Superconducting switch
The invention relates to a superconducting electrical switch. The switch comprises two parallel branches of superconducting material in a loop, and a magnetic field generator which generates a time-varying magnetic field through the loop in a direction generally parallel to the axis of the loop. The magnetic field generator is selectively activated and de-activated to switch the electrical switch between a low-resistance state and a higher-resistance state. In the low-resistance state, there is no magnetic field through the loop and transport current flows through the loop. In the higher-resistance state, a magnetic field through the loop induces a screening current such that the sum of the transport current and the screening current is substantially equal to the critical current or is greater than the critical current of the superconducting material. The switch may be used in, for example, a rectifier or fault current limiter.
1. An electrical switch comprising:
a loop of superconducting material,
wherein the loop comprises a first branch and a second branch, the first and second branches being electrically connected in parallel between a first terminal and a second terminal, and wherein the loop has an axis which is substantially normal to the plane of the loop, and
wherein the loop is configured to carry a transport current between the first terminal and the second terminal; and
a magnetic field generator,
wherein the magnetic field generator is configured to generate a time-varying magnetic field through the loop with the direction of the magnetic field through the loop being generally parallel to, or having a component which is generally parallel to, the axis of the loop,
wherein the magnetic field generator is configured to be selectively activated and de-activated to switch the electrical switch between a low-resistance state and a higher-resistance state, and
wherein, in the low-resistance state, the magnetic field generator does not generate the varying magnetic field through the loop and the transport current flows through the loop between the two terminals, and, in the higher-resistance state, the magnetic field generator generates the varying magnetic field through the loop, inducing a screening current in the loop, such that the sum of the transport current and the screening current in one or more of the first branch and second branch approaches the critical current, is substantially equal to the critical current or is greater than the critical current of the superconducting material.
2. The electrical switch of claim 1 , wherein the superconducting material comprises a high-temperature superconductor.
3. The electrical switch of claim 1 , wherein the superconducting material comprises rare-earth barium copper oxide (ReBCO).
4. The electrical switch of claim 1 , wherein the superconducting material is comprised as part of a tape.
5. The electrical switch of claim 1 , wherein the electrical switch further comprises joints, wherein the joints connect the first branch and/or second branch to the first terminal and/or second terminal.
6. The electrical switch of claim 5 , wherein the joints comprise a non-superconducting material.
7. The electrical switch of claim 1 , wherein the first branch comprises one or more coils of superconducting material and wherein the second branch comprises one or more coils of superconducting material.
8. The electrical switch of claim 7 , wherein the coils of the first branch are wound around the same axis as the coils of the second branch.
9. The electrical switch of claim 7 , wherein the coils of the first branch are wound in a first rotation direction and the coils of the second branch are wound in a second rotation direction, wherein the first rotation direction is different to the second rotation direction.
10. The electrical switch of claim 1 , wherein the magnetic field generator comprises an alternating power source.
11. The electrical switch of claim 1 , wherein, when the magnetic field generator is de-activated, it generates substantially no magnetic field, or a constant magnetic field.
12. The electrical switch of claim 1 , wherein in the higher-resistance state the branches of the superconducting material are superconducting.
13. A rectifier comprising at least one electrical switch according to claim 1 and a control mechanism configured to control each of the at least one electrical switch between the low-resistance state and the higher-resistance state in order to rectify current from an alternating current source.
14. The rectifier according to claim 13 , wherein the rectifier comprises a transformer comprising a primary side and a secondary side, wherein the at least one electrical switch is connected to the secondary side of the transformer.
15. The rectifier according to claim 14 , wherein the control mechanism controls each of the at least one electrical switch between the low-resistance state and the higher-resistance state based on the direction of a flow of alternating current in the transformer.
16. The rectifier according to claim 13 , wherein the rectifier is a half-wave rectifier.
17. The rectifier according to claim 13 , wherein the rectifier is a full-wave rectifier.
18. The rectifier according to claim 13 , wherein activation of the magnetic field generator induces a screening current in the branches which causes increased resistive dissipation in the superconducting material without quenching.
19. A fault current limiter comprising at least one electrical switch according to claim 1 and a control mechanism configured to put the at least one electrical switch in the higher-resistance state when a fault is detected.
20. The fault current limiter according to claim 19 , wherein activation of the magnetic field generator induces a screening current in the branches which causes the superconducting material to quench.