Submersible power distribution system and methods of assembly thereof

A submersible power distribution system is provided. The system includes at least one receptacle configured to be exposed to an underwater environment and a plurality of power conversion modules positioned within the at least one receptacle. Each of the plurality of power conversion modules includes a first enclosure configured to be exposed to the underwater environment, the first enclosure defining a first interior cavity configured to have a first pressure. Power conversion modules also include at least one second enclosure positioned within the first interior cavity. The at least one second enclosure defines a second interior cavity configured to have a second pressure that is lower than the first pressure. The at least one second enclosure is configured to restrict exposure of non-pressure-tolerant power electronics in the second interior cavity to the first pressure.

BACKGROUND

The present disclosure relates generally to power transmission and distribution and, more specifically, to power conversion modules for use in an underwater environment.

As oil and gas fields in shallow waters diminish, e.g., water depths less than approximately 500 meters (m) (1640 feet (ft.)), producers are tapping offshore fields in deeper waters, e.g., water depths of 500 m (1640 ft.) and greater. Such deep water fields not only include oil and gas production installations that operate far below the surface of the sea, but, also far away from the shore, e.g., greater than approximately 300 kilometers (km) (186 miles (mi)).

In many known subsea oil and gas production systems, typical equipment for such subsea oil and gas recovery and production includes gas compressors and pumps. Electric variable speed drive (VSD) and motor systems are one way to directly power such equipment in deep water environments. Reliable delivery of electric power from a remote utility grid or power generation source facilitates reliable production and processing of oil and gas in subsea locations. Typically, the transmission power requirement may be approximately one hundred megawatts for medium to large oil/gas fields.

As such, some known subsea oil and gas production systems are electric power intensive, and a robust, sturdy, and reliable electrical transmission and distribution (T&D) is required. Therefore, some known subsea oil and gas production systems use alternating current (AC) transmission and distribution systems for delivery of electric power to subsea locations. Such systems typically deliver AC power from a platform or terrestrial location to a subsea transformer through a power cable. Power is transferred from the subsea transformer to subsea AC switchgear through another power cable. The subsea AC switchgear feeds AC power to one or more subsea VSDs through yet another cable, or to other types of electrical loads. The VSDs each provide variable frequency AC power to electric motors through a power cable. Such AC transmission and distribution systems face technical challenges, which become more significant when the transmission distance is in excess of one hundred kilometers. For example, the significant reactive power drawn from the distributed subsea cable capacitance restrains the power delivery capability as well as increases the system cost.

Therefore, subsea oil and gas production systems may instead use high-voltage direct current (HVDC) transmission and distribution systems for delivery of electric power to subsea locations. Such HVDC systems typically include a land-based or topside converter substation where the AC-to-DC power conversion is performed. Also, these HVDC T&D systems may include undersea DC-to-AC and DC-to-DC converter stations proximate the subsea oil and gas production systems.

Active subsea power electronics components are generally contained inside enclosures (e.g. pressure vessels) protecting them from the surrounding subsea environment. Such known enclosures are pressurized to about 1 bar to enable at least some of the active subsea power electronics components to operate satisfactorily at increasing underwater depths. As the operating depths of undersea DC-to-AC and DC-to-DC converter stations increases, at least some known enclosures are being fabricated from more robust materials to facilitate withstanding increasing pressure differentials between the subsea environment and within the enclosures. Moreover, the enclosures are becoming increasingly large as required converter power ratings increase. Accordingly, known subsea enclosures operating in underwater environments of increasing depths are generally very large and heavy, which makes service and/or repair of the converter stations difficult.

BRIEF DESCRIPTION

In one aspect, a submersible power distribution system is provided. The system includes at least one receptacle configured to be exposed to an underwater environment and a plurality of power conversion modules positioned within the at least one receptacle. Each of the plurality of power conversion modules includes a first enclosure configured to be exposed to the underwater environment, the first enclosure defining a first interior cavity configured to have a first pressure. Power conversion modules also include at least one second enclosure positioned within the first interior cavity. The at least one second enclosure defines a second interior cavity configured to have a second pressure that is lower than the first pressure. The at least one second enclosure is configured to restrict exposure of non-pressure-tolerant power electronics in the second interior cavity to the first pressure.

In another aspect, a power conversion module for use in an underwater environment is provided. The module includes a first enclosure configured to be exposed to the underwater environment, the first enclosure defining a first interior cavity configured to have a first pressure. The module also includes at least one second enclosure positioned within the first interior cavity. The at least one second enclosure defines a second interior cavity configured to have a second pressure that is lower than the first pressure. The at least one second enclosure is configured to restrict exposure of non-pressure-tolerant power electronics in the second interior cavity to the first pressure.

In yet another aspect, a method of assembling a power conversion module is provided. The method includes providing a first enclosure configured to be exposed to an underwater environment, the first enclosure defining a first interior cavity configured to have a first pressure. The method also includes providing at least one second enclosure defining a second interior cavity configured to have a second pressure that is lower than the first pressure, identifying non-pressure-tolerant power electronics of the power conversion module, positioning the non-pressure-tolerant power electronics within the second interior cavity, and positioning the at least one second enclosure within the first interior cavity. The at least one second enclosure is configured to restrict exposure of the non-pressure-tolerant power electronics in the second interior cavity to the first pressure of the first interior cavity.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to submersible power distribution systems including modularized power electronics enclosures. In the exemplary embodiment, underwater-based direct current (DC)-to-DC and DC-to-alternating current (AC) power converters are modularized to facilitate service and repair of the converters, and to facilitate reducing an overall weight of a submersible power distribution system. For example, each module includes a first enclosure exposed to an underwater environment, and that houses at least one second enclosure and pressure-tolerant power electronics of the converter. The at least one second enclosure houses non-pressure-tolerant power electronics of the converter. Interior cavities of the second enclosures are pressurized at a lower pressure than an interior cavity of the first enclosure such that the non-pressure-tolerant components can operate satisfactorily at increasingly pressurized underwater depths. By identifying and isolating the non-pressure-tolerant power electronics from the pressure-tolerant components, and by housing the non-pressure-tolerant components in compact secondary enclosures, the diameter and side wall thickness of the first enclosure can be reduced. As such, the power converters described herein have a reduced weight relative to conventional subsea power converters.

FIG. 1is a schematic block diagram of an exemplary submersible power system100and a portion of a plurality of electrical loads126, e.g., without limitation, an exemplary submersible resource recovery system102.FIG. 2is a perspective view of submersible power system100and submersible resource recovery system102. In the exemplary embodiment, submersible power system100is shown as a stand-alone system supporting electrical loads126in submersible resource recovery system102. Alternatively, submersible power system100distributes electric power to electric loads126for any operation requiring electric power in an underwater environment105. Submersible resource recovery system102is any resource recovery system that enables operation of submersible power system100as described herein including, without limitation, subsea oil and gas production systems.

Submersible power system100is powered by a DC power source103. In the exemplary embodiment, DC power source103is a platform based AC to DC power converter that converts AC power from an AC power source104, e.g., without limitation, an AC power grid, to DC power. In other embodiments, DC power source103may be a land-based DC power source, a DC power generator (whether land or platform based), or any other suitable DC power source. Also, in the exemplary embodiment, submersible power system100includes a land-based AC-to-DC converter106coupled to AC source104. AC-to-DC converter106receives AC power and generates and transmits high voltage DC (HVDC) electric power at any voltage and any polarity that enables operation of submersible resource recovery system102and submersible power system100as described herein, e.g., without limitation, within a range between approximately ±50 kiloVolts (kV) and approximately ±100 kV. System100also includes at least one submersible power distribution system110(only one shown) coupled to AC-to-DC converter106through an HVDC umbilical cable112.

Submersible power distribution system110includes an HVDC receiving end114coupled to HVDC umbilical cable112through a plurality of dry-mateable connectors116. System110also includes a DC-to-DC converter section118coupled to HVDC receiving end114. DC-to-DC converter section118converts the HVDC voltage to medium voltage DC (MVDC), e.g., and without limitation, approximately ±10 kV. System110further includes a MVDC bus120coupled to DC-to-DC converter section118. System110also includes a plurality of wet-mateable connectors122. In alternative embodiments, a DC-to-AC converter section is used rather than DC-to-DC converter section118.

Submersible resource recovery system102includes a plurality of variable speed drive (VSD) units124coupled to MVDC bus module120through wet-mateable connectors122. Each VSD unit124is coupled to an electric power consuming device, i.e., one of loads126, e.g., without limitation, electrical motors driving pumping station128and compressor station130through wet-mateable connector122and subsea AC cable134. System102may also include other devices coupled directly to MVDC bus module120through a subsea MVDC cable135, including, without limitation, a remote station136including its own local VSD unit124.

FIG. 3is a perspective view of submersible power distribution system110. System110includes a receptacle150exposed to underwater environment105with a subsea template, i.e., receptacle150is open to water (not shown). System110also includes a plurality of power conversion modules151removably positioned within receptacle150. More specifically, in the exemplary embodiment, system110includes a plurality of DC-to-DC power conversion modules152removably positioned within receptacle150, and a plurality of variable speed drive (VSD) modules158removably positioned within receptacle150. DC-to-DC power conversion modules152form DC-to-DC converter section118(shown inFIG. 1). Each power conversion module151includes a first enclosure154configured to be exposed to underwater environment105. In some embodiments, first enclosure154is a pressure vessel. Each power conversion module151also includes an interior cavity that houses power electronics (neither shown inFIG. 3), discussed further below.

VSD modules158include first enclosure154housing VSD unit124(shown inFIG. 1). In the exemplary embodiment, system110includes three DC-to-DC power conversion modules152and three VSD modules158. In other embodiments, system110includes more or fewer subsea DC-to-DC power conversion modules152and/or VSD modules158. DC-to-DC power conversion modules152and VSD modules158may have any power rating that enables system110to function as described herein. Moreover, the number of power conversion modules151is generally selected based on the total accumulated size of the powered loads. Additional power conversion modules151may be included in one receptacle150to provide back-up redundancy in case of failure of one or several power conversion modules151. Also, in some embodiments, a plurality of receptacles150are used and each receptacle is configured to receive only one or several subsea power conversion modules151.

FIG. 4is a schematic diagram of an exemplary power conversion module151. More specifically, in the exemplary embodiment, power conversion module151is a DC-to-DC power conversion module152(shown inFIG. 3). Power conversion module151includes first enclosure154defining a first interior cavity155, and at least one second enclosure160positioned within first interior cavity155. In some embodiments, a plurality of second enclosures160are positioned within first interior cavity155, as will be described in more detail below. While shown as including three enclosures160, any number of enclosures160may be positioned in first interior cavity155that enables power conversion module151to function as described herein.

In the exemplary embodiment, first interior cavity155of first enclosure154receives second enclosures160and pressure-tolerant power electronics162, and a second interior cavity164of each second enclosure160receives non-pressure-tolerant power electronics166. As used herein, “pressure-tolerant power electronics” refers to electronic components that can, or that can be easily made to, operate satisfactorily when subjected to pressures above about one bar. Exemplary pressure-tolerant power electronics162include, but are not limited to, inductors, resistors, transformers, filter coils, mechanical switches, connectors, cables, capacitors, and busbars. Moreover, as used herein, “non-pressure-tolerant power electronics” refers to electronic components that are unable, difficult, or costly to be made to operate satisfactorily when subjected to pressures above about one bar. Exemplary non-pressure-tolerant power electronics166include, but are not limited to, active semiconductor devices (i.e., insulated-gate bipolar transistors (IGBT), integrated gate-commutated thyristors (IGCT), metal-oxide-semiconductor field-effect transistors (MOSFET)), related controllers for the active semiconductor devices, gate drivers, optical receivers, optical transmitters, and sensors.

First interior cavity155is at a first pressure and second interior cavity164is at a second pressure that is lower than the first pressure. Pressure-tolerant components162are housed in first enclosure154at the first pressure, and non-pressure-tolerant components166are housed in second enclosure160at the second pressure. Second enclosure160restricts exposure of non-pressure-tolerant power electronics166in second interior cavity164to the first pressure of first interior cavity155. Moreover, first enclosure154is exposed to a third pressure of underwater environment105. A magnitude of the third pressure is based on a depth of receptacle150(shown inFIG. 3) and first enclosure154in underwater environment105. In the exemplary embodiment, first enclosure154is pressurized at the first pressure to be substantially equalized with the third pressure of underwater environment105. Alternatively, first enclosure154may be pressurized at any pressure that enables power conversion modules151to function as described herein.

In some implementations, first interior cavity155of first enclosure154is at least partially filled with dielectric liquid168to pressurize first interior cavity155. Exemplary dielectric liquids168include, but are not limited to, transformer oil and silicon oil. At least partially filling first interior cavity155with dielectric liquid168facilitates maintaining the substantially equalized pressure between first interior cavity155and underwater environment105. Moreover, first enclosure154is at least partially filled with dielectric liquid168such that second enclosures160are at least partially submerged in dielectric liquid168. By submerging second enclosures160in dielectric liquid168, heat generated by non-pressure-tolerant power electronics166is conducted through second enclosures160, through dielectric liquid168, through first enclosure154, and into underwater environment105. Moreover, in the exemplary implementation, pressure-tolerant power electronics162are also at least partially submerged in dielectric liquid168, and heat generated by pressure-tolerant power electronics162is likewise conducted through dielectric liquid168and towards underwater environment105.

In the exemplary embodiment, a first differential pressure is defined between the first pressure of first interior cavity155and the third pressure of underwater environment105, and a second differential pressure is defined between the first pressure and the second pressure of second interior cavity164. For example, if first interior cavity155is pressurized at about 450 bar, and second interior cavity164is pressurized at about 1 bar, the first differential pressure is less than about 1 bar, and the second differential pressure is up to about 450 bar. As such, the dimensions of first enclosure154and second enclosure160are based at least partially on the first and second pressure differentials and, more specifically, to the ability of first enclosure154and second enclosure160to withstand the first and second pressure differentials.

First enclosure154has any suitable shape and dimensions that enable power conversion modules151to function as described herein. In the exemplary embodiment, first enclosure154has a substantially tubular shape having a length L and a diameter D. The shape and dimensions of first enclosure154are selected based on at least one of an operating depth of submersible power distribution system110, the material used to fabricate first enclosure154, and the differential pressure between the first pressure of first interior cavity155and the pressure of underwater environment105at the operating depth of submersible power distribution system110. For example, the length to diameter (L/D) ratio of first enclosure154can be increased to enable submersible power distribution system110to operate in increasing underwater depths. In some implementations, the L/D ratio of first enclosure154is at least about 5-to-1. Moreover, for example, if first interior cavity155is pressurized to be substantially equalized with the pressure of underwater environment105at operating depths of system110, a side wall thickness (not shown) of first enclosure154can be reduced to facilitate reducing an overall weight of each module151.

Second enclosure160has any suitable shape and dimensions that enable power conversion modules151to function as described herein. In the exemplary embodiment, second enclosure160has a substantially tubular shape and a greater side wall thickness (not shown) than first enclosure154. More specifically, the shape and dimensions of second enclosure160are selected based on at least one of the pressure within first interior cavity155, and the differential pressure between the first pressure of first interior cavity155and the second pressure of second interior cavity164. As described above, the differential pressure between first interior cavity155and second interior cavity164can be up to about 450 bar. As such, the dimensions of second enclosure160are modified to increase the side wall thickness of second enclosure160, for example, to facilitate withstanding the differential pressure between first interior cavity155and second interior cavity164.

In the exemplary embodiment, a plurality of second enclosures160are positioned within first interior cavity155. Second enclosures160may be arranged within first interior cavity155in any configuration that enables system110to function as described herein. Because the dimensions of second enclosures160are selected at least partially on the ability of second enclosures160to withstand comparatively large pressure differential pressures, space within each second enclosure160may be limited. Accordingly, in some embodiments, multiple second enclosures160housing non-pressure-tolerant power electronics166may be required to generate a suitable power rating. In the exemplary embodiment, non-pressure-tolerant power electronics166from each second enclosure160are coupled together in electrical communication through dry-mateable connectors116. Moreover, pressure-tolerant power electronics162and non-pressure-tolerant power electronics166are coupled together in electrical communication through dry-mateable connectors116to form a power converter (not shown).

Moreover, pressure-tolerant power electronics162and non-pressure-tolerant power electronics166are coupled in electrical communication with electrical components (not shown) outside of first enclosure154through wet-mateable connectors122coupled to first enclosure154and that extend between first interior cavity155and underwater environment105. Wet-mateable connectors122enable each power conversion module151to be individually disconnected from submersible power distribution system110to facilitate service and repair thereof. Because the pressures of first enclosure154and underwater environment105are substantially equalized, wet-mateable connectors122are less complex and less costly than wet-mateable connectors subjected to a substantially large differential pressure.

The systems and methods described herein facilitate reducing the weight of subsea power electronics enclosures. In the exemplary embodiments, pressure-tolerant and non-pressure-tolerant power electronics of a power conversion module are identified and separated from each other. The pressure-tolerant power electronics are housed in a first enclosure pressurized at a first pressure, and the non-pressure-tolerant power electronics are housed in a second enclosure positioned within the first enclosure and pressurized at a second pressure. The first pressure is substantially equalized to the pressure of an underwater environment at operating depths of the power conversion module, and the second pressure is lower than the first pressure to enable the non-pressure-tolerant power electronics to operate satisfactorily in the underwater environment. By compartmentalizing the non-pressure-tolerant power electronics into smaller secondary enclosures and by substantially equalizing the pressure between the first enclosure and the underwater environment, the dimensions of the first and second enclosures can be selected to reduce the weight of the power conversion module.

An exemplary technical effect of the systems and methods described herein includes at least one of (a) substantially reducing the weight of subsea power conversion enclosures; (b) enhancing cooling of heat-generating power conversion components; and (c) enabling modularization of various power converters to facilitate service and repair of the converters.

Exemplary embodiments of the submersible power distribution system are described above in detail. The system is not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the modules described herein may also be used in combination with other processes, and is not limited to practice with only the submersible power distribution system and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many applications where performing operations in subsea environments is desired.