CN116344109A - 27.5kV bipolar self-shielding cable for electrified railway, intermediate connector and cable terminal - Google Patents

Abstract

The invention discloses a 27.5kV bipolar self-shielding cable for an electrified railway, an intermediate joint for the cable and a cable terminal structure, wherein the bipolar self-shielding cable comprises: the inner conductor, the inner conductor shielding layer, the insulating shielding layer, the outer conductor, the inner sheath, the armor layer, the wrapping tape and the outer sheath are sequentially sleeved from inside to outside. Compared with the traditional 27.5kV single-phase alternating-current crosslinked polyethylene insulated cable for the electrified railway, the bipolar self-shielding cable for the electrified railway has the advantages that: the product adopts a bipolar structural design, combines the original positive and negative cables into one, and realizes a concentric compact structural form of the positive and negative cables. The bipolar self-shielding cable structure for the electrified railway provided by the invention can effectively weaken harmonic electromagnetic interference of the traditional single-core alternating-current cable on other cables around while self-attaching shielding, reduce the line loss of the cable and improve the current carrying capacity of the cable.

Description

27.5kV bipolar self-shielding cable for electrified railway, intermediate connector and cable terminal

Technical Field

The invention relates to the technical field of wires and cables, in particular to a 27.5kV bipolar self-shielding cable for an electrified railway, an intermediate joint for the cable and a cable terminal structure.

Background

In recent years, with the large-scale construction of high-speed electrified railways nationally, the problems of power grid pollution and power quality caused by nonlinear loads (harmonics) of the electrified railways are increasing. In particular, the cable can generate skin effect and proximity effect under the influence of harmonic wave, so that the cable line generates additional heat, and the service life of the cable is reduced. In addition, the harmonic wave can also cause the increase of cable loss and the reduction of current carrying capacity, seriously affecting the stability and safety of the power supply system.

The positive pole and the negative pole of the single-phase alternating current crosslinked polyethylene insulated cable of traditional electric railway 27.5kV are usually by two cables, in narrow and small electric railway laying environment, its great volume and weight can increase the laying degree of difficulty, and the harmonic that just, negative pole cable produced can produce electromagnetic interference to nearby communication cable, instrument cable and communications facilities, causes the misjudgement risk easily, causes the safety problem.

Disclosure of Invention

Aiming at the problems that harmonic waves generated by the positive electrode and the negative electrode of the existing cable in the background technology can cause electromagnetic interference to nearby communication cables, instrument cables, communication equipment and the like, so that misjudgment risks are caused, safety accidents are caused and the like, the invention provides a 27.5kV bipolar self-shielding cable for an electrified railway.

The invention is realized by the following technical scheme:

27.5kV bipolar self-shielding cable for electrified railway, characterized in that the bipolar self-shielding cable comprises: the inner conductor, the inner conductor shielding layer, the insulating shielding layer, the outer conductor, the inner sheath, the armor layer, the wrapping tape and the outer sheath are sequentially sleeved from inside to outside.

Specifically, the 27.5kV bipolar self-shielding cable for the electrified railway is designed by the invention, and compared with a traditional 27.5kV single-phase alternating-current crosslinked polyethylene insulated cable for the electrified railway: the product adopts a bipolar structural design, combines the original positive and negative cables into one, and realizes a concentric compact structural form of the positive and negative cables. The bipolar self-shielding cable structure designed by the invention can effectively weaken the harmonic electromagnetic interference of the traditional single-core alternating-current cable to other cables around while self-attaching shielding, reduce the line loss of the cable and improve the current carrying capacity of the cable. In addition, the bipolar self-shielding cable has better protection capability on the wire core structure by the outer conductor (outer conductor), and the cable structure after the optimal design is more compact and stable, has better electrical and physical stability than the traditional cable, can meet the requirements of diversified electrified railway laying and operating environments by the organic combination of the outer conductor and the sheath material, and is a high-cost performance cable integrating the performances of stability, safety, economy, environmental protection, energy conservation and the like.

Further, 27.5kV bipolar self-shielding cable for electrified railway: the inner conductor is formed by twisting copper wires and compacting or is formed by twisting strand block conductors.

Specifically, the inner conductor adopts a structure formed by twisting and compacting copper wires or twisting strand conductors, so that the cable has good electrical performance and relatively smaller cable outer diameter. The pitch of the twisted wire is reasonably controlled in the design and manufacturing process, so that the cable has certain flexibility while ensuring good electrical performance, and can be continuously bent and conveniently installed in a narrow space, thereby being convenient and quick.

Further, 27.5kV bipolar self-shielding cable for electrified railway: the inner conductor shielding layer, the insulating layer and the insulating shielding layer adopt a three-layer extrusion-supplying structure.

Preferably, the insulating layer is made of cross-linked polyethylene (XLPE).

Further, 27.5kV bipolar self-shielding cable for electrified railway: the bipolar self-shielding cable further comprises a cushion layer, wherein the cushion layer is arranged between the insulating shielding layer and the outer conductor; the pad layer adopts the semiconductive belt, the pad layer be used for keeping apart insulating shield with the outer conductor prevents that the outer conductor from stabbing insulating shield.

Preferably, in order to prevent the outer conductor from damaging the insulation shield, the bipolar self-shielding cable designed by the invention is buffered by wrapping a semi-conductive tape (cushion layer) on the outer side of the insulation shield.

Further, 27.5kV bipolar self-shielding cable for electrified railway: the outer conductor is made of round copper wires or special-shaped copper monofilaments through winding or wrapping, and the winding is round.

Specifically, the design section of the outer conductor should be determined according to the current requirement, and is generally selected to be consistent with the nominal section of the inner conductor, and the process of the outer conductor can be determined according to the nominal section. Taking a copper wire winding process as an example, when one layer of copper wire cannot meet the section requirement, a multi-layer structure can be adopted, contact among the multi-layer copper wires is ensured, and copper strips or semi-conductive tape strips are adopted when the multi-layer copper wire needs to be fastened.

Specifically, the outer conductor structure designed by the invention can reduce electromagnetic interference of harmonic waves generated by the positive electrode and the negative electrode to other peripheral communication cables while playing a role in self-shielding, ensuring stable electrical performance and reliable transmission performance, and weakening skin effect and proximity effect generated under the influence of the harmonic waves, thereby really achieving the effects of environmental protection and energy saving. And (3) injection: the skin effect is also called skin effect, and when an alternating current passes through a conductor, the current will concentrate on the surface of the conductor and flow through it. Skin effect is a term of electromagnetics, eddy current. The phenomenon is that a magnetic field with opposite directions is generated on the surface of a non-energized ferromagnetic material by the energized ferromagnetic material, and the current cutting magnetic lines is generated by the magnetic field, and the current is a so-called vortex current, and is a skin effect.

Further, 27.5kV bipolar self-shielding cable for electrified railway: the bipolar self-shielding cable further comprises a copper strip, wherein the copper strip is arranged between the outer conductor and the inner sheath, and the copper strip is arranged on the surface of the outer conductor in a clearance or overlapping winding mode.

Preferably, the copper strip designed by the invention can prevent the conductive performance from being influenced by broken copper wires of the outer conductor; on the other hand, the cable structure outer diameter can be optimized, and the anti-interference performance of the outer conductor can be improved.

Further, 27.5kV bipolar self-shielding cable for electrified railway: the inner sheath is used for isolating the outer conductor from the armor layer; the inner sheath is formed by extruding PVC, polyethylene or a material with flame retardant, fire-resistant, halogen-free and low-smoke flame retardant properties; the outer sheath is formed by extruding and wrapping a material with single or combined performance of flame retardance, halogen-free performance and low smoke performance.

Specifically, the inner sheath is formed by extruding and wrapping halogen-free low-smoke flame-retardant polyolefin materials with high crusting and low heat value release performance or other materials capable of meeting specific requirements of the electrified railway, such as PVC, polyethylene or materials with flame retardant, fire-resistant, halogen-free low-smoke flame retardant performance. The inner sheath is used for isolating the outer conductor and the armor layer, and plays a role in preventing the outer conductor from being damaged by the armor layer.

Further, 27.5kV bipolar self-shielding cable for electrified railway: the armor layer adopts a single-layer metal wire tightly-wound structure or adopts a metal belt overlapped-wound structure; the single-layer metal wire is selected from one of an aluminum wire, a copper wire, a steel wire or an aluminum alloy wire; the metal belt is selected from brass belt or nonmagnetic steel belt.

Specifically, the armor layer can prevent mechanical damage and ensure the integrity of the cable structure and the stability of the electrical performance.

The middle joint for the electric railway is characterized in that the middle joint is used for connecting any two sections of bipolar self-shielding cables for the electric railway into a whole;

the intermediate joint comprises: the connector comprises a connector outer protective layer, an armor layer connecting wire, an outer conductor connecting pipe, a connector insulating main body and an inner conductor connecting pipe;

wherein: the inner conductor connecting pipe is used for connecting inner conductors in the two sections of cables and recovering the connection of the inner conductors; the joint insulation main body is used for recovering insulation at the joint of two sections of cables and controlling an electric field; the outer conductor connecting pipe is used for butt-jointing outer conductors in the two sections of cables; the armor layer connecting wire is used for realizing the electric connection of armor layers in the two-section cable; the outer protective layer of the connector is used for restoring the sealing of the cable connection part and providing mechanical protection.

The cable terminal structure is characterized in that the cable terminal structure is used for realizing the electric connection between the bipolar self-shielding cable for the electrified railway and external equipment;

the cable termination structure includes: the cable terminal comprises an armor layer grounding wire, an outer conductor grounding wire, a sealing structure, a cable terminal main body and a connecting terminal;

wherein: the connecting terminal is used for realizing the electrical connection between the inner conductor in the cable and external equipment; the cable terminal main body is used for controlling an electric field at the stripped part of the cable and realizing insulation recovery; the outer conductor in the cable is stranded and led out to be connected with the outer conductor grounding wire, and the outer conductor grounding wire is connected with a copper terminal for grounding connection of the outer conductor; the armor layer grounding wire is used for leading out an armor layer in the cable to be grounded; the sealing structure is used for sealing the stripped part of the cable and providing mechanical protection.

The intermediate connector and the cable terminal are used as accessories of the cable and are matched with the cable.

The invention has the beneficial effects that:

(1) The 27.5kV bipolar self-shielding cable for the electrified railway can effectively save the cable laying cost, optimize the laying space and has higher cost performance: the 27.5kV bipolar self-shielding cable for the electrified railway is upgraded on the basis of a traditional 27.5kV single-phase alternating-current crosslinked polyethylene insulated cable for the electrified railway, and the original two cables are combined into one by adopting a bipolar structural design, so that the positive and negative electrodes of the cables are integrated in the same cable, the cable structure is greatly simplified, the compact structure, the light weight and the small volume of the cable are effectively ensured, the laying difficulty is greatly reduced, the laying workload and the cost are reduced, and the laying space is optimized. Meanwhile, the bipolar concentric type cable structure after the optimal design of the invention not only can ensure stable electrical and mechanical properties, but also is suitable for various laying environment requirements, and has higher cost performance than the traditional electrified railway cable.

(2) The 27.5kV bipolar self-shielding cable for the electrified railway has double anti-interference performance, can effectively reduce harmonic pollution in a power grid, and has higher safety and reliability: the cable designed by the invention adopts a bipolar structural design, and can play a role in dual anti-interference; firstly, the product organically integrates the traditional two positive and negative cables into the same cable, the concentric structure of the positive and negative electrodes greatly reduces the distance between the positive and negative electrodes of the cable, effectively reduces the harmonic electromagnetic interference of the single-phase alternating current cable to other cables in a narrow laying space, and is first anti-interference, namely, the interference of the single-phase alternating current cable to the outside. Then, the cable after optimization and upgrading can also protect itself from external interference under the structure of self-negative shielding, so that the signal transmission effect under the electrified railway laying environment is better, and the second interference is the second interference.

(3) The bipolar cable structure designed by the invention can reduce harmonic waves generated between the positive electrode and the negative electrode, further reduce harmonic pollution to a power grid, protect the quality of the power grid, further weaken the additional heating phenomenon of a cable line caused by harmonic interference and prolong the service life of the cable. Meanwhile, the cable structure after the optimization design of the invention is more stable, the corresponding electrical performance is better than that of the traditional structure, the electric field intensity distribution after improvement is more uniform, and the safety and reliability are better.

(4) The 27.5kV bipolar self-shielding cable for the electrified railway can reduce transmission loss, improve the current carrying capacity of the cable, and effectively realize cost reduction and energy saving in the cable industry: the product simplifies the ground wire of the original multi-core cable into a metal shielding structure on the coaxial cable, is not only beneficial to structural compensation of the cable, but also reduces the transmission loss of a cable line while overcoming harmonic interference, and improves the current carrying capacity of the electrified railway cable. Compared with the traditional electrified railway cable, the improved single-core alternating-current cable can achieve the effects of reducing loss and improving the current carrying capacity by about 10% while ensuring that the cable reactance is basically unchanged, and can effectively achieve cost reduction and energy saving in the cable industry. In addition, the bipolar structure of the invention can optimize the production procedure and process of the electrified railway cable, thereby not only greatly reducing the production and manufacturing cost, but also improving the production efficiency and quality and being more beneficial to the production and manufacturing of enterprises.

(5) The cable accessory (cable intermediate joint and cable terminal structure) designed by the invention has reasonable structure, can realize reliable connection of the inner conductor and the outer conductor of the cable, and can recover the insulation performance of the stripping part of the cable: compared with the conventional cable accessory, the design of the cable accessory fully considers the reliability of the connection of the outer conductor and the recovery of the current carrying capacity of the outer conductor. According to the invention, through the designed cable terminal and the middle joint, the insulation performance, the through-current capability and the mechanical protection performance of the cable end part and the cable butt joint part can be completely recovered, and the requirements of connecting and laying the medium-voltage coaxial cable of the electrified railway under different environments can be met.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of a bipolar self-shielding cable for an electrified railway according to embodiment 1 of the present invention;

fig. 2 is a schematic structural diagram of a bipolar self-shielding cable for an electrified railway according to embodiment 2 of the present invention;

fig. 3 is a schematic structural view of an intermediate joint for cables according to the present invention;

fig. 4 is a schematic structural diagram of a cable terminal provided by the invention.

The marks in the figure: 1 inner conductor, 2 inner conductor shielding layer, 3 insulating layer, 4 insulating shielding layer, 5 cushion layer, 6 outer conductor, 7 copper strip, 8 inner sheath, 9 armor layer, 10 belting, 11 outer sheath; the cable comprises a 12 joint outer protective layer, a 13 armor layer connecting wire, a 14 outer conductor connecting pipe, a 15 joint insulating main body, a 16 inner conductor connecting pipe, a 17 armor layer grounding wire, a 18 outer conductor grounding wire, a 19 sealing structure, a 20 cable terminal main body and a 21 connecting terminal.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In the description of the present invention, it should be understood that the terms "upper," "lower," "left," "right," "top," "bottom," and the like indicate orientations or positional relationships, merely to facilitate describing the present invention and simplify the description, and do not indicate or imply that the devices or elements being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may include one or more of the feature, either explicitly or implicitly. Moreover, the terms "first," "second," and the like, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein.

Example 1

As shown in fig. 1, a 27.5kV bipolar self-shielding cable for an electrified railway, wherein the bipolar self-shielding cable includes: the inner conductor 1, the inner conductor shielding layer 2, the insulating layer 3, the insulating shielding layer 4, the cushion layer 5, the outer conductor 6, the copper strip 7, the inner sheath 8, the armor layer 9, the wrapping tape 10 and the outer sheath 11 are sleeved in sequence from inside to outside;

wherein: the inner conductor 1 is formed by twisting and compacting copper wires or is formed by twisting strand block conductors;

the inner conductor shielding layer 2, the insulating layer 3 (XLPE) and the insulating shielding layer 4 adopt a three-layer extrusion-supplying structure;

the cushion layer 5 is made of a semi-conductive tape and is used for isolating the insulating shield 4 from the outer conductor 6, so that the outer conductor 6 is prevented from being crushed and the insulating shield 4 is prevented from being punctured, and the cushion layer plays a role in isolating and buffering;

the outer conductor 6 is made of round copper wires or special-shaped copper monofilaments through winding or wrapping, and is round and round; specifically, the outer conductor 6 is wound by adopting the scheme shown in the following table 1 to meet the requirements of different laying occasions; the design section of the outer conductor 6 is determined according to the current requirement, and a conductor which is consistent with the nominal section of the inner conductor 1 is generally selected, and the process of the conductor can be determined according to the nominal section; taking a copper wire winding process as an example, when a layer of copper wire cannot meet the section requirement, a multi-layer structure can be adopted, contact among the multi-layer copper wires is ensured, and copper strips or semi-conductive tape strips are adopted when the copper wires need to be fastened;

the copper strip 7 is arranged between the outer conductor 6 and the inner sheath 8, the copper strip 7 is arranged on the surface of the outer conductor 6 in a clearance or overlapping wrapping way, the copper strip 7 is used for preventing the copper wire broken wire in the outer conductor 6 from influencing the conductivity, and meanwhile, the cable structure outer diameter can be optimized, and the anti-interference performance can be improved;

the inner sheath 8 is used for isolating the outer conductor 6 from the armor layer 9; specifically, the inner sheath 8 is made of halogen-free, low-smoke and flame-retardant polyolefin materials with high crust and low heat value release performance or other materials capable of meeting specific requirements of the electrified railway (see table 2), for example, is formed by extrusion of PVC, polyethylene or materials with flame-retardant, fire-resistant, halogen-free, low-smoke and flame-retardant performances, and the inner sheath 8 is used for isolating the outer conductor 6 from the armor layer 9 and plays a role in preventing the outer conductor 6 from being crushed and damaged by the armor layer 9;

the armor layer 9 is formed by tightly wrapping a single-layer metal wire, wherein the metal wire can be one of an aluminum wire, a copper wire, a steel wire and an aluminum alloy wire, as shown in fig. 1;

the outer sheath 11 is made of a halogen-free low-smoke flame retardant polyolefin material with high cracking resistance, high crust formation and low heat value release performance or other materials capable of meeting specific requirements of the electrified railway, such as a material with single or combined performance requirements of flame retardance, halogen free, low smoke and the like (see table 2) through extrusion.

Specifically, for the actual material selection of the inner sheath 8 and the outer sheath 11, the selection schemes listed in table 3 can be referred to or any combination can be performed according to the actual requirements, so as to meet the performance requirements of specific laying or use occasions.

Example 2

Example 2 differs from example 1 in that: the armor layer 9 described in example 2 is a metal tape overlapping wrap structure and the metal tape is selected from brass tape or nonmagnetic steel tape; the bipolar self-shielded cable for an electrified railway provided in embodiment 2 has a structure as shown in fig. 2.

Table 1 shows the winding process of the outer conductor

Table 2 shows jacket materials

Table 3 shows the material selection scheme for the outer conductor winding, the inner sheath and the outer sheath and the applicable scenario

The invention provides a material selection scheme suitable for laying various electrified railways and suitable for the environment, and can meet the diversified performance requirements of the electrified railways.

The 27.5kV bipolar self-shielding cable for the electrified railway provided by the invention considers various outer conductor schemes to be suitable for different laying environment requirements under the condition of ensuring the electrical performance and quality requirements of the cable, and simultaneously provides a diversified sheath material scheme which can meet the requirements of the electrified railway cable under different running environments.

Example 3

As shown in fig. 3, an intermediate joint for a cable is provided, which is used for connecting any two sections of bipolar self-shielding cables for electrified railways provided in the above embodiment 1 into a whole; the intermediate joint comprises: a joint outer shield layer 12, an armor layer connecting wire 13, an outer conductor connecting pipe 14, a joint insulating body 15, and an inner conductor connecting pipe 16;

wherein: the inner conductor connecting pipe 16 is used for connecting the inner conductors 1 in the two sections of cables and restoring the connection of the inner conductors 1;

the joint insulating main body 15 is used for recovering the insulation of the joint of two sections of cables and controlling the electric field; the joint insulating main body is a silicone rubber integrated joint insulating main body;

the outer conductor connecting pipe 14 is used for butt-jointing the outer conductors 6 in the two sections of cables; the armor connecting wire 13 is used for realizing the electrical connection of the armor 9 in the two-section cable; the outer protective layer 12 of the joint is used to restore the seal at the cable junction and to provide mechanical protection.

Example 4

As shown in fig. 4, there is provided a cable termination structure for realizing the electrical connection between the bipolar self-shielded cable for an electrified railway and an external device according to the above-described embodiment 1;

the cable termination structure includes: an armor layer ground wire 17, an outer conductor ground wire 18, a sealing structure 19, a cable termination body 20, and a connection terminal 21;

wherein: the connecting terminal 21 is used for realizing the electrical connection between the inner conductor 1 in the cable and external equipment; the cable terminal body 20 is used for controlling an electric field at a cable stripping position and realizing insulation recovery; the outer conductor 6 in the cable is stranded and led out to be connected with the outer conductor grounding wire 18, and a copper terminal is connected to the outer conductor grounding wire 18 and used for grounding connection of the outer conductor 6; the armor layer grounding wire 17 is used for leading out an armor layer 9 in the cable to be grounded; the sealing structure 19 is used for sealing the stripped part of the cable and providing mechanical protection; the sealing structure 19 is made of sealant or heat-shrinkable tube; the cable termination body 20 is integrally molded.

The above-described preferred embodiments of the present invention are only for illustrating the present invention, and are not to be construed as limiting the present invention. Obvious changes and modifications of the invention, which are introduced by the technical solution of the present invention, are still within the scope of the present invention.

Claims (10)

1. 27.5kV bipolar self-shielding cable for electrified railway, characterized in that the bipolar self-shielding cable comprises: the inner conductor (1), the inner conductor shielding layer (2), the insulating layer (3), the insulating shielding layer (4), the outer conductor (6), the inner sheath (8), the armor layer (9), the wrapping tape (10) and the outer sheath (11) are sequentially sleeved from inside to outside.

2. The 27.5kV bipolar self-shielding cable for the electrified railway according to claim 1, wherein the inner conductor (1) is formed by tightly twisting copper wires or by twisting strand block conductors.

3. The 27.5kV bipolar self-shielding cable for the electrified railway according to claim 1, wherein the inner conductor shielding layer (2), the insulating layer (3) and the insulating shielding layer (4) adopt a three-layer extrusion-feeding structure.

4. The 27.5kV bipolar self-shielded cable for an electrified railway according to claim 1, further comprising a bedding layer (5), the bedding layer (5) being disposed between the insulating shielding layer (4) and the outer conductor (6);

the insulating shielding device is characterized in that the cushion layer (5) is a semi-conductive belt, and the cushion layer (5) is used for isolating the insulating shielding (4) and the outer conductor (6) and preventing the outer conductor (6) from being crushed and puncturing the insulating shielding (4).

5. 27.5kV bipolar self-shielded cable for electrified railways according to claim 1, characterized in that the outer conductor (6) is made of round copper wire or wound or wrapped with profiled copper monofilament and is subject to rounding of winding.

6. The 27.5kV bipolar self-shielding cable for an electrified railway according to claim 1, further comprising a copper strip (7), wherein the copper strip (7) is disposed between the outer conductor (6) and the inner sheath (8), and the copper strip (7) is disposed on the surface of the outer conductor (6) in a gap or overlapping wrapping manner.

7. 27.5kV bipolar self-shielded cable for electrified railways according to claim 1, characterized in that said inner sheath (8) is used to isolate said outer conductor (6) from said armor layer (9); the inner sheath (8) is formed by extruding PVC, polyethylene or a material with flame retardant, fire-resistant, halogen-free and low-smoke flame retardant properties;

the outer sheath (11) is formed by extruding and wrapping a material with single or combined performance of flame retardance, halogen-free performance and low smoke performance.

8. 27.5kV bipolar self-shielding cable for electrified railway according to claim 1, characterized in that said armor layer (9) adopts a single-layer wire tight-wrapping structure or adopts a metal tape overlapping-wrapping structure; the single-layer metal wire is selected from one of an aluminum wire, a copper wire, a steel wire or an aluminum alloy wire; the metal belt is selected from brass belt or nonmagnetic steel belt.

9. An intermediate joint for cables, which is characterized in that the intermediate joint is used for connecting any two sections of 27.5kV bipolar self-shielding cables for electrified railways as a whole;

the intermediate joint comprises: a joint outer protection layer (12), an armor layer connecting wire (13), an outer conductor connecting pipe (14), a joint insulating main body (15) and an inner conductor connecting pipe (16);

wherein: the inner conductor connecting pipe (16) is used for connecting the inner conductors (1) in the two sections of cables and restoring the connection of the inner conductors;

the joint insulation main body (15) is used for recovering insulation at the joint of two sections of cables and controlling an electric field;

the outer conductor connecting pipe (14) is used for butt-jointing the outer conductors (6) in the two sections of cables;

the armor layer connecting wire (13) is used for realizing the electric connection of the armor layers (9) in the two-section cable;

the outer protective layer (12) of the joint is used for restoring the sealing of the joint of the cable and providing mechanical protection.

10. A cable termination structure for effecting electrical connection between the 27.5kV bipolar self-shielding cable for an electrified railway of any one of claims 1 to 8 and an external device;

the cable termination structure includes: an armor layer ground wire (17), an outer conductor ground wire (18), a sealing structure (19), a cable terminal body (20) and a connection terminal (21);

wherein: the connecting terminal (21) is used for realizing the electrical connection between the inner conductor (1) in the cable and external equipment;

the cable terminal main body (20) is used for controlling an electric field at a cable stripping position and realizing insulation recovery;

the outer conductor (6) in the cable is stranded and led out to be connected with the outer conductor grounding wire (18), and the outer conductor grounding wire (18) is connected with a copper terminal for grounding connection of the outer conductor (6);

the armor layer grounding wire (17) is used for leading out an armor layer (9) in the cable to be grounded;

the sealing structure (19) is used for sealing the stripped part of the cable and providing mechanical protection.

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