Patent Description:
Traditionally, fixed or floating platforms, or floating production vessels, are used in the offshore oil and gas production. In the operation of offshore platforms, it can be necessary to install electrical equipment under water, e.g. for controlling functions of a subsea Christmas tree or a subsea blowout preventer. More recently, processing facilities are being relocated to the ocean floor. Installations on the ocean floor can comprise a range of components, including pumps, compressors and the like which require electric power for operation. Power supply can occur through a subsea power grid installed on the ocean floor, which may for example comprise a subsea transformer, a subsea switchgear and a subsea variable speed drive for powering the above mentioned subsea loads. It is essential that the installed equipment operates reliably even under the high pressure that prevails at the rated installation depth which can be <NUM>,<NUM> or more.

To protect the equipment from the corrosive environment of the surrounding seawater and to deal with the high pressures, two different solutions were proposed. A pressure resistant enclosure can be provided, which has a close to atmospheric internal pressure, enabling the use of conventional electric and electronic components therein. Such enclosures need to have relatively thick walls and are thus bulky and heavy, since they have to withstand high differential pressures. Another solution is the use of pressurized (or pressure compensated) enclosures, which comprise a pressure compensator that balances the pressure in the enclosure to the pressure prevailing in the ambient seawater.

The pressurized enclosure is generally filled with a liquid, and components operated inside the pressurized enclosure are made to be operable under high pressures. The pressure compensator balances the pressure and compensates variations in the volume of the liquid filling the enclosure, which may for example occur due to variations in outside pressure and/or temperature. Temperature changes can also be caused by internal heating, e.g. by electric losses of components provided inside the enclosure of the subsea device. The corresponding volume increase of the liquid filling the enclosure may then be taken up by the pressure compensator, which is thus also termed volume compensator.

Pressure compensators may include bellows, bladders, pistons, membranes or the like. Bellows can have the disadvantage that they are either expensive to produce, or their configuration is such that the stroke length of the bellows is limited. In the latter case, a pressure compensator for a large volume of liquid (i.e. for an enclosure of a large subsea device) needs to have a significant size to provide the required compensation capacity. For some types of bellows, the bellows needs to have a size of more than three times of the size of the compensated volume. This results in a low utilization factor of the volume of the compensator system. Furthermore, the liquid filling such pressure compensator needs to be compensated itself (i.e. changes of its volume due to temperature/pressure changes need to be taken up by the compensator). Such compensator systems can thus be relatively large and heavy.

Furthermore, the bellows of such pressure compensator is often exposed to the subsea environment, in particular, to seawater. This may cause corrosion problems for the bellows and may lead to the ingress of seawater into the enclosure of the subsea device upon failure of the bellows.

<CIT> describes a pressure compensator that has a first bellows chamber that is surrounded by a second bellows chamber, the second bellows chamber forming a closed intermediate space around the first bellows chamber. A double barrier against the ingress of sea water is thus provided. In the disclosed configuration, the compensation capacity is determined by the size of the first bellows. The whole volume inside the first bellows chamber and in addition the volume inside the second bellows chamber are dead volumes, the liquid filling these volumes additionally requiring pressure compensation. In such configuration, the pressure compensator needs to have a significant size and an increase in the compensation capacity results in a significant increase in the dead volume.

<CIT> relates to a pressure compensator for a subsea device with at least one outer bellows and a first chamber enclosed by the outer bellows.

<CIT> relates to a subsea transformer including a pressure compensation device with first and second bellows.

<CIT> discloses a pressure compensator for providing pressure compensation for a chamber of a subsea device is provided. The pressure compensator has an enclosure with at least an outer wall. A first compensation chamber is provided inside the enclosure. A flow connection from the first compensation chamber towards the chamber of the subsea device is further provided. As second compensation chamber is provided inside the enclosure. First and second separating walls are arranged inside the enclosure. A first bellows portion of the first separating wall and a second bellows portion of the second separating wall are deformable to provide pressure compensation between the chamber of the subsea device and a second inner volume around which the second separating wall extends.

It is desirable to provide a pressure compensator for use with a subsea device that can be manufactured easily and cost efficiently. It is further desirable that the pressure compensator is reliable during operation and has a long lifetime. It is desirable to reduce the size and weight of pressure compensators, and to increase the utilization factor and compensation capacity. Also, it is desirable that the pressure compensator is protected from corrosion and provides protection against seawater ingress. It is desirable to improve maintenance and handling of enclosures and connections to facilitate installation and retrieval from deep subsea locations which would otherwise be very high cost operations.

Importantly, it is an object of the present invention to provide an enclosure which is capable of utilising electrical connectors that are not suitable for high-pressure differentials such as very deep sea applications, for example at depths of <NUM> or more.

It is an object of the present invention to provide a pressure or volume compensated enclosure that addresses the above desires.

In accordance with a first aspect an enclosure for a subsea control and power arrangement. The enclosure comprises: a canister and a lid, the canister and the lid form an enclosure volume, a connector assembly, a first volume compensator having a first chamber, the first volume compensator is mounted to the enclosure outside the enclosure volume, the first chamber has a variable volume and a second volume compensator having a second chamber, the second chamber has a variable volume. The connector assembly extends through the lid and into the enclosure volume and comprises a housing forming a third chamber and a connector part. The connector part is mounted at least partly within the housing and the housing is located at least partly within the enclosure volume. The connector part extends through the housing and into the enclosure volume. The first chamber, the second chamber and the third chamber are liquidly connected to one another to form a compensator volume. The compensator volume is arranged, in liquid flow order, between the enclosure volume and ambient the enclosure thereby forming at least two sealing barriers between ambient and the enclosure volume.

In this arrangement, the enclosure is pressure compensated, in other words, the ambient pressure, e.g. <NUM> atmospheres, is present within the enclosure volume and the compensator volume. Thus, pressure differentials across the sealing barriers (and other seals) is greatly minimised. This minimised pressure differential means that the enclosure can be relatively lightweight and easy to install and retrieve, inexpensive and be highly durable. Further, the pressure differential is minimal so that a wide range of connectors, unsuitable for high pressure differentials, can be used.

The compensator volume and / or the enclosure volume may be completely filled with liquid. Preferably the liquid is a dielectric liquid and preferably a dielectric oil.

Any one or both the first volume compensator and the second volume compensator may comprise any one of the group a bellows arrangement, a balloon arrangement and a membrane. Preferably the membrane is deformable or stretchable.

The first volume compensator may comprise a housing and a membrane, the membrane is arranged within the housing and forms therein a first chamber. The first chamber is part of the compensator volume. The housing comprises an aperture to liquidly connect ambient with the opposite side of the membrane to the first chamber.

The first volume compensator may comprise a housing and a bellows. The bellows may be arranged within the housing and forms therein a first chamber. The first chamber may be part of the compensator volume. The housing may comprise an aperture to liquidly connect ambient with the opposite side of the bellows to the first chamber.

The first volume compensator may comprise a housing and a membrane. The membrane may be arranged within the housing and form therein a first chamber. The first chamber may be part of the compensator volume. The housing may comprise an aperture to liquidly connect ambient with the opposite side of the bellows to the first chamber.

The membrane may be deformable and/or stretchable.

The second volume compensator may comprise a bellows arrangement. The bellows arrangement may surround the housing of the connector assembly and may form therewith the second chamber. The housing of the connector assembly may comprise at least one aperture which liquidly connects the second chamber and the third chamber.

The second volume compensator may comprise a bellows arrangement. The bellows arrangement may form the second chamber. The bellows arrangement may be secured to an internal surface of the lid. A passage may extend through the lid and liquidly connects between the second chamber and the first chamber.

The second volume compensator may comprise a balloon arrangement. The balloon arrangement forms the second chamber. The balloon arrangement may be secured to an internal surface of the lid. A passage may extend through the lid and liquidly connects between the second chamber and the first chamber.

The lid may comprise a first sealing surface and a second sealing surface. The canister may comprise a first sealing surface and a second sealing surface. A first seal may be located between the first sealing surfaces. A second seal may be located between the second sealing surfaces. Any one or more of the first and second seals may be a double seal i.e. there are two or more seals forming the first seal and there are two or more seals forming the second seal.

Any one or more the first and second seals may be any one of a metallic seal or an elastomeric seal, such as a rubber or silicone based material.

The first pressure compensator may be mounted to an external surface of the lid or an external surface canister.

One or more input and/or output connectors may be connected to the enclosure.

Electronic and/or electrical equipment may be located within the enclosure volume.

An example of an enclosure for electronic and electrical components or equipment and associated method of operation in accordance with the present invention will now be described with reference to the accompanying drawings in which:.

<FIG> is a view on an enclosure <NUM> in accordance with the present invention. The enclosure <NUM> may be used for housing a subsea control and/or power arrangement. The enclosure <NUM> comprises a canister <NUM> and a lid <NUM>. In this example, a power-in connector <NUM>, two power-out connector <NUM>, <NUM> and a first volume compensator <NUM> are mounted to the enclosure <NUM> and as shown mounted to and through the lid <NUM>. Power cables <NUM>, <NUM> and <NUM> extend from the power-in connector <NUM> and the two power-out connectors <NUM>, <NUM> respectively. Further connectors may be present in other examples.

The power-in connector <NUM> is a SpecTron® connector, but other connectors may be used. The two power-out connectors <NUM> are DigiTron® connectors, but other connectors may be used. Other connectors made by other manufactures may also be used.

<FIG> is a schematic section through the enclosure <NUM> shown in <FIG> and in accordance with the present invention. The enclosure <NUM> is for housing a subsea control and power arrangement <NUM>. The subsea control and power arrangement <NUM> comprises known electronic and electrical components such as a transformer <NUM> and at least one connector assembly <NUM>. The connector assembly <NUM> is known and may be an input power connector as indicated as <NUM> in <FIG>. Other connectors are attached as shown in <FIG> and may be input and/or output connectors. The connectors are capable of being mated and de-mated by a remotely operated vehicle (ROV) as is known in the art. The input connector(s) may be connected to the output connector(s) via electrical components such as the transformer <NUM>.

The canister <NUM> is generally tubular and is sealed with a cap <NUM> at one end and with the lid <NUM> at its other end. The cap <NUM> is generally disc shaped and is welded to the canister <NUM>. Alternatively, the canister <NUM> and the cap <NUM> may be monolithically formed. The canister <NUM> and the lid <NUM> form an enclosure volume <NUM>. The electronic and electrical components <NUM> and connector assembly <NUM> are housed within the enclosure volume <NUM>. The connector assembly <NUM> is mounted to the lid <NUM> and extends through the lid <NUM> and into the enclosure volume <NUM>.

The connector assembly <NUM> comprises a connector part <NUM> for the electrical connection. The connector part <NUM> is a receptacle <NUM> in this example, but it may be a plug in other examples. In this example, the input power connector <NUM> comprises the receptacle <NUM> and a plug <NUM> as shown in <FIG> and as known in the art. The connector part <NUM> extends through the housing <NUM> and into the enclosure volume <NUM> so that connections can be made (not shown) to the electrical or electronic equipment, such as the transformer <NUM>, within the enclosure volume <NUM>.

The enclosure <NUM> comprises a first volume compensator <NUM> having a first chamber <NUM> and a second volume compensator <NUM> having a second chamber <NUM>. The connector assembly <NUM> comprises a housing <NUM> that forms a third chamber <NUM>. The first chamber <NUM>, the second chamber <NUM> and the third chamber <NUM> are liquidly connected to, i.e. liquid can flow between, one another to form a compensator volume <NUM>, <NUM>, <NUM>. The first volume compensator <NUM> and the second volume compensator <NUM> are capable of accommodating volume changes and will be described in more detail later. In all the embodiments described herein it should be noted that the first volume compensator <NUM> and the second volume compensator <NUM> have mechanisms that have variable volumes, i.e. variable compensator volumes <NUM>, <NUM>, that are capable of accommodating volume changes of liquids such as in this example a dielectric oil. The first volume compensator <NUM> is mounted to the enclosure <NUM> outside the enclosure volume <NUM> and as shown on an external surface <NUM> of the lid <NUM>, but it could be mounted to an external surface <NUM> of the canister <NUM>. The first chamber <NUM> has a variable volume and the second chamber <NUM> has a variable volume.

The enclosure volume <NUM> is completely filled with preferably a dielectric liquid <NUM> and the compensator volume <NUM>, <NUM>, <NUM> is completely filled with dielectric liquid <NUM>. Non-dielectric liquids could be used where the electrical or electronic equipment in the enclosure volume are otherwise electrically insulated. The term 'liquid' covers both dielectric and non-dielectric liquids and are both referred to as 'liquid' herein. Dielectric liquid <NUM> and dielectric liquid <NUM> have the same composition, but it is possible for the dielectric liquids <NUM>, <NUM> to have different compositions. The dielectric liquids <NUM>, <NUM> electrically insulate the electronic and electrical components <NUM>. The dielectric liquids <NUM>, <NUM> have a relatively low coefficient of thermal expansion, however, changes in temperature of the dielectric liquids <NUM>, <NUM> cause their volume to change. In use, the electronic and electrical components heat up and increase the temperature of the dielectric liquids <NUM>, <NUM> and in particular increase the temperature of the dielectric liquid <NUM> within the enclosure volume. The dielectric liquid <NUM> surrounds and is in direct contact with the transformer38 (and/or other electronic or electrical components) and therefore can receive a significant heat input. The dielectric liquids <NUM>, <NUM> increase in volume as they heat up and the first chamber <NUM> expands or increases in volume to accommodate the volume increase of the liquids <NUM>, <NUM>. Similarly, when the transformer <NUM> is less utilised or non-operational and cooler, the dielectric liquid <NUM>, <NUM> cools and reduces in volume and the first chamber <NUM> contracts or decreases in volume to accommodate the dielectric liquid's volume decrease.

It is very important that seawater does not contaminate the enclosure volume <NUM> and contact the electronic and electrical components. Seawater is corrosive and may cause premature failure of the electronic and electrical components <NUM>. It is very costly to mount a maintenance operation and replace the electronic and electrical components <NUM>. It is highly undesirable to allow failure of the electronic and electrical components <NUM> because this would result in a power failure to important loads that demand electrical power and / or control signals passing through the enclosure <NUM>. The present enclosure <NUM> described herein combats these problems in two ways.

Firstly, to provide two sealing barriers between ambient, e.g. seawater, and the enclosure volume <NUM>. As will become apparent, the compensator volume <NUM>, <NUM>, <NUM> is arranged, in liquid flow order, between the enclosure volume <NUM> and ambient seawater. In the very unlikely situation of seawater ingress to the enclosure volume <NUM>, the seawater (in liquid flow order) would have to leak through the first volume compensator <NUM> and into the compensator volume <NUM>, <NUM>, <NUM> and then through the second volume compensator <NUM> and into the enclosure volume <NUM>. Thus, the present enclosure <NUM> forms (at least) two sealing barriers between ambient and the enclosure volume <NUM> via the pressure compensating arrangement of the first volume compensator <NUM> and the second volume compensator <NUM>. Leakage of seawater through first barrier and into the compensator volume <NUM>, <NUM>, <NUM> will have no consequence for operation because components within the compensator volume <NUM>, <NUM>, <NUM> are resistant to damage from seawater.

Secondly, the enclosure is arranged to be pressure compensated, that is the internal pressure within the enclosure volume <NUM> is the same or approximately that of ambient seawater pressure. Note that the present enclosure is intended to be capable of operating at subsea depths of at least <NUM>. Pressure equalization is via seawater ports in the housing of the first volume compensator <NUM>. This aspect will be described in more detail later.

<FIG> shows the first volume compensator <NUM> in greater detail. The first volume compensator <NUM> comprises a housing <NUM>, the housing is formed by a wall <NUM>, a closing plate <NUM> and a base <NUM>. The base <NUM> and the closing plate <NUM> are bolted to the wall <NUM>. An internal sleeve <NUM> fits tightly inside the wall <NUM>. A membrane <NUM> is circumscribed by a bead <NUM> which runs around its periphery. The bead <NUM> is trapped between the wall <NUM> and the sleeve <NUM>. The first chamber <NUM> is defined one side, the inside, of the membrane <NUM> and is filled with the dielectric liquid <NUM>. On the other side, the outside, of the membrane <NUM> is seawater <NUM> which can ingress the first volume compensator <NUM> via a hole <NUM> in the closing plate <NUM>; additionally, holes <NUM> may be provided through the wall <NUM> and sleeve <NUM>. The base <NUM> comprises a series of apertures <NUM> that lead to a gallery <NUM>. The gallery <NUM> is formed between the base <NUM> and the lid <NUM>. A passage <NUM> is defined through the lid <NUM>, also see in <FIG>, and liquidly connects the gallery <NUM> and the third chamber <NUM> such that dielectric liquid <NUM> can flow between the first chamber <NUM> and the third chamber <NUM>.

The membrane <NUM> is an elastomeric material such as a silicone rubber, but other resilient materials are equally usable such as acrylonitrile butadiene rubber (NBR) or other rubber based materials. The membrane <NUM> may be reinforced to provide high durability.

<FIG> shows two positions of the membrane <NUM>. A first position of the membrane <NUM> is referred to as 50A and a second position of the membrane <NUM> is referred to as 50B. There is an increase in the volume of the first chamber <NUM> as the membrane <NUM> moves between position 50A and position 50B and in the direction from position 50A to position 50B. There is a decrease in the volume of the first chamber <NUM> as the membrane <NUM> moves between position 50A and position 50B and in the direction from position 50B to position 50A. The membrane <NUM> will tend towards position 50B when the dielectric liquids <NUM>, <NUM> increase in temperature or are 'hot' and will tend towards position 50A when the dielectric liquid <NUM>, <NUM> decrease in temperature or are 'cold'. Seawater <NUM> is forced out of and into the first volume compensator <NUM> on the outside of the membrane <NUM> according to increased or decreased volumetric changes respectively in the first chamber <NUM>. The membrane <NUM> is deformable between the first position 50A and the second position 50B and in this example the membrane <NUM> does not appreciably stretch or expand, although it may also do so. As can be seen most clearly in <FIG>, in position 50A the membrane <NUM> has a folded portion to accommodate the smaller volume of 'cold' dielectric liquid. In position 50B, the membrane has unfolded to accommodate a larger volume of 'hot' dielectric liquid. In other embodiments, the membrane <NUM> may be flexible and/or stretchable, in addition to being deformable, to accommodate the necessary volume changes of the dielectric oil.

<FIG> shows a schematic section through the second volume compensator <NUM> in greater detail than <FIG> and in accordance with the present invention. The second volume compensator <NUM> comprises a bellows arrangement <NUM>. The bellows arrangement <NUM> surrounds the housing <NUM> of the connector assembly <NUM> and forms the second chamber <NUM>. The bellows arrangement <NUM> comprises a first bellows <NUM> and a second bellows <NUM>. The first bellows <NUM> has a greater diameter (or cross-sectional area) than the second bellows <NUM>. The first bellows <NUM> and the second bellows <NUM> are attached to one another via a ring <NUM>. The first and second bellows <NUM>, <NUM> are formed from a metallic composition, but other materials may be used. The first and second bellows <NUM>, <NUM> are formed with corrugations or other known configuration and which is relatively flexible in compression or extension. The first bellows <NUM> is rigidly fixed relative to the housing <NUM> at its opposite end to the ring <NUM>. The second bellows <NUM> is rigidly fixed to the housing <NUM> at its opposite end to the ring <NUM>.

The housing <NUM> comprises at least one aperture <NUM> and preferably an array of apertures <NUM>. The apertures <NUM> liquidly connect the second chamber <NUM> and the third chamber <NUM> such that dielectric liquid <NUM> may flow from one chamber to the other chamber.

An increase in temperature and corresponding increase in volume of the dielectric liquid <NUM>, <NUM> increases pressure in the enclosure volume <NUM>. The increase in pressure forces the ring <NUM> to move in the direction of arrow A. As the ring <NUM> moves in the direction of arrow A, the first bellows <NUM> compresses and the second bellows <NUM> extends. The compression of the first bellows <NUM> causes a greater reduction in its volume than the increase in volume of the second bellows <NUM>. The nett reduction in volume of the second chamber <NUM> is approximately equivalent to the change in volume of the dielectric liquid <NUM> and <NUM> caused by its increasing temperature. In turn, dielectric liquid <NUM> in the third chamber <NUM> is forced through the passage <NUM> and into the first chamber <NUM>.

<FIG> is an enlarged view of the section through a second embodiment of the first volume compensator <NUM> and a second embodiment of the second volume compensator <NUM>. Like components are given the same reference numerals as before and otherwise operate in like manner as described herein. It should be noted that the present invention may be realised by using the first embodiment of the first volume compensator <NUM> with the first and / or second embodiments of the second volume compensator <NUM> and may be realised by using the second embodiment of the first volume compensator <NUM> with the first and / or second embodiments of the second volume compensator <NUM>.

For the second embodiment of the first volume compensator <NUM>, the membrane <NUM> is replaced by a bellows <NUM> which is located inside the housing <NUM>. The sleeve <NUM> is largely obsolete and could be omitted and optionally with the wall <NUM> being thickened to occupy the space left by omitting the sleeve <NUM>. The bellows <NUM> has an end plate <NUM> that closes one of its ends and at its other end the bellows <NUM> is open to the gallery <NUM>. The bellows <NUM> defines the first chamber <NUM>. The bellows <NUM> is affixed, for example by welding, at its open end to the wall <NUM> and towards or close to the gallery <NUM>. The gallery <NUM> is liquidly connected to the third chamber <NUM> via the passage <NUM> as described before. In use, the electronics and electrical components heat up and heat the dielectric liquids <NUM>, <NUM>, which in turn increase in volume. Dielectric liquid <NUM> in the third chamber <NUM> is forced through the passage <NUM> by virtue of the volume of the third chamber <NUM> not changing and dielectric liquid <NUM> in the second chamber <NUM> is forced through the passage <NUM> by virtue of the increase in volume of the dielectric liquid <NUM> in the enclosure volume <NUM> forcing the bellows arrangement <NUM> to compress as described with reference to <FIG>.

For the second embodiment of the second volume compensator <NUM>, the bellows arrangement <NUM> comprises a bellows <NUM> having an end plate <NUM> that closes one end of the bellows <NUM> and another end plate <NUM> at the other end of the bellows <NUM>. The end plate <NUM> is affixed directly, by welding for example or possibly by bolts in a conventional manner, to the inside surface <NUM> of the lid <NUM>. The bellows <NUM> defines the second chamber <NUM>. The end plate <NUM> defines an aperture <NUM> which is part of a passage <NUM> defined through the lid <NUM>. The passage <NUM> is arranged to allow liquid communication, i.e. the flow of dielectric liquid <NUM>, between the gallery <NUM> and the second chamber <NUM>. In use, the electronics and electrical components heat up and heat the dielectric liquids <NUM>, <NUM>, which in turn increase in volume. Dielectric liquid <NUM> in the third chamber <NUM> is forced through the passage <NUM> by virtue of the volume of the third chamber <NUM> not changing and dielectric liquid <NUM> in the second chamber <NUM> is forced through the passage <NUM> by virtue of the increase in volume of the dielectric liquid <NUM> in the enclosure volume <NUM> forcing the bellows <NUM> to compress from a first position 70A to a second position 70B and in the direction of arrow B.

Implementation of the second embodiment of the second volume compensator <NUM> may allow the absence of the first embodiment of the bellows arrangement <NUM>, i.e. removal of the first bellows <NUM> and the second bellows <NUM>, as shown and described with reference to <FIG> and <FIG> from one or all the connectors <NUM>, <NUM> and <NUM>.

With reference to <FIG>, there is shown one power-in connector <NUM> and two power-out connectors <NUM>, <NUM>. The enclosure <NUM> may have more or less connectors. The above embodiments have been described with reference to the power-in connector <NUM> having a connector assembly <NUM> which defines the third chamber <NUM>. It should be appreciated that the other connectors <NUM>, <NUM> also comprise similar connector assemblies <NUM> and which define similar third chambers <NUM>. All these third chambers <NUM> are liquidly connected to the gallery <NUM> of the first volume compensator <NUM> via similar passages <NUM>. The passages <NUM> extend through the lid <NUM> to the other connectors <NUM>, <NUM>. Alternatively, two or more first volume compensators <NUM> may be present and the other connectors <NUM>, <NUM> may be liquidly connected to any one of the first volume compensators <NUM>.

In addition to the dielectric liquid <NUM> in the third chamber(s) <NUM> increasing and decreasing in volume because of temperature changes, when mating and de-mating the plug and receptacle of the connectors <NUM>, <NUM>, <NUM> the dielectric liquid will be displaced to accommodate the volume of the electrical connector pins of the connectors <NUM>, <NUM>, <NUM>. Thus, when mating the plug and receptacle dielectric liquid is forced through the passage <NUM> and into the first volume compensator <NUM> and when de-mating the plug and receptacle dielectric liquid is forced through the passage <NUM> from the first volume compensator <NUM> to the third chamber <NUM>. This is independent to any temperature changes of the dielectric liquids <NUM>, <NUM>.

Good sealing is a vital aspect of the present invention and in addition to the two sealing barriers arrangement provided by the first and second volume compensators, the canister <NUM>, lid <NUM> and other components also have two independent seals where the components are releasably attached to one another.

<FIG> is an enlarged view of a section through a third embodiment of the first volume compensator <NUM> and a third embodiment of the second volume compensator <NUM>. <FIG> is similar <FIG> and has similar components which operate in a similar way unless stated otherwise.

The third embodiment of the first volume compensator <NUM> comprises an elastic membrane <NUM> which is stretchable between a first shape 100A and a second shape 100B. The elastic membrane <NUM> is stretchable to define the first chamber <NUM>. The second shape 100B defines a greater volume of the first chamber <NUM> than the first shape 100A. Similar to the membrane <NUM> of the first embodiment of the first volume compensator <NUM>, the membrane <NUM> is circumscribed by a bead <NUM> which runs around its periphery. The bead <NUM> is trapped between the wall <NUM> and the sleeve <NUM> to secure the membrane <NUM> to the housing <NUM> and to seal around it.

The third embodiment of the second volume compensator <NUM> comprises a balloon arrangement comprising a balloon <NUM> that is formed from an elastic material and is capable of expanding and contracting between a first shape 102A and a second shape 102B. The balloon <NUM> has a stem <NUM> or neck. The stem <NUM> has a bead <NUM> that is trapped by plates <NUM>, <NUM> which are bolted together and define seals <NUM> therebetween.

The balloon <NUM> may be protected by a shield <NUM> shown in dashed lines. The shield <NUM> has apertures or may be perforated to allow easy flow of dielectric liquid. The shield <NUM> is intended to only protect the balloon <NUM> from damage during use, installation and disassembly.

The membrane <NUM> (and <NUM>) and the balloon <NUM> are formed from an elastomeric material such as a silicone rubber, but other resilient materials are equally usable such as acrylonitrile butadiene rubber (NBR) or other rubber based materials.

As described above, there it is essential for the enclosure to have a very high level of sealing. As described herein the two volume compensators <NUM>, <NUM> each provide one seal barrier thereby in concert they provide two seal barriers and a compensator volume therebetween to ensure seawater cannot ingress to the enclosure volume <NUM>. The enclosure <NUM> further comprises conventional sealing arrangements that provide two seals between the enclosure volume <NUM> and seawater <NUM>. Referring to <FIG> again, the lid <NUM> comprises at least a first sealing surface <NUM> and a second sealing surface <NUM> and the canister <NUM> comprises at least a first sealing surface <NUM> and a second sealing surface <NUM>. A first seal <NUM> is located between the first sealing surfaces <NUM>, <NUM> and a second seal <NUM> is located between the second sealing surfaces <NUM>, <NUM>. The first and second seals <NUM>, <NUM> are conventional O-ring seals and either seal may be either metallic or non-metallic. As shown the seals <NUM>, <NUM> are located within a respective groove <NUM>, <NUM> within the sealing surfaces <NUM>, <NUM> respectively; however, the grooves <NUM>, <NUM> may be formed in the sealing surfaces <NUM>, <NUM> respectively of the canister <NUM>. There are two grooves <NUM> and seals <NUM> between the second sealing surfaces <NUM>, <NUM>. There may be more than one groove <NUM> and first seal <NUM> between the first sealing surfaces <NUM>, <NUM>. Other seals are provided which are effectively 'internal' or within the two-barrier system described herein. Still referring to <FIG>, conventional O-ring seals <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are fitted into grooves defined in and between abutting components. This enclosure <NUM> allows relatively easy assembly, achieving two-barrier sealing, without any need for seal-welding to take place, which would be more complicated and costly. The lid <NUM> may be made solely by machining with no welding operations. This enclosure <NUM> allows the use of electrical connectors having penetrators which, significantly, do not have sufficiently high sealing capability for high differential pressures (possibly approximately <NUM> atmospheres) that can be encountered subsea at for example depths of approximately <NUM>. This enclosure <NUM> therefore allows the use existing electrical connectors without any special adaptation of the electrical connectors. Furthermore, this enclosure <NUM> provides a lighter and smaller solution than previously known and hence reduces manufacturing costs and installation complexity and therefore further cost savings.

Any one or more of the embodiments of the first volume compensator <NUM> may be used with any one or more of the embodiments of the second volume compensator <NUM>. In any combination, there is always at least two leakage barriers between ambient seawater <NUM> and the enclosure volume <NUM>, hence the electronics and electrical components <NUM> in the enclosure volume <NUM>. As mentioned, the compensator volume <NUM>, <NUM>, <NUM> comprises the first, second and third chambers and is arranged between, in leakage flow sequence, ambient seawater <NUM> and the enclosure volume <NUM>.

While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that equivalents and/or combinations of embodiments that fall within the scope of the appended claims are intended to be included in this description.

Claim 1:
An enclosure (<NUM>) for a subsea control and power arrangement (<NUM>), the enclosure (<NUM>) comprises:
a canister (<NUM>) and a lid (<NUM>), the canister (<NUM>) and the lid (<NUM>) form an enclosure volume (<NUM>),
a connector assembly (<NUM>),
a first volume compensator (<NUM>) having a first chamber (<NUM>), the first volume compensator (<NUM>) is mounted to the enclosure (<NUM>) outside the enclosure volume (<NUM>), the first chamber (<NUM>) has a variable volume and
a second volume compensator (<NUM>) having a second chamber (<NUM>), the second chamber (<NUM>) has a variable volume,
the connector assembly (<NUM>) extends through the lid (<NUM>) and into the enclosure volume (<NUM>) and comprises
a housing (<NUM>) forming a third chamber (<NUM>) and
a connector part (<NUM>),
the connector part (<NUM>) is mounted at least partly within the housing (<NUM>) and the housing (<NUM>) is located at least partly within the enclosure volume (<NUM>), the connector part (<NUM>) extends through the housing (<NUM>) and into the enclosure volume (<NUM>),
the first chamber (<NUM>), the second chamber (<NUM>) and the third chamber (<NUM>) are liquidly connected to one another to form a compensator volume (<NUM>, <NUM>, <NUM>),
the compensator volume (<NUM>, <NUM>, <NUM>) is arranged, in liquid flow order, between the enclosure volume (<NUM>) and ambient (<NUM>) the enclosure (<NUM>) thereby forming at least two sealing barriers between ambient (<NUM>) and the enclosure volume (<NUM>).