NW type combustion class a mineral insulated cable

Abstract

The present application relates to the field of cable manufacturing, especially to a NW type combustion A level mineral insulated cable, comprising a core, an insulation layer, a shielding layer, a waterproof layer, a fireproof layer and a sheath, the core comprises a copper conductor, the core is used for transmitting electric energy; the insulation layer comprises powdered magnesium oxide, the particle size of the powdered magnesium oxide is 0.5-1 mu m, and the sheath is a copper sheath; the core, the insulation layer, the shielding layer, the waterproof layer, the fireproof layer and the sheath are sequentially wrapped from inside to outside; the outer diameter of the cable is greater than 20 mm; the surface of the copper sheath is a grid structure, and the surface of the copper sheath is smeared with an insect repellent. The present application also includes a method for detecting whether the cable is qualified, by dividing the cable to be detected into first, second and third cable samples, and detecting each performance respectively, which is helpful to reduce errors and improve the accuracy of detection.

Description

Technical Field

[0001] The invention relates to the field of cable manufacturing, in particular to an NW type combustion grade A mineral insulated cable. Background Art

[0002] DBJ / T 15-226-2021, "Technical Code for Fire Protection of Electric Wires and Cables in Civil Buildings," issued by the Guangdong Provincial Department of Housing and Urban-Rural Development, stipulates that the main power lines within buildings leading to fire pumps, fire control rooms, fire elevators, and lighting in fire work areas should use NW-type fire-resistant cables; in civil buildings with a building height greater than 250 meters, the power supply wires and cables for fire elevators and auxiliary evacuation elevators should use NW-type fire-resistant wires and cables with a combustion performance of Class A. 2 It also sets clear requirements for the performance of NW-type fire-resistant cables. Currently, the fire resistance test standards for wires and cables do not meet the requirements of the NW-type fire resistance test. Based on national standards and Guangdong Provincial standards, the Guangdong Wire and Cable Industry Association, in conjunction with Guangdong Provincial Wire and Cable Enterprises, has compiled T / GDWCA0074-2021, "NW-type Fire-Resistant Cables," which clearly stipulates the use characteristics, technical requirements, test conditions, and combustion performance levels of NW-type fire-resistant cables.

[0003] At present, the related technology of NW type combustion grade A mineral insulated cable is still a blue ocean. In order to solve the common problems in this field, the present invention is made. Summary of the Invention

[0004] The purpose of the present invention is to address the current deficiencies and propose an NW type combustion Class A mineral insulated cable.

[0005] In order to overcome the deficiencies of the prior art, the present invention adopts the following technical solutions:

[0006] An NW-type combustion-rated Class A mineral insulated cable comprises a core, an insulation layer, a shielding layer, a waterproof layer, a fireproof layer, and a sheath, wherein the core, insulation layer, shielding layer, waterproof layer, fireproof layer, and sheath are sequentially wrapped from the inside out; the core comprises a copper conductor, the insulation layer comprises powdered magnesium oxide having a particle size of 0.5 to 1 μm, and the sheath is a copper sheath; the surface of the copper sheath has a grid-like structure and is coated with an insect repellent; the outer diameter of the cable is greater than 20 mm;

[0007] The preparation process of the NW type combustion grade A mineral insulated cable comprises the following steps:

[0008] S1, prepare the materials required to make each layer of the cable;

[0009] S2, concentrically twisting a number of copper wires to obtain a core, and feeding the conductor composed of the core into an extruder;

[0010] S3, the extruder extrudes an insulation layer outside the conductor to obtain a first semi-finished cable and cools it;

[0011] S4, the laminating machine laminates the cooled first semi-finished cable, the laminating material is copper foil, and the braiding machine braids copper wires on the laminated first semi-finished cable to form a shielding outer layer, thereby obtaining a second semi-finished cable;

[0012] S5, the extruder extrudes a waterproof layer, a fireproof layer and a sheath on the second semi-finished cable in sequence to obtain a to-be-tested cable;

[0013] S6, the to-be-tested cable is tested for qualification, and the testing includes fire supply testing, mechanical impact testing and corrosion testing;

[0014] S7, the quality of the to-be-tested cable is analyzed according to the testing result.

[0015] Further, the shielding layer includes a shielding outer layer and a shielding inner layer, the shielding inner layer is attached to the insulation layer, the shielding inner layer is copper foil, the thickness of the shielding inner layer is 20-40 microns, and the shielding outer layer is braided by a plurality of copper wires, and the braiding density of the copper wires is 80%-90%.

[0016] Further, the waterproof layer is made of chlorobenzene 16-18 parts, sodium hydroxide 18-20 parts, phenylenediamine 20-22 parts, petroleum resin 33-35 parts, acrylic resin 20-22 parts, elastic fiber 24-26 parts, chlorobutyl glue 17 parts, silicone acrylic emulsion 17 parts, cyclohexanone 14-16 parts, methyl ethyl ketone 12-14 parts and potassium chloride 17 parts by weight.

[0017] Further, the fireproof layer is made of modified magnesium hydroxide 20-22 parts, aluminum silicate 11-13 parts, antimony oxide 10-13 parts, calcium carbonate 38-40 parts, magnesium chloride 8-10 parts, artificial mica 16-20 parts, sodium silicate 9-11 parts and chlorinated paraffin 8-10 parts by weight.

[0018] Further, the to-be-tested cable is tested for qualification, including the following steps:

[0019] S61, three cable samples of the same length are obtained from the to-be-tested cable to obtain a first cable sample, a second cable sample and a third cable sample;

[0020] S62, the first cable sample is clamped by a clamping device and connected to a test circuit, and whether the first cable sample is qualified is determined by the test circuit;

[0021] S63, measuring the heat value generated by the second cable sample in the test process according to the test method of GB / T14402, comparing the heat value with the set heat value threshold, and judging whether the second cable sample is qualified;

[0022] S64, dividing the third cable sample into two or more cable segments, placing different cable segments in different corrosive environments, and measuring the corrosion degree of different cable segments under different conditions.

[0023] Further, the step of judging whether the first cable sample is qualified by the test circuit comprises the following steps:

[0024] S621, connecting the first cable sample to the test circuit, turning on the power supply of the test circuit, and the power supply supplies power at the rated voltage;

[0025] S622, supplying fire to the first cable sample and mechanically impacting the first cable sample for 180 minutes, collecting various parameters of the first cable sample and the test circuit in the process;

[0026] S623, stopping mechanical impact on the first cable sample, continuing to supply fire to the first cable sample, and spraying water on the first cable sample for 5 minutes, collecting various parameters of the first cable sample and the test circuit in the process;

[0027] S624, observing whether the fuse of the test circuit is disconnected in S622 and S633, if not, the first cable sample is qualified, otherwise, the first cable sample is not qualified.

[0028] Further, the step of analyzing the quality of the cable to be detected comprises the following steps:

[0029] S71, collecting various parameters of the test circuit and the first cable sample in the test process, heat value generated by the second cable sample in the test process, and related data of the third cable sample being corroded;

[0030] S72, image recognition is performed on the first cable sample after the test is completed, and the defect condition of the cable surface of the first cable sample after the test is obtained;

[0031] S73, calculating the quality index of the cable to be detected according to the various parameters of the test circuit, the defects generated by the first cable, the heat value generated by the second cable sample, and the loss weight of the cable segment of the third cable sample after being corroded;

[0032] S74, judging whether the quality index of the cable is greater than the set threshold, if greater, the cable is unqualified, otherwise, it is qualified.

[0033] The beneficial effects achieved by the present application are: 1. By dividing the to-be-detected cable into first, second and third cable samples, and detecting each performance respectively, compared with directly detecting the to-be-detected cable, it is beneficial to reduce errors and improve the accuracy of detection.

[0034] 2. By calculating the quality index of the cable, it is beneficial to numerize the quality of the cable and analyze the overall quality of the cable; the staff can improve the cable and judge the improvement effect by comparing the quality indexes before and after the improvement, which is beneficial to continuously improve the quality of the cable. BRIEF DESCRIPTION OF DRAWINGS

[0035] The present application can be further understood from the following description made with reference to the accompanying drawings. The components in the drawings are not necessarily drawn to scale, but emphasis is instead placed upon illustrating the principles of the embodiments. Like reference numerals designate like parts throughout the different views.

[0036] Figure 1 It is a structural schematic diagram of the present application.

[0037] Figure 2 It is a cable preparation flowchart of the present application.

[0038] Figure 3 It is a flowchart of the present application for testing whether the to-be-detected cable is qualified.

[0039] Figure 4 It is a flowchart of the present application for analyzing the quality of the to-be-detected cable.

[0040] Reference numerals: core 01, insulation layer 02, shielding layer 03, waterproof layer 04, fireproof layer 05, sheath 06. DETAILED DESCRIPTION

[0041] The following is to illustrate the embodiments of the present application through specific specific embodiments, and those skilled in the art can understand the advantages and effects of the present application from the disclosed content of the specification. The present application can be implemented or applied through other different specific embodiments, and each detail in the specification can be modified and changed based on different viewpoints and applications without departing from the spirit of the present application. In addition, the drawings of the present application are only simple schematic illustrations, not the depiction according to the actual size, and the prior declaration is made. The following embodiments will further illustrate the related technical content of the present application in detail, but the disclosed content is not used to limit the protection scope of the present application.

[0042] Example one: according to Figure 1 , Figure 2 , Figure 3 and Figure 4The embodiment provides a NW type combustion A-level mineral insulated cable, which comprises a core, an insulation layer, a shielding layer, a waterproof layer, a fireproof layer and a sheath, the core comprises a copper conductor, and the core is used for transmitting electric energy; the insulation layer comprises powdered magnesium oxide, the particle size of the powdered magnesium oxide is 0.5-1 mu m, and the insulation layer is used for preventing electric energy leakage or cable short circuit of the cable; the shielding layer is used for reducing electromagnetic interference; the waterproof layer is used for preventing moisture from entering the shielding layer; the fireproof layer is used for isolating flame; the sheath is used for protecting the overall structure of the cable, and the sheath is a copper sheath; the core, the insulation layer, the shielding layer, the waterproof layer, the fireproof layer and the sheath are sequentially arranged from inside to outside; and the outer diameter of the cable is greater than 20 mm.

[0043] The preparation process of the NW type combustion A-level mineral insulated cable comprises the following steps.

[0044] S1, preparing materials required when each layer of the cable is prepared;

[0045] S2, concentrically twisting a plurality of copper wires to obtain a core, and feeding the conductor composed of the core into an extruding machine;

[0046] S3, extruding the insulation layer outside the conductor by the extruding machine to obtain a first semi-finished cable and cooling;

[0047] S4, coating the first semi-finished cable after cooling by a coating machine, the material of the coating is a copper foil, and a braiding machine twists copper wires on the first semi-finished cable after coating to form a shielding outer layer, thereby obtaining a second semi-finished cable;

[0048] S5, sequentially extruding the waterproof layer, the fireproof layer and the sheath on the second semi-finished cable by the extruding machine to obtain a cable to be detected;

[0049] S6, detecting whether the cable to be detected is qualified, and the detection comprises fire supply testing, mechanical impact testing and corrosion testing;

[0050] S7, analyzing the quality of the cable to be detected according to the detection result.

[0051] Specifically, the surface of the copper sheath is a grid structure, and the surface of the copper sheath is smeared with an insect repellent.

[0052] By adopting the grid surface, the insect repellent can be better preserved at the junction of the grid, and compared with a traditional plane structure, the insect repellent retention rate can be improved, and the insect repellent effect can be improved.

[0053] Further, the shielding layer comprises a shielding outer layer and a shielding inner layer, the shielding inner layer is attached to the insulation layer, the shielding inner layer is a copper foil, the thickness of the shielding inner layer is 20-40 microns, and the shielding outer layer is woven by a plurality of copper wires, and the density of the copper wire weaving is 80%-90%.

[0054] Specifically, by the double-layer metal shielding structure, the shielding layer can have the flexibility of the metal foil and the high shielding effectiveness of the metal braid. The metal foil is mainly used to block high-frequency electromagnetic waves, while the metal braid provides good electromagnetic shielding effect and maintains a certain flexibility.

[0055] Further, the waterproof layer is made of chlorobenzene 16-18 parts, sodium hydroxide 18-20 parts, phenylenediamine 20-22 parts, petroleum resin 33-35 parts, acrylic resin 20-22 parts, elastic fiber 24-26 parts, chlorobutyl glue 17 parts, silicone acrylic emulsion 17 parts, cyclohexanone 14-16 parts, methyl ethyl ketone 12-14 parts and potassium chloride 17 parts by weight.

[0056] Further, the fireproof layer is made of modified magnesium hydroxide 20-22 parts, aluminum silicate 11-13 parts, antimony oxide 10-13 parts, calcium carbonate 38-40 parts, magnesium chloride 8-10 parts, artificial mica 16-20 parts, sodium silicate 9-11 parts and chlorinated paraffin 8-10 parts by weight.

[0057] Further, the method for testing whether the to-be-tested cable is qualified comprises the following steps:

[0058] S61, obtaining three cable samples of the same length from the to-be-tested cable to obtain a first cable sample, a second cable sample and a third cable sample;

[0059] S62, clamping the first cable sample by using a clamping device, connecting the first cable sample into a test circuit, and determining whether the first cable sample is qualified by the test circuit;

[0060] S63, measuring a heat value generated by the second cable sample in a test process according to a test method of GB / T14402, comparing the heat value with a set heat value threshold, and determining whether the second cable sample is qualified;

[0061] Specifically, the test method of GB / T14402 belongs to the prior art, and will not be described here. The heat value threshold is 2.0 MJ / kg. If the heat value generated by the cable sample per unit weight is less than or equal to the heat value threshold, the flame-retardant property of the second cable sample meets the standard, and the second cable sample is qualified.

[0062] S64, dividing the third cable sample into two or more cable segments, placing different cable segments into different corrosive environments, and measuring the corrosion degrees of different cable segments under different conditions.

[0063] Specifically, the different corrosive environments include different corrosive substances, which can be gas or liquid, and the corrosive substances are set according to possible application scenarios of the cable, including subway tunnels, high-rise buildings, nuclear power plants or chemical plants, etc.; the different conditions include temperature, humidity and air flow rate.

[0064] Further, the step of determining whether the first cable sample is qualified by the test circuit includes the following steps:

[0065] S621, connecting the first cable sample into the test circuit, turning on the power supply of the test circuit, and the power supply supplies power at a rated voltage;

[0066] Specifically, the optional value of the rated voltage is between 0.6kV and 1kV, and preferably, the value of the rated voltage can be 750V; the structure of the test circuit belongs to the prior art, and will not be described here;

[0067] S622, supplying fire to the first cable sample, and mechanically impacting the first cable sample for 180min, and collecting various parameters of the first cable sample and the test circuit in the process;

[0068] Specifically, the mechanical impact is used to simulate the impact that the cable may be subjected to during a fire, and the type and intensity of the impact are set by those skilled in the art;

[0069] S623, stopping the mechanical impact on the first cable sample, supplying fire to the first cable sample, and spraying water on the first cable sample for 5min, and collecting various parameters of the first cable sample and the test circuit in the process;

[0070] S624, observing whether the fuse of the test circuit is disconnected in S622 and S633, if not, the first cable sample is qualified, otherwise, the first cable sample is unqualified.

[0071] Further, the step of analyzing the quality of the cable to be detected includes the following steps:

[0072] S71, collecting various parameters of the test circuit and the first cable sample during the test process, and the heat value generated per unit weight of the second cable sample during the test process;

[0073] S72, image recognition is performed on the first cable sample after the test, and the defect condition of the cable surface of the first cable sample after the test is obtained;

[0074] S73, calculating the quality index ZB of the cable to be detected according to the following formula:

[0075]

[0076]

[0077]

[0078]

[0079] wherein, k1 is the impact performance weight, k2 is the water resistance performance weight, k3 is the surface defect weight, k4 is the fire resistance test weight, k5 is the corrosion test weight, ZB1 is the surface damage index, A is the total number of defects on the surface of the first cable sample, S a is the detection area of the a-th defect on the surface of the first cable sample, e is the natural constant, D a is the depth of the a-th defect of the first cable sample, H is the heat value threshold, h is the heat value generated by the second cable sample per unit weight;

[0080] ZB2 is the fire resistance performance index, t1 is the time when the first cable is mechanically impacted and supplied with fire, t2 is the time when the first cable is sprayed with water and supplied with fire, i(t1) is the measured value of the current of the main circuit of the test circuit at t1 of the first cable, u(t1) is the measured value of the voltage across the first cable sample at t1 of the first cable, r(t1) is the measured value of the equivalent resistance across the first cable sample at t1 of the first cable, I is the ideal value of the current of the main circuit of the test circuit, U is the ideal value of the voltage across the first cable sample, R is the ideal value of the equivalent resistance of the first cable sample, ii(t2) is the measured value of the current of the main circuit of the test circuit at t2 of the first cable, uu(t2) is the measured value of the voltage across the first cable sample at t2 of the first cable, rr(t2) is the measured value of the equivalent resistance across the first cable sample at t2 of the first cable;

[0081] ZB3 is the corrosion performance index, J is the number of types of corrosive substances, the types of corrosive substances are set by a person skilled in the art according to the corrosive substances that may be contained in the application scenario of the cable, t is the experimental time, h j is the corrosion degree weight of the j-th corrosive substance, v jmax is the maximum loss weight of the cable segment under the j-th corrosive substance corrosion at different temperatures, humidities and air flow rates, which is obtained by statistical analysis of historical experimental data; v jset is the loss weight of the cable segment under the j-th corrosive substance corrosion in the experimental scenario, and the experimental scenario is a scenario set by simulating the temperature, humidity and air flow rate of the possible application scenario of the cable, jmax is the corresponding environmental temperature value of v jmax , T jset is the corresponding environmental temperature value of v jset , S jmax is the corresponding environmental temperature value of v jmaxThe corresponding environmental humidity value S jset is v jset The corresponding environmental humidity value Q jmax is v jmax The corresponding environmental average air flow rate value Q jset is v jset The corresponding environmental average air flow rate value

[0082] Specifically, the experimental scene is a simulation of the cable application scene, the temperature, humidity and average air flow rate of the application scene and the experimental scene are the same, and the experimental scene contains corrosive substances existing in the cable application scene.

[0083] Specifically, h j is set by a person skilled in the art according to the corrosiveness of the corrosive substance, assuming that the v jmax of all kinds of corrosive substances corresponds to the maximum value of h j is set to 1, then according to the v jmax of the remaining kinds of corrosive substances, the ratio of this v jmax can obtain the value of h jmax corresponding to the v j of the remaining kinds of corrosive substances; the loss mass is the weight difference of the cable segment before and after the experiment; the experimental scene is a scene set according to the temperature, humidity and air flow rate of the possible application scene of the cable, the value of v jset is different according to different simulated scenes, so as to obtain different corrosion performance indicators and the value of the quality indicator of the cable, and evaluate the quality of the cable according to the value of the different quality indicators and the corresponding set threshold, which is conducive to obtaining different quality indicator values and corresponding set threshold values according to different application scenes, thereby improving the comprehensiveness of evaluating the quality of the cable through the quality indicator.

[0084] Specifically, the number of defects on the cable surface, the defect detection area, and the defect depth can be obtained through image recognition technology; R, I, and U are known values ​​set by those skilled in the art based on the target performance value of the cable when designing the test circuit. The target performance value of the cable is set by those skilled in the art when designing the cable. One setting method of k1, k2, k3, k4, and k5 is that those skilled in the art set them based on the number of defects and defect depths generated during each experimental process. The greater the number of defects and the depth of the defects, the greater the corresponding weight value. For example, in the processes of impact, water resistance, flame retardancy, and corrosion, the greater the number of defects and the depth of the defects caused by the impact, the greater the value of k1 than k2 and k5. K4 can be the weighted average of k1 and k2. K2, k3, and k5 can be set in accordance with the number of defects and the severity of the defect depth with reference to the value of k1. In addition, k1, k2, k3, k4, and k5 can also be set according to the degree of impact of each test on the cable. The specific selection can be set according to the specific application requirements, and this embodiment does not limit this.

[0085] Specifically, the smaller the quality index of the cable, the better the quality of the cable.

[0086] S74, determining whether the quality index of the cable is greater than a set threshold. If so, the cable is unqualified; otherwise, it is qualified. The set threshold is set by a person skilled in the art.

[0087] Beneficial effects of this program:

[0088] 1. By dividing the cables to be tested into first, second and third cable samples and testing the performance of each cable separately, it is helpful to reduce errors and improve the accuracy of detection compared to directly testing the cables to be tested.

[0089] 2. By calculating the quality indicators of the cable, it is helpful to quantify the quality of the cable and analyze the overall quality of the cable; the staff can improve the cable and judge the effect of the improvement by comparing the quality indicators before and after the improvement, which is conducive to continuously improving the quality of the cable.

[0090] Embodiment two: this embodiment should be understood as containing all the features of any one of the preceding embodiments, and further improving on the basis thereof, the preparation process of the insulated cable is realized by a cable production and quality detection system for producing the cable and detecting the quality of the cable, the system comprises a material collecting module, a stranding machine, an extruding machine, a film coating machine, a detection module and a quality analysis module; the material collecting module is used to collect the materials required for making each layer of the cable, and the materials are distributed according to the set weight of each material; the stranding machine is used to strand the copper wire; the extruding machine is used to extrude the materials of each layer of the cable onto the cable; the film coating machine is used to cover the copper foil onto the cable; the detection module is used to detect whether the produced cable is qualified; the quality analysis module is used to analyze the quality of the qualified cable;

[0091] The detection module comprises a test circuit and a detection device, which are built by those skilled in the art according to the detection requirements; the detection device is used to detect whether the first cable sample and the second cable sample are qualified;

[0092] The quality analysis module comprises an information acquisition unit, a calculation unit and a judgment unit, the information acquisition unit is used to acquire various parameters generated during the detection of the first cable sample and the second cable sample, the calculation unit is used to calculate the cable quality index, and the judgment unit compares the cable quality index with the grade threshold value, and judges the quality grade of the cable according to the range of the grade threshold value where the cable quality index is located.

[0093] The beneficial effects of this embodiment: by integrating the production quality of the cable, the qualified detection of the cable and the quality detection of the cable in one system, it can be detected whether the cable is qualified immediately after the cable production is completed, and the quality of the cable is judged, which is beneficial to realize the integration of production and detection, improve the working efficiency of the system, and adjust the production process or material proportioning of the cable according to the quality analysis result of the cable.

[0094] Embodiment three: this embodiment should be understood as containing all the features of any one of the preceding embodiments, and further improving on the basis thereof, further, the k1, k2, k3, k4, k5 can also be set by the following method:

[0095] For k1 (impact performance weight):

[0096]

[0097] Wherein, F is the impact force when the cable starts to appear defects in the impact and fire supply process, F max is the maximum impact that the impact device can exert, F and F maxThe smaller the ratio of M to A, the smaller the impact of the impact force on the cable when the cable begins to produce defects.

[0098] For k2 (water resistance performance weight) :

[0099]

[0100] The greater the ratio of M to A, the greater the impact of the water spray on the cable, as the proportion of defects produced by the water spray in all defects is greater.

[0101] For k3 (surface defect weight) :

[0102]

[0103] D is the radius of the cable, and D max is the maximum depth of the defects on the surface of the first cable sample, and the greater the ratio of D to D max , the greater the impact of the defects on the cable, as the defects are more likely to affect the internal structure of the cable.

[0104] For k4 (fire resistance test weight) :

[0105]

[0106] The fire resistance test includes mechanical impact with fire and water spray with fire. The weight corresponding to mechanical impact with fire is k1 (impact performance weight), and the weight corresponding to water spray with fire is k2 (water resistance performance weight). The value of the fire resistance test weight can be the result of weighting the corresponding weights of the two according to time.

[0107] For k5 (corrosion test weight) :

[0108]

[0109] v jmax is the maximum loss weight of the cable segment under different temperatures, humidity, and air flow rates when corroded by the jth corrosive substance, and v jset is the loss weight of the cable segment in the experimental scenario when corroded by the jth corrosive substance.

[0110] The beneficial effects of the present embodiment are that by setting the weight values, it is beneficial to distinguish the influence of different indicators and different parameters on evaluating the quality of the cable, and it is beneficial to more accurately evaluate the quality of the cable.

[0111] The above disclosed is only the preferred feasible embodiment of the present application, and does not limit the protection scope of the present application, so any equivalent technical change made by applying the content of the present application specification and drawings is included in the protection scope of the present application, and furthermore, the elements can be updated as the technology develops. The above units are only an example, and the corresponding units can be used in different designs according to actual needs when the present solution is implemented by the person skilled in the art.

Claims

1. An NW type combustion grade A mineral insulated cable, comprising a core, an insulation layer, a shielding layer, a waterproof layer, a fireproof layer and a sheath, wherein the core, the insulation layer, the shielding layer, the waterproof layer, the fireproof layer and the sheath are sequentially wrapped from the inside to the outside; the core comprises a copper conductor, characterized in that: The insulating layer comprises powdered magnesium oxide, the particle size of the powdered magnesium oxide is 0.5 to 1 μm, the sheath is a copper sheath; the surface of the copper sheath has a grid-like structure, and the surface of the copper sheath is coated with an insect repellent; the outer diameter of the cable is greater than 20 mm; The preparation process of the NW type combustion grade A mineral insulated cable comprises the following steps: S1, prepare the materials required to make each layer of the cable; S2, concentrically twisting a number of copper wires to obtain a core, and feeding the conductor composed of the core into an extruder; S3, an extruder extrudes an insulating layer on the outside of the conductor to obtain a first semi-finished cable and cools it; S4, a laminating machine coats the cooled first semi-finished cable with a copper foil, and a braiding machine twists copper wires on the coated first semi-finished cable to form a shielding outer layer, thereby obtaining a second semi-finished cable; S5, an extrusion machine sequentially extrudes a waterproof layer, a fireproof layer, and a sheath onto the second semi-finished cable to obtain a cable to be tested; S6, check whether the cable to be tested is qualified, including fire test, mechanical impact test and corrosion test; S7, analyzing the quality of the cable to be tested according to the test results; Check whether the cable to be tested is qualified, including the following steps: S61, obtaining three cable samples of the same length from the cable to be tested to obtain a first cable sample, a second cable sample, and a third cable sample; S62, clamping the first cable sample using a clamping device, connecting the first cable sample to a test circuit, and determining whether the first cable sample is qualified through the test circuit; S63, measuring the heat value generated by the second cable sample during the test according to the test method of GB / T14402, comparing the heat value with a set heat value threshold, and determining whether the second cable sample is qualified; S64, dividing the third cable sample into two or more cable segments, placing different cable segments in different corrosive environments, and measuring the corrosion degree of the different cable segments under different conditions; Analyzing the quality of the cable to be tested includes the following steps: S71, collecting various parameters of the test circuit and the first cable sample cable during the test, the heat value generated by the second cable sample during the test, and relevant data on the corrosion of the third cable sample; S72, performing image recognition on the first cable sample after the test to obtain defects on the cable surface of the first cable sample after the test; S73, calculating a quality index of the cable to be tested based on various parameters of the test circuit, defects generated in the first cable, a heat value generated by the second cable sample, and a weight loss of the cable segment of the third cable sample after corrosion; S74, judging whether the quality index of the cable is greater than a set threshold value, if so, the cable is unqualified, otherwise qualified.

2. The NW type combustion grade A mineral insulated cable according to claim 1, characterized in that: The shielding layer includes a shielding outer layer and a shielding inner layer. The shielding inner layer is attached to the insulating layer. The shielding inner layer is copper foil. The thickness of the shielding inner layer is 20~40 microns. The shielding outer layer is woven by multiple copper wires, and the copper wire weaving density is 80%~90%.

3. The NW type combustion grade A mineral insulated cable according to claim 2, characterized in that: The waterproof layer is made of 16-18 parts of chlorobenzene, 18-20 parts of sodium hydroxide, 20-22 parts of phenylenediamine, 33-35 parts of petroleum resin, 20-22 parts of acrylic resin, 24-26 parts of elastic fiber, 17 parts of chloroprene rubber, 17 parts of silicone acrylic emulsion, 14-16 parts of cyclohexanone, 12-14 parts of methyl ethyl ketone and 17 parts of potassium chloride, which are mixed in proportions by weight.

4. The NW type combustion grade A mineral insulated cable according to claim 3, characterized in that: The fireproof layer is made of 20-22 parts of modified magnesium hydroxide, 11-13 parts of aluminum silicate, 10-13 parts of antimony oxide, 38-40 parts of calcium carbonate, 8-10 parts of magnesium chloride, 16-20 parts of artificial mica, 9-11 parts of sodium silicate and 8-10 parts of chlorinated paraffin, which are mixed in proportions by weight.

5. The NW type combustion grade A mineral insulated cable according to claim 4, characterized in that: Determining whether the first cable sample is qualified by testing the circuit includes the following steps: S621, connecting the first cable sample to the test circuit, turning on the power supply of the test circuit, and supplying power at the rated voltage; S622, applying fire to the first cable sample and subjecting the first cable sample to mechanical shock for 180 minutes, and collecting various parameters of the first cable sample and the test circuit during the process; S623, stop mechanically impacting the first cable sample, continue applying fire to the first cable sample, and spray water on the first cable sample for 5 minutes, collecting various parameters of the first cable sample and the test circuit during this process; S624, observe whether the fuse of the test circuit in S622 and S633 is broken. If not, the first cable sample is qualified; otherwise, the first cable sample is unqualified.

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