Subsea electrical architectures

Abstract

The subject-matter of the present invention concerns an electrical architecture for power distribution to subsea equipment comprising at least one variable speed drive, VSD, module, wherein said at least one VSD module comprises at least one self commutated line side converter including power semiconductor.

Claims

1. A subsea installation for electrical power distribution to subsea equipment, the subsea installation comprising: a transformer, receiving AC from the surface, a plurality of variable speed drive (VSD) modules, wherein each VSD module comprises at least one active front end (AFE) rectifier comprising at least one semiconductor to rectify AC to DC, and a bus bar, distributing transformed AC from the transformer to the plurality of VSD modules, wherein each AFE rectifier has a rated voltage greater than 3 kV, and is directly connected to the bus bar through a circuit breaker and without a VSD transformer between the transformer and the VSD module.

2. The subsea installation of claim 1, wherein each AFE rectifier includes at least six power semiconductors.

3. The subsea installation of claim 1, wherein each power semiconductor is a transistor or thyristor.

4. The subsea installation of claim 1, wherein the at least one VSD module further comprises a pre-charge circuit to reduce the in-rush current.

5. The subsea installation of claim 1, further comprising a transformer, wherein the at least one VSD module further comprises at least one built-in circuit breaker and without any subsea transformer between the transformer and the VSD module.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an electrical power distribution architecture known in the art;

(2) FIG. 2 illustrates an electrical architecture according to an embodiment of the present invention;

(3) FIG. 3 illustrates an electrical architecture according to another embodiment of the present invention;

DETAILED DESCRIPTION OF THE DRAWINGS

(4) Two preferred embodiments are described hereafter in details referring to the annexed FIGS. 2 to 3.

(5) The present invention aims at providing AC or DC electrical power for subsea applications. Hence, the present invention proposes new electrical architectures 100 and 200 for compression and pumping applications, including the supply of AC from the surface, via a very long subsea cable, to subsea production fields that include subsea processing units with pump and compressor equipment.

(6) FIG. 2 illustrates an electrical architecture 100 according to a first embodiment of the present invention. The electrical architecture 100 is configured to supply power to subsea equipment, and as illustrated in figure the equipment is a compressor C and a pump P. The skilled person will recognize that these are merely examples of subsea electrical equipment for which the present invention can be configured to supply electrical power, and should not be construed as limiting. Moreover, whilst two pieces of subsea equipment are illustrated, the skilled person will recognize that the present invention can equally be configured to supply electrical power to a larger or smaller number of pieces of equipment.

(7) As illustrated in FIG. 2, electrical power is received from a remote source located above the sea surface (topside) via an umbilical 11. This umbilical 11 can be an electrical cable for subsea electrical supply known from the art. Electrical power from the umbilical 11 is fed to a transformer 12.

(8) Electrical power from the transformer 12 is fed to a bus bar BB for ultimate distribution to the loads C, P. The bus bar BB comprises electrical conductors which are connected to each load C, P via a circuit breaker CB. Thus, electrical power can be transferred from the transformer 12 to each of the loads C, P if the respective circuit breaker CB is in the closed position. If a circuit breaker CB is in the open position, then the respective load is electrically isolated from the source of electrical power.

(9) Also connected to the bus bar BB are two LV auxiliaries. Each LV auxiliary is connected to the bus bar BB via a circuit breaker. Thus, if power is required from a LV auxiliary, the respective circuit breaker can be closed to thereby transfer electrical power to the bus bar BB. The skilled person will recognize that the LV auxiliaries are not essential to the functioning of the described embodiment. Moreover, whilst two LV auxiliaries are illustrated, the architecture can equally function with a larger or smaller number of LV auxiliaries. The LV auxiliaries are connected to the bus bar BB using a transformer.

(10) Each LV auxiliary is housed within a water resistant housing 130.

(11) The bus bar BB is also housed within a water resistant housing 120 which can either be pressure compensated or not pressure compensated.

(12) Power from the bus bar BB is fed to each load C, P via a VSD module 110.

(13) As illustrated in FIG. 2, each VSD module 110 includes a pre-charge circuit PC. The skilled person will recognize the function and composition of this circuit, and so a complete description will be omitted here. It is sufficient to note that the circuit employed in this manner can act to reduce the in-rush current.

(14) The housing for the VSD modules can either be pressure compensated or not pressure compensated.

(15) The active self commutated line side converter located in 111 includes a plurality of power semiconductors SC.

(16) Thus, by adopting the architecture as described above, the number of connectors/penetrators and the number of subsea module are reduced in comparison to architectures known from the prior art. This is achieved since the VSD transformer has been eliminated by using the Active Front End (AFE) rectifier architecture. In general, the reliability of the system is improved by reducing the number of subsea modules and connectors/penetrators.

(17) By using an active Front End VSD it is also possible to absorb the reactive power that results from use of a long upstream electrical cable. Accordingly, the voltage level at the subsea point of connection can also be controlled. As a result of this, the embodiment provides an architecture wherein fewer disturbances will be present on the driven loads, since the VSD DC bus voltage can now be maintained at a constant voltage, rather than being subject to voltage variation from the upstream power supply.

(18) The permanent control of the power factor also provides a means to optimize the transmission line (electrical cable). It further allows reducing the size, weight and the cost of the electrical cable since a part of the cable charging current is consumed now subsea by the AFE rectifier.

(19) In contrast, for architectures known from the prior art the whole cable charging current travels along the cable to be consumed onshore. Thus, prior art architectures require comparatively greater current, which necessitates an increased size, weight and the cost of the electrical cable in comparison to the presently described architecture.

(20) The presently described architecture also permits a simplification to the circuit breaker module CB, which does not need to include a pre-charge system as this is now part of the VSD module. Accordingly, by employing an AFE rectifier, harmonic current pollution by the subsea VSD is also reduced compared to a VSD with a DFE rectifier.

(21) FIG. 3 illustrates a second embodiment of the present invention in which is illustrated an alternative electrical architecture 200 for power distribution to subsea equipment such like a compressor C or a pump P.

(22) As illustrated in FIG. 3, electrical power is received from a remote source located above the sea surface (topside) via an umbilical 11. This umbilical 11 can be an electrical cable for subsea electrical supply known from the art. Electrical power from the umbilical 11 is fed to a transformer 12.

(23) Electrical power from the transformer 12 is fed to the loads C, P via a VSD module 210. Each load C, P has a dedicated VSD module 210. The VSD modules 210 are of similar construction to those described above in relation to FIG. 2. However, the VSD modules 210 use in this embodiment additionally comprise a circuit breaker BICB.

(24) Thus, electrical power can be transferred from the transformer 12 to each of the loads C, P if the respective circuit breaker CB is in the closed position. If a circuit breaker CB is in the open position, then the respective load is electrically isolated from the source of electrical power.

(25) Also connected to the transformer 12 are LV auxiliaries. The LV auxiliaries are of similar construction to those described above in relation to FIG. 2. However, each of them additionally comprises a circuit breaker BICB. Thus, if power is required from an LV auxiliary, the respective circuit breaker BICB can be closed to thereby transfer electrical power to the transformer 12 As noted above in relation to FIG. 2, the skilled person will recognize that the LV auxiliaries are not essential to the functioning of the described embodiment. Moreover, whilst two LV auxiliaries are illustrated, the architecture can equally function with a larger or smaller number of LV auxiliaries.

(26) Each LV auxiliary is housed within a water resistant housing 130 as discussed above in relation to FIG. 2.

(27) As discussed above in relation to FIG. 2, the VSD module 210 includes a pre-charge circuit PC. The nature and function of this circuit is essentially the same as noted above in relation to FIG. 2. Again, the VSD modules are housed in water resistant housings.

(28) Since the architecture of the second embodiment eliminates the need for the bus bar BB, the architecture is further simplified form that disclosed in the first embodiment. Since there are fewer subsea modules in this second embodiment in comparison to the first embodiment, the reliability of the system will be generally enhanced.

(29) While there has been illustrated and described what are presently considered to be the preferred embodiments of the present invention, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from the true scope of the present invention. Additionally, many modifications may be made to adapt a particular situation to the teachings of the present invention without departing from the central inventive concept described herein. Furthermore, an embodiment of the present invention may not include all of the features described above. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the invention as broadly defined above. In particular, the embodiments describe above could be combined.

(30) Expressions such as comprise, include, incorporate, contain, is and have are to be construed in a non-exclusive manner when interpreting the description and its associated claims, namely construed to allow for other items or components which are not explicitly defined also to be present. Reference to the singular is also to be construed in be a reference to the plural and vice versa.

(31) A person skilled in the art will readily appreciate that various parameters disclosed in the description may be modified and that various embodiments disclosed may be combined without departing from the scope of the invention.

(32) It is stipulated that the reference signs in the claims do not limit the scope of the claims, but are merely inserted to enhance the legibility of the claims.

(33) The embodiments above are intended to be illustrative and not limiting. Additional embodiments may be within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

(34) Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention.