Medium-voltage waterproof and fireproof cable

Abstract

The utility model provides a medium-voltage waterproof and fireproof cable, which comprises a conductor and an extrusion shielding layer coated outside the conductor. The insulating layer is coated outside the extrusion shielding layer; the metal shielding layer is coated outside the insulating layer; the thermal insulation layer is coated outside the metal shielding layer; the heat insulation layer is coated with the cooling layer; the cooling layer is coated with the fireproof layer; and the sheath is coated outside the fireproof layer. The cable has a good waterproof effect.

Description

Technical Field

[0001] The utility model relates to the field of cables, in particular to a medium-voltage waterproof and fireproof cable. Background Art

[0002] The sheath and insulation of cables are typically made of plastic and rubber, making them highly susceptible to fires in densely populated areas. These locations are primarily concentrated in densely populated areas such as high-rise buildings, subways, large entertainment venues, and major national projects like nuclear power plants, petrochemical plants, tunnels, airports, large industrial and mining enterprises in the postal and telecommunications sector, and underground engineering projects. These cable installations place high demands on the cable's flame retardancy and fire resistance. Flame-retardant cables can only confine combustion to a specific area; in the event of a fire, the cables should not be energized. However, in critical locations, personnel evacuation, corridor lighting, fire alarms, automatic firefighting systems, and other emergency equipment all require that the cables remain energized for a specified period of time. Therefore, fire-resistant cables have emerged as a necessity. Currently, the voltage level of fire-resistant power cables is mostly concentrated at 1kV and below. However, if some large high-rise buildings and major national key projects use 0.6 / 1kV low-voltage power distribution as a convention, the cable usage and installation workload will increase by dozens of times compared to ordinary buildings, and the cable laying space will increase several times, which will not only consume materials but also energy. In addition, the excessive number and size of cables in the building will also have an adverse impact on safe use. Therefore, in places like these that require both medium and high voltage power transmission and distribution and flame retardancy and fire resistance, medium and high voltage fire-resistant power cables must be used.

[0003] Typically, low-voltage fire-resistant cables do not require an insulating shield. Instead, the fire-resistant insulation layer can be applied directly to the conductor surface, ensuring insulation performance at flame temperatures. There are three main types of fire-resistant cables: magnesium oxide insulation with a copper tube (BTT2) or steel tube (MI) jacket; mica tape-wrapped fire-resistant cables; and silicone rubber insulation, which generates silicon dioxide (SiO2) upon combustion to provide a fire barrier.

[0004] For medium and high voltage fire-resistant cables of 6kV and above, their structural design must meet the requirements of high voltage resistance and flame retardancy and fire resistance at the same time. Medium and high voltage power cables require a semi-conductive shielding layer between the conductor and the insulation to achieve the effect of uniform electric field. Flame retardant and fire-resistant cables are required to be flame retardant, fire-resistant, halogen-free, low halogen, low smoke and low toxic. That is, they are required to block and delay the spread of flames along the wires and cables to prevent the fire from expanding; they can maintain operation for a certain period of time and maintain the integrity of the line under the condition of flame combustion; the materials constituting the wires and cables do not contain halogens, and the corrosion of the combustion products is low: the materials constituting the wires and cables may contain halogens, but the content is low; the smoke generated when the wires and cables burn is less and the light transmittance is higher; the gas generated when the wire and cable materials burn is less toxic.

[0005] However, when existing cables are installed underground or in relatively humid environments, they easily absorb water vapor in the air. The probability of cross-linked polyethylene generating water trees when it is exposed to moisture and then operated under voltage is greatly increased. When the water trees grow to a certain length, permanent electrical tree defects will form at the tips of the water trees, and the cable insulation will be punctured in a short period of time, causing power outages or fires. Utility Model Content

[0006] The utility model aims to overcome the above-mentioned defects and provide a medium-voltage waterproof and fireproof cable with good moisture-proof performance.

[0007] The utility model provides a medium-voltage waterproof and fireproof cable, which is characterized by comprising:

[0008] conductor,

[0009] Extruded shielding layer, covering the outside of the conductor;

[0010] Insulation layer, covering the outside of the extruded shielding layer;

[0011] Metal shielding layer, covering the outside of the insulation layer;

[0012] A heat-insulating layer, covering the outside of the metal shielding layer;

[0013] A cooling layer, covering the outside of the thermal insulation layer;

[0014] Fireproof layer, covering the outside of the cooling layer;

[0015] The sheath is covered on the outside of the fireproof layer.

[0016] Furthermore, the utility model provides a medium-voltage waterproof and fireproof cable, which is also characterized in that the above-mentioned extruded shielding layer adopts a cross-linkable semi-conductive shielding material.

[0017] Furthermore, the utility model provides a medium voltage waterproof and fireproof cable, which is also characterized by:

[0018] The thickness of the extruded shielding layer is controlled at 0.5-0.7 mm.

[0019] Furthermore, the utility model provides a medium voltage waterproof and fireproof cable, which is also characterized by:

[0020] The above-mentioned insulation layer adopts cross-linked polyethylene insulation material.

[0021] Furthermore, the utility model provides a medium voltage waterproof and fireproof cable, which is characterized in that: the metal shielding layer is formed by overlapping and wrapping soft copper tape, and the average overlap rate is not less than 15%. Furthermore, the utility model provides a medium voltage waterproof and fireproof cable, which is characterized in that:

[0022] The thickness of the metal shielding layer is 0.05-0.10 mm.

[0023] Furthermore, the utility model provides a medium-voltage waterproof and fireproof cable, which is also characterized in that the above-mentioned thermal insulation layer is filled with inorganic fiber material and wrapped with inorganic fiber tape.

[0024] Furthermore, the utility model provides a medium voltage waterproof and fireproof cable, which is also characterized by:

[0025] The cooling layer is made of inorganic metal hydrate.

[0026] Furthermore, the utility model provides a medium-voltage waterproof and fireproof cable, which is also characterized in that the above-mentioned fireproof layer is made of ceramic polymer composite fire-resistant silicone rubber.

[0027] Furthermore, the utility model provides a medium-voltage waterproof and fireproof cable, which is also characterized in that the above-mentioned moisture-proof layer is a longitudinally wrapped layer of aluminum-plastic composite tape, and the overlapping rate of the longitudinal wrapping is not less than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 , a schematic structural diagram of a medium-voltage waterproof and fireproof cable provided in this embodiment; DETAILED DESCRIPTION

[0029] The present invention is capable of various modifications and embodiments, and therefore specific embodiments are illustrated and described in the accompanying drawings. However, this is not intended to limit the present invention to specific embodiments, but rather should be understood to include all modifications, equivalents, and even substitutes that fall within the spirit and technical scope of the present invention.

[0030] like Figure 1 As shown, this embodiment provides a medium-voltage waterproof and fireproof cable, characterized by comprising:

[0031] Conductor 1. The conductor is made of oxygen-free copper wire with high conductivity. In order to ensure that the product has good electrical properties and a certain degree of flexibility, and is easy to install and lay, the cross-section is reasonably controlled during the design and manufacturing process. The conductor's compression degree reaches more than 90%, and the roundness reaches more than 98%. The conductor surface is smooth and free of burrs and scratches. The cross-sectional area is 500m 2 Conductors of this size and above must be wrapped with semi-conductive tape.

[0032] Extruded shield layer 2, covering the conductor, is made of a cross-linked semi-conductive material with a thickness of approximately 0.5-0.7mm. The conductor shield, insulation layer, and insulation shield are extruded simultaneously using a three-layer co-extrusion process, ensuring uniform thickness and close coverage of the conductor shield, insulation, and insulation shield layers. The maximum partial discharge (PD) at 1.73U does not exceed 5pc.

[0033] Insulation layer 3, covering the outside of the extruded shielding layer, is made of cross-linked polyethylene insulation material with good flexibility, mechanical strength and electrical properties. While ensuring the electrical insulation performance of the cable, it also enhances the tensile strength and anti-extrusion performance of the insulation layer;

[0034] The metal shielding layer 4 is coated on the outside of the insulating layer and is formed by overlapping and wrapping the cable soft copper tape with a thickness of 0.05-0.10mm, with an average overlap rate of not less than 15%;

[0035] The thermal insulation layer 5, wrapped around the metal shielding layer, is filled with inorganic fiber material and wrapped with inorganic fiber tape. When flames strike the cable, the highly flame-retardant inorganic fiber filling and tape decompose into metal oxides and release crystalline water. The decomposed metal oxides form a network structure that has a certain adsorption effect on smoke. The crystalline water not only has a significant sedimentation effect on smoke particles, but also has a good heat absorption effect. In addition, a salty carbonized structure is formed during the combustion process. This carbonized layer hinders the supply of air and the flow of combustible gases, thereby effectively protecting the insulation layer.

[0036] The cooling layer 6, covering the exterior of the insulation layer, is made of an inorganic metal hydrate (magnesium hydroxide). Due to its excellent thermal conductivity and flame retardancy, it fully ensures the cable's high flame retardancy. During the cable combustion process, this material, upon encountering high temperatures, precipitates crystallized water and decomposes into metal oxides. The metal oxides adsorb onto the surface of the refractory layer, forming a porous shell. This shell has a certain adsorption effect on smoke, while the precipitated water also effectively cools and protects the refractory layer.

[0037] The fireproof layer 7, covering the cooling layer, is made of a ceramicized polymer composite fire-resistant silicone rubber. When subjected to flame erosion, organic matter is rapidly ablated and then quickly transformed into a hard ceramic-like substance during the ceramicization reaction, forming a strong insulating layer that blocks further flame combustion and provides excellent fire protection. While ordinary polymer materials are reduced to ash after flame erosion, ceramicized fire-resistant silicone rubber can sinter into a hard, porcelain-like structure at flameless temperatures exceeding 500°C and flame erosion temperatures exceeding 620°C. The longer the ablation time and the higher the temperature, the more pronounced the ceramicization effect, with a maximum ablation temperature of 3000°C. Ceramicized fire-resistant silicone rubber can be produced using conventional rubber processing equipment, and the resulting products possess all the properties of silicone rubber and exhibit excellent processability. The main chain of ceramicized fire-resistant silicone rubber is Si-O bonds. Main chain cleavage and oxidation of side groups are the primary reactions of silicone rubber in a high-temperature oxygen atmosphere. The main chain breaks to form cyclic siloxanes, softening the silicone rubber. Oxidation of the side groups generates active free radicals, which react with each other, causing the silicone rubber to crosslink and harden. Above 300°C, the silicon-carbon bonds in the silicone rubber's side chains also cleave, forming crosslinks between the molecules. At higher temperatures, the ash burns to form silicon oxide, forming a barrier layer composed of carbon, silicon, and oxygen on the surface. This barrier layer is powdery, discontinuous, and weak, making it difficult to provide thermal insulation or fire resistance alone. Ceramicized fire-resistant silicone rubber is a material that forms a hard, ceramic-like structure after combustion at high temperatures. The ceramicization process involves the continuous solidification and binding of the silicone rubber combustion products, tightly binding the dispersed, loose, and discontinuous inorganic particles. Because both the formation mechanism and the final product resemble ceramic, it is aptly called ceramicized silicone rubber. This ceramicized material possesses the advantages of ceramic, including insulation, heat resistance, fire resistance, water resistance, shock resistance, and low thermal weight loss.

[0038] The moisture-proof layer 8 is coated on the outside of the fireproof layer. When a layer of aluminum-plastic composite tape is longitudinally wrapped, the overlap rate of the longitudinal wrapping is not less than 20%;

[0039] The sheath 9 is covered on the outside of the moisture-proof layer. The sheath is made of halogen-free low-smoke flame-retardant material and is a large cable sheath with metal armor.

[0040] Performance test and product parameters:

[0041] 1. Basic characteristics

[0042] (1) The rated power frequency voltage U is 3.6 / 6kV to 26 / 35kV.

[0043] (2) The allowable long-term operating temperature of the cable conductor is: 90°C

[0044] (3) The allowable short-circuit temperature of the cable conductor is: no more than 250℃, and the duration is no more than 5 seconds.

[0045] (4) The ambient temperature for cable laying should not be lower than 0℃, and it should be preheated if it is lower than 0℃.

[0046] (5) Minimum bending radius during cable laying: single-core cable ≥20 (D + d) ± 5% m, three-core cable ≥15 (D + d) ± 5% m, where D is the outer diameter of the cable and d is the outer diameter of the conductor.

[0047] (6) Voltage can be applied to the cable, and the cable will not break down when powered for 90 minutes under 950°C flame conditions.

[0048] 2. Product technical characteristics

[0049] (1) The DC resistance of the conductor of the finished cable at 20°C shall comply with the provisions of GB / T3956;

[0050] (2) The elongation at break before insulation aging is ≥ 200%, and the tensile strength is ≥ 12.5 MPa; the change rate of elongation at break after insulation aging (135°C, 168h) is ≤ ± 25%, and the change rate of tensile strength is ≤ ± 25%;

[0051] (3) Hot elongation test (0.2 MPa, 200°C / 15 min), elongation under load ≤ 175%, permanent elongation after cooling ≤ 15%;

[0052] (4) The elongation at break of the sheath before aging is ≥125%, and the tensile strength is ≥9.0 Mipa; the change rate of the elongation at break after insulation aging (100°C, 168h) is ≤±30%, and the change rate of the tensile strength is ≤±30%;

[0053] (5) The low-temperature impact test of the sheath reaches -15℃, and the cable has no cracks and no breakdown; the low-temperature bending test is -15℃, and the cable has no cracks and no breakdown;

[0054] (6) Sheath high temperature pressure test (80℃ / 6h) indentation depth ≤500;

[0055] (7) The finished cable should pass the smoke density test specified in GB / T17651.2, and its light transmittance should not be less than 60%

[0056] (8) The finished cable should pass the bundled combustion test specified in GB / T18380.33;

[0057] (9) The finished cable should pass the halogen acid gas content test specified in GB / T17650.2, and the output value should be no less than 3.3 and the conductivity should be no more than 10us / n;

[0058] (10) The finished cable shall be sampled and tested according to Appendix B of TICW08-2012. The fire time shall be 180 minutes and the flame temperature shall be 950-1000℃. The test results shall meet the requirements.

[0059] (11) After the fire resistance test of the finished cable, the cable is not broken down at 3.5U / 5min; the partial discharge at 1.73U is less than 5pc.

[0060] (12) The finished cable has achieved radial water resistance. The cable sample is immersed in water at room temperature for 72 hours. After removing all the composite layers outside the insulation layer, the outer surface of the insulation layer should be dry when observed with the naked eye.

[0061] Comparative Example 1 ：

[0062] The difference from the embodiment is that after the moisture-proof layer is removed, water mist appears on the outer surface of the insulation layer of the cable after it is immersed in water for 72 hours.

[0063] Comparative Example 2:

[0064] The difference from the embodiment is that the heat insulation layer is removed, and the cable breaks down after 130 minutes of testing.

[0065] Comparative Example 3:

[0066] The difference from the embodiment is that the temperature-reducing layer of the cable is removed, and the cable breaks down when the test lasts 85 minutes.

[0067] Comparative Example 4:

[0068] The difference from the embodiment is that the fireproof layer of the cable is removed, and the cable breaks down when the test lasts 95 minutes.

[0069] The effects and effects of this embodiment:

[0070] This cable utilizes a unique three-in-one composite fire-resistant structure (insulation layer, cooling layer, and fireproof layer) to fully guarantee the fire resistance and post-fire repairability of the medium-voltage cable. The inner layer is an inorganic fiber insulation layer, and the second outer layer is a cooling layer. Water molecules generated by this material under high temperature or combustion conditions cool the adjacent layers, ensuring that the temperature transmitted to the inner layer is appropriately reduced, achieving excellent flame retardancy. The fireproof layer is constructed from a soft thermosetting elastomer. Upon exposure to fire, this material transforms into a fireproof insulation layer. Upon exposure to fire or high temperatures, it rapidly transforms into a shell-and-tube fireproof insulation structure, becoming a fire barrier. This structure can remain intact for a certain period of time in fire conditions, effectively preventing damage to the inner insulation layer caused by fire or high temperatures. The outer sheath is extruded from a halogen-free, low-smoke, flame-retardant polyolefin sheathing material, giving the cable both excellent flame retardancy and low-smoke, halogen-free properties.

[0071] In addition, due to the high temperature and pressure of the outer sheath melt, the polyethylene film on the surface of the aluminum-plastic composite tape is well bonded to the inner surface of the sheath, and the overlap between the longitudinal packages of the aluminum-plastic composite tape is also well bonded. This completely blocks the path for moisture (gas) to penetrate into the cable, achieving an excellent water-blocking effect.

[0072] While the above description focuses on the embodiments, this is merely illustrative and does not limit the present invention. Persons skilled in the art will appreciate that various modifications and applications not shown above are possible without departing from the essential characteristics of the embodiments. For example, the various components specifically illustrated in the embodiments may be implemented in various variations. Furthermore, any differences associated with such variations and applications should be construed as being included within the scope of the present invention as defined in the appended claims.

Claims

1. A medium voltage waterproof and fireproof cable, characterized in that: Include: conductor, Extruded shielding layer, covering the outside of the conductor; Insulation layer, covering the outside of the extruded shielding layer; Metal shielding layer, covering the outside of the insulation layer; A heat-insulating layer, covering the outside of the metal shielding layer; A cooling layer, covering the outside of the thermal insulation layer; Fireproof layer, covering the outside of the cooling layer; Moisture-proof layer, covering the outside of the fire-proof layer; A sheath covering the outside of the moisture barrier; The heat insulation layer is filled with inorganic fiber material and wrapped with inorganic fiber tape; The cooling layer is made of inorganic metal hydrate; The fireproof layer is made of ceramic polymer composite fire-resistant silicone rubber.

2. A medium voltage waterproof and fireproof cable according to claim 1, characterized in that: The extruded shielding layer adopts cross-linkable semi-conductive shielding material.

3. A medium voltage waterproof and fireproof cable according to claim 1, characterized in that: The thickness of the extruded shielding layer is controlled at 0.5-0.7 mm.

4. A medium voltage waterproof and fireproof cable according to claim 1, characterized in that: The insulating layer is made of cross-linked polyethylene insulating material.

5. The medium voltage waterproof and fireproof cable according to claim 1, characterized in that: The metal shielding layer is formed by overlapping and wrapping soft copper tapes, with an average overlapping rate of not less than 15%.

6. The medium voltage waterproof and fireproof cable according to claim 1, characterized in that: The thickness of the metal shielding layer is 0.05-0.10 mm.

7. The medium voltage waterproof and fireproof cable according to claim 1, characterized in that: The moisture-proof layer is a longitudinally wrapped layer of aluminum-plastic composite tape, and the overlapping rate of the longitudinal wrapping is not less than 20%.

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