Underground modular high-voltage direct current electric power transmission system
High capacity (10 GW, for example) passively cooled non-superconducting underground high voltage direct current electric power transmission lines ( 100 ) of very low loss (1% per 1,000 km, for example) and competitive cost. The transmission lines ( 100 ) include segment modules ( 101 ) linked together with compliant splice modules ( 102 ) between the segments ( 101 ), typically installed in a protective conduit ( 103 ). The segment modules ( 101 ) include relatively rigid pipe-shaped conductors ( 117 ) insulated by pipe-like solid insulating layers ( 131 ) to form segment modules ( 101 ) that resemble pipe. The segment modules ( 101 ) are linked together through radially and axially compliant splice modules ( 102 ) to form the transmission line ( 100 ). There are preferably wheels ( 300 ) deployed to ease insertion and removal of the assembled segment modules ( 101 ) and splice modules ( 102 ) into the conduit ( 103 ), to center each segment module ( 101 ) within the conduit ( 103 ), and/or to provide motive force and/or braking to allow the assembled segment modules ( 101 ) and splice modules ( 102 ) to be installed on a slope.
1. A modular high-voltage direct current electric power transmission system, comprising:
a plurality of segmented insulated conductors on wheels, wherein the segmented insulated conductors are flexibly linked together;
wherein at least some of the segmented insulated conductors comprise a plurality of metallic wedges that have a void that contains a volume compensation device and sodium; and
a track or mating surface on which the wheels run.
2. The modular high-voltage direct current electric power transmission system of claim 1 wherein the metallic wedges comprise a low thermal expansivity alloy; and wherein the majority of the current flowing through each segmented insulated conductor that comprises sodium flows within the sodium.
3. The modular high-voltage direct current electric power transmission system of claim 1 wherein:
the sodium and the volume compensation device together substantially fill each void;
the volume compensation device is constructed and arranged to change its volume enough to equal or exceed the total volume change of the sodium over a temperature range; and
the volume compensation device is under axial tension, and a cross-section of the volume compensation device is nearly constant when the sodium is at the upper limit of the temperature range.
4. The modular high-voltage direct current electric power transmission system of claim 1 in which the segmented insulated conductors each comprise at least one cable segment.
5. The modular high-voltage direct current electric power transmission system of claim 1 wherein at least one of the segmented insulated conductors comprises sodium within a shell and a volume compensation device within the shell, wherein the majority of the current flowing through the segmented insulated conductor flows within the sodium, and wherein the volume compensation device is under axial tension, and a cross-section of the volume compensation device is nearly constant.
6. The modular high-voltage direct current electric power transmission system of claim 1 wherein at least some of the segmented insulated conductors comprise at least one portion of a superconducting insulated cable.
7. The modular high-voltage direct current electric power transmission system of claim 1 wherein at least two segmented insulated conductors are electrically linked through a polymeric elastomer bag, and further comprising a metal with a resistivity less than 10 −7 ohm-m between the at least two segmented insulated conductors.
8. The modular high-voltage direct current electric power transmission system of claim 1 further comprising:
a plurality of splice insulators that define opposing internally threaded ends; and
a plurality of module insulator segments that comprise external threads;
wherein at least one of the spice insulators is coupled to the external threads on two adjacent module insulators segments.
9. The modular high-voltage direct current electric power transmission system of claim 1 further comprising:
a primary insulator that has a rigid pipe-like construction; and
a semiconducting lubricant;
wherein the primary insulator is mechanically attached to the segmented insulated conductor; and
wherein the semiconducting lubricant is between the primary insulator and the segmented insulated conductor.
10. The modular high-voltage direct current electric power transmission system of claim 9 further comprising at least one biaxially-oriented retractable elastomeric sleeve that is located over the segmented insulated conductor; and
wherein an interface between the biaxially-oriented retractable elastomeric sleeve and the segmented insulated conductor is dry.
11. The modular high-voltage direct current electric power transmission system of claim 4 wherein at least one cable segment comprises a subsea cable.
12. The modular high-voltage direct current electric power transmission system of claim 10 further comprising:
an outer elastomer boot; and
a high dielectric strength grease;
wherein the outer elastomer boot overlaps a portion of the biaxially-oriented retractable elastomeric sleeve; and
wherein the high dielectric strength grease is located between the biaxially-oriented retractable elastomeric sleeve and the outer elastomer boot.
13. The modular high-voltage direct current electric power transmission system of claim 1 further comprising a containment system, wherein the wheels are located between the insulated conductors and the containment system.
14. The modular high-voltage direct current electric power transmission system of claim 1 wherein the conductor insulation comprises a spirally-wrapped insulation structure, the spirally-wrapped insulation structure comprising at least two layers, wherein at least one of the layers is insulative and at least one of the layers is semiconductive.
15. The modular high-voltage direct current electric power transmission system of claim 14 wherein the semiconductive layer is in the form of a spiral semiconducting path from the segmented insulated conductor to an electrical ground.
16. The modular high-voltage direct current electric power transmission system of claim 1 further comprising:
at least one generally conical insulator; and
an elongated containment system for the segmented insulated conductors, the elongated containment system comprising a dielectric fluid;
wherein there is a distance between the segmented insulated conductors and the elongated containment system;
wherein the at least one generally conical insulator spans the distance between a first portion of a segmented insulated conductor and the elongated containment system; and
wherein the dielectric fluid is maintained at a positive pressure and fills the distance where the at least one generally conical insulator does not exist between a second, different portion of the segmented insulated conductor and the elongated containment system.
17. The modular high-voltage direct current electric power transmission system of claim 6 further comprising a cryostat surrounding the superconducting insulated cable.
18. The modular high-voltage direct current electric power transmission system of claim 10 further comprising a lubricant between the biaxially-oriented retractable elastomeric sleeve and the segmented insulated conductor.
19. A modular high-voltage direct current electric power transmission system, comprising:
a plurality of segment modules, each with a central portion, the central portions comprised of primary conductors that are elongated, generally annular and rigid;
a plurality of generally annular primary insulators, wherein each of the primary conductors is surrounded by a primary insulator;
a plurality of compliant conductive electrical splice members each located between and electrically coupled to opposed ends of two primary conductors;
a plurality of splice insulators, wherein each compliant conductive electrical splice member is surrounded by a splice insulator; and
a plurality of wheels that are constructed and arranged to support the segment modules.