Superconducting direct current transmission system
A DC superconducting coaxial transmission system provides electrical transmission of 5,000 megawatts of energy while simultaneously delivering liquid hydrogen. The transmission system includes a coaxial transmission segment including an inner superconductor, an outer superconductor disposed in surrounding relation to the inner conductor, and a dielectric insulator disposed between the inner superconductor and the outer superconductor. Liquid hydrogen surrounds the superconductors. Three phase transformers and poly phase rectifier/inverters provide a DC voltage source to the superconductors from the electrical grid. In one embodiment, a switching circuit connected between the voltage source and the superconductor injects a cancellation current component into the direct current flow. The cancellation current component is polarized to flow in a direction opposite to the direct current flow to produce a current zero, thus enabling safe interruption of the high DC current while minimizing the magnitude of transient voltages during switching.
1. A direct current coaxial superconducting transmission segment, comprising:
a cylindrical inner superconductor defining a core, the core adapted to flow a first coolant medium;
a vacuum dielectric insulator disposed in surrounding relation to the inner superconductor;
an outer superconductor disposed in surrounding relation to the insulator;
a cylindrical housing disposed in surrounding relation to the outer superconductor, the housing defining a containment adapted to flow a second coolant medium;
a thermal insulation barrier disposed in surrounding relation to the housing; and
an electrical insulation layer disposed in surrounding relation to the thermal insulation barrier and a stainless steel protective outer shell disposed in surrounding relation to the electrical insulation layer.
2. The transmission segment of claim 1 , wherein the first and second coolant medium is liquid hydrogen.
3. The transmission segment of claim 1 , wherein the insulator is provided by a vacuum disposed between a non-magnetic inner stainless steel cylinder encasing the outside of the inner superconductor, and a non-magnetic stainless steel outer cylinder encasing the inside of the outer superconductor, the inner and outer cylinders defining the insulator.
4. The transmission segment of claim 1 , further comprising a non-magnetic inner cylinder encasing the outside of the inner superconductor, and a non-magnetic outer cylinder encasing the inside of the outer superconductor, the inner and outer cylinders defining the insulator.
5. The transmission segment of claim 1 , wherein a positive voltage or a negative voltage with respect to ground is electrically coupled to said cylindrical inner superconductor, and the other of said positive voltage or said negative voltage with respect to ground is electrically coupled to said outer superconductor such that the voltage between said inner superconductor and said outer superconductor is about double said positive voltage or said negative voltage.
6. The transmission segment of claim 5 , wherein a voltage difference between said outer superconductor and ground is about said positive or said negative voltage.
7. A direct current coaxial superconducting transmission segment, comprising:
a cylindrical inner superconductor defining a core, the core adapted to flow a first coolant medium;
a non-magnetic inner stainless steel cylinder encasing the outside of the inner superconductor;
an outer superconductor disposed in surrounding relation to the insulator;
a non-magnetic stainless steel outer cylinder encasing the inside of the outer superconductor;
a vacuum dielectric insulator disposed in surrounding relation to the inner superconductor between said non-magnetic inner stainless steel cylinder encasing the outside of the inner superconductor and said non-magnetic stainless steel outer cylinder encasing the inside of the outer superconductor;
a cylindrical housing disposed in surrounding relation to the outer superconductor, the housing defining a containment adapted to flow a second coolant medium;
a thermal insulation barrier disposed in surrounding relation to the housing; and
an electrical insulation layer disposed in surrounding relation to the thermal insulation barrier and a stainless steel protective outer shell disposed in surrounding relation to the electrical insulation layer.
8. The transmission segment of claim 7 , wherein a positive voltage or a negative voltage with respect to ground is electrically coupled to said cylindrical inner superconductor, and the other of said positive voltage or said negative voltage with respect to ground is electrically coupled to said outer superconductor such that the voltage between said inner superconductor and said outer superconductor is about double said positive voltage or said negative voltage.
9. The transmission segment of claim 8 , wherein a voltage difference between said outer superconductor and ground is about said positive or said negative voltage.
10. A direct current coaxial superconducting transmission segment, comprising:
a cylindrical inner superconductor defining a core, the core adapted to flow a first coolant medium;
a non-magnetic inner stainless steel cylinder encasing the outside of the inner superconductor;
an outer superconductor disposed in surrounding relation to the insulator;
a non-magnetic stainless steel outer cylinder encasing the inside of the outer superconductor;
a vacuum dielectric insulator disposed in surrounding relation to the inner superconductor between said non-magnetic inner stainless steel cylinder encasing the outside of the inner superconductor and said non-magnetic stainless steel outer cylinder encasing the inside of the outer superconductor;
a cylindrical housing disposed in surrounding relation to the outer superconductor, the housing defining a containment adapted to flow a second coolant medium; and
a thermal insulation barrier disposed in surrounding relation to the housing;
an electrical insulation layer disposed in surrounding relation to the thermal insulation barrier; and
a stainless steel protective outer shell disposed in surrounding relation to the electrical insulation layer.
11. The transmission segment of claim 10 , wherein a positive voltage or a negative voltage with respect to ground is electrically coupled to said cylindrical inner superconductor, and the other of said positive voltage or said negative voltage with respect to ground is electrically coupled to said outer superconductor such that the voltage between said inner superconductor and said outer superconductor is about double said positive voltage or said negative voltage.
12. The transmission segment of claim 11 , wherein a voltage difference between said outer superconductor and ground is about said positive or said negative voltage.
13. A direct current coaxial superconducting transmission segment, comprising:
a cylindrical inner superconductor defining a core, the core adapted to flow a first coolant medium;
a vacuum dielectric insulator disposed in surrounding relation to the inner superconductor;
an outer superconductor disposed in surrounding relation to the insulator;
a cylindrical housing disposed in surrounding relation to the outer superconductor, the housing defining a containment for adapted to flow a second coolant medium;
a thermal insulation barrier disposed in surrounding relation to the housing; and
wherein a positive voltage or a negative voltage with respect to ground is electrically coupled to said cylindrical inner superconductor, and the other of said positive voltage or said negative voltage with respect to ground is electrically coupled to said outer superconductor such that the voltage between said inner superconductor and said outer superconductor is about double said positive voltage or said negative voltage.
14. The transmission segment of claim 13 , wherein the first and second coolant medium is liquid hydrogen.
15. The transmission segment of claim 13 , wherein the insulator is provided by a vacuum disposed between a non-magnetic inner stainless steel cylinder encasing the outside of the inner superconductor, and a non-magnetic stainless steel outer cylinder encasing the inside of the outer superconductor, the inner and outer cylinders defining the insulator.
16. The transmission segment of claim 13 , further comprising a non-magnetic inner cylinder encasing the outside of the inner superconductor, and a non-magnetic outer cylinder encasing the inside of the outer superconductor, the inner and outer cylinders defining the insulator.
17. The transmission segment of claim 13 , further comprising an electrical insulation layer disposed in surrounding relation to the thermal insulation barrier and a stainless steel protective outer shell disposed in surrounding relation to the electrical insulation layer.
18. The transmission segment of claim 13 , wherein a voltage difference between said outer superconductor and ground is about said positive or said negative voltage.