Superconducting Switch

Abstract

The present invention relates to a superconducting electrical switch. The switch comprises two parallel branches of superconducting material in a loop and a magnetic field generator that 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 deactivated to switch the electrical switch between a low-resistance state and a high-resistance state. In the low-resistance state, there is no magnetic field through the loop, and a transport current flows through the loop. In the high-resistance state, the magnetic field through the loop induces a shield current such that the sum of the transport current and the shield current is substantially equal to or greater than the critical current of the superconducting material. The switch can be used, for example, in a rectifier or a fault current limiter.

Description

[Technical Field]

[0001] The present technology relates to electrical switches, and although the present technology may find particular application as a superconducting switch, it should not be seen as limiting the present invention. [Background technology]

[0002] In superconducting circuits, it is often difficult to introduce components with similarly low- or zero-resistance conductive paths. Introducing non-superconducting components can degrade circuit performance and reduce the overall efficiency of the circuit. Furthermore, adding resistance to a high-current superconducting circuit requires more cooling to counteract the heating of the resistive components.

[0003] A further problem with introducing resistive components into superconducting circuits is that DC current flowing through said circuits decays quickly when the current supply is removed. In contrast, in superconducting circuits, the current decays according to the time constant (L / R) of the circuit. In other words, superconducting circuits have the advantage of being able to support DC current flow long after the power supply has been turned off. The current decay rate in these superconducting circuits is determined by the non-zero resistance associated with the normal-conducting junctions in the circuit.

[0004] There is therefore a need to be able to provide components or arrangements that can function efficiently in superconducting circuits without significantly degrading their performance.

[0005] One type of component used in these superconducting circuits is the variable resistance current switch. However, existing current switch devices have several known drawbacks. For example, thermally controlled switches typically have slow response and are not suitable for use in high-speed switching applications. Current-controlled switches typically apply current pulses that exceed the critical current of the superconductor, making these types of switch devices prone to degradation. Existing magnetic field-controlled switch devices are controlled by high-intensity magnetic fields, but in the actuated state, these magnetic field-controlled switch devices have a small resistance per unit length, and their switching rate is generally limited by the large inductance of the applied magnetic field coil. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present technology is to provide an electrical switch. Alternatively, an object of the present technology is to provide an electrical switch that can be controllably switched between a high resistance state and a low resistance state.

[0007] Alternatively, it is an object of the present technology to provide a superconducting electric switch.

[0008] Alternatively, the objective is to provide a superconducting electric switch that is smaller, more efficient, less expensive, switches faster, and / or has a higher switching resistance than at least existing superconducting electric switches.

[0009] Alternatively, it is an object of the present technology to provide a rectifier that includes a superconducting electric switch.

[0010] Alternatively, the object of the present technology is to provide a fault current limiter using a superconducting electric switch.

[0011] Alternatively, the goal of the present technology is to at least provide the public with useful options. [Means for solving the problem]

[0012] According to a first aspect of the present technology, there is provided an electrical switch.

[0013] According to a second aspect of the present technology, there is provided an electrical switch configured to switch a resistance due to a current flowing between terminals from a low resistance state to a high resistance state.

[0014] According to a further aspect of the present technology, a loop of superconducting material including 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, the loop having an axis substantially perpendicular to a plane of the loop; a magnetic field generator configured to generate a time-varying magnetic field through the loop, the direction of the magnetic field through the loop being substantially parallel to an axis of the loop or having a component that is substantially parallel to the axis of the loop; the loop is configured to carry a transport current between the first terminal and the second terminal; the magnetic field generator is configured to be selectively activated and deactivated to switch the electrical switch between a low resistance state and a high resistance state; An electrical switch is provided in which, in a low resistance state, the magnetic field generator does not generate a varying magnetic field through the loop and the transport current flows through the loop between two terminals, and in a high resistance state, the magnetic field generator generates a varying magnetic field through the loop and induces a shielding current in the loop such that the sum of the transport current and the shielding current in one or more branches approaches, is greater than, or is substantially equal to the critical current of the superconducting material.

[0015] Preferably, the superconducting material is a high-temperature superconductor. The use of a high-temperature superconductor can advantageously enable the present technology to be utilized at higher temperatures, thereby reducing the cost of the electrical switch and increasing the range of possible operating temperatures. For example, the superconducting material can include rare-earth barium copper oxide (ReBCO) or any other suitable high-temperature superconductor. For example, the rare-earth component can include yttrium (Y), gadolinium (Gd), samarium (Sm), neodymium (Nd), or any other suitable element. In alternative embodiments of the present technology, the superconducting material can be a conventional low-temperature superconductor, such as magnesium diboride (MgB2) or bismuth strontium calcium copper oxide (BSCCO), or niobium titanium alloy (NbTi).

[0016] Preferably, the superconducting material is included as part of the tape; for example, the tape may include a thin film of superconductor deposited on a metal substrate and / or ceramic layer. In some cases, this thin film is coated with an additional outer protective layer of metal, as known to those skilled in the art. However, this should not be considered a limitation of the present technology. For example, the superconducting material may include one or more filaments or wires of superconducting material embedded within a metal matrix.

[0017] In preferred embodiments, the electrical switch may include one or more junctions between superconducting elements within the switch, such as a junction of branches of superconducting material at each terminal. Additionally, junctions may be provided between branches of superconducting material. These junctions may be constructed of non-superconducting materials or may otherwise have non-zero resistance. For example, the junctions may be formed with a normal-conducting metal solder, such as lead-tin (PbSn) or indium-silver (InAg) alloy, that has non-zero resistance at the operating temperature of the circuit. In some embodiments of the present technology, the switch may be constructed without junctions between branches; for example, the branches may be formed by splitting a continuous strip of superconducting material or tape to create two integrally joined branches.

[0018] Preferably, the branches of superconducting material may further each include one or more coils of superconducting material. For example, the first branch may include at least one coil and the second branch may include at least one coil. The use of superconducting coils may advantageously allow for greater coupling between the magnetic field generator and the loop. In alternative embodiments, no coils may be used.

[0019] Each coil of superconducting material may include one or more turns, which may be arranged about a common axis. Providing one or more turns about a common axis may advantageously allow for a simpler construction and / or greater coupling between the varying magnetic field generator and the superconducting material.

[0020] If coils are used, it may be advantageous for the coils in each branch of the loop to be wound in opposite directions (i.e., one coil takes the form of a right-handed spiral and the other coil takes the form of a left-handed spiral). For example, the coil in a first branch of the two branches may be wound in a clockwise direction, while the coil in a second branch of the two branches may be wound in a counterclockwise direction. In other words, the coil in the first branch is wound in a first rotational direction and the coil in the second branch is wound in a second rotational direction, which is different from the first rotational direction. This arrangement may advantageously further promote the generation of shielding currents in the loop. Furthermore, counter-winding the coils may cancel or minimize the total inductance between the terminals of the switch.

[0021] Preferably, the magnetic field generator may comprise a power source in the form of an alternating current power source, such as an AC current or voltage source. For example, the magnetic field generator may comprise an AC power source magnetically coupled to a loop of superconducting material via one or more turns of a conductor.

[0022] Preferably, the magnetic field generator may be magnetically coupled to the loop of superconducting material by a core. In a preferred embodiment, the core is a magnetic or iron core, including iron or ferrite, although in alternative embodiments, the core may be a non-magnetic core or an air core, as known to those skilled in the art. The use of a ferrite core may be particularly advantageous when the switch is used at high frequencies.

[0023] In embodiments in which a magnetic core is used, it may be advantageous for the magnetic core to consist of a closed loop of magnetic material, which may allow the magnetic field generated by the magnetic field generator to be magnetically coupled to the branch of superconducting material.

[0024] Preferably, the magnetic field generator may include a magnetic field generator coil consisting of one or more turns of a conductor. The generator coil may be configured to generate a magnetic field within the core by coupling current from an AC power source to the core through one or more turns. For example, the generator coil may include one or more turns wound around the core. The magnetic field generated within the core may be magnetically coupled to a loop of superconducting material by looping the superconducting material around at least a portion of the core. Furthermore, if coils are added to the loop of superconducting material as described herein, these coils may be used to couple the magnetic field to the superconducting loop. In other words, a coil may be wound around the magnetic core to enhance the magnetic coupling between the magnetic field generator and the superconducting loop.

[0025] In other forms of the present technology, the magnetic field generator coil may be disposed inside the loop and / or coil of superconducting material. Alternatively, the generator coil may be wound around the loop and / or coil of superconducting material. In yet another alternative, the generator coil may be disposed along a common axis with respect to the loop and / or coil. In each of the aforementioned configurations, it may be preferable for the generator coil and the superconducting loop and / or coil to be coaxial with one another. In other words, the generator coil is disposed such that the axis of the generator coil is parallel to the axis of the superconducting loop and / or coil of the loop, and the direction of the magnetic field generated by the generator coil through the loop and / or coil is parallel to the axis of the loop. It should further be appreciated that in embodiments of the technology in which no coils are used, the above configurations may apply only to the loop.

[0026] Preferably, the conductors used in the generator coils may be non-superconducting materials such as copper or aluminum. The use of non-superconducting materials may advantageously enable low-cost magnetic field generators. However, this should not be considered a limitation of the present technology, and in alternative embodiments, the generator coils may include one or more superconductors such as yttrium barium copper oxide (YBCO).

[0027] Preferably, the magnetic field generator is configured to generate a time-varying magnetic field through the loop in a direction substantially parallel to the axis of the loop. Passing a time-varying magnetic field through the loop in a direction having a substantially parallel component may be advantageously more efficient than passing a magnetic field through one or more conductors of the loop.

[0028] In one or more embodiments of the present technology, the transport current passing between the terminals of the electrical switch may be direct current (DC). In alternative embodiments, alternating current (AC) may be used.

[0029] Preferably, the magnetic field generator, when activated, Quench The shielding current may be configured to induce sufficient shielding current in the branch to cause resistive dissipation in the superconducting material without causing Quench It should be understood that occurs when the temperature exceeds the critical temperature. Therefore, if there is sufficient cooling to keep the superconducting material below the critical temperature, the total current in the superconducting material will be Quench In other words, if the local heat dissipation in the superconducting material exceeds the rate at which it can remove heat, Quench For example, in one or more applications of the present technology, the superconductor Quench It may be beneficial to operate the device in an unpowered state, especially in applications where high switching speeds are required, such as the switching elements of a rectifier.

[0030] In an alternative embodiment of the present technology, the magnetic field generator is configured such that when activated, the total energy dissipation in the branch is Quench The superconducting material may be configured to induce a shielding current in the branch that is sufficient to Quench is a function of the cooling of the system, and in one or more embodiments, the critical current of the superconducting material when the sum of the transport current and the shielding current is equal to or greater than the critical current of the superconducting material. Quench This can be configured to occur. Quench The condition may be particularly advantageous when electrical switches are used in fault current limiters, as it may be possible to create higher current limiting resistances.

[0031] Preferably, when the magnetic field generator is deactivated, the magnetic field generator generates substantially no magnetic field, a constant magnetic field, or a magnetic field that is insufficient to induce shielding currents that increase the resistance of the branch.

[0032] Preferably, the branches of superconducting material may be superconducting when in the low resistance state. For example, it may be advantageous for the branches of superconducting material to have substantially zero resistance in the low resistance state. It should be understood that the junctions between branches of superconducting material, while incorporated in the form of the present technology, as described herein, may have some non-zero resistance.

[0033] Preferably, when the magnetic field generator is activated, the branches may be in a high resistance state where they are still superconducting. For example, the branches of superconducting material may advantageously be superconducting while still having a resistance higher than the resistance of the superconducting material in the low resistance state. However, this should not be considered as limiting the invention, and for example, in the high resistance state, the branches of superconducting material may be non-superconducting, e.g., the superconducting material may Quench or the current may exceed the critical current of the superconductor.

[0034] In accordance with a further aspect of the present technology, there is provided a rectifier comprising the electrical switches described herein and a control mechanism configured to control each of the at least one electrical switch between a low resistance state and a high resistance state to rectify current from an AC power source.

[0035] Preferably, the rectifier includes a transformer having a primary side and a secondary side, and the at least one electrical switch is connected to the secondary side of the transformer. The control mechanism can control each of the at least one electrical switch between a low resistance state and a high resistance state based on the direction of alternating current flow in the transformer. For example, the control mechanism can be configured to control the at least one electrical switch based on the direction of alternating current flow in the primary side of the transformer.

[0036] In one embodiment, the rectifier may be a half-wave rectifier. In an alternative embodiment, the rectifier may be a full-wave rectifier.

[0037] Preferably, the rectifier may include one or more switches according to the present technology.

[0038] In accordance with a further aspect of the present technology, there is provided a fault current limiter including the electrical switches described herein and a control mechanism configured to place the at least one electrical switch in a high resistance state when a fault is detected.

[0039] Preferably, the fault current limiter may include one or more switches according to the present technology. [Effects of the Invention]

[0040] From the foregoing description, it becomes apparent that the present technology may provide one or more advantages over conventional switches, including the following: Higher switching resistance, i.e., higher resistance (superconducting or non-superconducting) in the higher resistance state while maintaining superconductivity in the low resistance state. · A more compact switch, especially in embodiments where the generator coil and the superconducting coil are coaxially aligned. A switch that can operate using a smaller magnetic core than conventional switches because of the resistance created by the superconducting loop. · More efficient switches that can further reduce overall losses in cryogenic systems. - Lower cost and simpler structure than existing superconducting switches. A switch that can transition between low and high resistance states more quickly than existing switches. A switch that allows for smaller magnetic field generator currents and voltages than existing switches, particularly in embodiments where the switch is non-inductive or has low inductance. A switch structure that can operate with a smaller magnetic field generator coil size because it does not require applying a magnetic field perpendicular to the surface of the superconductor. Switches that can operate using smaller applied magnetic fields because the magnetic field does not need to penetrate the superconducting material. · Switches that can mitigate or reduce the occurrence of localized hot spots in superconductors.

[0041] Further aspects of the present technology, which should be considered in all novel aspects, will become apparent to those skilled in the art upon reading the following description, which provides at least one example of a practical application of the technology.

[0042] One or more embodiments of the present technology are described below, by way of example only and not by way of limitation, with reference to the following drawings: [Brief explanation of the drawings]

[0043] [Figure 1] 1 shows an example of a graph of electric field versus current for a high temperature superconductor. [Figure 2A] 1 illustrates a first embodiment of a switch according to the present technology. [Figure 2B] 2B shows the switch of FIG. 2A in a low resistance state. [Figure 2C] 2B shows the switch of FIG. 2A in a high resistance state. [Figure 3] 1 illustrates a further embodiment of a switch according to the present technology. [Figure 4] 1 illustrates how a magnetic field generator can be coupled to a switch in accordance with the present technology. [Figure 5] 1 shows a graph comparing the voltage measured across the terminals of a superconducting switch in the presence and absence of a varying magnetic field. [Figure 6] 10 illustrates an alternative method of coupling a magnetic field generator to a switch according to the present technology. [Figure 7] 1 shows a schematic diagram of a full-wave rectifier using switches according to the present technology. [Figure 8] 1 shows a schematic diagram of a half-wave rectifier using switches according to the present technology; [Figure 9] One way to build a full-wave rectifier using switches according to the present technology is shown. [Figure 10] 10 shows exemplary current and voltage waveforms for a full-wave rectifier constructed in accordance with the embodiment of FIG. 9. [Figure 11] 1 shows a schematic diagram of a fault current limiter using a switch according to the present technology; DETAILED DESCRIPTION OF THE INVENTION

[0044] [background] To help understand this technology, -Critical temperature of superconductors ·Critical current of superconductors It should be understood that superconductivity terminology includes:

[0045] For the benefit of the reader, these concepts are briefly explained below. The critical temperature of a superconductor is conventionally defined as the temperature below which the resistance of the superconductor drops to zero or nearly zero. In other words, when the temperature of a superconductor is below the critical temperature, it is said to be in a superconducting state, and when it is above the critical temperature, it is said to be in a non-superconducting state. Many superconductors have critical temperatures close to absolute zero. For example, the critical temperature of mercury is known to be 4.1 K. However, the critical temperatures of some materials are known to be much higher, ranging from 30 to 125 K. For example, the critical temperature of magnesium diboride is approximately 39 K, and the critical temperature of yttrium barium copper oxide (YBCO) is approximately 92 K. These superconductors are commonly referred to as high-temperature superconductors (HTS).

[0046] The critical current of a high-temperature superconducting wire or tape is conventionally defined as the current flowing in the superconducting wire / tape that results in a field drop of 100 μV / m (=1 μV / cm) along the wire. It should be understood that the critical current is a function of both the superconducting material used and the physical arrangement of the superconducting material. For example, a wider tape / wire may have a higher critical current than a thinner tape / wire composed of the same material. However, it should be understood that throughout this specification, references will be made to the critical current of the superconductor / superconducting material to simplify the discussion.

[0047] In a superconductor / superconducting material, when the current I is approximately equal to the critical current Ic, the resistance of the superconductor is small, but not zero. However, if I is much greater than the critical current Ic, the resistance of the superconductor becomes large enough that heat dissipation occurs, heating the superconductor above its critical temperature and causing it to cease to be superconducting. This condition, sometimes called a "quench," can damage the superconductor itself. Some fault current limiters use the quenching effect of the superconductor to quickly switch a large resistance into the power circuit in a one-time operation. These fault current limiters can usually be reset and reused, but this is usually a slow process because the superconducting material must be recooled below its critical temperature.

[0048] An exemplary plot showing the internal electric field versus current curve for a high temperature superconductor is shown in Figure 1. It should be understood that the electric field shown in this plot is related to the resistance by the following equation: E=IR / L During the ceremony: E is the electric field, ·I is the current flowing through the superconductor, R is the resistance of the wire, ·L is the length of the wire.

[0049] The plot in Figure 1 therefore relates the resistance per unit length of the superconductor, and since the curve depicted is nonlinear, the resulting resistance of the superconductor is nonlinear with respect to current.

[0050] In this figure, we can see that below the critical current (Ic) of the superconductor, the electric field strength in the superconductor is essentially zero. As the current in the superconductor approaches the critical current, the electric field in the superconductor begins to increase. At the critical current, the electric field in the superconductor is 100 μV / m. Increasing the current in the superconductor further above the critical current causes a rapid increase in the electric field strength in the conductor.

[0051] It should be understood that throughout this specification, reference is made to the relative resistance of superconducting switches and their components. Those skilled in the art should understand that superconducting materials when in a superconducting state can have resistances that are zero or substantially zero, and therefore these resistances are more generally expressed in terms of the electric field that exists across the superconducting material for a given current. Nevertheless, throughout this specification, reference has been made to relative resistance, low resistance, and high resistance states to simplify the foregoing discussion.

[0052] Form of technology FIG. 2A is a schematic diagram of a switch 200 in accordance with the present technology. The switch 200 includes a superconducting material 202 connected between a first terminal 204 and a second terminal 206. In describing the technology herein, the switch, including its components, will be referred to as "superconducting." It will be apparent to those skilled in the art that this term is not intended to limit the scope of the technology, and it should be understood that under certain conditions, the switch and its components may not be superconducting, i.e., the switch may be described as superconducting but not superconducting. However, for consistency, the switch and its components may be described as "superconducting" throughout this specification.

[0053] In a preferred embodiment of the present invention, the superconducting material 202 comprises a rare earth barium copper oxide (ReBCO) tape, such as a yttrium barium copper oxide tape or a gadolinium barium copper oxide tape, however, it should be understood that this should not be considered a limitation of the present invention, as the present invention is compatible with other superconducting materials, including high temperature superconductors, and the use of tape should not be considered a limitation.

[0054] In use, transport current I t is selectively supplied to flow between the first terminal 204 and the second terminal 206. In other words, the transport current I t can be turned off and on as needed.

[0055] In FIG. 2A, to simplify the preceding discussion, the first terminal 204 is shown as the positive terminal and the second terminal 206 is shown as the negative terminal. Similarly, the transport current I tis shown flowing from a first (positive) terminal 204 to a second (negative) terminal 206, as would be expected for a conventionally defined direct current (DC) voltage. However, the use of a DC voltage should not be considered limiting of the technology, as is clear from the foregoing discussion. Furthermore, when DC current is used, the superconducting material experiences negligible losses due to the low, zero, or near-zero resistance of the superconducting material 202. When AC current is used, the total losses will be significantly less than for an equivalent non-superconducting material, although losses will generally be greater due to parasitic effects.

[0056] The superconducting material 202 between the two terminals 204, 206 is formed into a loop 210 that includes two electrically parallel superconducting branches 212a, 212b.

[0057] These superconducting branches 212 a, 212 b may be formed by joining two or more superconducting materials together using methods known to those skilled in the art, including methods that provide a non-zero junction resistance. Alternatively, the branches 212 a, 212 b may be formed using any method that provides a substantially zero resistance junction, such as by splitting a superconducting tape into two parallel branches.

[0058] In use, a transport current is applied between the first terminal 204 and the second terminal 206 using an electrical circuit (not shown) connected between the first terminal 204 and the second terminal 206. This electrical circuit may include a power source, such as a voltage or current source, a transformer, or any other suitable electronic circuit known to those skilled in the art. Next, a time-varying magnetic field B app(t) is selectively applied to or within loop 210 in a direction that is perpendicular to the plane of loop 210 (or has a component that is perpendicular to the plane of loop 210), i.e., parallel to the axis of loop 210, with the axis perpendicular to the plane of loop 210. In Figure 2, a time-varying magnetic field is applied to loop 210 such that the magnetic field passes through loop 210. It may be advantageous to provide a time-varying magnetic field in a direction that is substantially or at least partially perpendicular to the plane of the loop to reduce losses caused by the magnetic field penetrating or attempting to penetrate superconducting material 202.

[0059] This time-varying magnetic field B app (t) causes a shielding current (I) to flow between branches 212a, 212b of loop 210 to oppose the magnetic flux change in loop 210. s ) flows. This shielding current I s is added to the transport current flowing around loop 210, resulting in an increase in the total current flowing. This increase in current either slightly increases the resistance of the superconducting material (e.g., until the current exceeds the critical current I as shown in FIG. 1) or c less than 1000 kJ), or the resistance of the superconducting material may increase significantly (e.g., when the current I c is close to, greater than, or equal to the critical current of the superconductor).

[0060] 2B, which illustrates how the switch 200 of FIG. 2A operates in the absence of a time-varying magnetic field, or in the presence of a non-time-varying or weak time-varying magnetic field. In FIG. 2B, the current flowing through loop 210 is a transport current I t When a time-varying magnetic field is applied, or the magnitude of the magnetic field is increased or decreased, the shielding current I s flows around the loop 210. A transport current I t and the shielding current I s approaches or exceeds the critical current of the superconductor, the effective resistance of branches 212a, 212b increases. As a result, a time-varying magnetic field can be applied to transition the switch between low and high resistance states.

[0061] The low resistance state of switch 200 can be considered equivalent to a closed state of switch 200, while the high resistance state is similar to an open state of switch 200. However, the high resistance state is not an electrical open circuit, as is typical with mechanical switches, but rather a T c represents a highly resistive conductive state in which the loop remains superconducting unless subsequent heating beyond

[0062] In some embodiments, the low resistance state can be a superconducting state in which the resistance of branches 212 a, 212 b of loop 210 is near or substantially zero. That is, in preferred embodiments, the low resistance state of the switch is one in which at least a portion of loop 210 is in a superconducting state. However, this should not be considered a limitation of the technology, and in alternative embodiments, the low resistance state can be a partially superconducting state, for example, when one or more low resistance junctions are formed between the superconducting elements of the loop by ordinary conductive metal solder joints.

[0063] Similarly, the high resistance state may be a superconducting state in which the resistance of branches 212 a, 212 b of loop 210 is near zero but higher than the resistance of the low resistance state. In one application of the present technology, the resistance of branches 212 a, 212 b of loop 210 in the high resistance state may be substantially non-zero. For example, loop 210 may be in a non-superconducting state or a partially superconducting state.

[0064] Thus, the present technology provides a switch that can transition between low and high resistance states when exposed to a time-varying magnetic field or when the amplitude of the time-varying magnetic field is changed. This may advantageously enable the construction of faster-switching contactless switches that are more reliable than conventional current switches. Other potential benefits include the ability to create switching elements that: As is clear from the above description, it is smaller than conventional switches. - Faster switching is possible than with thermal switches, especially in applications where the high resistance state of the switch is a superconducting state. Achieves higher off-resistance than existing AC field-controlled switches. · More efficient than conventional switches because the exclusion of the magnetic field from the superconductor reduces dissipation in the superconductor. The switch is contactless and dissipates less energy, making it more reliable than existing switches. Low inductance allows for a low power drive source for the magnetic field generator.

[0065] A further embodiment of a switch 300 in accordance with the present technology is shown in Figure 3. As with the previous embodiment, the superconducting material 202 is arranged in a loop 310 that includes two electrically parallel branches 312a, 312b. However, in this embodiment, each branch 312a, 312b includes a coil 314a, 314b of superconducting material, each coil including one or more turns.

[0066] With reference to the drawings and the foregoing description, it will be understood that the loops of the present technology include two or more electrically parallel conductive paths, in contrast to the coils of the present technology each having a single conductive path consisting of one or more turns.

[0067] In use, a time-varying magnetic field B is applied through the loop 310 across both coils 314a, 314b in a direction that is perpendicular (or has a component that is perpendicular) to the plane of the loop 310 and / or coils 314a, 314b. app is selectively applied. This causes the shielding current I s flows around the closed loop 310 formed by the two parallel-connected branches 312a, 312b. This shielding current can be used to selectively transition the switch 300 between a low resistance state and a high resistance state, as in the previous embodiment.

[0068] It may be desirable for the first branch 312a to include one or more coils 314a wound in a clockwise direction and the second branch 312b to include one or more coils 314b wound in a counterclockwise direction, or vice versa. This arrangement may be useful for ensuring that the shielding current in the first coil 314a is induced in the same direction as the shielding current in the second coil 314b, thereby encouraging the shielding current to flow around the loop 310. Furthermore, the use of coils 314a, 314b may advantageously make it easier to substantially equalize the inductance of each branch 312a, 312b. For example, by using coils 314a, 314b having one or more turns, the geometric difference between each branch 312a, 312b is a smaller fraction of the current-turns in each branch.

[0069] A further potential advantage of this arrangement is that it may allow for higher switching resistance than the previous embodiment due to the longer switching length of each branch.

[0070] Figure 4 is a schematic diagram illustrating one practical application of the switch 300 of Figure 3. In this embodiment, the coupling between the varying magnetic field generator 402 and the switch 404 can be improved by directing the magnetic flux through the core 406. The arrangement of Figure 4 is similar to that of a transformer, as is well known to those skilled in the art.

[0071] Core 406 is preferably a high permeability magnetic core, such as an iron core, although this should not be considered a limitation on the technology, as will become apparent from the preceding discussion.

[0072] For simplicity, the magnetic field generator 402 is shown as an AC source 408 magnetically coupled to a core via a coil 410 containing one or more turns. However, this should not be considered limiting of the technology, and alternative methods of generating a varying magnetic field may be used, for example, by switching a DC current source.

[0073] To simplify the foregoing discussion and to distinguish the magnetic field generator coil 410 from the coils 414a, 414a of the switch 402, the magnetic field generator coil 410 will be referred to herein as the magnetic field generator coil 410, or simply as the generator coil.

[0074] It should also be appreciated that the magnetic field generator coil 410 may be constructed of any suitable conductive material, including superconducting materials such as YBCO or non-superconducting materials such as copper and aluminum. In a preferred embodiment, the generator coil 410 is constructed of copper. This can advantageously provide a lower cost switch than similar switches that use superconducting generator coils 410.

[0075] To continue the transformer analogy, the generator coil 410 can be considered the primary side of the transformer, and the switch coils 414a, 414b can be considered the secondary side of the transformer.

[0076] Unlike a conventional transformer, however, the superconducting coils 414a, 414b of switch 404 are wound around core 406 in opposite directions and electrically connected in parallel to each other. As a result, when coils 414a, 414b each have the same number of turns, the secondary winding coil is shorted and the net magnetic flux encircled by coils 414a, 414b is approximately zero. The purpose of core 406 is to couple an applied magnetic field to the pair of coils 414a, 414b, which form loop 416. This generates a shielding current in loop 416 to oppose the magnetic flux changes from magnetic field generator 402.

[0077] In use, the magnetic field generator 402 can be selectively enabled or varied in amplitude as needed to transition the switch 404 between low and high resistance states.

[0078] In a low resistance state where the magnetic field generator 402 is not generating a varying magnetic field in the core 406 or is generating a weak magnetic field in the core 406, the transport current I ttends to be shared equally between the two parallel branches 412 a, 412 b. In this state, these branches 412 a, 412 b have zero or near-zero resistance, and further, because the coils 414 a, 414 b are wound in opposite directions, there is little or no inductance present between the terminals 204 and 206. Furthermore, because the coils 414 a, 414 b are wound in opposite directions and connected in parallel, there is substantially zero or very minimal magnetic flux induced into the core 406 from the coils 414 a, 414 b.

[0079] When the magnetic field generator 402 is activated or the magnitude of the applied magnetic field is increased or decreased, a shielding current I flows through the loop 416 of superconducting wire as described above. s is formed. A transport current I in one or both of the branches 414a, 414b t and the shielding current I s is close to, equal to, or exceeds the critical current of the superconducting material, there is a non-zero resistance in the branch. Thus, the magnetic field generator 402 can be activated or its amplitude can be varied to switch the switch 404 between a low resistance state and a high resistance state.

[0080] 5 shows an example of measuring the voltage across the switch terminals 204, 206 in accordance with one form of the present technology. In this illustration, the voltage across the switch is the voltage measured across the switch terminals 204, 206. The magnetic field generator current reflects the amplitude of the current applied by the magnetic field generator 402 to the generator coil 410.

[0081] For completeness, it should be noted that a current source was used to apply a DC current of approximately 80 amps between terminals 204, 206. The superconducting coils 414a, 414b each consisted of one turn of 4 mm wide YBCO tape, and the generator coil used 200 turns of copper wire.

[0082] It can be seen that in the absence of a varying magnetic field (after approximately 80.5 seconds), the voltage measured across terminals 204, 206 was substantially zero. In other words, in the absence of a time-varying magnetic field, the superconducting material is superconducting. This represents a low resistance state of the switch. In contrast, when a varying magnetic field was applied (prior to 80.5 seconds), the voltage measured across the terminals varied, representing a change in the resistance of the superconducting material. Furthermore, when this varying magnetic field was applied, a peak voltage was observed across the terminals, representing a high resistance state of the switch. It should be understood that this high resistance state of the switch may represent a superconducting or non-superconducting state, depending on the intended use of the switch.

[0083] 6 illustrates yet another embodiment of a switch 600 in accordance with the present technology. In this embodiment, the generator coil 410 of the changing magnetic field generator 402 is coaxially aligned with the coils 414 a, 414 b of the switch 600. This may advantageously improve magnetic field coupling between the generator coil 410 and the superconducting coils 414 a, 414 b of the switch.

[0084] In the illustrated embodiment, the turns of the superconducting coils 414a, 414b of the switch 600 are interwoven with the turns of the generator coil 410. However, this should not be considered limiting in any way. For example, the superconducting coils 414a, 414b may be disposed axially inward of the generator coil 414. Alternatively, the generator coil 410 may be disposed axially inward of the superconducting coils 414a, 414b. In yet another alternative, the generator coil 410 may be longitudinally spaced apart from the coils 414a, 414b. It is also envisioned that the first superconducting coil 414a may be disposed in an alternating position with the second superconducting coil 414b. For example, the first superconducting coil 414a may be disposed below the generator coil 410, and the second superconducting coil 414b may be disposed above the generator coil 410.

[0085] An additional benefit of coaxially aligning the generator coil 410 and the superconducting coils 414a, 414b is the ability to use a non-magnetic or air core 602, which advantageously reduces the size, weight, and cost of the switch. Additional benefits of using an air core, such as the ability to drive higher shield currents without saturating the core, will also be apparent to those skilled in the art.

[0086] Technology Applications 7 and 8 show exemplary circuit diagrams of a full-wave rectifier 700 and a half-wave rectifier 800, respectively, in accordance with embodiments of the present technology. These examples are representative of applications of the switches of the present technology and are not intended to be considered limiting of the scope of the technology. Further applications of the switches will be apparent to those skilled in the art; in particular, the superconducting switches of the present technology are an improvement over existing current switches and may find application in superconducting magnets, magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR), flux pumps, fault current limiters, and magnetic energy storage systems. Alternatively, the switches of the present invention can be used to replace conventional switches, such as AC field switches, semiconductor switches, and / or mechanical switches, in a wide range of applications.

[0087] In these embodiments, switches S1 and S2 are represented symbolically to simplify the foregoing discussion. However, it should be understood that these switches S1 and S2 may be constructed using any of the methods described herein. Furthermore, to simplify the foregoing discussion, it is assumed that both switch symbols represent superconducting switches in accordance with the present technology. However, it should be understood that one or more of the illustrated switches may instead be conventional switches, such as AC field switches, semiconductor switches such as transistors, or mechanical switches such as relays or resistors.

[0088] Referring initially to FIG. 7, the overall circuit topology is that of a known full-wave rectifier 700. A transformer 704 has a primary side 702a including at least one inductor and a secondary side 702b including at least one inductor. An AC source is provided on the primary side 702a. Two switches S1 and S2 are connected to the secondary side 702b of the transformer 704. A load 706 is connected in parallel with the switches S1 and S2 between a first terminal 708 and a second terminal 710. The first terminal 708 is connected to an intermediate winding of the secondary side 702b of the transformer 704, for example, via a common center tap connection.

[0089] The general principles of this circuitry should be familiar to those skilled in the art, but for clarity, a brief summary of its operation is given.

[0090] In use, an alternating current I1 is applied to the primary side 702a of the transformer 704. This current induces a current flow I2 in the secondary side 702b of the transformer. As known to those skilled in the art, the ratio of the primary side 702a current to the secondary side 702b current is a function of the ratio of the number of turns on the primary side 702a of the transformer 704 to the number of turns on the secondary side 702b of the transformer 704.

[0091] The rectifier 700 includes a control mechanism (not shown). The control mechanism is configured to control the state of each of the switches S1 and S2 to rectify the AC current source. For example, the control mechanism controls each of the switches S1 and S2 such that the state of each switch is based on the direction of AC current flow in the primary side 702a or the secondary side 702b of the transformer 704. The AC current flow depends on the phase of the current, and the control mechanism controls the state of each of the switches S1 and S2 in a timed manner.

[0092] When current in the secondary side 702b of the transformer 704 is flowing in a first direction (e.g., when the current is positive), the first switch S1 is placed in a low resistance state and the second switch S2 is placed in a high resistance state. This creates a low impedance path around the top half of the circuit, allowing current to flow from the first terminal 708 to the second terminal 710 through the load 706. In this state, the first switch S1 is in series with the load and the second switch S2 is in parallel with the load. This load can be any suitable load known to those skilled in the art. For example, it can be a load coil or a resistive element. In yet another embodiment, the load is substantially open circuit or large enough to simply provide an open circuit voltage.

[0093] One application of this technology is to attach a superconducting coil as a load, which can be attached using conventional conductive solder joints while still being incorporated into the technology's form factor.

[0094] When current in the secondary side 702b of the transformer 704 is flowing in a second direction (e.g., when the current is negative), the first switch S1 is placed in a high resistance state and the second switch S2 is placed in a low resistance state. In this state, the first switch S1 is in parallel with the load and the second switch S2 is in series with the load. This creates a low impedance path around the bottom half of the circuit, causing current to flow from the first terminal 708 through the load 706 to the second terminal 710.

[0095] In this way, current always flows in one direction through the load, from the positive terminal to the negative terminal, regardless of the direction of the current induced in the secondary 702b of the transformer 704. Thus, the AC current in the primary 702a of the transformer 704 is full-wave rectified to DC through the load 706.

[0096] By way of example, the control mechanism may be configured such that when transitioning switches S1, S2 from a high resistance state to a low resistance state, or vice versa, the control mechanism may initially temporarily transition both switches S1, S2 to a high resistance state to reduce "crowbar" currents or short circuits that may exist during switching.

[0097] It should be understood that the full-wave rectifier can be configured such that the current path on the secondary side 702b is substantially superconducting. This may advantageously provide a full-wave rectifier that is more compact or otherwise efficient than existing designs. Furthermore, it should be understood that the rectifier may also include non-superconducting components while maintaining a substantially superconducting secondary current path. For example, the transformer primary side 702a may be constructed using non-superconducting materials such as copper or aluminum, and the generator coils (not shown) of switches S1, S2 may also use non-superconducting components as described herein. Furthermore, joints between any components of the present technology, including superconducting elements, may be formed using non-superconducting materials such as metal solders while remaining incorporated in the form of the present technology.

[0098] In rectifier applications, fast switching times between high and low resistance states can be important. Quench It may be preferable for the superconductor material to remain below its critical temperature, as switching may introduce a thermal time lag after switching during which the superconductor must cool down to its operating temperature.

[0099] Referring now to FIG. 8, the general circuit topology is that of a known half-wave rectifier 800. A transformer 704 has a primary side 702a including at least one coil and a secondary side 702b including at least one coil. An AC source is provided on the primary side 702a. Two switches S1 and S2 are connected to the secondary side 702b of the transformer 704 as shown. A load 706 is connected in parallel across one of the switches, S2 in the example of FIG. 8. The load is connected between a first terminal 708 and a second terminal 710.

[0100] The general principles of this circuitry should be familiar to those skilled in the art, but for clarity, a brief summary of its operation is given.

[0101] As in the previous embodiment, the primary 702a of the transformer 704 is driven with an AC current I1 which induces an AC current I2 in the secondary winding 702b of the transformer.

[0102] The rectifier 800 includes a control mechanism (not shown). The control mechanism is configured to control the state of each of the switches S1 and S2 to rectify the AC source. For example, the control mechanism controls each of the switches S1 and S2 such that the state of each switch is based on the direction of AC current flow in the primary side 702a or the secondary side 702b of the transformer 704. Because the direction of AC current flow depends on the phase of the current, the control mechanism controls the state of each of the switches S1 and S2 in a timed manner.

[0103] When the secondary current I2 is flowing in a first direction (i.e., when the current is positive), the first switch S1 is placed in a low-resistance state and the second switch S2 is placed in a high-resistance state. This low-resistance path is formed around the outside of the loop, from the secondary side of the transformer 702b, through switch S1, across the load 706 from the first terminal 708 to the secondary terminal 710. When the current polarity changes (e.g., from positive to negative), switch S1 transitions to a high-resistance state and switch S2 transitions to a low-resistance state. The high-resistance state of S1 prevents current flow from the transformer and provides a means to block negative current flow. At the same time, the low-resistance state of S2 provides a path for current to continue flowing to the load, even while it is decaying. Thus, the current through the load is half-wave rectified.

[0104] Those skilled in the art will understand suitable control mechanisms for controlling the states of switches S1, S2 in the embodiments of the technology shown in Figures 7 and 8 as described. For example, switches S1 and S2 can activate their respective varying magnetic field generators in synchronization with the polarity (either primary or secondary) of the transformer current to achieve low and high resistance states. This can be achieved using any control mechanism known in the art, including using a half-wave rectified current signal as a means of activating the magnetic field generators. This half-wave rectified current signal can be provided as an additional secondary winding on transformer 704 or using any other method known to those skilled in the art.

[0105] However, it should be understood that the magnetic field generators do not have to operate in synchronism with the transformer current, for example it may be advantageous to have some dead time (neither S1 nor S2 active / low resistance state) around the zero crossings of the transformer current.

[0106] It should be further appreciated that in embodiments in which multiple switches are provided, such as the half-wave rectifier 800 and full-wave rectifier 700 described herein, a single magnetic field generator may be configured to generate shielding currents in one or more switches. For example, a magnetic field generator may have two or more generator coils, each configured to generate a varying magnetic field across a respective switch. The magnetic field generator may then be configured to change which generator coils it drives based on the polarity of the adjusted current. In such embodiments, the rectifier's control mechanism includes a mechanism for controlling the magnetic field generator to operate in this manner. Using a single magnetic field generator in a rectifier application can advantageously reduce the size, cost, and / or complexity of the rectifier.

[0107] Reference is now made to FIG. 9, which illustrates an example of how the full-wave rectifier 900 of FIG. 7 may be constructed in accordance with the present technique. In this embodiment, the circuit's drive or transport current I tA drive transformer 902 is provided to generate I / I2. In a preferred embodiment, the drive transformer 902 is a step-down transformer; in other words, to achieve the high currents used in superconducting circuits, it is desirable for the drive transformer 902 to have more turns on the primary side 904a compared to the secondary side 904b. For example, this drive transformer 902 may have a turns ratio between 300:1 and 600:1. In the embodiment shown, the transformer has approximately 900 primary windings and two secondary windings, for a ratio of 450:1. Furthermore, reducing the number of turns on the secondary side 904b of the drive transformer 902 can reduce costs, as fewer turns of expensive superconducting material are required. Using a large turns ratio can also be useful for generating large superconducting AC secondary currents using a normal conducting primary current. Using a small number of primary turns to achieve this reduces resistive losses on the primary side while keeping the size small. In alternative applications where it is advantageous to reduce leakage flux, it may be advantageous to increase the number of turns on the secondary.

[0108] It should be appreciated that this drive transformer 902 substantially mirrors the transformer 704 of FIG.

[0109] Also shown in this figure are a first switch 906 and a second switch 908. Each switch includes a coupling core 910a, 910b and a varying magnetic field generator 912a, 912b. The coupling cores 910a, 910b are used to couple the magnetic field generated by generator coils 914a, 914b to respective coils 916a, 916b, 916c, 916d to activate switches S1 and S2 of FIG. 7. The illustrated cores 910a, 910b are preferably ferrite cores or laminated steel / iron cores. However, alternative cores with high relative permeability at the operating frequency may be used. In alternative embodiments of the present technology, the cores may instead include a substantially non-magnetic material or an air core, as described in connection with FIG. 6.

[0110] In a preferred embodiment, switches 906, 908 have a greater number of turns in generator coils 914a, 914b compared to the number of turns in superconducting coils 916a, 916b, 916c, 916d. This ratio may advantageously allow for greater magnetic flux density in the superconductor coils without requiring a large number of turns of relatively expensive superconducting material. For example, each switch 906, 908 may have a turns ratio between 50:1 and 150:1. In the embodiment shown, switches 906 and 908 each have approximately 200 primary (generator coil) turns and two secondary (superconducting coil) turns, for a ratio of 100:1.

[0111] 9 is that the windings of the drive transformer primary 904a are electrically isolated from the superconductor windings of the drive transformer secondary 904b. Additionally, the generator coils 914a, 914b of each switch 906, 908 are electrically isolated from their respective coils 916a, 916b, 916c, 916d of superconducting material. This advantageously provides a safer structure than existing rectifier circuits and may further allow for charging the DC magnet while operating at high currents.

[0112] It will be apparent to those skilled in the art that this topology mirrors that of Figure 7. Therefore, the discussion regarding the operation of Figure 7 also applies to the embodiment of Figure 9.

[0113] In one form, a suitable control mechanism for controlling the timing of the change of state of switches 906 and 908 between the low resistance state and the high resistance state is a ratio of primary current I1 in primary 904a of driving transformer 902 to current I1 in generator coils 914a and 914b of switches 906 and 908. s1 and I s2 Alternatively, the current I s1 and I s2 Control of I can be based on secondary current I or by a third coil coupled to drive transformer 902 (not shown). For example, the connection may be such that I is positive when primary current I in primary side 904a of drive transformer 902 flows in a first direction (e.g., is positive). s1flows, and when the primary current I1 of the primary side 904a of the drive variable 902 flows in a second direction (e.g., negative), I s1 does not flow, and when the primary current I1 of the primary side 904a of the driving transformer 902 flows in a second direction (e.g., negative), I s2 flows, and when the primary current I1 of the primary side 904a of the driving transformer 902 flows in a first direction (e.g., positive), I s2 As mentioned previously, it may be advantageous for the control mechanism to include a period of dead time (neither switch 906, 908 is in a low resistance state) around the zero crossing of the transformer current.

[0114] In one example of the present technology, the control mechanism controls the current I s1 and I s2 As previously mentioned, the inverter includes one or more windings connected to a drive transformer 902 that provides a current I s1 and I s2 may be advantageously operated in synchronization with the current in the drive transformer 902. For example, if the drive current is positive, then the current I s1 is activated and the current I s2 Similarly, if the drive current is negative, the current I s1 is activated and the current I s2 may be deactivated (or vice versa). This may be accomplished using any adjustment method known to those skilled in the art, including semiconductor switches such as diodes and transistors. For example, diodes may be provided to activate the varying magnetic field generators 912a, 912b in synchronization with the respective phases of the drive current. In some examples, the forward voltage drop of the semiconductor switches (such as diodes) may provide periods of dead time for the circuit when neither switch is conducting.

[0115] In another example of the technology described herein, a current I s1 and I s2 It may be advantageous for the current I to operate at a higher frequency than the drive current. In these instances, the control mechanism may adjust the current I based on the polarity of the drive current. s1 and I s2The drive current may be configured to activate the variable magnetic field generators 912a, 912b based on the polarity of the drive current. For example, the drive current may be configured to enable the variable magnetic field generators 912a, 912b based on the polarity of the drive current. For example, a semiconductor switch, such as a transistor, may be used to turn on the variable magnetic field generator 912a when the drive current is positive and turn on the variable magnetic field generator 912b when the drive current is negative. Alternatively, a single variable magnetic field generator may be used, in which case the phase of the drive current may be used to switch the output of the variable magnetic field generator between the switches 906 and 908 using methods apparent to those skilled in the art.

[0116] Figure 10 shows the resulting current and voltage waveforms measured in a circuit constructed according to the embodiment of Figure 9. The figure includes five graphs, shown from top to bottom. The current applied to the primary coil 904a of the driving transformer 902. · Current measured in the secondary (superconducting) coil 904b of the driving transformer 902. · Current applied to the generator coil 914a of the first varying magnetic field generator 912a. · Current applied to the generator coil 914b of the second varying magnetic field generator 912b. · Open circuit voltage measured across terminals 204 and 206.

[0117] From these graphs, it can be seen that the frequency of the current applied to the drive transformer 902 is lower than the frequency of the current generated in the generator coils 914a, 914b of the switches 906, 908. In practice, the drive frequency was approximately 4 Hz, and the shield current was approximately 200 Hz. By using a higher frequency for the generator coils 914a, 914b, it is possible to ensure that at least one cycle of the shield current is completed while the switches 906, 908 are energized. As shown in FIG. 10, it may be even more advantageous for the switches to complete one or more cycles of the shield current while they are energized (i.e., in a high resistance state), as this may provide a more stable high resistance state.

[0118] The resulting open-circuit voltage waveform between terminals 204, 206 is shown to be full-wave rectified. In other words, regardless of the polarity of the current in drive transformer 902, the voltage across terminals 204, 206 has negative voltage peaks corresponding to the high-resistance states of switches 906, 908, respectively. The voltage between terminals 204, 206 during regulation has a constant polarity (negative), and the current that may flow between terminals 204, 206 to load 706 may likewise be constant, thereby being full-wave rectified during the period when one or more switches are in a high-resistance state. In other words, the circuit of FIG. 9 can convert AC current to DC under superconducting conditions.

[0119] It can be seen that when both switches 906, 908 are in the deactivated state, there is substantially zero output voltage across the rectifier terminals 204, 206. One use of this rectified DC voltage is to charge a superconducting magnet, although this is not meant to be considered a limitation of the invention and other uses will be apparent to those skilled in the art.

[0120] FIG. 11 shows an active fault current limiter 1100 using a switch 1102 in accordance with one form of the present technology.

[0121] In this embodiment, an AC power source 1104 is connected in series with the switch 1102 and the load 1106. During use, the variable magnetic field generator 1108 of the switch 1102 is deactivated or generates a variable magnetic field that is small enough so that the current through each of the branches 1110a, 1110b of the loop 1112 does not exceed the critical current of the superconducting material 1114. This places the switch 1102 in a low resistance state, minimizing the voltage drop across the superconducting material 1114. When a fault 1116, such as an overload or short circuit, is applied to the circuit, an increase in current can be detected using any method known to those skilled in the art. Upon such detection, a control mechanism can be configured to activate the variable magnetic field generator 1108 or increase the drive current to transition the switch 1102 to a high resistance state, thereby limiting the total power that can be delivered to the fault 1116.

[0122] If the fault current limiter 1100 is used in a domestic AC or grid power application (typically 50 to 60 Hz), it may be advantageous to drive the varying magnetic field generator 1108 at a frequency of a few kilohertz or higher, for example, 2 kHz to 100 kHz. This will ensure that multiple screening cycles are provided for each cycle of the supply voltage, allowing for more stable current limiting in the circuit.

[0123] The fault current limiter 1100 of the present technology may have many advantages over existing fault current limiters, including the following. The switch 1102 can be quickly transitioned to a high resistance state. For example, the fault current limiter 1100 can operate within milliseconds of detecting a fault condition. The fault current limiter 1100 can be actively enabled based on any criteria, such as selecting the current at which the fault current limiter 1100 trips, determining when to deactivate the fault current limiter 1100, or dynamically adjusting the trigger fault current based on, for example, the current load of the circuit. Provides a safe, low rebound voltage to the AC power source 1104. In other words, the switch 1102 can be constructed in a low or substantially zero inductance configuration, allowing the use of a substantially resistive load to limit current flow and reduce spikes that may occur due to the switching of an inductive element.

[0124] Furthermore, this technique may provide greater resilience against damage caused by hot spots. Generally speaking, hot spots are areas where the critical current I of a superconducting wire is exceeded. c This phenomenon is caused by a local decrease in I, which is the phenomenon where the superconducting material is locally heated by the transport current. c Localized reductions in current can be caused by defects in the superconductor material or by localized thermal or magnetic conditions that cause localized heating, resulting in significant localized temperature increases. These temperature increases can damage the superconductor. This situation can be particularly dangerous in fault current limiters.

[0125] The technology can generate a shielding current that flows around the entire loop of superconducting material, driving a significant portion, if not all, of the superconductor into a high-resistance state. Thus, the switch based on this technology operates more uniformly along a long superconducting line than existing switches. Quench This can reduce the effects of localized heating.

[0126] Applications of this technology therefore include superconducting magnets, magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR), flux pumps, fault current limiters, and magnetic energy storage systems.

[0127] Unless the context clearly requires the contrary, throughout the specification and claims, the words "comprise," "comprising," and the like, are to be construed in an inclusive sense, i.e., "including but not limited to," rather than in an exclusive or exhaustive sense.

[0128] The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference.

[0129] The reference herein to any prior art is not, and should not be construed as, an acknowledgment or implication that the prior art forms part of the general knowledge in that field anywhere in the world.

[0130] The technology may also be broadly described as consisting of the components, elements and features referred to or shown herein, individually or collectively, in any and all combinations of two or more of the components, elements or features.

[0131] Where the foregoing description refers to components having whole entities or their known equivalents, those whole entities are incorporated herein as if individually set forth.

[0132] It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present technology and without diminishing its attendant advantages. Accordingly, it is intended that such changes and modifications be embraced by the present technology.

Claims

1. 1. An electrical switch comprising a loop of superconducting material and a magnetic field generator, the loop includes 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, the loop having an axis substantially perpendicular to a plane of the loop; the loop is configured to carry a transport current between the first terminal and the second terminal; the magnetic field generator is configured to generate a time-varying magnetic field through the loop, the direction of the magnetic field through the loop being substantially parallel to an axis of the loop or having a component that is substantially parallel to the axis of the loop; the magnetic field generator is configured to be selectively controlled to switch the electrical switch between a low resistance state and a high resistance state; 1. An electrical switch, comprising: in a low resistance state, the magnetic field generator does not generate a time-varying magnetic field through the loop, or the time-varying magnetic field through the loop is relatively weak, and the transport current flows through the loop between two terminals; and in a high resistance state, the magnetic field generator generates a time-varying magnetic field through the loop, or increases the time-varying magnetic field through the loop, and induces a shielding current in the loop such that a sum of the transport current and the shielding current in the first branch, the second branch, or both the first branch and the second branch approaches, is substantially equal to, or is greater than, a critical current of the superconducting material.

2. 10. The electrical switch of claim 1, wherein the superconducting material comprises a high temperature superconductor.

3. 3. The electrical switch of claim 1, wherein the superconducting material comprises rare earth barium copper oxide (ReBCO).

4. 4. An electrical switch according to any one of claims 1 to 3, wherein the superconducting material is included as part of a tape.

5. 5. An electrical switch according to claim 1, further comprising a junction connecting the first branch and / or the second branch to the first terminal and / or the second terminal.

6. 6. The electrical switch of claim 5, wherein the junction comprises a non-superconducting material.

7. 7. An electrical switch according to any one of claims 1 to 6, wherein the first branch comprises one or more coils of superconducting material.

8. 8. An electrical switch according to any one of claims 1 to 7, wherein the second branch comprises one or more coils of superconducting material.

9. 9. An electrical switch according to claim 8 when dependent on claim 7, wherein the coil of the first branch is wound about the same axis as the coil of the second branch.

10. 10. An electrical switch according to claim 8 or 9 when dependent on claim 7, wherein the coil of the first branch is wound in a first rotational direction and the coil of the second branch is wound in a second rotational direction, the first rotational direction being different from the second rotational direction.

11. 11. An electrical switch according to any one of claims 1 to 10, wherein the magnetic field generator comprises an AC power source.

12. 12. An electrical switch according to any one of claims 1 to 11, wherein the magnetic field generator is magnetically coupled to the loop of superconducting material by a core.

13. 13. The electrical switch according to claim 12, wherein the core is an iron-based core or a magnetic core containing iron or ferrite.

14. 14. The electrical switch of claim 13, wherein the core comprises a closed loop of magnetic material.

15. 15. An electrical switch according to any preceding claim, wherein the magnetic field generator comprises a magnetic field generator coil comprising one or more turns of a conductor.

16. 16. The electrical switch of claim 15, wherein the conductor comprises a non-superconducting material.

17. 17. An electrical switch according to any one of claims 1 to 16, wherein when the magnetic field generator is deactivated it generates substantially no magnetic field or a constant magnetic field.

18. 18. An electrical switch according to any one of claims 1 to 17, wherein in a high resistance state, branches of the superconducting material are superconducting.

19. At least one electrical switch according to any one of claims 1 to 18; a control mechanism configured to control each of the at least one electrical switch between a low resistance state and a high resistance state to rectify current from an AC source; A rectifier comprising:

20. 20. The rectifier of claim 19, comprising a transformer including a primary side and a secondary side, the at least one electrical switch being connected to the secondary side of the transformer.

21. 21. The rectifier of claim 20, wherein the control mechanism controls each of the at least one electrical switch between a low resistance state and a high resistance state based on a direction of AC current flow in the transformer.

22. 22. A rectifier according to any one of claims 19 to 21, which is a half-wave rectifier.

23. 22. A rectifier according to any one of claims 19 to 21, which is a full-wave rectifier.

24. 24. A rectifier according to any one of claims 19 to 23, wherein operation of the magnetic field generator induces shielding currents in the branches, increasing resistive dissipation of the superconducting material without quenching.

25. At least one electrical switch according to any one of claims 1 to 19; a control mechanism configured to place the at least one electrical switch in a high resistance state when a fault is detected; A fault current limiter comprising:

26. 26. A fault current limiter as claimed in claim 25, wherein activation of said magnetic field generator induces a shielding current in said branch causing said superconducting material to be quenched.

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