Fault current limiting superconducting charging cable

Abstract

The application discloses a superconducting charging cable of fault current limiting type, and mainly solves the problems that existing superconducting cables cannot be used for bidirectional direct-current high-power charging and have complex structures. The superconducting charging cable comprises a cable framework and liquid nitrogen passage (1), a composite conductor layer (2) and a thermal insulation shell (3). The cable framework supports the composite conductor layer and the thermal insulation shell. The composite conductor layer is composed of inner and outer superconducting tape layers and inner and outer fault current limiting stabilizing layers, and is wrapped on the cable framework. The inner composite conductor layer and the outer composite conductor layer are separated by using an intermediate layer insulating bushing, so that the bidirectional direct-current charging function of the superconducting cable is realized. The fault current limiting stabilizing layer is armored on the superconducting tape layer, so that the fault current limiting function of the superconducting cable is realized. The thermal insulation shell is wrapped on the outer liquid nitrogen bellows, so that the heat leakage of the cable body to the outside is greatly reduced. The superconducting charging cable has a compact structure, does not need to use a fault current limiter, and can be used for connecting electrode terminals to perform high-power direct-current fast charging on electric vehicles.

Description

Technical Field

[0001] This invention belongs to the field of cable technology, specifically relating to a superconducting charging cable that can be used to connect electrode terminals for high-power DC fast charging of electric vehicles. Background Technology

[0002] High-temperature superconducting cables utilize the unique unobstructed current-carrying characteristics of superconductors in their operating state to achieve low-voltage, high-power, and low-loss electrical energy transmission. With the gradual increase in the superconductor transition temperature and the maturation of high-temperature superconducting tape manufacturing processes, research on power transmission using high-current-density high-temperature superconducting cables has gradually progressed from the experimental testing stage to the development and application stage. Against the backdrop of increasingly scarce fossil fuels and severe environmental pollution, the electric vehicle industry has developed rapidly. However, traditional DC charging methods suffer from drawbacks such as slow charging speed, low charging power, and low energy utilization. Furthermore, to achieve overload protection for the transmission circuit, traditional high-temperature superconducting transmission cables are large in size, complex in structure, and require coordination with fault current limiters.

[0003] To address the issues of low charging power and slow charging speed in traditional electric vehicle charging stations, the increasingly mature superconducting cable technology can be combined to miniaturize the structure of traditional superconducting power transmission cables and use high-temperature superconducting cables for superconducting DC fast charging of electric vehicles, thereby greatly improving the charging rate and energy utilization.

[0004] Patent document CN200710063118.2 discloses "a superconducting cable with integrated insulation and heat insulation," which includes a supporting inner tube, a cable conductor, and a cable outer shell. A sandwich layer exists between the cable outer shell and the inner tube. The inner tube contains a low-temperature coolant channel and a superconducting conductor. Both the cable outer shell and the inner tube are provided with corrugated expansion sections. The sandwich layer between the cable outer shell and the inner tube is an insulation and heat insulation layer, and at least one set of sandwich insulators is placed therein. The insulation and heat insulation layer formed between the cable outer shell and the inner tube is a vacuum sandwich layer or a layer filled with lightweight foam or powdered insulation and heat insulation material.

[0005] US Patent 20080119362 discloses a "superconducting cable" comprising a tubular support structure, multiple superconducting conductors, and a cable shell. The tubular support structure, located at the center of the superconducting cable, is made of stainless steel. The multiple superconducting conductor layers are composed of superconducting materials with different critical transition temperatures; the critical transition temperature of the inner conductor layer differs from that of the outer conductor layer. A cavity channel between the inner and outer conductor layers is used for the flow of cryogenic coolant, and an electrical insulation layer is arranged between the different conductor layers.

[0006] The above cables all have the following shortcomings:

[0007] Firstly, because the supporting frame is a rigid structure, it cannot be bent after it is laid.

[0008] Secondly, its conductor layer can only achieve unidirectional current flow and cannot achieve coaxial bidirectional current flow. It can only be used as a high-power unidirectional current-carrying cable and is not convenient for high-power DC fast charging of loads.

[0009] Third, because superconducting cables lack overload protection for the line, they need to be used in conjunction with fault current limiters, resulting in a complex structure and poor economic efficiency. Summary of the Invention

[0010] The purpose of this invention is to address the shortcomings of the prior art by providing a fault-limiting superconducting charging cable, which significantly improves the power and charging rate of DC charging for electric vehicles, simplifies the cable structure, reduces the footprint, and enables the miniaturization of superconducting power components.

[0011] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0012] A fault-limiting superconducting charging cable includes: a cable skeleton and a liquid nitrogen passage 1, a composite conductor layer 2, and a heat-insulating outer shell 3, characterized in that:

[0013] The cable skeleton and liquid nitrogen channel 1 use inner and outer flexible metal corrugated pipes 12 and 14 as the cable skeleton to support the cable conductor layer and bend within a set limit; the inner liquid nitrogen corrugated pipe 12 is provided with an inner liquid nitrogen channel 11, and the outer liquid nitrogen corrugated pipe 14 is provided with an outer liquid nitrogen channel 13 between it and the composite conductor layer 2. The conductor layer is introduced with a low-temperature working medium for cooling through these two channels 11 and 13.

[0014] The composite conductor layer 2 is composed of inner and outer superconducting tape layers 23 and 25 and inner and outer fault current limiting and stabilizing layers 22 and 26 respectively. The inner superconducting tape layer 23 has an inner fault current limiting and stabilizing layer 22, and the outer superconducting tape layer 25 has an outer fault current limiting and stabilizing layer 26. The cable itself can limit the overload current through these two fault current limiting and stabilizing layers 22 and 26.

[0015] The heat insulation shell 3 is composed of a composite heat insulation layer 31 and an outermost metal sleeve 32. The composite heat insulation layer 31 is located outside the outer liquid nitrogen corrugated pipe 14 to reduce heat leakage from the cable body to the outside. The outermost metal sleeve 32 is located outside the composite heat insulation layer 31.

[0016] Furthermore, the inner fault current limiting stabilizing layer 22 is fixed to the inner superconducting tape layer 23 as a whole; the outer fault current limiting stabilizing layer 26 is fixed to the outer superconducting tape layer 25 as a whole; the inner and outer fault current limiting stabilizing layers 22 and 26 are both made of conductive materials with high resistivity to improve the quench resistance when the cable body experiences a fault current surge.

[0017] Furthermore, an inner insulating bushing 21 is provided between the inner liquid nitrogen corrugated pipe 12 and the inner fault current limiting and stabilizing layer 22; an intermediate insulating bushing 24 is provided between the inner superconducting tape layer 23 and the outer superconducting tape layer 25 to separate the inner and outer superconducting tape layers and realize the bidirectional high-power DC charging function of the superconducting cable; an outer insulating bushing 27 is provided between the outer fault current limiting and stabilizing layer 26 and the outer liquid nitrogen channel 13; the inner, intermediate, and outer insulating bushings 21, 24, and 27 are all made of multi-layer insulating material to provide good insulation performance at the kilovolt voltage level.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention uses a flexible corrugated pipe as the cable skeleton and a composite insulation layer or flexible vacuum interlayer as the cable insulation layer, which allows the cable body to be bent, resulting in a simple and compact structure that enables the miniaturization, flexibility, and modularization of superconducting power equipment.

[0020] 2. By using multi-layer insulating bushings to separate the inner superconducting tape layer from the outer superconducting tape layer, the present invention enables the inner and outer superconducting tapes to be energized independently, thereby realizing the bidirectional high-power DC fast charging function of the cable. For high-power DC charging of electric vehicles, it can significantly improve the charging power and accelerate the charging rate.

[0021] 3. By setting inner and outer fault current limiting and stabilizing layers on the inner and outer superconducting tape layers respectively to form a composite conductor layer, the invention significantly improves the quench resistance of the composite conductor layer, which can play a current limiting protection role for the charging system circuit when an overload current surge occurs. This achieves the goal of maintaining the compact structure of the superconducting cable while improving the safety margin, and eliminates the need for additional fault current limiter components.

[0022] 4. Because the present invention uses two different types of composite insulation layers, it can significantly reduce heat leakage from the cable body to the outside, improve the charging power of the cable, and enhance the stability of the cable during operation. Furthermore, since the two types of composite insulation layers can be flexibly selected and switched freely according to actual working conditions, the application scenarios of superconducting power equipment are broadened. Attached Figure Description

[0023] Figure 1 This is an overall structural diagram of the present invention;

[0024] Figure 2 yes Figure 1 Radial cross-sectional view;

[0025] Figure 3 yes Figure 1 Axial cross-sectional view. Detailed Implementation

[0026] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0027] Example 1:

[0028] Reference Figure 1 , Figure 2 , Figure 3 The superconducting charging cable designed in this embodiment includes: a cable skeleton and a liquid nitrogen passage 1, a composite conductor layer 2, and a heat insulation shell 3; the composite conductor layer 2 is wrapped around the inner layer of the cable skeleton 1 layer by layer; the heat insulation shell 3 is wrapped around the outer layer of the cable skeleton 1.

[0029] The cable skeleton and liquid nitrogen passage 1 are used to support the cable conductor layer and insulation layer, and serve as a channel for liquid nitrogen to enter and cool the composite conductor layer. It includes an inner liquid nitrogen channel 11, an inner liquid nitrogen corrugated pipe 12, an outer liquid nitrogen channel 13, and an outer liquid nitrogen corrugated pipe 14. The inner liquid nitrogen corrugated pipe 12 is connected to an external liquid nitrogen supply pipeline, and liquid nitrogen flows in from the inner liquid nitrogen channel 11 located inside the inner liquid nitrogen corrugated pipe 12. The outer liquid nitrogen corrugated pipe 14 is connected to an external liquid nitrogen discharge pipeline, and liquid nitrogen flows out from the outer liquid nitrogen channel 13 located between the outer liquid nitrogen corrugated pipe 14 and the composite conductor layer 2, forming a closed circulation of the cryogenic working fluid inside the cable body.

[0030] In this embodiment, a 304 stainless steel flanged bellows with a specification of Ф25×5mm is used as the inner liquid nitrogen bellows 12, and a 304 stainless steel flanged bellows with a specification of Ф50×5mm is used as the outer liquid nitrogen bellows 14.

[0031] The composite conductor layer 2, used to carry high-power DC current, includes an inner insulating bushing 21, an inner fault current limiting and stabilizing layer 22, an inner superconducting tape layer 23, an intermediate insulating bushing 24, an outer superconducting tape layer 25, an outer fault current limiting and stabilizing layer 26, and an outer insulating bushing 27. The inner insulating bushing 21 is wrapped around the inner liquid nitrogen corrugated tube 12, so that the diameter of the cable after wrapping the inner insulating bushing is approximately 27 mm, providing an insulation strength greater than 10 kV. The inner fault current limiting and stabilizing layer 22 is armored and welded to the inner superconducting tape layer 26. The inner side of the conductive strip layer 23 is fixed together with the outer superconducting strip layer 25 to form an inner composite conductor layer, which is wrapped around the inner insulating bushing 21. The intermediate insulating bushing 24 is wrapped around the inner superconducting strip layer 23. The outer fault current limiting and stabilizing layer 26 is armored and welded to the outer side of the outer superconducting strip layer 25. The two are fixed together to form an outer composite conductor layer, which is wrapped around the intermediate insulating bushing 24. The outer insulating bushing 27 is wrapped around the outer fault current limiting and stabilizing layer 26. After wrapping the outer insulating bushing 27, the cable diameter is approximately 44 mm.

[0032] In this embodiment, both the inner superconducting tape layer 23 and the outer superconducting tape layer 25 are made of, but are not limited to, Bi-based high-temperature superconducting tape wound at a 5° helical angle. The cross-section of the high-temperature superconducting tape is rectangular, with a width of approximately 5 mm and a thickness of approximately 1 mm. The inner superconducting tape layer 23 has 18 conductors, and the outer superconducting tape layer 25 has 20 conductors. Since the current direction of the inner superconducting tape layer 23 and the outer superconducting tape layer 25 is opposite when the cable is charged, the inner and outer superconducting tapes need to be wound in the same direction to counteract the magnetic field generated during the energizing process. The inner fault current limiting stabilizing layer 22 and the outer fault current limiting stabilizing layer 26 are armored using, but are not limited to, low-temperature solder multi-point segmented welding to ensure the structural strength of the solder contact points under ultra-low temperature operating conditions and to minimize the contact resistance between the fault current limiting layer and the superconducting tape layer.

[0033] The fault current limiting stabilizing layer can be made of conductive materials with high resistivity at liquid nitrogen temperature, such as nickel-chromium alloy, stainless steel, and copper-nickel alloy. In this embodiment, both the inner fault current limiting stabilizing layer 22 and the outer fault current limiting stabilizing layer 26 are made of flexible stainless steel braided strips, but not limited to these. When the stainless steel braided strips are armored and welded with the superconducting strips, the quench resistance of the composite conductor layer can be significantly improved to achieve the overload protection function of the cable body.

[0034] In this embodiment, the inner insulating bushing 21, the middle insulating bushing 24, and the outer insulating bushing 27 are all constructed using, but not limited to, multi-layer polypropylene laminated paper wrapped under pressure. Since the outer insulating bushing 27 needs to be in direct contact with the liquid nitrogen in the outer liquid nitrogen channel 13, it can be made of, but not limited to, a flexible polytetrafluoroethylene sleeve, and is wrapped on multi-layer polypropylene laminated paper to form a composite insulating bushing, ensuring that the outer insulating bushing 27 maintains stable insulation performance during cable service.

[0035] The heat insulation shell 3 is used to reduce heat leakage from the cable body to the outside and to achieve a temperature transition from ultra-low temperature to room temperature. It includes a composite heat insulation layer 31 and an outermost metal sleeve 32. The multi-layer composite heat insulation layer 31 is disposed on the outside of the outer liquid nitrogen corrugated pipe 14, and the outermost metal sleeve 32 is wrapped around the outside of the multi-layer composite heat insulation layer 31.

[0036] The composite insulation layer 31 can be made of low thermal conductivity insulation materials such as multilayer aluminized polyester fiber film, multilayer glass fiber cloth, and aerogel insulation felt. In this embodiment, the multilayer aluminized polyester fiber film is wrapped around the outer liquid nitrogen corrugated pipe 14, and multilayer glass fiber cloth and aerogel insulation felt are wound around its outer side in sequence. Finally, a flexible polytetrafluoroethylene sleeve is used to armor the composite insulation layer 31.

[0037] The outermost metal sleeve 32 can be, but is not limited to, a stainless steel corrugated pipe.

[0038] Example 2:

[0039] Reference Figure 1 , Figure 2 , Figure 3 The superconducting charging cable designed in this embodiment includes: a cable skeleton and a liquid nitrogen passage 1, a composite conductor layer 2, and a heat insulation shell 3; the composite conductor layer 2 is wrapped around the inner layer of the cable skeleton 1 layer by layer; the heat insulation shell 3 is wrapped around the outer layer of the cable skeleton 1.

[0040] The structure of the cable skeleton, liquid nitrogen passage 1, and composite conductor layer 2 is the same as that of Example 1.

[0041] The insulating outer shell 3 includes a composite insulation layer 31 and an outermost metal sleeve 32; the multi-layer composite insulation layer 31 is disposed outside the outer liquid nitrogen corrugated pipe 14, and the outermost metal sleeve 32 wraps around the outside of the multi-layer composite insulation layer 31. Wherein:

[0042] The composite insulation layer 31 is composed of a radiation shield and a flexible vacuum interlayer. Radiation shields are set on the inner side of the outermost metal sleeve 32 and the outer side of the outer liquid nitrogen corrugated pipe 14, respectively. A flexible vacuum interlayer is set between the outermost metal sleeve 32 and the outer liquid nitrogen corrugated pipe 14. The flexible vacuum interlayer and the radiation shield together constitute the composite insulation layer 31.

[0043] The radiation shield can be made of, but is not limited to, metal reflective films such as aluminum foil and stainless steel, or ceramic fiber, carbon fiber, and glass fiber films.

[0044] The outermost metal sleeve 32 is made of the same material as that used in Example 1, namely, stainless steel corrugated pipe.

[0045] The fault current limiting effect of this invention can be verified by calculating the current carried by a single superconducting tape under an energy impact of 1kA fault current. The verification process is as follows:

[0046] The first step is to weld the fault current limiting and stabilizing layer armor onto the superconducting tape. The two are approximately in dense contact. For the sake of calculation simplicity, the following assumptions are made:

[0047] Assume that the fault-limiting current-stabilizing layer of the armor and the superconducting tape constitute a binary alloy composite conductor layer;

[0048] Assume that the fault inrush current passes uniformly through the aforementioned binary alloy composite conductor layer.

[0049] Since Bi-based superconducting tape is used in this embodiment, its quench resistance is approximately equivalent to the resistance of copper.

[0050] The second step, based on the above assumptions, is to calculate the superconducting tape as a two-dimensional planar structure:

[0051] Given a superconducting tape with thickness w = 1 mm, length L = 1 m, and width d = 5 mm, calculate its equivalent resistance R:

[0052]

[0053] Where, ρ Cu Let R be the resistivity of the superconducting tape, L be the length of the superconducting tape, w be the thickness of the superconducting tape, and d be the width of the superconducting tape; the calculated equivalent quench resistance of the superconducting tape is R = 0.0034Ω.

[0054] Take I F Taking a fault impulse current of 1kA as an example, assuming a fault time of t = 3s, calculate the Joule heat Q generated in the superconducting tape without an armored fault current-limiting layer during the fault current impulse:

[0055] Q = I F 2 Rt

[0056] Calculations show that in I F Under a fault current impact of 1kA, the Joule heat generated by the superconducting tape is approximately Q = 10kJ;

[0057] The third step, based on the above assumptions, is to treat the composite conductor layer after the armored fault current limiting and stabilizing layer as a planar two-dimensional configuration for calculation:

[0058] For the aforementioned planar two-dimensional superconducting tape, combined with the stainless steel braided tape fault current limiting and stabilizing layer selected in this embodiment, a 1mm thick stainless steel braided tape is armored onto the superconducting tape to form a composite conductor layer. At this time, the thickness w1 = 2mm, the width d1 = 5mm, and the length L = 1m of the composite conductor layer, and its equivalent resistivity ρ' can be calculated by the following formula:

[0059]

[0060] In the formula, ρ1 is the equivalent resistivity of the armored stainless steel braided tape, ρ2 is the equivalent resistivity of the original superconducting tape, L1 is the length of the armored stainless steel braided tape, and L2 is the length of the original superconducting tape; the calculated equivalent resistivity of the above composite conductor layer is ρ' = 7.33 × 10⁻⁶. -7 Ω / m,

[0061] The fourth step is to calculate the resistance R' of the composite conductor layer after the armored fault current limiting stabilization layer based on the calculated equivalent resistivity ρ':

[0062]

[0063] In the formula, ρ' is the equivalent resistivity of the composite conductor layer after the armor fault current limiting stabilization layer, L is the length of the composite conductor layer after the armor fault current limiting stabilization layer, w1 is the thickness of the composite conductor layer after the armor fault current limiting stabilization layer, and d1 is the width of the composite conductor layer after the armor fault current limiting stabilization layer; the calculated equivalent quench resistance R' of the above composite conductor layer is 0.0733Ω.

[0064] Step 5, with the initial I F Taking the Joule heat Q = 10kJ generated by a 1kA fault current surge as an example, calculate the fault current I of the composite conductor layer after the armored fault current limiting and stabilizing layer. F ':

[0065]

[0066] The calculation results show that the fault current of the composite conductor layer after the armored fault current limiting and stabilizing layer of the present invention is reduced by about 78.6%, which greatly improves the safety margin of the cable, and only causes an increase of 4mm in the diameter of the cable body.

Claims

1. A fault-limiting superconducting charging cable, comprising: The cable frame and liquid nitrogen passage (1), composite conductor layer (2), and heat insulation shell (3) are characterized by: The cable skeleton and liquid nitrogen channel (1) are constructed using two layers of flexible metal corrugated pipes, inner and outer, to support the cable conductor layer and bend within a set limit. The two layers of flexible metal corrugated pipes are an inner liquid nitrogen corrugated pipe (12) and an outer liquid nitrogen corrugated pipe (14). The inner liquid nitrogen corrugated pipe (12) has an inner liquid nitrogen channel (11) inside, and the outer liquid nitrogen corrugated pipe (14) has an outer liquid nitrogen channel (13) between it and the composite conductor layer (2). The conductor layer is supplied with a low-temperature working medium for cooling through these two channels (11, 13). The composite conductor layer (2) is composed of inner and outer superconducting tape layers (23, 25) and inner and outer fault current limiting and stabilizing layers (22, 26). The inner superconducting tape layer (23) has an inner fault current limiting and stabilizing layer (22) on its inner side, and the outer superconducting tape layer (25) has an outer fault current limiting and stabilizing layer (26) on its outer side. The cable itself can limit the overload current through these two fault current limiting and stabilizing layers (22, 26). The heat insulation shell (3) is composed of a composite heat insulation layer (31) and an outermost metal sleeve (32). The composite heat insulation layer (31) is located outside the outer liquid nitrogen corrugated pipe (14) to reduce heat leakage from the cable body to the outside. The outermost metal sleeve (32) is located outside the composite heat insulation layer (31). The two channels (11, 13) supply the conductor layer with a low-temperature working fluid for cooling. The fluid flows in from the inner liquid nitrogen channel (11) and flows out from the outer liquid nitrogen channel (13), forming a complete closed liquid nitrogen cycle. The inner fault current limiting stabilizing layer (22) and the inner superconducting tape layer (23) are fixed together; The external fault current limiting stabilizing layer (26) and the external superconducting tape layer (25) are fixed together; The inner and outer fault current limiting and stabilizing layers (22, 26) are both made of high resistivity conductive materials to improve the quench resistance when the cable body experiences a fault current surge and quench. The inner superconducting tape layer (23) and the outer superconducting tape layer (25) are both made of several high-temperature superconducting tapes wound at the same helix angle, and the inner superconducting tape layer (23) and the outer superconducting tape layer (25) are insulated from each other and the current directions are opposite. When the cable is working, the inner superconducting tape layer (23) serves as the negative electrode of the charging cable, and the outer superconducting tape layer (25) serves as the positive electrode of the charging cable. Together, they form a complete charging circuit. An inner insulating bushing (21) is provided between the inner liquid nitrogen bellows (12) and the inner fault current limiting and stabilizing layer (22). An intermediate insulating bushing (24) is provided between the inner superconducting tape layer (23) and the outer superconducting tape layer (25) to separate the inner and outer superconducting tape layers and realize the bidirectional high-power DC charging function of the superconducting cable. An outer insulating bushing (27) is provided between the outer fault current limiting stabilizing layer (26) and the outer liquid nitrogen channel (13). The inner, middle, and outer insulating bushings (21, 24, 27) are all made of multiple layers of insulating material to provide good insulation performance at the kilovolt voltage level.

2. The cable as described in claim 1, characterized in that, The composite insulation layer (31) is composed of multiple layers of low thermal conductivity material and is located between the outer liquid nitrogen corrugated pipe (14) and the outermost metal sleeve (32) to achieve good insulation effect without the need for a vacuum assembly.

3. The cable as described in claim 1, characterized in that, The composite insulation layer (31) is composed of a flexible vacuum insulation interlayer and a radiation shield. The flexible vacuum insulation interlayer is located between the outer liquid nitrogen corrugated pipe (14) and the outermost metal sleeve (32). The radiation shield is located on the outside of the outer liquid nitrogen corrugated pipe (14) and the inside of the outermost metal sleeve (32).

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