GB2496050A

GB2496050A - Turbine support tolerates axial misalignment between engaging surfaces

Info

Publication number: GB2496050A
Application number: GB1219245.6A
Authority: GB
Inventors: James Orme
Original assignee: SWANTURBINES Ltd
Current assignee: SWANTURBINES Ltd
Priority date: 2011-10-27
Filing date: 2012-10-26
Publication date: 2013-05-01
Anticipated expiration: 2032-10-26
Also published as: GB201118577D0; GB2496050B; GB201219245D0

Abstract

An arrangement for connecting a tidal stream turbine to a support structure on a sea bed comprises a socket including a member 7 which engages with a surface 10 of a male engaging element. The member 7 is movable relative to the socket wall when forced by the male element 10. The member 7 may have an annular inner engaging head, surrounded by a relatively flexible annular neck to allow movement. The male member may have two engaging elements 9 and 10, which engage with members 5 and 7 in the socket. The flexibility of the member 7 accommodates manufacturing tolerances in the length between elements 9 and 10. The engaging surfaces may be conical. There may be guiding portions of a softer, sacrificial material before each engaging portion (25, 26, 27, figure 5).

Description

Support Arranliement for a Turbine The present invention relates to improvements to a system for connecting an energy transfer means to an immovable object, and in particular for connecting a tidal stream turbine into a preinstalled support structure on the sea bed.

With the drive to harness energy sources as alternatives to fossil fuels, there is a large amount of interest in ways to harness energy from new sources such as the sun, wind and sea. Whilst the use of solar energy is becoming more accessible, and wind turbines continue to be erected on land and at sea, the problems with harnessing tidal stream power or energy from running water present numerous additional challenges. There are environmental issues associated with tidal stream power, especially with floating or suiface arrangements which are deemed by some to obscure views and additionally there is the added difficulty with the marine environment which is particularly harsh, with extremes of weather arid saltwater.

It has been envisaged that turbines may be planted onto the sea bed which removes the apparent eyesore, allowing a large number of turbines to be positioned in optimum tidal areas without being generally visible. However, this provides difficulties in that the mechanisms by which the turbines are connected to the sea bed must be able to be installed beneath the surface in a variety of weather and environmental conditions. This is made more technically challenging by the motion of the fluid, the subsequent forces on and resultant relative motion of aspects of the installation system and the potential lack of visibility owing to circumstances including suspended particulate matter. In addition known arrangements may be attached to the sea bed, however when maintenance is required, undersea interventions must be employed to carry out any inspections required and repair necessary which is both costly and inconvenient.

According to the invention described in PCT/0B2007/001571 there is a turbine and support for fixing to the ground, said turbine and support comprising complementary male and female engaging portions such that when the turbine is lowered onto the support, the male and female portions contact thereby providing an operational engagement there between. The advantage of such an arrangement is that when inspection or repair is required, the support means and turbine may be lifted from the base structure with little or no skill or expertise, and lifted onto, for example, a boat. If necessary, the active turbine may be taken to a suitable location for examination andlor repair. Additionally, when locating or removing the turbine from the support, divers or motorised means wiH not be required to release the turbine from the support, reducing costs associated with service, which can be substantial in such a harsh environment. Operational engagement' is defined as being in a fit state for use without further assembly.

The present invention aims to make improvements to the system descnbed in PCTIGB2007IOO 1571 to address the specific technical challenges described below.

To enable one turbine to be removed from a particular foundation and be immediately replaced with a second turbine for example in a maintenance procedure, the pair of male and female engaging portions of the system must be capable of forming an operational engagement with other either female or male engaging portions respectively. Ideally this inter-mateability between operational pairs would be achieved by ensuring during manufacture that all systems were identical. However, fine manufacturing tolerances on a pair of machined cone bearing faces are difficuli to achieve as a small angular inaccuracy leads to large vertical misalignment. This could cause unbalanced loads in the operationally engaged system. A simple way to rectify this for a particular mating pair of male and female engaging portions is to adapt the distance between the female bearing suifaces using shims or other method during assembly. However owing to the requirement for inter-mateability a male engaging portion could then be subsequently be mated to a female engaging portion for which the distance between the female bearing surfaces has not been adjusted equally.

A solution is therefore required to allow inter-mateability of non-paired male and female engaging portions.

According to a first aspect of the present invention there is a support arrangement for a turbine, the support arrangement comprising a socket defined by at least one socket wall, the socket including a first engaging member having an engaging surface arranged to cooperate with a corresponding engaging surface of a male engaging dement, wherein the first engaging member is configured to facilitate displacement thereof relative to the at least one socket wall upon a force acting on the engaging surface by a male engaging element.

This reduction of sensitivity to vertical misalignment has a benefit of reducing the requirement for very fine manufacturing tolerances and hence reducing manufacturing cost. The solution presented here is to effectively introduce a flexibility into the location of the frustoconical bearing surfaces of the female engaging portion or socket, Such flexibility is enabled by the design of the bearing support (engaging member) such that vertical misalignment can be accommodated without introducing a significant reduction in the stiffness of the overall system as to cause a worsening in the frequency response performance of the turbine support.

A force acting on the first engaging surface by the engaging surface of the male engaging element preferably causes elastic deformation of at least part of the first engaging member relative to at least one socket wall. Accordingly, the first engaging member preferably deforms to accommodate the vertical misalignment between this socket and the male engaging element.

The first engaging member preferably projects inwardly into the socket from the at least one socket wall, the first engaging member preferably including a head carrying the first engaging surface and a neck, both the head and neck projecting into the socket. Such a configuration means that most of the deflection of the first engaging member occurs in the neck.

The first engaging member is preferably annular. This is beneficial as a corresponding annular engaging surface of a male engaging element means that engagement can occur in any rotational orientation.

The first engaging surface is preferably frustoconical and preferably projects inwardly and downwardly from the at least one socket wafl into the socket. The first engaging surface therefore effectively provides a shelf or shoulder onto which the corresponding engaging surface of the male engaging element seats.

The first engaging member is preferably a separate component to the at least one socket wall. This provides a benefit in terms of manufactunng ease and speed. Furthermore, the male engaging element may be rep'aced as necessary following wear. I0

A fixing element is preferably provided arranged to secure the first engaging member to the socket. The at least one socket wall preferably comprises a shoulder engagement surface for engaging with the first engaging member, the shoulder engagement surface being provided substantially orthogonally to the longitudinal length of the at least one socket wall.

The first engaging member preferably projects through the thickness of the at least one socket wall.

The socket preferably comprises a flange extending radially outwarWy of the at least one socket wall, wherein the fixing element secures the first engaging member to the flange.

The fixing element preferably extends generally parallel to the longitudinal length of the at least one socket wail.

The first engaging member is preferably secured between first and second socket wall portions. The first and second socket wall portions are preferably separated by the first engaging member in the longitudinal length.

The head of the first engaging member is preferably of a trapezoidal cross-section. The trapezoidal cross-section has a height extending in axis generally parallel to the longitudinal length of the at least one socket wall.

The portion of the head is preferably spaced apart radially from the internal surface of the at least one socket wall. This ensures that the first engaging member is able to flex or deflect freely in response to a communication with a male engaging element.

A guide is preferaNy provided for guiding and engaging an engaging surface of a male engaging element to the engaging member. The guide is preferably provided adjacent to the first engaging member and preferably upstream in the socket. Upstream means closer to the opening of the socket.

The guide material is preferably of a different material to the first engaging member.

A second socket engaging member is preferably provided having a second socket engaging surface positioned spaced apart upstream in the socket from the first engaging member.

A male engaging dement is preferably provided having a first mak engaging surface for co-operating with the first socket engaging surface.

The male engaging elements are provided on a male engaging portion.

A second male engaging element is preferably provided having a second male engaging surface for co-operating with the second socket engaging surface.

The rotatably mounted nature of the system is particularly useful when the turbine must be rotated within the fluid flow to optimise energy transfer and can provide a benefit in that the attitude of the male and female portions does not need to be controlled during the engagement process which reduces the complexity of this process in the marine environment. However this results in a requirement for the transmission of electricity and or data information through the rotating submerged joining of the static and rotating parts.

The existing engineering solution would be to employ a water sealed slip ring assembly that is commonly available. These slip rings are generally intended for use in very deep water environments for operationally critically activities in the offshore oil and gas industries and hence are both very expensive and designed to a higher specification than necessary for the application in tidal turbines.

According to the second aspect of the present invention there is a machine turbine generator housing comprising: -a rotating transmission means for conducting electricity from the turbine generator; -a power take off conductor line for conducting electricity from the rotating transmission means; where the rotating transmission means is provided in a chamber in the housing and in use the chamber is allowed to partially flood with water leaving the head space dry, the rotating transmission means being positioned in the dry head space.

This second aspect of the present invention offers a solution which utilises the relative densities of air and water respectively in conjunction with the constant vertical orientation of the male engaging portion to remove the requirement for watertight rotating sealing of the rotating electrical transmission means such as the slip ring and hence increases reliability arid reduces the cost of the system. The male engaging portion of the system can be easily adapted to incorporate a vertically orientated air chamber which can encapsulate the rotating joint for the transmission of electricity and data information without a requirement for watertight rotating sealing. Such an arrangement is extremely advantageous in the environments in which the turbine operates. By shaping the chamber such that it maintains air therein as the chamber is lowered into water provides a dry head space in which the rotating transmission means may be provided. It will be appreciated that as the chamber partially floods providing the chamber remains substantially vertical complex sealing is not required for rotating transmission means.

The rotating transmission means is beneficially arranged to facilitate an electrical connection between a rotating portion moveable with the turbine generator and a non-rotating portion including the power take off conductor line. The rotating transmission means beneficially comprises a slip ring arrangement. The slip ring arrangement is thus not in communication with the water which partially floods the chamber. A seal is beneficially provided between the rotating transmission means and the predicted water level, however, this is provided in order to reduce the possibility of splashing or moisture coming into communication with the rotating transmission means.

The chamber is beneficially configured to receive a turbine generator housing support arrangement. The cross-sectional area of the opening of the chamber is beneficially greater than the cross-sectional area of the head space. The area having a greater cross-section area is beneficially provided such that a greater diameter bearing can be provided for enabling rotation between the machine turbine generator housing and a machine turbine generator housing support arrangement.

The machine turbine generator housing beneficially comprises one or more protrusions projecting into the chamber arranged to linilt insertion of a turbine generator support arrangement therein. These protrusions are beneficially bulk heads which are fixedly mounted to the inside of the turbine structure. The one or more protrusions beneficiafly are arranged to receive one or more bearings. This combination of protrusions and bearings provide a seal between the rotating transmission means and the water level. This seal reduces the chance of splashing water reaching the rotating transmission means.

The chamber beneficially comprises a socket. One or more bearings are preferably configured to enable rotation of the machine turbine generator housing relative to a turbine generator housing support arrangement, wherein at least one or more bearings are configured to be flooded with water in use. Wet running bearings are beneficial in such an environment due to no sealing requirements and low maintenance.

The chamber beneficially has a cylindrical cross-section. and preferably the diameter of the cross-section is different at different locations in the chamber. The cross-sectional area of the chamber may taper from the opening into the chamber.

The machine turbine generator housing preferably includes a turbine generator housing support arrangement arranged to be received in the chamber.

An important third aspect of the invention is the ability to form an operational engagement between the male and female engaging portions by being lowered into position in a marine environment. This environment may be characterised by strong and variable water currents and also ocean wave action which may apply hydrodynamic forces to aspects of the system and associated installation platform such as ships or other vessels during the installation and retrieval procedures. These forces may act to displace aspects of the system and installation platfoim dunng mating and dc-mating operations in both linear and angular fashion in both the honzontal and vertical planes and axes. These environmental forces give rise to a requirement for the system to be able to complete the mating operation successfully within a defined envelope of allowable displacements of aspects of the system.

According to a third aspect of the present invention there is support arrangement for a turbine comprising a socket and a male engaging member for engaging the socket wherein the socket and the male engaging member are provided with engaging portions for engaging one another when the male engagiag member is seated in operational engagement in the socket, a respective engagement portion having a leading portion of a first material and a bearing portion trailing the leading portion of a material different in composition to the first material.

To extend the weather windows and tidal current conditions in which the system can be mated and hence reduce operational risk and cost, the male and female engaging portions are characterised by features which allow the smooth installation and location from various angles, directions of fluid flow and varying weight of turbine loading the system.

The features which allow the smooth installation and location of the male and female engaging portions are characterised by the addition of a series of smooth transitions between the different areas on the mating surfaces of both the male and female engaging portions. In addition to this some areas can be comprised of a low friction material to ease the action of connection and protect the mating surfaces from wear. This low friction material has an additional advantage in that during installation the contact and sliding of the male engaging portion against the female engaging portion can lead to the removal of the protective coating on either portion which could leave aspects of the system vulnerable to colTosion and weakening of the structure during its lifetime. The leading portion comprising the first material is a sacrificial material. This means that it might deform.

either elastically or plastically, to ensure that the bearing portion is in the best possible condition for mating with the corresponding bearing portion in either the socket or the male engaging member.

The leading portion is preferably arranged to guide into communication with the respective engaging portions of the male engaging member and the socket. The first material of the leading portion beneficially has a friction coefficient lower than that of the material of the bearing portion thus allowing smooth installation of the turbine.

The leading portion preferably projects out of the plane of the bearing portion. This improves contact capabibty.

The male engaging member preferably comprises first and second longitudinally spaced engaging portions. The first engaging portion is preferably positioned adjacent the tip of the male engaging member. The second male engaging portion preferably comprises a substantially frustoconical projection. where the leading edge portion of the engaging portion is closer to the distal end of a male engaging member, and preferably wherein the frustoconical projection tapers inwardly towards the tip of the male engaging member. A second male engaging portion is preferably annular.

The first material of the leading portion preferably has a friction coefficient lower than that of the material of the bearing portion.

The leading portion of the socket engaging portion is preferably provided upstream of the bearing portion. Upstream is defined as meaning closer to the opening defining the opening of the socket.

The socket preferably comprises first and second longitudinally spaced socket engaging portions. The first socket engaging portion is preferably arranged to engage with the first engaging portion of the male engaging member, and the second socket engaging portion is arranged to engage with the second engaging portion of the male engaging member.

The leading portion of the first socket engaging portion is preferably secured to a wall separately from the bearing portion. The bearing portion of the socket is preferably arranged to deflect longitudinally.

It will be appreciated that all three aspects of the present invention can be utilised in combination to form a marine turbine system. In particular but not exclusively, the features of the first aspect and third aspect may be combined to provide advantageous embodiments, however, each feature of the first aspect has not been described with the respect to the third aspect nor vice versa, however, it will be appreciated that features may be beneficial to both aspects.

Aspects of the present invention will now be described by way of example only with referral to the accompanying figures: Figure 1 -The male engaging portion and female engaging portion (socket) attached to a turbine body and foundation respectively prior to forming an operational engagement.

Figure 2 -The turbine body and foundation connected by the male and female (socket) portions in operational engagement.

I

Figure 3-Across-section view of the internals of the system as shown in Figure 1.

Figure 4-A cross-section view of the internals of the system as shown in Figure 2.

Figure 5 -Enlarged views of the systems used to facilitate smooth connection and disconnection of the male and female engaging portions.

Figure 6 -Rotating joint for the transmission of electricity and data information shown on the male engaging portion.

Figures I and 2 illustrate the general working context of the invention wherein (1) is the turbine body and (2) is the turbine rotor blades. These are connected to a tower arrangement (3) which extends from the turbine body in a generally downward direction.

The tower arrangement (3) comprises a central section which has male frustoconical bearing surfaces (9) and (10) which maybe termed engaging surfaces arranged around the outside of the central section with a vertical separation between them. The tower arrangement and male frustoconical beanng surfaces (9) and (10) comprise the male engaging portion of the present invention.

The turbine body and the male engaging portion are lowered together from a lifting means on or at the surface of the fluid in which the turbine is to be immersed. It is lowered such that the male engaging portion is received by the receiving cone (4). This cone is characterised by a shape that enables the male engaging portion to be further lowered into a concentric and mating position with the female frustoconical bearing surfaces (5) and (7).

The female frustoconical bearing surfaces have a vertical separation between them which can be maintained by a structural element such as the transition piece (6). The receiving cone 4), female frustoconical bearing surfaces (5) and (7) (carried by the engaging member) and the transition piece (6) together comprise the female engaging portion of the present invention.

After the male engaging portion has been lowered into position inside the female engaging portion operational engagement is achieved. This connects the turbine body to the foundation structure (8).

Figures 3 and 4 illustrate a sectioned view of the systems shown in Figures 1 and 2.

The bearings that can enable the rotation of the turbine body about the vertical axis of the tower are shown (13). These may allow the turbine to adjust its directional heading to maximise the benefit from changes in environmental conditions such as direction of fluid flow. These bearings are connected to an internal structure of the turbine body (12) which can rotate similarly to the turbine rotation. This structure can also provide a region of trapped air in the upper portion of the inside of this structure owing to the relative densities of air and water and the constant vertical orientation of this structure. A means of transmitting electricity and information through a rotating joint (ii) can be encapsulated in the region of trapped air. The rotating joint is made between the turbine body (1) which maybe rotating and the male engaging portion which may be stationary.

The electricity and information can be transmitted via a cable or other conduit (15) which is protected against the operating environment. This cable or conduit travels in a vertical direction towards the base of the male engaging portion. Whilst the turbine is being installed, the cable or conduit can be stored in this region to avoid becoming trapped or damaged during the installation process.

The receiving cone (4) is positioned above the upper female conical bearing surface (5) to allow the smooth insertion of the tip of the male engaging portion into the position required for operational engagement. The upper female frustoconical bearing surface is fixedly connected (19) to the transition piece (6) as to provide operational stability. The lower female frustoconical bearing surface is connected (20) to the transition piece (6) fixedly in the honzontal plane but to allow a limited range of motion in the vertical plane to accommodate a requirement for varying vertical separation between the upper and lower female frustoconical bearing surfaces.

When operational engagement is achieved as shown in Figure 4, the upper set of frustoconical bearing surfaces (9) and (5) form a mate which may transmit vertical, horizontal and rotational loads through the mate from the male engaging portion to the female engaging portion. In addition the lower set of frustoconical bearing surfaces (10) and (7) form a mate which may transmit vertical, horizontal and rotational loads through the mate from the male engaging portion to the female engaging portion. The cable or conduit carrying the electricity and information (15) is connected to a similar cable or conduit of the female engaging portion by a connection comprised of two components (17) and (24).

In Figure 5 some detail of the invention is shown, in particular the aspects of the invention that facilitate the smooth and effective installation and connection of the male and female engaging portions. The upper male frustoconical bearing surface (9) is characterised by dimensions that match the respective female bearing surface (5). It may be of benefit to the construction process of this component and the associated attachment to the tower arrangement (14) if the lower annular surface of this component is welded onto the tower arrangement. The region then presents the potential for the installation process to become halted as a non-smooth lip at this point could cause ajam in conjunction with the joint between the receiving cone and the upper female bearing surface (5). This could cause delays, damage and undesirable forces in the structure during installation. To avoid this scenario a smooth guide (26) is added to the surface of the bearing surface (9). This guide comprises a material that provides adequately low levels of friction to allow the smooth installation of the turbine to proceed unimpeded. It is affixedly connected to the structure such that it wifi withstand the large forces present during the installation process. A similar inverse smooth guide (27) is added to the internal join between (6) and (7).

The lower male frustoconical beanng surface (10) may necessarily make contact with the internal surface of the receiving cone during the installation process whilst the receiving cone is rigidly affixed to the seabed via the foundation and the male bearing surface is rigidly affixed to the male engaging portion of the turbine. The relative motion between the two components may be strongly influenced by environmental conditions including tidal currents, ocean waves and wind. The relative motions may therefore be difficuli to control and the large mass associated with the turbine may cause large forces to be transmitted through the lower male frustoconical bearing surface to the receiving cone during installation. These large forces may cause local deformation of the contacting components and in particular this may reduce the abihty of the components to resist environmental degradation for example corrosion over the lifetime of the system. A low friction guide (25) is added to the male engaging portion to reduce the risk of jamming or damage to the contacting components during installation. This guide comprises a material that provides adequately low levels of friction to allow the smooth installation of the turbine to proceed unimpeded. It is affixedly connected to the structure such that it will withstand the large forces present during the installation process.

The lower female frustoconical bearing surface (7) carried by the engaging member is connected (20) to the transition piece (6) fixedly in the horizonta' plane but to allow a limited range of motion in the vertical plane to accommodate a requirement for varying vertical separation between the upper and lower female frustoconical bearing surfaces. In this embodiment a method is used to provide the vertical flexibility using the cantilever effect, the outer aspect of (7) connected to transition piece (6) whereas the inner aspect is free to deflect in response to a vertical load. This flexibility could also be facilitated by flexible fixings and materials or mechanical adjustors. The extent to which the flexibility exists can be determined by sizing of the lower female frustoconical bearing surface in terms of cantilever arm thickness and length and also geometry particu'arly as the shape of the mating surface and the additional stiffness that may be provided by the male engaging portion during operational engagement may affect the degree of flexibility in the component.

In Figure 6, apparatus is shown by which the electricity generated by the turbine and other electrical or optical information is transmitted through the rotating joint in the male engaging portion. The brushes, optical rotating joint or other rotating transmission means (11) comprises two parts which rotate relative to one another, one of which is fixedly connected to the internal structure of the turbine body (29), the other of which is fixedly connected to the extension of the tower arrangement (33) which is fixedly connected to the top of the tower arrangement (36). Such a rotating transmission means may be termed a slip ring, rotary electrical integers, rotating electrical connectors, collectors, swivels or electrical rotating joints. The most commonly used arrangement is termed a slip ring. The internal structure of the turbine body (29) therefore rotates about the tower arrangement (36) and is supported by a number of rotating bearings shown in this embodiment to include (30), (34) and also the bearings used to rotate the turbine about the tower axis (37) which may be co-axial.

In use therefore the turbine body (29) including the bulkheads (31, 35), cable glands (40, 41,42) and part of the split ring (11) rotate relative to the tower arrangement (33, 36).

The internal structure (29) may provide a region of trapped air or other fluid with a density lower than water in the upper portion of the inside of this structure above the example waterline (32) owing to the relative densities of the fluid and water and the substantially constant vertical orientation of this structure. In addition to this the pressure of the water will increase as the system is being lowered through the water which will compress the trapped other fluid and hence reduce its volume. The internal structure may accommodate this volumetric variation by providing an adequate initial volume of trapped air or other fluid to maintain the required region of trapped fluid in the upper portion of the inside of the structure. Additional non-compressible buoyancy can be added to the system to adjust the effect of the compression of the air or other fluid, also the system could be pre-pressurised to reduce this effect.

The rotating transmission means (11) may then be encapsulated in the region of trapped fluid provided by the head space and kept free from splashes, humidity and marine life by a tightly fitting rotating joints or dust seals at the bearings (30) and (34). The bearings and dust seals (30) and (34) may therefore operate without a fluid pressure gradient across them. Bearings (30) and (34) are mounted in bulkheads (31) and (35) respectively which are in turn fixedly mounted to the inside of the internal turbine structure (29) preferably making use of a sealing means at the join such as an 0-ring or gasket or sealant or similar.

The cables or other conduits calTying the electricity and information to and from the rotating transmission means 39) and (15) are passed out of the static and rotating aspects of the system respectively via the static sealing and clamping methods for example cable glands at (40), (41) and (42).

The present invention has been described by way of example only and it will be appreciated by the skilled addressee that modification and variations may be made without departing from the scope of protection afforded by the appended claims.