RU2639316C1 - Superconducting fault current limiter - Google Patents

Abstract

FIELD: electricity.SUBSTANCE: superconducting fault current limiter contains a set of superconducting current limiters module installed in the cryostat, a supplying and a rejecting buses and current leads where the superconducting modules electrically and mechanically are linked to the supplying and rejecting buses with the formation of the electrical parallel connection of superconducting modules, while the mentioned bus is fitted with terminals, located at opposite ends of the supplying and rejecting buses and connected to the current leads.EFFECT: ensuring the stable operation of a high current superconducting current limiter by implementing the same supplying and rejecting resistance in the circuit to each current limiter module, reducing the dimensions of the superconducting current limiter and its simplifying.9 cl, 6 dwg

Description

Technical field

The invention relates to the field of electrical engineering, in particular to high-current superconducting short-circuit current limiters with electrically parallel connection of superconducting modules.

State of the art

The current limiter protects the electric circuit from the flow of current exceeding the rated current (current for which the electric circuit is designed). High current (exceeding the rated current) can flow through the circuit due to, for example, a short circuit.

The current limiting mode is possible due to the unique property of superconductors, namely, the nonlinearity of the increase in material resistance. Depending on the type and type of superconductor, current limiting can occur under different conditions, with different losses and different limiting times, but the basic principle is the same: when the current flows higher than the critical current of the superconductor embedded in the device, the material begins to pass from superconducting state to normal, as a result of which there is a resistance that prevents the increase in current.

In traditional electric power industry, current limiters are reactors: coils that are connected in series to the network and create reactance of the desired magnitude, which prevents current surges during short circuits. A clear drawback of such products is the appearance of a DC component due to the accumulated reactive energy, which leads to a jump in the current amplitude, which is dangerous for electrical devices in the network. This problem is solved by using a resistive superconducting current limiter.

Most of the known such solutions primarily consider the creation of long-length superconducting current limiters with a short recovery time. For example, in patent RU 2587680, a superconducting current limiter is disclosed comprising an insulating cage, a spiral bifilar made of a superconductor strip with a substrate and electrical tape, wherein the insulating casing is made of a main and fixing parts tightened by a threaded connection, each of which is made in the form of an outer ring and a central strip rigidly connected by ribs, while the ribs of the main part of the insulating frame have grooves in which a spiral bifilar from a superconductor tape is placed, covered by two arc inserts mi fixed in the peripheral grooves of the ribs. This design allows the cryogenic liquid to wash the bifilar tape with liquid nitrogen as much as possible, as well as compensate for the deformation of the superconducting tape that occurs due to cooling to the temperature of liquid nitrogen. Moreover, the amount of current that limits the invention is limited by the throughput of the superconducting tape in the bifilar coil. The patent does not disclose the possibility of creating a current limiter that works with transport current values that significantly exceed the critical current of one tape in value.

The closest current limiter to the proposed is a resistive current limiter according to the application US 7345858.

The current limiter in accordance with this patent contains a superconducting current limiter module, consisting of one or more superconducting short-circuit current limiting devices, an external magnet in the cavity of which there is a superconducting current limiter module.

As a superconducting part, various variations of superconducting modules are described in the patent: from single tapes to disks with a superconductor laying in a meander. Then these superconducting modules were placed in the center of the magnet, and one of the current leads to the superconducting part was connected directly to the superconductor, and the second from the superconductor went to the magnet and already from the magnet to the source.

This design of the current limiter suggests that when a short circuit occurs and a current jump, the magnetic field created by the coil increases sharply, and the critical current of the superconducting part will fall, starting to limit the transport current. At some point, such a system will go into equilibrium.

The big drawback of this model of a superconducting current limiter is primarily the dimensions. In addition to the superconducting part, a magnet isolated from the housing must be placed in the current limiter.

In addition, the authors consider the connection of superconducting modules both sequentially and in parallel, but the method of parallel connection of superconducting modules is not specified at all. The authors use the concept of parallel connection of superconducting modules immediately after the concept of serial connection, without distinguishing between connection methods and without giving examples of such connection. Serial connection of superconducting modules makes it possible to limit the current comparable to the critical current of a single module, in contrast to a parallel connection, where the critical currents of the modules are added. And if these modules are connected in parallel, but without taking into account the uneven distribution of the transport current, then the stable operation of the limiter is also difficult to achieve due to the uneven distribution of currents across the modules.

Disclosure of the invention

The technical problem eliminated by the invention is the stable operation of a high-current superconducting current limiter due to the implementation of the same input and output resistance in the circuit to each module of the current limiter, as well as reducing the dimensions of the structure and its simplification. This technical problem is eliminated by the superconducting short-circuit current limiter, which contains a set of superconducting current limiter modules installed in the cryostat, supply and return busbars and current leads, where the said superconducting modules are electrically and mechanically connected to the input and output buses with the formation of electrical parallel connection of superconducting modules, when the said tires are provided with contact terminals located at opposite ends of the supply and discharge th bus and connected to the current leads.

In particular embodiments of the invention, the problem is solved by a limiter in which the superconducting module includes second-generation high-temperature superconducting tapes.

In the limiter, the superconducting module can be made in the form of a packet of connected together parallel strips.

In the limiter, the superconducting module can be made in the form of a package of tapes connected together by twisting.

In the limiter, the superconducting module can be made in the form of a bifilar coil of said tapes.

In the limiter, the cryostat can be made in the form of a container with a lid equipped with a cryocooler.

In the limiter, the current leads are sealed in the cryostat cover.

A contact terminal connected to the current lead by a flexible connecting bus can be made in the limiter.

In the limiter, the superconducting current limiter module may include an additional rigid connecting bus installed between the current lead and the output terminal of the take-off bus, where said additional bus is mechanically connected to the limiter without forming an electrical connection, and the contact leads of the take-off and lead-in buses are turned to the center of the said package of superconducting modules .

A brief description of the drawings.

In FIG. 1 is a schematic illustration of a superconducting current limiter.

In FIG. 2 is a schematic illustration of connecting a set of superconducting current limiter modules to the input and output buses.

In FIG. 3 is a schematic illustration of a superconducting module in the form of a bifilar coil.

In FIG. 4 shows a compact arrangement of bifilar current-limiting modules using an additional bus.

In FIG. Figure 5 shows an electric circuit with a parallel arrangement of superconductors in the module and asymmetrical connection of the contact terminals.

In FIG. Figure 6 shows the electric circuit of a superconducting current limiter with a symmetrical connection of the contact terminals (comparative example).

Positions in the drawings mean the following:

1. Cryostat

2. A set of superconducting current limiter modules

3. Drive rail

4. Contact output lead

5. Take-off tire

6. Contact output of the discharge bus

7. Cryostat cover

8. Current lead

9. Cryocooler

10. Connecting busbars

11. Current limiter module in the form of a bifilar coil

12. Superconducting wire in insulation

13. Copper contacts

14. Rigid connection rail

The implementation of the invention

In our proposed design of a superconducting short-circuit current limiter, including a cryostat with a set of superconducting current limiter modules inside it, these modules are placed between the input and output buses with the formation of both a mechanical connection and an electrical parallel connection in which current is supplied to the contact terminals located at opposite ends of the take-off and lead-in buses (unbalanced connection).

As follows from the drawings shown in FIG. 1 and 2, the superconducting current limiter of short circuit currents includes a cryostat (1), which houses a set of superconducting modules (2) of a superconducting current limiter between the input (3) bus with the contact terminal (4) and the output (5) bus with the contact terminal (6) ) (see Fig. 2). The contact terminals (4) and (6) of the inlet (3) and outlet (5) tires are located at opposite ends of these tires.

Two current leads (8) are hermetically installed in the cover (7) of the cryostat (1), which are connected to the contact terminals (4, 6) either directly or through the connecting busbars (10) (Fig. 2), which are braided copper wires.

Tires (3, 5) are electrically interconnected by a set of superconducting modules (2) with the formation of a parallel electrical connection of all the individual modules included in the set.

A constant temperature inside the working cryostat (1) can be maintained using a cryocooler (9). However, the presence of a cryocooler (9) or a cryostat cover (7) is not necessary for all embodiments of the invention — liquid nitrogen can be filled into the cryostat in the most usual way.

In this embodiment of the invention, the set of current limiter modules (2) is made of high-temperature superconductors (briefly HTSC) of the 2nd generation, where each module is a bifilar coil (11) (see Fig. 2 and 3) from insulated superconducting wires (12) , for example, from HTSC tapes, and copper plates (13), to which the supply and discharge tires are attached (3, 5).

The superconducting wire consists of a single tape in insulation, laid in such a way that when current flows through it in two adjacent layers, the current flows in opposite directions. The process of winding such a coil is carried out in a spiral generally as follows: a piece of tape is fixed, and from it at both edges simultaneously, tightly, over the insulation strip, the rest of the tape is laid in one direction. With this type of winding, the magnetic field created by adjacent turns is compensated, and the total magnetic field is extremely small. That is, the bifilar coil allows compact packing of current-carrying wires of large length without creating reactance due to the inductance characteristic of solenoids and tori.

The 2nd generation HTSC tape includes a substrate, for example, of nickel-based alloy, sequentially arranged buffer layers of aluminum oxide, lanthanum manganite, magnesium oxide and cerium oxide, etc., a superconducting layer based on yttrium-barium cuprate, a layer silver and a layer of copper.

HTSC ribbons of the 2nd generation have recently gained wide distribution due to high current densities and a temperature of transition to the superconducting state above 77 K.

However, to implement a superconducting module, depending on the requirements for limiting the network voltage, any types of superconductors used in electrical devices can be used: low-temperature superconductors (NiTi, NiSn and others), transition superconductors (MgB ₂ , and others), as well as HTSC 1 th generation.

It should be noted that the superconducting part of the set of superconducting modules (2) of the current limiter is not exhausted by the bifilar coil.

The geometry of the implementation of superconductors in a module is arbitrary and meets the requirements for limiting the short-circuit current in a specific task, it is significant that the superconductors in the set of modules (2) are installed geometrically in parallel and form a parallel electrical connection, and the design of superconductors can be arbitrary.

In particular, the set of modules (2) can be represented as:

- modules of single superconducting tapes or stacks of parallel stacked superconducting tapes;

- modules in the form of a wound superconducting cable or solenoid;

- modules in the form of a superconducting wire laid in a bifilar coil;

- combinations of the above solutions, for example, a stack of superconducting tapes wound in a bifilar coil.

In FIG. Figure 3 shows the connection diagram of the module of the superconducting current limiter (2) to the current leads - connection from the contact terminals (4, 6) to the current leads (6) is carried out through flexible connecting buses (10), which are braided copper wires.

However, to reduce the size of the current limiter for connecting one of the buses (3, 5) with a current lead, a rigid connecting bus (14) can be used. In FIG. Figure 4 shows yet another embodiment of a current limiter module, in which an additional connecting rigid bus (14) is connected in series to the outlet bus (5) through the terminal (6) so as not to go beyond the dimensions of the superconducting module and at the same time organize the current output from the take-off bus (5). The supply (3) and additional rigid (14) buses are equipped with flexible connecting buses (10) located above the set of superconducting current limiter modules (2), and the contact leads (4, 6) are deployed to the center of the set of current limiter modules (2) (cf. from Fig. 2, where the contact pins (4, 6) are located at different levels and deployed from the center of the package of modules (2)).

This module design further reduces the size of the superconducting current limiter.

The present invention is based on the following views.

When performing geometrically parallel placement of the contact leads to the superconducting modules, as well as, provided that the contact leads are located at opposite ends of the discharge and supply buses (unbalanced connection), on two parallel buses of the same cross section made of the same material, the transport current supplied to the buses, distributed evenly across all superconducting modules connected to the contact pins.

Moreover, the uniformity of the inlet and outlet tires matters only between the contact terminals - the shape and material of the tires in another area are not important. Fulfillment of the above-described requirements for parallelism and homogeneity of the material between the contact terminals, as well as to their asymmetric arrangement (at different ends of the supply and discharge tires), leads to the fact that the resistance between the corresponding contact terminals of the supply and discharge tires is equal to each other. From here, no matter how the current flows, the resistance will be the same.

To do this, we compare the resistance that is formed when current flows along paths 1, 2, and 3 (Fig. 5) (asymmetric arrangement of the contact leads).

The superconductor resistance (SC ₁ , SC ₂ , SC ₃ , ..., SC _N ) is zero. Therefore, the total resistance along path 1 is equal to:

R = R ₀ + SC ₁ (= 0) + R ₁ + R ₂ + R ₃ + ... + R _N-1 + R _N = R ₀ + R ₁ + R ₂ + R ₃ + ... + R _N-1 + R _N.

Similar resistance for path 2:

R = R ₀ + R ₁ + SC ₂ (= 0) + R ₂ + R ₃ + ... + R _N-1 + R _N = R ₀ + R ₁ + R ₂ + R ₃ + ... + R _N-1 + R _N.

And for path 3:

R = R ₀ + R ₁ + R ₂ + R ₃ + ... + R _N-1 + SC _N (= 0) + R _N = R ₀ + R ₁ + R ₂ + R ₃ + ... + R _N-1 + R _N.

From this it can be seen that with this type of connection, the resistances are equal to each other for any current flow path.

In FIG. 6 is a comparison diagram of a symmetrical connection of a supply and discharge bus. In this case, for the paths analogous to the asymmetric connection, we have the following resistances:

For path 1:

R = R ₀ + SC ₁ (= 0) + R _N = R ₀ + R _N.

For path 2:

R = R ₀ + R ₁ + SC ₂ (= 0) + R ₁ + R _N = R ₀ + 2R ₁ + R _N.

And for path 3:

R = R ₀ + R ₁ + R ₂ + R ₃ + ... + R _N-1 + SC ₁ (= 0) + R _N-1 + ... + R ₃ + R ₂ + R ₁ + R _N =

= R ₀ + 2R ₁ + 2R ₂ + 2R ₃ + ... + 2R _N-1 + R _N.

It is seen that the resistance is different, and therefore, the current flowing along each of the paths will be different, which will lead to the failure of the device.

The invention is as follows.

The superconducting current limiter through current leads 4 is connected to an electric circuit.

In the normal mode of operation of the current limiter, the current flowing through the limiter has no resistance.

The current from the current input (6) via a flexible connecting bus (10) is supplied to the contact output (4) and the supply bus (3).

The current then travels in accordance with the circuit of FIG. 5 arrives from the discharge bus (5) to the contact terminal (6) located on the opposite end of the discharge bus (5) and leaves the current limiter either through the flexible connecting bus (10) and the current lead (6) or through the rigid connecting bus (14) and current lead (6).

As soon as a short circuit occurs, an overvoltage occurs on the entire network, and, of course, it arises on the current limiter. In this case, the set of modules (2) passes from the superconducting state to the normal state, resistance arises in it, and the lion's share of the current is delayed by the current limiter and does not pass further into the network.

An important advantage of the current limiter, in contrast to similar safety devices, is its recoverability. After a short circuit occurred, a resistance appeared on the current limiter, and after 100 ms the key disconnects the network. Then, the current limiter module is cooled in a cryostat (1) in just 30 s, goes back to the superconducting state, and can continue to work.

Another advantage of the claimed superconducting current limiter is that it is capable of limiting currents of the order of 5 kA.

Claims (9)

1. A superconducting short-circuit current limiter, characterized in that it comprises a set of superconducting current limiter modules installed in a cryostat, supply and return buses and current leads, where said superconducting modules are electrically and mechanically connected to the input and output buses to form an electrical parallel connection of the superconducting modules, wherein said tires are provided with contact terminals located at opposite ends of the supply and discharge tires and connected current leads. 2. The limiter according to claim 1, characterized in that the superconducting module includes second-generation high-temperature superconducting tapes. 3. The limiter according to claim 2, characterized in that the superconducting module is made in the form of a packet of connected together parallel tapes. 4. The limiter according to claim 2, characterized in that the superconducting module is made in the form of a packet of tapes connected together by twisting. 5. The limiter according to claim 2, characterized in that the superconducting module is made in the form of a bifilar coil of the said tapes. 6. The limiter according to claim 1, characterized in that the cryostat is made in the form of a container with a lid equipped with a cryocooler. 7. The limiter according to claim 6, characterized in that the current leads are sealed in the cryostat cover. 8. The limiter according to claim 1, characterized in that the contact terminal is connected to the current lead by a flexible connecting bus. 9. The limiter according to claim 1, characterized in that the superconducting current limiter module includes an additional rigid connecting bus installed between the current lead and the output terminal of the outlet bus, where the said additional bus is mechanically connected to the limiter module without forming an electrical connection, and the contact leads of the outlet and the supply bus are deployed to the center of the package of superconducting modules.

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