Current modulation of direct current transmission lines

• US 6,714,427 B1
• Filed: 11/07/2002
• Issued: 03/30/2004
• Est. Priority Date: 11/07/2002
• Status: Active Grant

• Current Assignee: Lionel O. Barthold
• Original Assignee: Lionel O. Barthold
• Inventors: Barthold, Lionel O.
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US10/289,771
• Time in Patent Office: 509 Days
• Field of Search: 323/205, 323/207, 323/907, 363/50, 363/51, 361/103
• US Class Current: 363/51
• CPC Class Codes: H02J 3/36 Arrangements for transfer of electric power between ac networks via a high-tension dc link
• CPC Class Codes: Y02E 60/60 Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

A current-modulation method of transmitting high voltage direct current (HVDC) power over a transmission system comprising at least three conductors, wherein each conductor has a nominal thermal limit to its current-carrying capacity. The method involves transmitting DC current over at least one conductor at a level which can exceed each such conductor'"'"'s nominal thermally-limited current-carrying capacity, returning the transmitted current over a quantity of conductors greater than the quantity used to transmit at the higher level, so that each return current is less than the transmitted current, and periodically switching the current level in the conductors so as to rotate the higher level current among at least two of the conductors, such that, over time, the resistance heating of the conductors does not exceed any conductors'"'"' thermal limit.

Claims

1. A current-modulation method of transmitting high voltage direct current (HVDC) power over a transmission system comprising three conductors, wherein each conductor has a nominal thermal limit to its current-carrying capacity, the method comprising:

transmitting DC current over one conductor at a level which may be above the conductor'"'"'s nominal thermally-limited current-carrying capacity;

returning the transmitted current over the other two conductors, such that each return current is less than the transmitted current, wherein the total transmitted and return currents are nominally equal; and

periodically switching the current level in the conductors so as to rotate the higher level current among the three conductors, such that, over time, losses are reduced and the resistance heating of the conductors does not exceed the conductors'"'"' thermal limits.

2. The HVDC current-modulation transmission method of claim 1 wherein each of the three conductors transmits current at the high level nominally for one-third of the time, and returns current at a lower level nominally for two-thirds of the time.

3. The HVDC current-modulation transmission method of claim 2 wherein the high current level is nominally two times that of the lower current level.

4. The HVDC current-modulation transmission method of claim 1 wherein the current flow in one conductor is always in the same direction.

5. The HVDC current-modulation transmission method of claim 4 wherein the current flow in the return conductors switches direction.

6. The HVDC current-modulation transmission method of claim 5 wherein the current in each of the return conductors conducts in the return direction, opposite to that of the transmitting conductor, nominally for two-thirds of the time.

7. The HVDC current-modulation transmission method of claim 1 wherein, for any conductor, the average of the square of each level of DC current multiplied by the time to which it carries that current is no more than that which would exceed the conductor'"'"'s AC thermal limit.

8. The HVDC current-modulation transmission method of claim 1 further comprising converting AC to DC before transmission, and converting DC to AC after transmission.

9. The HVDC current-modulation transmission method of claim 8 wherein the conversion is accomplished using thyrister-based converters.

10. The HVDC current-modulation transmission method of claim 9 wherein the switching is accomplished by control of the thyrister-based converters.

11. The HVDC current-modulation transmission method of claim 1 wherein the switching is accomplished using thyrister-based converters.

12. A current-modulation method of transmitting high voltage direct current (HVDC) power over a transmission system comprising at least three conductors, wherein each conductor has a nominal thermal limit to its current-carrying capacity, the method comprising:

transmitting DC current over at least one conductor at a level which may be above each such conductor'"'"'s nominal thermally-limited current-carrying capacity;

returning the transmitted current over a quantity of conductors greater than the quantity used to transmit at a higher level, such that each return current is less than the transmitted current; and

periodically switching the current level in the conductors so as to rotate the higher level current among at least two of the conductors, such that, over time, losses are reduced and the resistance heating of the conductors does not exceed the conductors'"'"' thermal limits.

13. The HVDC current-modulation transmission method of claim 12 wherein, for any conductor, the average of the square of each level of DC current multiplied by the time to which it carries that current is such as to ensure that the heating of that conductor does not exceed its thermal limits.

14. The HVDC current-modulation transmission method of claim 13 wherein the sum of currents in all conductors carrying the high current level is equal and opposite to the sum of currents in conductors carrying the lower current level.

15. The HVDC current-modulation transmission method of claim 12 wherein the current flow in one or more conductors is always in the same direction.

16. The HVDC current-modulation transmission method of claim 15 wherein the current flow in one or more of the return conductors switches direction.

17. The HVDC current-modulation transmission method of claim 16 wherein the levels of higher current and lower current are rotated among conductors such that the fraction of time which each conductor experiences each level of currents is such that no conductor is overheated.

18. The HVDC current-modulation transmission method of claim 12 wherein current levels and the time during which each conductor is subjected to each level is such that no conductor'"'"'s AC thermal limit is exceeded.

19. The HVDC current-modulation transmission method of claim 12 further comprising converting AC to DC before transmission, and converting DC to AC after transmission.

20. The HVDC current-modulation transmission method of claim 19 wherein the conversion is accomplished using thyrister-based converters.

21. The HVDC current-modulation transmission method of claim 20 wherein the switching is accomplished by control of the thyrister-based converters.

22. The HVDC current-modulation transmission method of claim 12 wherein the switching is accomplished using thyrister-based converters.