Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
  • H02J3/34—Arrangements for transfer of electric power between networks of substantially different frequency
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K47/00—Dynamo-electric converters
  • H02K47/18—AC/AC converters
  • H02K47/20—Motor/generators
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
  • H02J2310/10—The network having a local or delimited stationary reach
  • H02J2310/12—The local stationary network supplying a household or a building

Definitions

• the present invention relates to equipment located subsea far away from onshore or topside locations, particularly equipment for fluid pressure boosting requiring high alternating current electric power level, but also other equipment of various types.
• the problems are enhanced at increasing power level, therefore operation of subsea equipment requiring a high level of electric power, such as subsea pressure boosting equipment like subsea compressors, subsea multiphase pumps and subsea pumps, is most challenging.
• the problems increase with increasing subsea step out cable length, increasing voltage, increasing frequency and increasing capacitance.
• the maximum achievable subsea step out length is about 150 km.
• VSD-variable speed drive also called variable frequency drive, VFD, and other terms
• VFD variable frequency drive
• the invention provides a system for operation of electric power subsea loads or loads supplied through an alternating current subsea crossing cable, particularly high electric power subsea loads.
• the system is distinctive in that it comprises an alternating current subsea step out cable or subsea crossing cable divided into at least two subsea cable segments connected in series, each segment has a length feasible for stable operation, the connection between the segments comprises a motor-generator set where the motor part is not electrically connected to the generator part, the motor-generator set is arranged in at least one housing.
• connection between the segments comprises a motor- generator set where the motor part is not electrically connected to the generator part, means that the power is generated by the generator for each new cable segment connected in series but electrical problems as discussed above and below are in substance not transferred from one step out cable segment to the next.
• the step out cable segment toward the onshore or topside end, the near end or nearer step out cable segment, is connected to the motor and drives the motor of the motor-generator set.
• the step out cable segment further away from the near end onshore or topsides, the far end or further out step out cable segment is connected to the generator and receives the power generated by the motor-generator set between said segments.
• the near end and the far end cable segments are not electrically connected, meaning that Ferranti effect- induced voltage peaks, resonances and other transients or electric problems are not transferred from one cable segment to the next.
• the motor-generator set does not necessarily comprise any material for electric insulation between the motor and generator, since the coupling between the motor and generator is mechanical, hydraulical and/or magnetic.
• the motor-generator set provides inductance to the system, which is an important feature for stability.
• the subsea step out cable or subsea crossing can be divided into two, three, four or more step out cable segments connected in series.
• subsea step out cable a subsea cable delivering power to subsea loads, like subsea compressors and pumps.
• subsea crossing cable it is meant a cable where both the near end and the far end are located topsides or onshore, but the cable has a long subsea distance, which subsea distance may exceed the maximum distance up to now considered feasible for alternating current supply, as explained above.
• the subsea crossing cable can be used to cross an ocean or fjord stretch.
• each segment has a length feasible for stable operation, means in the context of the invention stable operation at the prevailing operating conditions or the design conditions.
• the motor-generator set is preferably of a rotating type, inter alia because of good efficiency, but can alternatively be of another type, such as a linear type motor-generator set.
• the subsea electric power step out cable or subsea crossing cable must be divided into segments of length so that each segment can be operated with stability, for example maximum 100, 150, 200 or 250 km for each segment for typical subsea pressure boosting equipment, dependent upon power level and frequency and other factors as herein discussed or mentioned.
• the voltage and power can be much higher than for subsea loads, and maximum length for stable operation can be as low as about 10 km, but more typical 20, 50 or 100 km.
• the maximum segment length is also dependent on the redundancy required for the application, for example dividing the power level by having two or more parallel cables for critical applications open up for longer segments.
• the at least one housing of the motor-generator set isolates the motor and generator from the surrounding water, said housing is preferably a pressure housing at least rated to ambient pressure if it is gas filled and it is preferably a low pressure rated pressure housing, termed an enclosure, if it is liquid filled and pressure compensated to ambient seawater pressure. If the liquid is oil it can also provide electrical insulation, lubrication of bearings and cooling of motor and generator.
• the motor-generator set comprises a common shaft.
• common shaft also includes any coupled shafts or assembled shafts comprising parts or sections that are connected or coupled by a rigid, flexible or other coupling so that the individual shafts of motor and generator rotate with the same speed.
• a motor-generator set with a common shaft can conveniently be arranged in one pressure housing, with fewer bearings and connectors.
• the motor generator frequency ratio can be 1 : 1 or with stepping up or down of the frequency by selecting pole numbers accordingly.
• the at least one pressure housing may comprise a pressure compensator.
• the motor-generator set may comprise a mechanical gear but this is not preferable because of high friction, lower reliability and increased utility system requirements.
• the motor-generator set may comprise a hydraulic coupling or gear connecting the motor and generator.
• any means connecting the motor and generator without transferring the electrical anomalies from one cable segment to the next can be used.
• the motor-generator set can be arranged in a common pressure housing or in separate pressure housings. Reference is made to NO 201 1 1233 for more detailed information on rotating motor-generator sets, and the contents of NO 201 1 1233 is herein incorporated by reference. According to NO 201 1 1233 the motor-generator set is used only at the subsea step out cable far end, according to the present invention it is used in between serial connected subsea step out cable segments in order to prolong the maximum subsea step out cable length for subsea alternating current loads.
• each of the motor and generator comprises more than 2 poles, such as 4, 6, 8, 12 or 24 poles, in order to reduce the speed of rotation and thereby the frictional losses.
• the friction can also be reduced by increasing the gap between the rotor and stator.
• there will be a feasible number of poles and feasible gaps dependent on many factors such as size, power factor, length of cable segments, power level and other factors, for each specific case and each motor-generator set. It is a question of optimization to find the best solution in each case.
• the motor-generator set in the system of the invention comprises a high voltage electric motor, e.g. a Motorformer (ABB), and/or a high voltage generator, e.g. a Powerformer (Alstom), both of which indicatively can have a voltage range of 30-150 kV and power range of 40-200 MW.
• ABB Motorformer
• Alstom Powerformer
• This may eliminate transformers and reduce the electrical losses further.
• high voltage cables like the high voltage cables used for power transmission are used instead of the traditional stator bars or stator coils, allowing high power, particularly high voltage power directly through the windings.
• a significant development work must be undertaken in order to marinise high voltage motors and generators.
• the system comprises motor-generator sets with contactless magnetic bearings.
• Magnetic bearings will reduce losses due to friction, also because a gas filled pressure housing can be used. This is described in further detail in the patent application NO 201 10396, in the name of the applicant, to which reference is made, and the contents of said publication is herein incorporated by reference.
• the system comprises one or more of the loads: a subsea compressor, a subsea multiphase pump, a subsea pump, a control system, a heat tracing system, a valve actuator, a processing facility, an uninterruptible power supply, a rectifier, an onshore or topside grid point or load at the far end of the cable, and other loads.
• the system of the invention can provide the main power supply or contingency power supply for each and every one of the mentioned equipment and systems, in different numbers, simplifying the overall system.
• using electric power generated by the generators of the system for operating a heat tracing system arranged along a subsea pipeline may eliminate methanol or glycol systems for hydrate inhibition, which will be a very favorable feature for remote subsea field developments for which the step out cable and pipelines can be arranged more or less in parallel, with power take out from generators along the pipeline.
• the invention also provides a method of arranging a system for operation of electric power subsea loads or other loads supplied through an alternating current subsea crossing cable, particularly high electric power subsea loads, distinctive by dividing a subsea electric power step out cable or subsea crossing cable into at least two subsea cable segments connected in series, each segment has a length feasible for stable operation, by arranging a motor- generator set between the segments so that the motor part is not electrically connected to the generator part, and arranging the motor-generator set in at least one housing.
• the subsea electric power step out or crossing cable must be divided into segments of length so that each segment can be operated with stability, for example maximum 10, 20, 50, 100, 150, 200 or 250 km for each segment, dependent upon power level and frequency and other factors as herein discussed or mentioned.
• the invention provides use of a subsea operable electric motor-generator set, for dividing an alternating current subsea electric power step out cable or an alternating current subsea crossing cable into subsea cable segments of lengths that each can be operated with stability.
• the invention also provides a subsea step out or subsea crossing cable for alternating current, distinctive in that the cable is divided into at least two subsea cable segments connected in series, each segment has a length feasible for stable operation, the connection between the segments comprises a motor-generator set where the motor part is not electrically connected to the generator part, and the motor- generator set is arranged in at least one housing.
• Each segment can be for example maximum 10, 20, 50, 100, 150, 200 or 250 km, dependent upon power level and frequency and other factors as herein discussed or mentioned.
• the invention provides a system for operation of electric power subsea loads or loads supplied through a subsea crossing cable, particularly high electric power subsea loads; and flow assurance for transport of
• hydrocarbons or other fluid through a subsea pipeline.
• the system is distinctive in that it comprises:
• each segment has a length feasible for stable operation
• a motor-generator set arranged so as to connect cable segments and in the far end of the cable, wherein the motor part is not electrically connected to the generator part, the motor-generator set is arranged in at least one housing, or a static frequency step up device or a variable speed drive at the far end of the cable and optionally for connecting cable segments, and
• the equipment for electric heating is for direct electric heating, heat tracing or other electric heating, alone or in combination, and coupled from the generator at the end of the subsea step out cable, and optionally to further generators along the subsea cable, or coupled from static frequency step up devices or variable speed drives, for heating the pipeline in a situation where flow through the pipeline has been shut down.
• the loads comprises subsea pumps or compressors or both, arranged so as to boost the fluid pressure for transport of hydrocarbon fluids through the subsea pipeline, powered through the subsea step out cable comprising one or several segments, but in a situation of shut down of the subsea pipeline the subsea cable is used to power electric heating of the subsea pipeline in order to avoid hydrate formation.
• the subsea step out cable is one of:
• each segment has a length feasible for operation of the operatively connected loads at the frequency and power level as operated in the cable, a motor- generator set is arranged at the end and between cable segments, the motor generator set in the cable far end is a frequency step up device or a rectifier, equipment for electric heating of the pipeline is powered from at least one of the generators,
• each segment has a length feasible for operation of the operatively connected loads at the frequency and power level as operated in the cable, a static frequency step up device or a variable speed drive is arranged at the far end of the cable and optionally for connecting cable segments, equipment for electric heating of the pipeline is powered from at least one of the step up devices or variable speed drives, or
• each segment has a length feasible for operation of the operatively connected loads at the voltage and current level as operated in the cable, a inverter is arranged at the far end of the cable and optionally for connecting cable segments, each inverter is one of: a motor generator set or a static inverter, equipment for electric heating of the pipeline is powered from at least one of the inverters.
• FIG. 1 illustrating a motor-generator set feasible for use in the system of the invention
• Figure 1 illustrating a motor-generator set in an enclosure that is pressure compensated to ambient seawater pressure. More specifically, Figure 1 illustrates a motor-generator set 2 for use in a system of the invention.
• the motor generator set 2 comprises a motor part 3 and a generator part 4, connected together by a common shaft 5. Penetrators 6 for power in are illustrated, and penetrators 7 for power out are illustrated, the penetrators are the electrical connections through the housing 9 of the motor generator set 2.
• the housing of the invention must not be a pressure housing, in the illustrated embodiment it can be a rather thin walled enclosure since the illustrated embodiment thereof is filled with oil or other liquid, with a pressure compensator for pressure compensation to ambient pressure.
• a pressure balancing unit 8 also called a pressure compensator, and an oil cooler 10 are illustrated. Gas filled housings must however be pressure housings.
• the penetrators 6 for power in are connected to the motor and the subsea step up cable nearer topside or onshore.
• the penetrators 7 for power out are connected to the generator and the subsea step out cable segment further away from topside or onshore, that is closer to the subsea loads.
• the penetrators 6 for power in can be said to be electrically isolated or insulated from the penetrators 7 for power out.
• a motor-generator set functioning as a transmission stabilizer in a subsea step out or subsea crossing cable will typically have equal numbers of poles in motor and generator, the illustrated motor-generator set has a 6-pole motor and a 6-pole generator.
• the result is that a power frequency in of 25 Hz results in a power frequency out of 25 Hz, i.e. equal in and out frequencies.
• the rotating speed will be only 500 rpm, which is beneficial with respect frictional losses.
• FIG. 2 illustrating a system 1 of the invention.
• the system comprises a subsea step out cable 1 1 divided into three segments 1 1 s, the segments are connected in series by motor-generator sets 2.
• the illustrated subsea step out cable has a near end 1 1 n topsides on a platform or onshore.
• a VSD a variable speed drive 12 is arranged to the cable at the near end in order to control power frequency fed into the cable at the near end and a transformer downstream to the VSD controls the voltage fed into it.
• the loads are compressors.
• the subsea step out cable can be connected directly to the grid 15 and therefore have constant transmission frequency of 50 or 60 Hz or it can be connected to other power sources or to other means than a VSD for control of frequency and power level, e.g. a diesel aggregate.
• the subsea step out cable is 600 km long as it comprises three 200 km subsea step out cable segments 1 1 s connected in series.
• the cable receives 150 MW power from surface, at the near end, the power can be delivered to two subsea compressor loads 13 positioned 600 km away, the operation transmission frequency through the cable is for example 25 Hz.
• the maximum stable cable segment distance is estimated to be about 200 km. At higher power loads or higher frequencies the maximum segment distance is reduced.
• transformers are arranged in order to transform the power characteristics into parameters feasible for operation of the motor- generator sets, the VSD and the connected loads.
• the loads are compressors 13 with high speed motor, and therefore the motor-generator sets connected to the compressors are step up devices 14. Said step up gears or devices have larger generator pole number than motor pole number, the pole number ratios correspond to the frequency or rotational speed step up ratios.
• motor- generator set can be varied freely as long as the electrical problems described above are not transferred from one cable segment to the next cable segment connected in series.
• High voltage motors and high voltage generators can be used as motor-generator set components, eliminating transformers or reducing the rating of transformers.
• the systems of the invention can comprise any features as described or illustrated in this document in any operative
• each such combination is an embodiment of the present invention.
• the method of the invention can comprise any features or steps as described or illustrated in this document in any operative combination, each such
• the subsea step out cable or subsea crossing cable of the invention can comprise any features as described or illustrated in this document in any operative combination, each such combination is an embodiment of the present invention.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Connection Of Motors, Electrical Generators, Mechanical Devices, And The Like (AREA)
• Laying Of Electric Cables Or Lines Outside (AREA)
• Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
• Control Of Multiple Motors (AREA)
• Catching Or Destruction (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (2)

Citations (2)

Family Cites Families (7)

• 2011
  • 2011-10-26 NO NO20111448A patent/NO333443B1/no not_active IP Right Cessation
• 2012
  • 2012-10-26 WO PCT/NO2012/050209 patent/WO2013062422A1/en active Application Filing
  • 2012-10-26 RU RU2014119541A patent/RU2618517C2/ru active
  • 2012-10-26 AU AU2012329632A patent/AU2012329632B2/en not_active Ceased
  • 2012-10-26 BR BR112014009898A patent/BR112014009898A2/pt not_active Application Discontinuation
  • 2012-10-26 CN CN201280052523.XA patent/CN103959588B/zh not_active Expired - Fee Related

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