Current limiting element for superconducting current limiter and superconducting current limiter

Abstract

The invention relates to a current limiting element used for a superconducting current limiter and the superconducting current limiter, the current limiting element used for the superconducting current limiter comprises superconducting strips, a stainless steel encircling strip and a copper terminal, the superconducting strips are welded together to form a superconducting strip group, and the superconducting strip group is connected with the stainless steel encircling strip. The stainless steel surrounding belt is wound outside the superconducting belt material group in a spiral form, the stainless steel surrounding belt is connected with two ends of the superconducting belt material group through welding, a cooling flow channel is formed between the stainless steel surrounding belt and the superconducting belt material group, and the copper terminal is connected with the superconducting belt material group through welding. Compared with the prior art, the cooling efficiency is effectively improved, and the strip is prevented from being burnt out.

Description

Technical Field

[0001] The present invention relates to the field of power accessories, and in particular to a current limiting element for a superconducting current limiter and a superconducting current limiter. Background Art

[0002] Superconducting current limiter is a fast and effective current limiting device developed using superconducting technology. At present, the development of superconducting current limiter mainly has two directions. One is to use the quenching characteristics of superconductors to suppress short-circuit current. Its advantage is that the principle and structure are simple and can realize fault self-detection. The other is to combine with power electronics technology, make full use of the high-density unimpeded current carrying capacity of superconductors, and combine with control technology. It has good action characteristics. The advantage of this type of current limiter is flexibility and controllability.

[0003] Depending on whether superconductors are used to generate magnetic fields, superconducting current limiters are mainly divided into two categories: resistance-type and inductance-type. The working principle of the resistance-type superconducting current limiter is based on the zero resistance effect of superconductors. It is connected in series in the line and has basically no resistance during normal operation. When a short circuit occurs in the line and the short-circuit current exceeds the critical current, the superconductor quenches and the resistance value increases rapidly, thereby limiting the short-circuit current. There are many types of inductance-type superconducting current limiters, and their principles are more complex and diverse than those of resistance-type. There are mainly saturated iron core type, transformer type, magnetic shielding type, etc. In general, resistance-type superconducting current limiters are commonly used.

[0004] As one of the important components of the current limiting element of the superconducting current limiter, the superconducting tape is subjected to the transmission of large currents under normal working conditions. When a fault current occurs, the fault current is greater than the critical current of the superconducting tape, so the current will pass through the package of the tape. In order to ensure the current limiting function of the current limiting unit when a fault current occurs, the package of the superconducting tape is usually made of stainless steel thin strips. Superconducting tapes packaged with stainless steel are prone to local quenching, resulting in local heat accumulation, which can damage the superconducting tape. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a current limiting element for a superconducting current limiter and a superconducting current limiter, so as to effectively increase the cooling efficiency and prevent the strip from burning out.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A current limiting element for a superconducting current limiter comprises a superconducting tape, a stainless steel surrounding tape and a copper terminal. The superconducting tapes are welded together to form a superconducting tape group. The stainless steel surrounding tape is wound around the outside of the superconducting tape group in a spiral form. The stainless steel surrounding tape is connected to both ends of the superconducting tape group by welding. A cooling channel is formed between the stainless steel surrounding tape and the superconducting tape group. The copper terminal is connected to the superconducting tape group by welding.

[0008] Furthermore, the current limiting element also includes a temperature measuring optical fiber sensor, which is fixed on the inner surface of the stainless steel surrounding belt and the surface of the superconducting tape group through a low-temperature insulating material, and the temperature of the superconducting tape group and the stainless steel surrounding belt is measured by the temperature measuring optical fiber sensor to evaluate the size and impact of the fault current.

[0009] Furthermore, the low-temperature insulating material includes multiple materials selected from polyimide and glass fiber.

[0010] Furthermore, the selection of the superconducting tape is matched with the fault current size and fault frequency of the power line and the design of the superconducting current limiter.

[0011] Furthermore, the superconducting tape includes multiple types of copper-encapsulated superconducting tape, stainless steel-encapsulated superconducting tape and superconducting mother tape without an encapsulation layer.

[0012] Furthermore, the spiral intercept, width and thickness of the stainless steel surrounding belt match the structure of the superconducting current limiter.

[0013] Furthermore, the material of the stainless steel surrounding belt is non-magnetic stainless steel.

[0014] Furthermore, the copper terminal is provided with a through hole, and the current lead is connected to the current limiting element through the through hole.

[0015] Furthermore, when the power system operates normally, current passes through the superconducting tape group, and the stainless steel surrounding tape is used to protect and support the superconducting tape group; when a fault current occurs and the fault current is greater than the critical current that the superconducting tape group can withstand, the fault current is diverted to the superconducting tape group and the stainless steel surrounding tape through the copper terminal, thereby limiting the current.

[0016] A superconducting current limiter comprises the current limiting element for a superconducting current limiter.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention increases the cooling surface area of ​​the superconducting tape by winding the stainless steel surrounding tape in a spiral form around the outside of the superconducting tape group and leaving a certain space between the stainless steel surrounding tape and the superconducting tape group, so as to make the cooling efficiency higher and the temperature more controllable, solve the problem that long-length stainless steel encapsulated superconducting tape is prone to local quenching, resulting in local heat accumulation, thereby damaging the superconducting tape, and improve the reliability of the superconducting current limiter.

[0019] 2. The present invention uses a temperature measuring optical fiber sensor to convert optical signals into electrical signals by relying on a photoelectric conversion device. When a normal current passes through the superconducting current limiter, the operating status of the superconducting current limiter is reflected in real time. When a fault current occurs, the size and impact of the fault current are effectively evaluated, and the temperature rise of the superconducting tape and the stainless steel surrounding tape when the fault current passes through and the recovery status after the fault current passes through are judged in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the structure of a current limiting element for a superconducting current limiter proposed by the present invention;

[0021] Figure 2 It is a schematic diagram of the structure of the copper terminal;

[0022] Figure 3 A schematic longitudinal section diagram of a current limiting element for a superconducting current limiter proposed by the present invention;

[0023] Figure 4 Schematic diagram of the structure of the current limiting element in the embodiment;

[0024] Figure 5 A schematic diagram of the coil manufacturing of the non-inductive pancake coil in the embodiment;

[0025] Figure 6 It is a structural schematic diagram of the non-inductive pancake coil in the embodiment;

[0026] Figure 7 Schematic diagram of the structure of the superconducting current limiter in the embodiment;

[0027] Legend: 1. Superconducting tape; 2. Stainless steel surrounding tape; 3. Fiber optic sensor for temperature measurement; 4. Copper terminal; 401, through hole; 5. Epoxy skeleton; 6. Current lead; 7. Non-inductive pancake coil; 8. Current limiting group; 9. Support rod; 10. Cooling medium. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] This embodiment provides a current limiting element for a superconducting current limiter, such as Figure 1 As shown, it includes a superconducting tape 1, a stainless steel surrounding tape 2 and a copper terminal 4. The superconducting tape 1 is welded together to form a superconducting tape group. The stainless steel surrounding tape 2 is spirally wound around the outside of the superconducting tape group. The stainless steel surrounding tape 2 is connected to both ends of the superconducting tape group by welding. A cooling channel is formed between the stainless steel surrounding tape 2 and the superconducting tape group. The copper terminal 4 is connected to the superconducting tape group by welding.

[0031] As one of the important components of the current limiting element of the superconducting current limiter, the superconducting tape 1 can withstand the transmission of large current under normal working conditions when the transmission current is less than the critical current of the superconducting tape 1. When the fault current comes, the fault current is greater than the critical current of the superconducting tape 1. Therefore, the fault current will not pass through the superconducting layer in the superconducting tape 1, but the stainless steel surrounding tape 2 will be selected to pass. When the fault on the power line is restored, the load current is less than the critical current of the superconducting tape 1, and the temperature of the superconducting tape 1 is restored to below the critical temperature, the superconducting tape 1 can continue to be responsible for the transmission of large current. The selection of the superconducting tape 1 can be specifically selected according to the fault current size, fault frequency and design of the superconducting current limiter of the power line during the actual application process. Due to the presence of the stainless steel winding tape 2, the selection of the superconducting tape 1 becomes wider, and copper-encapsulated superconducting tapes, stainless steel-encapsulated superconducting tapes and superconducting mother tapes without encapsulation layers can be selected. The number of superconducting tapes 1 is also determined according to the actual application requirements to increase the flow capacity. When multiple superconducting tapes 1 are selected, the multiple superconducting tapes 1 can be divided into multiple groups, and each group is welded together as a whole to ensure integrity; or the groups can be welded together with the stainless steel surrounding tape 2 at the copper terminal 4.

[0032] The stainless steel surrounding belt 2 mainly plays the role of protecting and supporting the superconducting tape 1, and when a fault current occurs, as a part of the resistance-type current limiting element, it is responsible for the transmission of the fault current. The spiral intercept of the stainless steel surrounding belt 2 is determined according to the structural design of the actual superconducting current limiter and the design of the current limiting element. The stainless steel surrounding belt 2 is one of the paths for the transmission of the fault current, so its width and thickness are determined according to the design of the current limiting element of the actual superconducting current limiter. In addition, since the fault current is usually transient, it can be known from Faraday's law that the change of current will cause the change of the magnetic field. Therefore, the stainless steel surrounding belt 2 will be subjected to a certain Ampere force in the process of passing the fault current. In order to prevent the Ampere force from being too large, the stainless steel surrounding belt 2 should be made of non-magnetic stainless steel, such as 310 stainless steel.

[0033] The temperature of the superconducting tape 1 and the stainless steel surrounding tape 2 is monitored in real time during the operation of the superconducting current limiter by the optical fiber sensor 3 for temperature measurement. When the superconducting current limiter passes normal current, the temperature of the superconducting tape 1 and the stainless steel surrounding tape 2 is monitored in real time, and the operation of the superconducting current limiter is reflected in real time. When a fault current occurs, the temperature of the superconducting tape 1 and the stainless steel surrounding tape 2 is monitored in real time, and the magnitude of the fault current and the impact are effectively evaluated, and the temperature rise of the superconducting tape 1 and the stainless steel surrounding tape 2 when the fault current passes through is judged in real time, as well as the recovery status after the fault current passes, which is conducive to judging the performance of the superconducting current limiter. In actual application, the model and quantity of the optical fiber sensor 3 for temperature measurement can be determined according to the actual situation and the specific design of the superconducting current limiter.

[0034] like Figure 2 As shown, a through hole 401 is provided on the copper terminal 4, and the current lead is connected to the current limiting element through the through hole 401.

[0035] In actual use, first select the appropriate model and quantity of superconducting tape 1, and the material, quantity and specifications (width, thickness and length) of stainless steel surrounding tape 2 according to the actual grid application requirements and the design requirements of the superconducting current limiter. Then, when making the current limiting unit, first weld the superconducting tape 1 together in an appropriate manner as required to form a superconducting tape group, so that the overall structure of the superconducting tape 1 is stable and consistent. At the same time, in order to measure the temperature of the superconducting tape group during operation, a temperature measuring optical fiber sensor 3 for measuring the temperature of the superconducting tape group is fixed on the surface of the superconducting tape group using materials such as polyimide and glass fiber that have good insulation properties at low temperatures, and try to make the temperature measuring optical fiber sensor 3 close to the surface of the superconducting tape group to ensure the accuracy of the measurement. Subsequently, the stainless steel surrounding tape 2 is spirally wound around the outside of the superconducting tape group. When the stainless steel surrounding tape 2 is wound, a circular winding is generally adopted, that is, from the cross-section of the current limiting unit of the present invention, the stainless steel surrounding tape 2 is circular, such as Figure 3 As shown, the stainless steel surrounding belt does not overlap when winding and leaves a certain gap to form a cooling flow channel to ensure the bending radius of the entire current limiting unit. The temperature measuring optical fiber sensor 3 is fixed on the inner surface of the stainless steel surrounding belt 2 using materials with good insulation properties such as polyimide. After the temperature measuring optical fiber sensor 3 is fixed, the stainless steel surrounding belt 2 and the two ends of the superconducting tape 1 are welded to the copper terminal 4 through a solder with high affinity and good welding effect. When the fault current passes through, the fault current is shunted to the superconducting tape group and the stainless steel surrounding belt 2 through the copper terminal 4, thereby playing a role in current limiting.

[0036] The optical fiber sensor 3 for temperature measurement can be welded together with the superconducting tape 1 and the stainless steel surrounding tape 2 to form a whole, or can be led out separately. The solution of welding the optical fiber sensor 3 for temperature measurement with the superconducting tape 1 and the stainless steel surrounding tape 2 is relatively simple in manufacturing process. The optical fiber sensor 3 for temperature measurement can also be led out separately, such as polyimide tape, and fixed on the superconducting tape 1 and the stainless steel surrounding tape 2. When working, the current limiting unit wrapped with the stainless steel surrounding tape 2 is connected to the current lead through the copper terminal 4, and the current flows from the current lead through the copper terminal 4 into the current limiting unit. When the power system is normal, the current passes through the superconducting tape group welded by the superconducting tape 1, and the stainless steel surrounding tape 2 serves as the protection and support of the superconducting tape group. The optical fiber sensor 3 for temperature measurement detects the temperature of the superconducting tape group and the stainless steel surrounding tape 2. When a fault current occurs, and the fault current is greater than the critical current that the superconducting tape group can withstand, most of the fault current is transferred from the superconducting tape group to the stainless steel surrounding tape 2. The temperature measuring optical fiber sensor 3 detects the temperature of the superconducting tape 1 and the stainless steel surrounding tape 2 in real time, and implements measures for the occurrence of fault current. After returning to normal state, the current is transferred from the stainless steel surrounding tape 2 to the superconducting tape 1.

[0037] Example 2

[0038] This embodiment provides a superconducting current limiter.

[0039] The model and quantity of the superconducting tape 1 are selected according to the actual situation. When selecting, only the number of superconducting tapes 1 is needed to form two groups of superconducting tape groups, and then one end of the superconducting tape group is welded together, while the other ends of the two superconducting tape groups are separated. The temperature measuring optical fiber sensor 3 is installed on the two superconducting tape groups. Since one end of the two superconducting tape groups is welded together, the temperature of the two superconducting tape groups can be measured by one optical fiber sensor 3 for temperature measurement. The optical fiber sensor 3 for temperature measurement is fixed on the surface of the superconducting tape group with polyimide tape, and the stainless steel surrounding belt 2 is respectively wound around the outside of each superconducting tape group. At one end where the two superconducting tape groups are welded together, the stainless steel surrounding belts 2 outside the two superconducting tape groups are also welded together to ensure that the fault current can be transferred from the stainless steel surrounding belt 2 of one superconducting tape group to the stainless steel surrounding belt 2 of another superconducting tape group. The other ends of the two superconducting tape groups and the stainless steel surrounding belt 2 are respectively welded on two copper terminals 4. Like the temperature measuring optical fiber sensor 3 on the superconducting tape group, only one temperature measuring optical fiber sensor 3 can be arranged on the two groups of stainless steel surrounding belts 2. One temperature measuring optical fiber sensor 3 is arranged on the inner surface of the stainless steel surrounding belt 2 by using polyimide tape. The two ends of the temperature measuring optical fiber sensor 3 are placed inside the copper terminal 4 to provide conditions for the subsequent transmission of the temperature measuring optical signal. Figure 4 shown.

[0040] Set the current limiting unit as follows Figure 5 Since there is already a stainless steel surrounding belt 2 outside the superconducting tape group, the step of supporting the superconducting tape 1 can be omitted. In order to further increase the mechanical strength of the non-inductive pancake coil 7, an epoxy skeleton 5 can be further installed outside as a support for the entire non-inductive pancake coil 7, as shown in FIG. Figure 6 shown.

[0041] A plurality of non-inductive pancake coils 7 are connected in series through a support rod 9 to form a current limiting group 8, which increases the current limiting resistance value of the overall current limiter. Both ends of the current limiting group 8 are connected to the current lead 6 of the superconducting current limiter to achieve the purpose of connecting the superconducting current limiter in series to the circuit, such as Figure 7 As shown. In actual normal operation, the non-inductive pancake coils 7 are all immersed in the cooling medium 10. Normal current passes through the superconducting tape group, and there is no current on the stainless steel surrounding belt 2, and no heat is generated. When a fault current occurs, the fault current passes through the stainless steel surrounding belt 2, and the stainless steel surrounding belt 2 generates heat. However, since the stainless steel surrounding belt 2 is not in close contact with the superconducting current group, a certain gap is left between them. Therefore, the actual cooling surface area of ​​the present invention is larger, so that the cooling efficiency is higher, the temperature is more controllable, and the reliability of the superconducting current limiter can be improved.

[0042] The rest is the same as in Example 1.

[0043] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A current limiting element for a superconducting current limiter, characterized in that: The invention comprises a superconducting tape (1), a stainless steel surrounding tape (2) and a copper terminal (4), wherein the superconducting tape (1) is welded together to form a superconducting tape group, the stainless steel surrounding tape (2) is wound around the outside of the superconducting tape group in a spiral form, the stainless steel surrounding tape (2) is connected to both ends of the superconducting tape group by welding, a cooling channel is formed between the stainless steel surrounding tape (2) and the superconducting tape group, and the copper terminal (4) is connected to the superconducting tape group by welding.

2. The current limiting element for a superconducting current limiter according to claim 1, characterized in that: The current limiting element further comprises a temperature measuring optical fiber sensor (3), which is fixed on the inner surface of the stainless steel surrounding belt (2) and the surface of the superconducting tape group via a low-temperature insulating material. The temperature of the superconducting tape group and the stainless steel surrounding belt (2) is measured by the temperature measuring optical fiber sensor (3), so as to evaluate the magnitude and influence of the fault current.

3. The current limiting element for a superconducting current limiter according to claim 2, characterized in that: The low temperature insulating material includes polyimide or glass fiber.

4. The current limiting element for a superconducting current limiter according to claim 1, characterized in that: The selection of the superconducting tape (1) is matched with the fault current size and fault frequency of the power line and the design of the superconducting current limiter.

5. The current limiting element for a superconducting current limiter according to claim 1, characterized in that: The superconducting tape (1) includes multiple types of copper-encapsulated superconducting tape, stainless steel-encapsulated superconducting tape and superconducting mother tape without an encapsulation layer.

6. The current limiting element for a superconducting current limiter according to claim 1, characterized in that: The spiral intercept, width and thickness of the stainless steel surrounding band (2) match the structure of the superconducting current limiter.

7. The current limiting element for a superconducting current limiter according to claim 1, characterized in that: The material of the stainless steel surrounding belt (2) is non-magnetic stainless steel.

8. The current limiting element for a superconducting current limiter according to claim 1, characterized in that: The copper terminal (4) is provided with a through hole (401), and the current lead is connected to the current limiting element through the through hole (401).

9. The current limiting element for a superconducting current limiter according to claim 1, characterized in that: When the power system operates normally, current passes through the superconducting tape group, and the stainless steel surrounding tape (2) is used to protect and support the superconducting tape group; when a fault current occurs and the fault current is greater than the critical current that the superconducting tape group can withstand, the fault current is shunted to the superconducting tape group and the stainless steel surrounding tape (2) through the copper terminal (4), thereby limiting the current.

10. A superconducting current limiter, characterized in that: The invention comprises a current limiting element for a superconducting current limiter as claimed in any one of claims 1 to 9.

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