and the casing. Flexibility of this connection allows for relative displacement of the shaft seal gland and the casing. Particularly, the flexible sleeve may allow relative displacement between the shaft seal gland and casing in a radial and/or an axial direction. Said relative displacement can originate from thermal expansion. At the same time, the flexible sleeve creates a seal between the shaft seal gland and the casing that allows to maintain pressure conditions within the casing. In other words, an air gap or space between the shaft seal gland and the casing is sealed with the flexible sleeve. There are known ways to make such flexible sleeve, i.e. , that are both flexible and can withstand pressure conditions as well as operating temperature of the rotating machine. It follows that there are many ways to create this flexible sleeve and so there is no need to specify details thereof. In embodiments, the flexible sleeve can have the shape of a cylinder or annular disc. Other shapes are also suitable to be used.

[0013] The flexible sleeve provides an effective sealing between the casing and the shaft seal gland while there is relative displacement between the casing and the shaft seal gland. The sealing may therefore be performed without transferring forces or movement between those two components. As a result, the risk of rubbing or of seal wear may be decreased or prevented. As previously explained, this ensures longer life of the shaft seal gland and thus increases time intervals between servicing of the shaft seal gland. In other words, this allows to increase the time when the rotating machine is operating. Therefore, the overall efficiency of the rotating machine is increased. Among the additional benefits of the flexible sleeve are: there is no need to disengage of the rotating shaft for the flexible sleeve to be installed or serviced. It follows that unlike other solutions that require time and effort to disengage the rotating shaft, the flexible sleeve can be installed faster, easier and safer as well as can be serviced faster, easier and safer. This is especially seen for the flexible sleeve made in situ with one or more elements.

[0014] Throughout this disclosure, fixing may refer to providing a rigid connection. The connected elements can therefore not move with respect to the other. For example, if a shaft seal gland is fixed to a bearing block rotatably supporting a turbine shaft, there is substantially no relative displacement between the bearing block and the seal shaft gland in any direction, i.e. in axial direction, circumferential direction and/or radial direction. It may therefore be understood that a fixation element as disclosed herein provides a rigid connection.

[0015] Throughout this disclosure, a flexible connection (and variants such as flexibly connecting and others) may refer to a connection which is flexible, not rigid. The connected elements can move in at least one direction with respect to the other. For example, if a flexible connection is provided between a seal shaft gland and a casing, a relative displacement between the seal shaft gland and the casing is allowed at least in one direction. In particular, relative moment in all directions, i.e. in axial direction, circumferential direction and radial direction of the rotating machine, is allowed. It may therefore be understood that a flexible sleeve as disclosed herein provides a flexible connection.

[0016] Throughout this disclosure, a casing may refer to a casing or housing which surrounds at least in part a portion of the rotating machine, and in particular a portion of the rotatable shaft. The casing may also refer to the casing surrounding the rotating machine. A casing may in some examples house a plurality of electromagnetic elements such as windings or magnets. A casing may house a flywheel in other examples. For instance, a steam turbine power plant may comprise a first casing for housing a generator with electromagnetic elements such as windings, and may optionally further comprise a second casing for housing a flywheel. This likewise applies to a synchronous condenser, which may comprise at least one casing, e.g. a first casing for housing electromagnetic elements and a second casing for housing a flywheel if a flywheel is provided.

[0017] Throughout this disclosure, a rotating machine may be understood as a structure which comprises a rotatable shaft and further comprises a casing (which is not rotatable). In operation, a rotatable shaft will rotate and for this reason, the terms rotatable shaft and rotating shaft may be used interchangeably throughout the present disclosure.

[0018] Throughout the present disclosure, the expression of the casing including a shaft may be interpreted as a portion of the shaft being arranged inside the casing. In other words, a part of the shaft is housing inside the casing.

[0019] The shaft sealing assembly may further comprise a support element configured to radially support the flexible sleeve. In embodiments, the support is provided around the rotatable shaft. The support element may help to reduce or eliminate stress in the flexible sleeve and may help to ensure long term tightness and sealing reliability. Said stress on the flexible sleeve originates from the above-described conditions (e.g., temperature, pressure etc.). The support element may be configured to be radially arranged between the flexible sleeve and the rotatable shaft. This configuration is particularly beneficial when the rotating machine is configured to operate in vacuum. The support element may be configured to be arranged radially outside the flexible sleeve. This configuration is particularly beneficial when the rotating machine is configured to operate at overpressure. Since the support element provides support to the flexible sleeve, it reduces the stress or eliminates it on the flexible sleeve and prevents from collapsing of the flexible sleeve. Therefore, the support element increases the lifetime of the flexible sleeve. The support element also prevents or decrease degeneration of the flexible sleeve thereby contributing to maintain the pressure conditions within the rotating machine for a longer period of time. This affects the overall efficiency of the rotating machine.

[0020] In some embodiments, the support element can have a segmented structure. In other embodiments, the support element can be a disc or ring. Other shapes are also possible to be used.

[0021] The shaft seal gland and the flexible sleeve may be configured to be connected by a spring-loaded connection. This connection can be provided on both ends of the flexible sleeve, i.e., on the end closer to, for example, electric generator and on the end which is closer to the shaft seal gland. Providing a spring-loaded connection between the shaft seal gland and the flexible sleeve may help to compensate creep and compression or tension of the flexible sleeve. Providing the spring-loaded connection on both ends is more efficient in comparison to providing only on one end of the flexible sleeve. It should be noted that the term spiring- loaded connection is known in this field.

[0022] In this aspect, the shaft seal gland is not limited to a particular type of seal. This indicates that the shaft sealing assembly is a flexible design that can be used with various types of shaft seal glands.

[0023] In a further aspect of the disclosure, a rotating machine is provided. The rotating machine comprises: a casing, a rotatable shaft, and two bearing blocks supporting the rotatable shaft on the opposite sides of the casing. The rotatable shaft is included in the casing. The rotating machine further comprises a shaft sealing assembly as described herein mounted on the rotating shaft and between the casing and one of the bearing blocks for sealing the casing. The rotating machine is configured to work under pressure conditions within the casing and the pressure conditions are selected from a substantial overpressure and a substantial vacuum. The rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser.

[0024] This aspect has benefits listed above for the aspect including the shaft sealing assembly. Said benefits will not be repeated here for the reasons of brevity.

[0025] In some examples, two shaft sealing assemblies are used to seal opposite sides of the casing. This indicates that the shaft sealing assembly can be combined with other known assemblies that seal the casing. The examples that include two shaft sealing assemblies as described herein provide double benefits to the rotating machine. [0026] In a further aspect of the disclosure, a fossil, renewable-energy, waste-to-energy, combined-cycle or nuclear power plant comprising a rotating machine as described herein is provided. Increasing of efficiency of the rotating machine and decreasing the need for servicing and downtime is in fact increasing efficiency of any power plant that includes this rotating machine. This aspect also underlines flexibility of the shaft sealing assembly as it can be used at power plants implementing different technologies for production of power.

[0027] In a further aspect of the disclosure, a method for sealing a casing of a rotating machine is provided. The rotating machine includes at least one bearing block supporting a rotatable shaft. The rotatable shaft is included in the casing. The method comprises arranging a shaft seal gland around the rotatable shaft of the rotating machine. The rotating machine is selected from the group of including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser. The rotating machine is configured to work under pressure conditions within the casing. The pressure conditions are selected from a substantial overpressure and a substantial vacuum. The method further comprises fixing the shaft seal gland to the bearing block around the rotatable shaft through a fixation element thereby avoiding or decreasing relative displacement of the shaft seal gland and the bearing block; and flexibly connecting the shaft seal gland to the casing through a flexible sleeve to create a seal between the shaft seal gland and the casing for maintaining pressure conditions within the casing.

[0028] This aspect pertains to servicing or upgrading of the rotating machine. The beneficial aspects in addition to the ones explained above include in particular that said servicing or upgrading can be done without disengaging the rotatable shaft.

[0029] In some examples, the method may further comprise arranging a support element for radially supporting the flexible sleeve around the rotatable shaft.

[0030] In some examples, the flexible sleeve is formed around the rotatable shaft by adhesively or thermally joining a portion of the flexible sleeve with another portion of the flexible sleeve.

[0031] Particular aspects, examples and elements of aspects or examples disclosed herein can be combined together in any number and order to form new aspects and examples that form part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 schematically illustrates a side view of a schematic example of a rotating machine comprising two shaft sealing assemblies. [0033] Figure 2 schematically illustrates an enlarged perspective view of a shaft sealing assembly arranged on the rotating machine of figure 1 , as indicated with dotted lines in figure 1.

[0034] Figure 3 schematically illustrates an enlarged cross-sectional view of a shaft sealing assembly of figure 1, as indicated with full lines in figure 1.

[0035] Figure 4 schematically illustrates a side view of an example of an electric generator or a synchronous condenser comprising a flywheel and comprising four shaft sealing assemblies.

[0036] Figure 5 shows a flowchart of a method for sealing a space between a rotatable shaft and a casing for a rotating machine mounted on the rotatable shaft.

DETAILED DESCRIPTION OF EXAMPLES

[0037] 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.

[0038] Figure 1 schematically illustrates a side view of a schematic example of a rotating machine, in particular an electric generator 1 or a synchronous condenser, comprising two shaft sealing assemblies 2. For simplicity, reference will be made to the electric generator-of figure 1 from now onwards, but it should be noted that the following teaching with respect to the functionalities and structure of the sealing assembly may also apply to an implementation with a synchronous condenser.

[0039] The electric generator 1 of this example comprises a rotatable shaft 3 axially extending along the electric generator 1. The rotatable shaft 3 is rotatably supported by bearings inside two bearing blocks 4. The bearing blocks 4 are stationary structures as understood throughout this disclosure, as the bearing blocks 4 do not move during rotation of the rotatable shaft 3.

[0040] The electric generator 1 of figure 1 further comprises a (e.g., generator) casing 5. Although not shown in figure 1, the casing includes a generator stator and a part of the rotatable shaft 3, both carrying electromagnetic elements, like coils. [0041] In the example of figure 1 , each shaft sealing assembly 2 is arranged between the casing 5 and a corresponding stationary structure 4, i.e. a corresponding bearing block 4 in this example.

[0042] In an aspect of the present disclosure, a shaft sealing assembly 2 for sealing a casing 5 of a rotating machine 1 is provided. The casing 5 includes a rotatable shaft 3. The rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser. The rotating machine is configured to work under pressure conditions within the casing 5. The pressure conditions are selected from a substantial overpressure and a substantial vacuum. The shaft sealing assembly is configured to be mounted on the rotatable shaft 3 and between the casing 5 and a bearing block 4 that supports the rotatable shaft. The shaft sealing assembly comprises a shaft seal gland configured to be arranged around the rotatable shaft 3, a flexible sleeve configured to flexibly connect the shaft seal gland to the casing 5 and to create a seal between the shaft seal gland and the casing 5 for maintaining pressure conditions within the casing 5. The shaft sealing assembly further comprises a fixation element configured to fix the shaft seal gland to the bearing block 4, thereby avoiding or decreasing relative displacement between the shaft seal gland and the bearing block 4.

[0043] The stationary structure 4 may be a bearing block 4 or an element of the bearing block 4, for example, an adapter ring 9 attached to the bearing block in the example of figures 1 - 3. In various example, extensions, rings, and/or arms can be mounted on the stationary structure 4 (in particular the bearing block) and all those elements are considered to be part of the stationary structure 4 (bearing block). The stationary structure 4 is arranged around the rotatable shaft 3, and the casing 5 is also arranged around the rotatable shaft 3. The stationary structure 4 and the casing 5 are separated from each other in an axial direction. An axial direction may herein be regarded as a direction coinciding with, or parallel to, a longitudinal axis of the rotatable shaft.

[0044] Figure 2 schematically illustrates an enlarged perspective view of a shaft sealing assembly 2 arranged on the electric generator 1 of figure 1 , as indicated with dotted lines in figure 1. Figure 3 schematically illustrates an enlarged cross-sectional view of a shaft sealing assembly of figure 1 , as indicated with full lines in figure 1 . In these figures, the shaft seal gland 8, the fixation element 6 and the flexible sleeve 7 of the shaft sealing assembly 2 can be seen.

[0045] The shaft seal gland 8 is arranged around the rotatable shaft 3. The shaft seal gland 8 has a through hole through which the rotatable shaft 3 extends. One or more seals 14, 15, 16, see figure 3, may be provided along a face of the shaft seal gland 8 which is configured to face the rotatable shaft 3. The one or more seals may completely surround the rotatable shaft 3 along a circumferential direction of the shaft. In this manner, a fluid, e.g. air, may not flow axially towards or away from the casing 5.

[0046] The flexible sleeve 7 may be configured to extend entirely around the rotatable shaft 3. I.e., the flexible sleeve 7 is configured such that when it connects the shaft seal gland 8 and the casing 5, a fluid, e.g. air, is prevented from radially flowing towards or away from a space enclosed by the shaft seal gland 6, the flexible sleeve 7 and the casing 5. When arranged in the shaft sealing assembly 2 around the rotatable shaft 3, the flexible sleeve may be of conical or of an annular shape. The flexible sleeve may have a cylindrical shape or an annular disc shape in some examples.

[0047] As can be seen in the example of figure 3, an axial space may be provided between the shaft seal gland 8 and the casing 5 (or adapter ring 9).

[0048] The flexible sleeve 7 may be configured to be attached to the shaft seal gland 8, e.g. at an outer circumference of the shaft seal gland. The flexible sleeve 7 is also configured to be attached to the casing 5 or to an adapter ring 9 of the casing, e.g. at an outer face (radially facing away from the rotatable shaft 3) of the adapter ring 9. Depending on the outer shape of the casing 5, the flexible sleeve 7 may be attached directly to the casing 5 in some examples. In other examples, an adapter ring 9 may be provided between the casing 5 and the flexible sleeve 7. In these examples, the adapter ring 9 may be attached to the casing 5, and the flexible sleeve 7 may be attached to the adapter ring 9. In these examples, the adapter ring 9 is considered to be part of the casing.

[0049] The flexible sleeve 7 may be mechanically attached, e.g. bolted, to the shaft seal gland 8 and to the casing 5 or adapter ring 9. In other examples, an adhesive or a thermal process may be used for attaching the flexible sleeve 7. Still in other examples, both a combination of, including all, the previously mentioned mechanisms may be used to attach the flexible sleeve. In general, a suitable attachment will keep the flexible sleeve 7 in place and will allow the flexible sleeve 7 and the shaft assembly 2 to operate as described herein.

[0050] In the example of figures 1 - 3, the flexible sleeve 7 is secured to an outer radial face of the shaft seal gland 8 by a spring-loaded connection 17. The flexible sleeve 7 can also by secured to an outer radial face of the adapter ring 9 by another spring-loaded connection. The adapter ring 9 is axially bolted to the casing 5.

[0051] The flexible sleeve 7 may be integrally formed, e.g. provided in a single piece, in some examples. In other examples, the flexible sleeve 7 may be provided in more than one piece (e.g., in two pieces), and the pieces may be attached to form the flexible sleeve 7. In a specific embodiment, the flexible sleeve 7 may be an opened profile that requires to be joined in-situ that involves vulcanization or use any cold or hot cured process.

[0052] The shaft sealing assembly may further comprise a support element 13 configured to radially support the flexible sleeve around the rotatable shaft. Depending on the pressure at which the casing 5 will operate, the support element 13 may be arranged radially inside or radially outside of the flexible sleeve 7. The support element 13 may therefore be configured to be radially arranged between the flexible sleeve 7 and the rotatable shaft 3 in some examples, in particular when the rotating machine is configured to operate in vacuum. The support element 13 may be configured to be arranged radially outside the flexible sleeve 7 when the rotating machine is configured to operate at overpressure.

[0053] The support element 13 is arranged between the flexible sleeve 7 and the rotatable shaft 3 in the example of figures 1 - 3. Accordingly, the electric generator 1 may operate at a pressure that is lower than ambient pressure, e.g. under vacuum operation, and the support element 13 may therefore help to support the flexible sleeve 7 when the sleeve bends and moves radially towards the rotatable shaft 3.

[0054] The support element 13 may be ring-shaped or disc-shaped in some examples. The support element 13 may be made of an integrally formed piece which extends circumferentially. In other examples, the support element 13 may comprise a plurality of subelements or segments which together form the support element. A segmented structure can facilitate mounting the support around the shaft.

[0055] The shaft seal gland 8 and the support element 13 may be configured to be connected by a spring-loaded connection. However, it is preferred to use a fixed connection between the support element 13 and the shaft seal gland 8. As can be seen in figure 3, a spring-loaded connection 17 may be used to connect the flexible sleeve 7 to the shaft seal gland 8, e.g. along a radial direction.

[0056] The fixation element 6 is configured to fixedly connect the shaft seal gland and the stationary structure 4. Similarly to the flexible sleeve, in some examples the fixation element 6 is attached to the stationary structure 4. In other examples, the fixation element 6 is attached to an adapter ring 9. The adapter ring 9 is attached, e.g. bolted, to the stationary structure 4.

[0057] The fixation element 6 may have any suitable shape. In the example of figures 1 - 3, the fixation element 6 comprises a plurality of arms, in particular distributed radially around the rotatable shaft. The arms may be spaced along a circumferential direction of the rotor. An arm may comprise a first end or first flange 10 which is configured to be attached to the shaft seal gland 8, e.g. to an outer radial face of the shaft seal gland 8 as illustrated in figure 3. The arm may comprise a second end or second flange 11 which is configured to be attached to the stationary structure, e.g. a bearing block 4 or an adapter ring 9. The arm may further comprise an elongated connector 12 between the two bases 10, 11. In this example, a first base 10 is bolted to the shaft seal gland 8 and a second base 11 is bolted to the adapter ring 9. In other examples, other types of fixation elements 6 may be provided. In specific embodiments, the elements with references 6, 10, 11 and 12 are forming a single element.

[0058] The fixation element 6 may be sized and shaped for providing an axial separation between the shaft seal gland 8 and the stationary structure 4 or an adapter ring 9, as illustrated in figure 3.

[0059] According to a further aspect of the disclosure, a rotating machine 1 comprising a casing 5 and a rotatable shaft 3 is provided. The rotating machine further comprises two bearing blocks 4 supporting the rotatable shaft 3 on opposite sides of the casing 5. The rotatable shaft 3 is included in the casing 5. The rotating machine further comprises a shaft sealing assembly 2 as described herein mounted on the rotatable shaft 3 and between the casing 5 and one of the bearing blocks 4 for sealing the casing 5. The rotating machine is configured to work under pressure conditions within the casing. The pressure conditions are selected from a substantial overpressure and a substantial vacuum. The rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser.

[0060] Sealing can therefore be provided between a stationary element 4 of the rotating machine, e.g. a bearing block, and a casing 5 of the rotating machine 1 . The casing may house a plurality of electromagnetic elements such as windings. The casing may house at least one flywheel in other examples.

[0061] The rotating machine, e.g. an electric generator, may comprise a rotor including a rotatable shaft 3 and a plurality of electromagnetic elements connected to the rotatable shaft 3. The electric generator 1 may further comprise a stator including a casing 5 configured to house the electromagnetic elements.

[0062] In some examples, see figure 1 , the electric generator 1 may comprise a first bearing block 4 rotatably supporting the rotatable shaft 3, e.g. at a first (axial) side of the casing 5. The electric generator 2 may comprise a second bearing block 4 rotatably supporting the rotatable shaft 3 axially opposite the first bearing block, e.g. at the other (axial) side of the casing 5.

[0063] In some examples the rotating machine may include two shaft sealing assemblies 2 as described herein. Each assembly may be mounted on the rotating shaft 3 and between the casing and one of the bearing blocks 4 for sealing the casing. The shaft sealing assemblies 2 may be mounted on opposite sides of the casing 5. For example, a first shaft sealing assembly 2 may be arranged between the casing and a first bearing block 4 rotatably supporting the rotatable shaft 3 arranged at a first side of the casing 5. A second shaft sealing assembly 2 may be arranged between the casing 5 and a second bearing block 4 rotatably supporting the rotatable shaft 3. The second bearing block is at a second side of the casing that is axially opposite the first side.

[0064] If the rotating machine is an electric generator or a synchronous condenser, the rotating machine may further comprise a flywheel connected to the rotatable shaft 3. Figure 4 schematically illustrates a side view of an example of an electric generator or a synchronous condenser comprising a flywheel and comprising four shaft sealing assemblies. In these examples, the rotating machine, e.g. an electric generator, may further comprise an additional casing 5 configured to house the flywheel (at the right of the figure). The electric generator 1 may further comprise a third bearing block 4 and a fourth bearing block 4 rotatably supporting the shaft. A third shaft sealing assembly 2 may be arranged between the third bearing block and the additional casing. A fourth sealing assembly may be arranged between the additional casing and a fourth bearing block.

[0065] According to a further aspect of the disclosure, a fossil, renewable-energy, waste- to-energy, combined-cycle or nuclear power plant comprising a rotating machine as described herein is provided.

[0066] According to a further aspect of the present disclosure, a method 20 for sealing a casing 5 of a rotating machine is provided. The rotating machine includes at least one bearing block 4 supporting a rotatable shaft 3. The rotatable shaft 3 is included in the casing 5. At least one shaft sealing assembly according to an example described herein may be provided to perform this method. The method is schematically illustrated in the flow chart of figure 5. The method comprises, at block 21 , arranging a shaft seal gland 8 around the rotatable shaft of the rotating machine. The rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser. The rotating machine is configured to work under pressure conditions within the casing. The pressure conditions are selected from a substantial overpressure and a substantial vacuum. The method further comprises, at block 22, fixing the shaft seal gland 8 to the bearing block 4 arranged around the rotatable shaft 3 through a fixation element 6, thereby avoiding or decreasing relative displacement between the shaft seal gland 8 and the bearing block 4. This avoids or decreases relative displacement between the shaft seal gland 8 and the rotatable shaft 3 and thereby extends the lifetime of the shaft seal gland 8. The method further comprises, at block 23, flexibly connecting the shaft seal gland 8 to the casing 5 through a flexible sleeve 7 to create a seal between the shaft seal gland 8 and the casing 5 for maintaining pressure conditions within the casing 5.

[0067] The shaft seal gland 8 comprises at least one shaft seal 14, 15, 16, see figure 3. The shaft seal gland 8 may include one seal arranged on a face of the shaft seal gland which is configured to face a rotatable shaft 3.

[0068] Depending on the structure of the shaft seal gland 8, the shaft seal gland may be arranged around the rotatable shaft 3 in several manners. For example, if the shaft seal gland 8 is provided in more than one segment, the segments may be arranged around the rotatable shaft and then attached between them. Bolts may be used for attaching the segments forming the shaft seal gland. If the shaft seal gland is integrally formed, the shaft seal gland may e.g. be pushed along the rotatable shaft.

[0069] The flexible sleeve 7 may be attached to the shaft seal gland 8 in several manners. In some examples, an adhesive process or a thermal process may be used for forming the flexible sleeve 7 around the shaft. For example, a sheet may be formed into a sleeve 7 around the shaft without the need for disconnecting shafts or unmounting other components. The sleeve may then be closed by a joint, e.g. a thermal or adhesive joint. In some examples, the flexible sleeve 7 may be connected to an adapter ring 9 of the casing.

[0070] The fixation element 6 may be attached to the shaft seal gland 8 before the shaft seal gland 8 is arranged around the rotatable shaft 3 in some examples. In other examples, the fixation element 6 may be attached to the shaft seal gland 8 after the shaft seal gland 8 has been arranged around the rotatable shaft 3.

[0071] The method may further comprise arranging a support element 13 for radially supporting the flexible sleeve 7 around the rotatable shaft 3. The flexible sleeve 7 can therefore be supported along a circumferential direction.

[0072] The method may further comprise attaching the fixation element 6 and/or the flexible sleeve 7 to an adapter ring 9. In these examples, an adapter ring 9 works as an interface between the stationary structure 4 and the fixation element 6 or between the flexible sleeve 7 and the casing 5. An adapter ring 9 is attached to the stationary structure 4 such that the stationary structure comprises the adapter ring. In examples, further interfaces, adapter rings etc. can be included, but all those elements are deemed to be part of the stationary structure 4 or casing 5.

[0073] Method 20 can be used to assemble a rotating machine from scratch as well to retrofit existing rotating machines. It can also be used as a servicing or upgrading of an existing rotating machine. [0074] The disclosure and explanations of this method can be combined an applied with the other aspects described herein. For example, the disclosure with respect to figures 1 - 4 is applicable to method 20 and vice versa.

[0075] 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 any incorporated 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. Aspects from the various embodiments 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 and techniques within the scope of this 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

1. A shaft sealing assembly for sealing a casing of a rotating machine, wherein the casing includes a rotatable shaft, and wherein the rotating machine is configured to work under pressure conditions within the casing, wherein the pressure conditions are selected from a substantial overpressure and a substantial vacuum, and the rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser, and the shaft sealing assembly is configured to be mounted on the rotatable shaft and between the casing and a bearing block that supports the rotatable shaft, and wherein the shaft sealing assembly comprises: a shaft seal gland configured to be arranged around the rotatable shaft, a flexible sleeve configured to flexibly connect the shaft seal gland to the casing and to create a seal between the shaft seal gland and the casing for maintaining pressure conditions within the casing, and a fixation element configured to fix the shaft seal gland to the bearing block thereby avoiding or decreasing relative displacement between the shaft seal gland and the bearing block.

2. The shaft sealing assembly of claim 1 , wherein the fixation element includes a plurality of arms distributed radially around the rotatable shaft.

3. The shaft sealing assembly of any of claims 1 -2, further comprising a support element configured to radially support the flexible sleeve.

4. The shaft sealing assembly of claim 3, wherein the rotating machine is configured to operate in vacuum and the support element is configured to be arranged radially between the flexible sleeve and the rotatable shaft.

5. The shaft sealing assembly of claim 3, wherein the rotating machine is configured to operate at overpressure and the support element is configured to be arranged radially outside the flexible sleeve.

6. The shaft sealing assembly of any claims 3 - 5, wherein the support element is substantially ring-shaped or disc-shaped.

7. The shaft sealing assembly of any of claims 3 - 6, wherein the shaft seal gland and the flexible sleeve are configured to be connected by a spring-loaded connection.

8. The shaft sealing assembly of any of claims 1 — 7, wherein the flexible sleeve has a cylinder or annular disc shape.

9. A rotating machine comprising: a casing, a rotatable shaft, two bearing blocks supporting the rotatable shaft on opposite sides of the casing, wherein the rotatable shaft is included in the casing, and wherein the rotating machine further comprises a shaft sealing assembly according to any of claims 1 - 8 mounted on the rotatable shaft and between the casing and one of the bearing blocks for sealing the casing, wherein the rotating machine is configured to work under pressure conditions within the casing, wherein the pressure conditions are selected from a substantial overpressure and a substantial vacuum, and wherein the rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser.

10. The rotating machine according to claim 9, wherein the rotating machine includes two shaft sealing assemblies, each mounted on the rotating shaft and between the casing and one of the bearing blocks for sealing the casing, wherein the shaft sealing assemblies are mounted on opposite sides of the casing.

11 . A fossil, renewable-energy, waste-to-energy, combined-cycle or nuclear power plant comprising the rotating machine according to any of claims 9 or 10.

12. A method for sealing a casing of a rotating machine, wherein the rotating machine incudes at least one bearing block supporting a rotatable shaft, and wherein the rotatable shaft is included in the casing, the method comprising: arranging a shaft seal gland around the rotatable shaft of the rotating machine, wherein the rotating machine is selected from the group including an electric generator, a synchronous condenser, and a flywheel for the electric generator or for the synchronous condenser and wherein the rotating machine is configured to work under pressure conditions within the casing, wherein the pressure conditions are selected from a substantial overpressure and a substantial vacuum; fixing the shaft seal gland to the bearing block around the rotatable shaft through a fixation element thereby avoiding or decreasing relative displacement between the shaft seal gland and the bearing block; and flexibly connecting the shaft seal gland to the casing through a flexible sleeve to create a seal between the shaft seal gland and the casing for maintaining pressure conditions within the casing.

13. The method of claim 12, further comprising arranging a support element for radially supporting the flexible sleeve.

14. The method of claim 12 or claim 13, wherein the flexible sleeve is formed around the rotatable shaft by adhesively or thermally joining a portion of the flexible sleeve with another portion of the flexible sleeve.