Patent Publication Number: US-8525631-B2

Title: Underwater power connector system and use thereof

Description:
RELATED APPLICATION 
     This application claims the benefit of priority from Norwegian Patent Application No. 2010 1526, filed on Nov. 1, 2010, the entirety of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an underwater power connection system, for example for transferring electrical power in underwater environments via connector elements which can be coupled together and mutually decoupled. Moreover, the present invention also concerns methods of coupling and uncoupling connector elements of underwater power connection systems. 
     BACKGROUND OF THE INVENTION 
     In contemporary off shore installations, for example oil and gas production platforms, drilling rigs, offshore wind energy facilities, ocean wave energy facilities and mining activities, there often arises a need to transfer considerable electrical power, for example for providing electrical power to electric motors and for coupling outputs from electrical generators. Such transfer of considerable power is beneficially achieved at elevated potentials in an order of kilovolts (kV) for reducing an amount of associated electrical current flowing in electrical wires and cables. It is contemporarily found in practice difficult to provide high-reliability electrical connections in underwater environments, especially when elevated operating potentials are required. Saline seawater leaks, or even elevated humidity resulting from ingress of seawater at elevated operating pressures, are susceptible to cause flashovers and associated short circuits in electrical apparatus. Electrical flashover damage is often permanent when polymer insulators become thereby charred and/or ablated. 
     Power transfer via magnetic coupling through connector elements which are susceptible to being coupled together and mutually uncoupled is known from a published United Kingdom patent no. GB 2 318 397A (Wilson, GEC). There is described a connector comprising a pair of pistons defining respective mating surfaces. One of the pistons is mounted within a bore in a first support member for movement along a first axis and arranged to engage a resilient seal mounted within the bore. Another of the pistons is mounted within a bore in a second support member for movement along a second axis that is parallel to the fist axis and arranged to engage a resilient seal mounted within the bore. The first and second support members are arranged for relative movement only in a direction at right angles to first and second axes for enabling the two axes to be mutually aligned. Springs are included for biasing the pistons towards each other such that their mating surfaces operably wipe each other during alignment of the two axes. The magnetic coupling also includes a fluid connector for admitting pressurized fluid between each piston and its associated support member whereby, in operation, the aligned pistons are operable to press the mating surfaces together. 
     Such a known magnetic coupling has several potential operating problems associated therewith. For example, fluid connection to the pistons creates for complication with yet more fluid-bearing tubes that are susceptible to rupture under high operating pressures. Moreover, the wiping action of the abutting surfaces is potentially inadequate for avoiding significant build up of non-magnetic growth onto the abutting mating surfaces. Furthermore, known magnetic couplings are also potentially difficult to manoeuvre and align during attachment in underwater environments where optical viewing is impaired, for example as a consequence of silt or marine microbes. 
     These contemporary known systems suffer many problems which render them unsuitable for coupling significant power in an order to tens, or even hundreds, of kilowatts (kW) magnitude. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved underwater power connection system which is capable of operating more reliably and/or transferring greater magnitudes of electrical power therethrough. 
     According to a first aspect of the present invention, there is provided an underwater power connection system comprising at least two separable magnetic cores which are operable when coupled together to form a magnetic circuit, wherein the at least two cores are provided with respective one or more windings and said cores include a transverse magnetic member arrangement supporting magnetic limbs, wherein the limbs are elongate and are adapted to intermesh with their lateral sides mutually abutting for providing the magnetic circuit when the system is in its assembled state, characterized in that the limbs are of tapered form towards their distal ends. 
     The invention is of advantage in that the underwater power connection system, by way of its intermeshing elongate magnetic limbs is capable of at least one of: performing more reliably in operation, coupling greater quantities of power therethrough. 
     Optionally, the underwater power connection system is implemented so that the limbs are elongate in a direction corresponding to a direction in which the cores are mutually coupled together and/or decoupled from one another. 
     Optionally, the underwater power connection system is implemented so that the cores are fabricated from at least one of: laminate magnetically permeable sheet, magnetically permeable wire, ferrite materials. 
     Optionally, the underwater power connection system is implemented so that the cores have associated therewith multiple windings for enabling the system to couple multi-phase alternating electrical power therethrough. 
     Optionally, the underwater power connection system is implemented so that the windings are included within hollow non-magnetic metal enclosures including insulating fluid which is arranged to be maintained at a substantially similar pressure to an underwater operating environment of the system. 
     Optionally, the underwater power connection system is implemented to include frequency conversion units coupled to the windings for enabling power to be transferred via the cores at an increased alternating frequency. 
     Optionally, the underwater power connection system is implemented to include a latching mechanism for maintaining the at least two cores coupled together when in a mutually coupled state. 
     According to a second aspect of the invention, there is provided a method of coupling an underwater power connection system comprising at least two separable magnetic cores which are operable when coupled together to form a magnetic circuit, wherein the at least two cores are provided with respective one or more windings, 
     characterized in that said method includes: 
     
         
         (a) arranging for the at least two separable magnetic cores to include a transverse magnetic member arrangement supporting magnetic limbs, wherein the limbs are elongate; and 
         (b) intermeshing the limbs at their lateral sides in a mutually abutting manner for providing the magnetic circuit when the system is in its assembled state. 
       
    
     According to a third aspect of the invention, there is provided a method of decoupling an underwater power connection system comprising at least two separable magnetic cores which are operable when coupled together to form a magnetic circuit, wherein the at least two cores are provided with respective one or more windings, 
     characterized in that said method includes: 
     
         
         (a) arranging for the at least two separable magnetic cores to include a transverse magnetic member arrangement supporting magnetic limbs, wherein the limbs are elongate; and 
         (b) separating the limbs from an intermeshed state with their lateral sides in a mutually abutting manner for breaking the magnetic circuit when the system is in its disassembled state. 
       
    
    
    
     
       DESCRIPTION OF THE DIAGRAMS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein: 
         FIG. 1  is a cross-sectional view of an underwater power connector system pursuant to the present invention, 
         FIG. 2A  is a schematic view of the two magnetic cores of an underwater power connection system pursuant to the present invention, in a first step of their coupling, 
         FIG. 2B  is a schematic view of the cores of  FIG. 2A , in a coupled configuration, 
         FIG. 2C  is a schematic view of the two magnetic cores of an underwater power connection system pursuant to the present invention, in a first step of their decoupling, 
         FIG. 3  is a cross-sectional view of a modified implementation of the power connector system of  FIG. 1 . 
     
    
    
     In the accompanying diagrams, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing. 
     DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Referring to  FIG. 1 , there is shown an underwater power connector system pursuant to the present invention. The connector system is indicated generally by  10 , and is operable to provide underwater power connections for electrical power supply at potentials of 6 kV and above. The connector system  10  is required, for example, for future installations where high-voltage (HV) cables are to be coupled to sub-sea equipment in oil and gas installations, offshore wind turbine parks (“farms”) and sub-sea power grids. The connector system  10  potentially replaces contemporary 13.4 kV wet connectors wherein electrical contacts between mating electrodes are utilized, namely magnetic coupling is not employed. These contemporary wet connectors have difficulty achieving reliable insulation on account of electrical stresses that are encountered along their wetted surfaces. Although magnetic couplers are known as described in the foregoing, such known magnetic connectors are generally unsuitable for transferring large amounts of power in underwater applications. The connector system  10  illustrated in  FIG. 1  is devoid of high-voltage (HV) insulation problems associated with contemporary connectors because a new manner of implementing a magnetic connection is employed in the system  10 , wherein electrical components can be thoroughly enclosed and encapsulated, thereby completely avoiding exposure to saline sea water. Beneficially, the system  10  is used in conjunction with sea bottom placed production units that require in operation large amounts of power to function optimally, for example in excess of 20 MW. 
     In  FIG. 1 , the system  10  includes primary circuit cables  20  and secondary circuit cables  30  connected to corresponding primary and secondary windings respectively. Moreover, the system  10  employs magnetic coupling between the primary and secondary windings via a transformer implemented from a first magnetic core  40  associated with the primary windings, and a second magnetic core  50  associated with the secondary windings as illustrated. The first magnetic core  40  includes a transverse member  60  supporting three projecting limbs  70 . Optionally, the limbs  70  are slightly tapered towards their distal ends remote from their transverse member  60 . Likewise, the second magnetic core  50  includes a transverse member  80  supporting three projecting limbs  90 . Optionally, the limbs  90  are slightly tapered towards their distal ends remote from their transverse member  80 . Optionally, the transverse member  60  and its limbs  70  are an integral component fabricated from magnetic material of relative permeability considerably greater than unity. Moreover, the transverse member  60  and its limbs  70  are fabricated from at least one of: laminated magnetic material (for example from laminated silicon steel), from magnetic wires, from a ferrite composite material. Optionally, the transverse member  80  and its limbs  90  are an integral component fabricated from magnetic material of relative permeability considerably greater than unity. Moreover, the transverse member  80  and its limbs  90  are also fabricated from laminated magnetic material, for example fabricated from at least one of: laminated silicon steel, from magnetic wires, from a ferrite composite material. The limbs  70  of the first magnetic core  40  are dimensioned to intermesh as illustrated in  FIG. 1  with the limbs  90  of the second magnetic core  60  when the system  10  is in its coupled state for transferring power by way of alternating magnetic coupling between the primary and secondary windings. Optionally, at least a portion of the limbs  70 ,  90  are implemented as at least part annuli; alternatively, the limbs  70 ,  90  are of a substantially rectilinear form as illustrated. The limbs  70 ,  90  are, as aforementioned, beneficially optionally slightly tapered, for example by an angle less than 5° in respect of an axis  100  as illustrated. The aforementioned primary and secondary windings are disposed to encircle on or more of the limbs  70 ,  90  so that the windings are magnetically coupled to a magnetic field which is established within the cores  40 ,  50  when the system  10  is in operation. 
     When the connector system  10  is to be decoupled, the first and second cores  40 ,  50  are pulled apart from one another with their corresponding primary and secondary windings attached respectively. The system  10  is of advantage in that the limbs  70 ,  90  are elongate in a direction denoted of the axis  100  in which the cores  40 ,  50  are coupled together as denoted by arrows  110 . Such an arrangement as illustrated in  FIG. 1  has several benefits as follows:
     (a) there is a considerable mutually abutting surface area at sides of the limbs  70 ,  90  whereat they meet; this provides for better magnetic coupling in operation in comparison to known magnetic couplers described in the forgoing and renders the system  10  more tolerant to debris and growth which may occur onto sides of the limbs  70 ,  90 . The optionally tapered nature of the limbs  70 ,  90  provides for yet further improved magnetic coupling and insensitivity to contamination collected on use onto the limbs  70 ,  90 ;   (b) the limbs  70 ,  90  abutting onto the transverse members  60 ,  80  define an extent to which the cores  40 ,  50  are brought together when the system  10  is in a coupled state; and   (c) the limbs  70 ,  90  are beneficial in providing the system  10  with lateral rigidity transverse to the axis  100  and in-line with the axis  100  when the connector system  10  is in its coupled state.   

     Although not shown in  FIG. 1  the system  10  includes insulating encapsulation of the cores  40 ,  50  and their windings to protect them from corrosion and ingress of saline sea water. Such insulating encapsulation is beneficially manufactured from epoxy, rubber, silicone, polyurethane or other robust insulating materials which are impervious to ingress of saline sea water. Optionally, the windings are enclosed in a thin-walled stainless steel (or similar non-magnetic metal) hollow housing filled with degasified insulating fluid so that pressures inside and outside the hollow housing are balanced in operation of the system  10 . 
     Optionally, the system  10  is provided with a latching or locking mechanism for maintaining the cores  40 ,  50  tightly bound together when the system  10  is in its coupled state; optionally, the mechanism is implemented by way of a non-alternating electromagnet, namely direct current electromagnet. Optionally, the mechanism is implemented by way of a non-alternating current applied to additional attraction windings included spatial concurrently with the primary and/or secondary windings. The latching or locking mechanism is released when the system  10  is to be decoupled for mutually separating the cores  40 ,  50 . Optionally, the latching or locking mechanism is implemented, at least in part, by actuated mechanical components which are arranged to mutually engage to provide a locking action when the system  10  is in its coupled state. 
     In  FIG. 2 , the system  10  in its decoupled state is indicated by  200 ,  220 , and in its coupled state by  210 . In the decoupled state  200  when progressing to couple the system  10  together, the cores  40 ,  50  are mutually brought together as indicated by broad arrows. In the coupled state  200  when progressing to decouple the system  10 , the cores  40 ,  50  are mutually separated as indicated by broad arrows in the state  220 . 
     In  FIG. 3 , the primary and secondary windings are provided with high-frequency switching units  300 ,  310  which include solid state switching devices and are operable to temporally chop signals supplied and/or generated at the primary and secondary windings for enabling the cores  40 ,  50  to operate at higher alternating frequencies. Such higher frequency operation, for example at substantially 400 Hz or even greater, enables the cores  40 ,  50  to be smaller and weigh less for a given power coupling capability of the system  10 . 
     The system  10  is capable of coping with power transfer magnitudes in an order of Megawatts (MW), and also accommodating multi-phase power transfer by way of using multiple limbs  70 ,  9 ; for example, the system  10  is capable of supporting 3-phase power transfer therethrough. Such high power operation is starkly juxtaposed to contemporary magnetic couplers which typically are operable to couple in an order of Watts or a few kilowatts (kW). In the system  10 , primary and secondary windings follow respective cores  40 ,  50  as aforementioned when the cores  40 ,  50  are mutually separated in operation. 
     Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. Expressions such as “including”, “comprising”, “incorporating”, “consisting of”, “have”, “is” used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.