Patent Grant
7806708
The invention relates to means for the transferral of electric power and/or signals between two elements rotating in relation to each other, which elements for instance may be a floating unit and an underwater installation and the method of assembling the means and is concerned particularly, although not exclusively, with a system for transferring electrical power in a turret-moored vessel.
When developing an oilfield one may for instance use underwater installations and lines up to an turret arranged in a floating unit for instance a vessel. The turret allows the floating unit to rotate in relation to the underwater installation, and thereby the lines running from the floating unit to the underwater installation will not be tangled or experience unnecessary stresses. An example on such a solution is described in U.S. Pat. No. 6,176,193.
The turret is arranged rotating in relation to the vessel, and there are normally arranged swivel means within or on top of the turret construction for transferral of fluids, electric power or signals between the vessel and the underwater installation. U.S. Pat. No. 6,302,048 and WO 9965762 describe such solutions. The turret with swivel means are normally designed for a specific use, for instance for a specific oil or oil/gas or gas field. The swivels and turrets have to be designed for optimum weight and size. Due to the requirements of weight and use of space there is normally limited options for expanding the swivel means with additional functionalities as for instance transferral of additional electric power which were not part of the initial criteria of the swivel means. These additional functionalities are criteria which may arise when the field is partly developed, which arise due to new available technology or development in the field which was not predicted. However, when an additional function of the swivel has to be retrofitted there is very limited space on the turret to add to or adapt the original swivel means to make room for the necessary changes. In addition it is also quite important to achieve a solution where the down time is as short as possible. To disassemble the original swivel means and replacing the whole assembly with another swivel means is not a preferred solution, and is often impractical.
It is therefore a need to develop a solution for transferring electrical power which gives a possibility to add additional transfer opportunities to a turret with an existing swivel means, without the need for extra space on top of the swivel and with as little or no down time for the existing transfer arrangement in the turret.
An aim of the present invention is to fulfil these needs. The present invention as defined in the following claims solves these needs.
The present invention relates to a system for achieving transfer of electric power, and/or signals, between a vessel and an underwater installation. Where one rotating element, the vessel, is connected to the static element and the underwater installation, through a turret, is rotationally attached to the vessel or rotating element. The system may be the only system for transfer between the elements.
The present invention provides an advantage over the known arrangements by providing means for the transferral of electric power and/or signals between two elements rotating in relation to each other, which elements for instance may be a vessel and an underwater installation and is concerned particularly, although not exclusively, with a system for transferring electrical power in a turret-moored vessel.
According to a first aspect of the present invention there is provided means for transferring electric power and/or signals between a vessel and an underwater installation via a turret, wherein the means for transferring electric power and/or signals comprises a slip-ring arrangement comprising a housing containing an electrical conductor means and a brush carrier unit that is in slidable contact with the electrical conductor means.
Preferably, the housing is connected to the structure of the vessel and the brush carrier is fixed to the turret. Alternatively, the brush carrier is connected to the structure of the vessel and the housing is fixed to the turret.
Preferably, the housing is formed by a plurality of sub-units, wherein each sub-unit comprises a section of the electrical conductor means. The housing sub-units may be prefabricated and tested prior to being assembled on the vessel and preferably the housing sub-units may be prefabricated and tested away from the vessel and then assembled on the vessel.
The housing is preferably mounted outside any swivel stacks and most preferably the housing is disposed outside and above any swivel stacks.
The housing is preferably a substantially annular shape formed by a plurality of sector sub-units. The sub-units may be secured together by a “cold work” method such as bolts or clamps. It is preferable that the sub-units are secured together by a securing means that does not require any “hot work” such as welding because during the operation of the vessel there may be a hazardous environment.
The housing unit is preferably an enclosed structure formed with an access channel through which the brush carrier unit extends.
The access channel preferably extends through the length of the housing.
Preferably the channel extends around the circumference of the housing.
The housing is preferably suspended from a support structure mounted on the vessel.
The housing is preferably suspended by three mounting points on the support structure.
The support structure preferably extends along the length of the housing.
The support structure preferably extends around the circumference of the housing.
The housing preferably comprises means for sealing the channel. The sealing means helps to prevent the ingress of the ambient (potentially explosive) atmosphere.
The means for sealing the channel preferably comprises a seal that extends along the length of the channel.
The seal means preferably comprises an internal seal member and an external seal member.
The seal means preferably comprises a sealing plate that extends the length of the seal means.
The seal means preferably comprises a sealing plate that extends the length of the seal means, the arrangement being such that in use a seal member is in sealing contact with the sealing plate.
The seal means is preferably a dynamic seal having a continuous sealing surface.
In use, there is preferably a positive pressure difference between the pressure in the housing compared with the atmospheric pressure outside the housing. The greater than atmospheric pressure inside the housing helps to prevent the ingress of the ambient (potentially explosive) atmosphere.
Preferably the slip-ring arrangement is a passive system that does not require drive means. It shall be appreciated that the rotation of the vessel provides the drive means.
The slip-ring arrangement preferably comprises damping means to restrict minor movements of the slip-ring arrangement. The damping means preferably comprises a torque assembly mounted to the slip-ring arrangement. The torque assembly preferably connects the bush carrier to the turret.
According to a second aspect of the present invention there is provided a method of assembling a slip-ring arrangement comprising a plurality of sub-units, wherein each sub-unit comprises a section of the electrical conductor means according to the first aspect of the present invention, wherein the method comprises the steps of installing a support track on the vessel and transferring each sub-unit onto the support rack to form the completed slip-ring arrangement.
The housing sub-units may be prefabricated and tested prior to being assembled on the vessel and preferably the housing sub-units may be prefabricated and tested away from the vessel and then assembled on the vessel.
It shall be appreciated that one or more of the features described below with reference to the drawings of the invention may be used in conjunction with the features of the first and second aspects of the invention described above.
A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which:—
a, 12b, 13a, 13b and 14, are a further detailed views of further embodiments of a seal arrangement for the slip-ring housing;
With reference to the Figures, there is shown a turret 2, means for transferring electric power and/or signals comprising an electrical power slip-ring system (EPSR) 3 comprising a housing 4 containing electrical slip-rings. The housing 4 is connected to a support structure 6 of a vessel 7 and a brush carrier unit 8 is in slidable contact with the electrical conductor means. The brush carrier 8 is fixed to the turret 2 and a swivel unit 10 extends thorough the centre of the housing 4. The turret 2 and support structure 6 may be disposed on the vessel in various configurations such as an internal turret configuration, a submerged turret configuration or an external turret configuration.
The housing 4 is an enclosed square box structure formed with an access channel 5 through which the brush carrier 8 unit extends. The channel 5 extends around the circumference of the housing 4.
The support structure 6 is formed with three tubular column sections 11a, 11b, 11c. Disposed at the top of section 11a is a cantilever crane 12. The housing 4 of the EPSR system 3 has a relatively large diameter slip-ring compared to existing solutions. Typical range of large diameter slip-ring systems are in the region from 2.05 meters up to 15 meters.
The main challenges for the EPSR system 3 of the present invention through the conceptual development phase have been:
The EPSR system 3 transfers power between the rotating deck of the vessel 7 and the deck of the stationary turret 2. The EPSR system 3 includes four off three phase high voltage (HV) circuits 15 kV/300 A for the transfer of power to sub sea pumps as well as low voltage (LV) circuits (440 V/16 A, 230 V/16 A and 24 VDC/16 A) for powering equipment located on the turret 2.
The EPSR system 3 is designed with two high voltage (HV) ring stacks 14, 15 located on two diameters, each stack holding two off three phase HV circuits. In between the two stacks 14, 15, the carrier 8 is located holding all the brushes. The carrier 8 can travel between the two stacks 14, 15 all the way around the circle of the two stacks. The following typical electrical data for the HV slip rings:
The rings in the HV stack will have the following dimensions: h=8 mm and w=75 mm. Each ring will have a cross section of: 8×75 mm=600 mm2.
The rated current of each phase is In=300 A. The current will flow from the cable through the ring to the brush. Depending on the position of the brush relative to the cable termination to the ring, the current distribution in the ring will change. If the brush and the termination point is 180 degree spaced, the current will follow from the termination point to the brush in each half of the ring. This corresponds to a current in each half of the ring of 150 A, corresponding to a current density of: i=150/600=0.25 A/mm2. If the brush and the termination point is in the same position/very close, the current will tend to follow the shortest way between the termination and the brush. The current in the ring will therefore be max. 300 A, corresponding to a current density of: i=300/600=0.5 A/mm2. The current load may be very low, and the current rating can easily be increased.
Each ring will be split into eight sections 26 in order to follow each enclosure section of the EPSR system 3. This means that there are splices in each ring. The rating of each splice is holding the same current rating as the rest of the system.
Each phase will include two brushes. This solution is included in order to give redundancy, robustness as well as to cater for maintaining the current rating every time a brush passes a splice. Each brush has a current capacity of 400 A. the total current rating is thereby 800 A pr phase, utilizing the brushes to 37.5% (300 A) of the rated current.
From the brushes located on the carrier, a single conductor HV cable will be routed to the EPSR turret junction box, one cable from each brush. In the junction box there will be a HV connector interfacing to the turret HV cables, which are routed to the umbilical junction box on the turret. These connectors will secure a compact termination area as well as providing easy disconnection of the turret cables from the EPSR during maintenance. The junction box can be splitted in an upper section hanging on the EPSR carrier and a lower section holding the turret cables, all in order to ease the disconnection work during maintenance
From the vessel side, cables are routed directly to the stacks 14, 15 in the EPSR system 3. From the carrier/brushes, intermediate cables are routed to a turret 2 HV junction box hanging on to the carrier, outside of the EPSR housing 4.
The LV rings are located in the top section of the EPSR system 3, with the rings fixed to the housing 4 and the brushes fixed to the carrier 8. The cables will be routed to an external LV junction box, with intermediate cables into the LV rings inside the EPSR system 3. From the LV brushes on the carrier 8, intermediate cables are routed to an external junction box located on the turret 2. From these junction boxes cables are routed to the different consumers on the turret 2.
The EPSR system 3 includes a system for protecting of the internal components of the housing 4 by using an overpressure system. The system will purge the EPSR system 3 prior to applying electrical power to the housing 4. During operation the overpressure system will maintain a predefined overpressure and compensate for the natural leakage from the housing 4. On loss of pressure, the system will initiate an alarm to be used for operator information or power shutdown.
The HV turret junction box may be an integral part of the EPSR system 3 and thereby be a part of the housing 4.
The main mechanical equipment assemblies of the EPSR system 3 are the slip-ring housing 4, the slip-ring internals, a sealing system and the brush carrier 8.
The sealing system between ambient and slip-ring system internals is a key part of the EPSR system 3. The internally over pressurized sealing system shall help to prevent any gas to enter into the internals of the high voltage environment. An external seal 17 is included to ensure that wind loads/other environmental conditions will not influence the internal sealing action.
The pressurization system serves to create (initial purging) and then maintain an overpressure in the EPSR enclosure. This overpressure shall prevent the ingress of the ambient (potentially explosive) atmosphere.
System Overview:
The EX pressurization system comprises of the following main items:
In addition to the requirements defined above the following items are design basis:
With reference to
With reference to
The EPSR system 3 is based on the following design philosophy:
The geometry of the EPSR system 3 is based on the following conditions:
The main mechanical equipment assemblies of the EPSR system 3 are the slip-ring housing 4, slip-ring internals 14, 15, sealing system and the brush carrier 8.
The main purpose of the slip-ring housing 4 is to:
The main purpose of the slip-ring internals 14, 15 are:
The main purpose of the brush carrier 8 is to:
The EPSR housing 4 is designed as a plate stiffener solution, with stiffeners outside the main box profile. Outside and inside the ring box are access hatches 28 for hook-up and maintenance purposes.
The brush carrier 8 is fixed to the turret structure 2 and therefore geo-stationary, i.e. the vessel and EPSR housing 4 is moving relative to the brush carrier 8. The brush carrier 8 is a junction box (lower end—outside of EPSR housing 4) for the cables that enters the turret 2, as well as structural assembly for the high voltage, and low voltage brushes in contact with the HV&LV rings.
The
In order to reduce wear of brushes and sealing system, the brush carrier will be mounted to a torque arm with a dead-band mechanism, such that the brush carrier do not follow the vessel rotation for a few degrees at any location. This will reduce wear and stress on bearings and brushes due to cyclic movements of the vessel back and forth.
The total EPSR system 3 is hanged up in the gantry support tract 22 by three support bearings 24a, 24b, 24c. The bearings 24a, 24b, 24c are of pin type free to rotate in x- and Y directions. The EPSR loads are transferred via the guide rails/bearings and fastening clamp into a web on the supporting girders.
The sealing system between ambient and slip-ring system 3 internals is an important part of the EPSR system 3 requirement. The present invention may comprise one of two different types of sealing solutions.
The first type of seal arrangement is based on a seal 17 (See
The first type of seal arrangement of the sealing system may comprise an external seal 17 and an internal seal 18 in sealing contact with a plate 19. The internally over pressurized sealing system should prohibit any gas to enter into the internals of the high voltage environment. An external seal is included to ensure that wind loads/other environmental conditions will not influence the internal sealing action. These two functional requirements are important design requirements of the sealing system. The sealing system features dynamic seals with continuous sealing surface around the whole circumference of the EPSR system 3. The seal plate 19 is running on rollers evenly distributed through the complete circumference.
With reference to
The alternative sealing system (see
With reference to
With reference to
With reference to
With reference to
The advantage of the second type of sealing arrangement is that there is only sliding friction contact between the plates of the carrier and the sealing elements as the carrier moves relative to the seals.
The EPSR system 3 is designed for easy handling during installation offshore. Therefore the housing 4 (complete with electrical equipment) and the support track 22 are divided into sections for easy handling during offshore assembly. The system 3 includes the following items:
Installation of the final EPSR section 26 (number eight) is planned as follows:
When the 8 sections 26 are lifted into place the trolley system is removed and the EPSR system 3 is lifted up and secured to the support track 22. The cables from the vessel side to the EPRS system 3 can then be connected.
The seal system is installed after completion of the EPSR housing assembly. The brush carrier 8 is locked in one of the sections 26. Installation sequence may be as follows:
With reference to the
Once the EPSR system 3 is installed with the seal system and the next step is to install the torque arrangement 80 and power connectors. A typical installation sequence is as follows:
It will be appreciated that the installation of the present invention may be a retro-fit on an existing turret and vessel arrangement or alternatively it may be assembled as part of a new turret and vessel fabrication.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20044873 | Nov 2004 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO2005/000422 | 11/9/2005 | WO | 00 | 10/18/2007 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/052144 | 5/18/2006 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3544949 | Panasjuk | Dec 1970 | A |
| 3729699 | Briggs et al. | Apr 1973 | A |
| 4003620 | O'Brien et al. | Jan 1977 | A |
| 4050765 | Duesterhoeft et al. | Sep 1977 | A |
| 4142767 | Karl et al. | Mar 1979 | A |
| 4252388 | Brady | Feb 1981 | A |
| 4294500 | Wilson | Oct 1981 | A |
| 5517937 | Lunde | May 1996 | A |
| 6050747 | Midttveit | Apr 2000 | A |
| 6176193 | Whitby et al. | Jan 2001 | B1 |
| 6302048 | Smedal | Oct 2001 | B1 |
| Number | Date | Country |
|---|---|---|
| 0259072 | Mar 1988 | EP |
| 0 833 770 | Sep 2001 | EP |
| 928599 | Jun 1963 | GB |
| 1447413 | Aug 1976 | GB |
| 1468133 | Mar 1977 | GB |
| WO 9965762 | Dec 1999 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20080121162 A1 | May 2008 | US |
