High-temperature electrical cable

Abstract

This utility model relates to high-temperature electric cable designs for transmitting low-power electrical signals. The technical result consists of increased operational reliability under long-term continuous exposure to temperatures up to +1000°C and is achieved by eliminating internal thermomechanical shear stresses between layers and rigidly fixing the inorganic dielectric barrier. The cable comprises a conductive core insulated by a multilayer dielectric barrier based on mica-containing tapes, a protective metal shield in the form of a wire braid, and an outer protective coating of inorganic fiber. The core and metal shield are made of pure nickel. The multilayer dielectric barrier consists of first and second multilayer dielectric barriers formed by concentrically applied layers of phlogopite mica tapes.First and second continuous fixing braids made of silica or quartz threads are applied over the first and second dielectric barriers, respectively. The outer protective coating is also made in the form of a braid made of silica or quartz threads. 1 c.p. fil., 2 fig.

Description

[0001] FIELD OF TECHNOLOGY

[0002] This utility model relates to cable technology, specifically to high-temperature electrical cable designs intended for transmitting low-power electrical signals under conditions of prolonged exposure to extreme temperatures up to +1000°C and peak temperature loads up to +1200°C. The utility model can be applied in heavy metallurgy, thermal power engineering, high-temperature chemical synthesis units, and the aerospace industry.

[0003] STATE OF THE ART

[0004] The utility model relates to cable technology, namely to the designs of high-temperature electrical cables intended for transmitting low-power electrical signals under conditions of prolonged exposure to extreme temperatures up to +1000°C and peak temperature loads up to +1200°C.

[0005] From the prior art, various designs of heat-resistant and fire-resistant cables are known, intended for operation in difficult operating conditions.

[0006] A high-performance heat-resistant wire or cable is known under invention patent RU 2530779 C2 (published October 10, 2014), intended for use in extreme conditions exposed to open flame. The known cable comprises a functional core and a multilayer polymer sheath. The inner sheath layer is a polyetheretherketone (PEEK) tape, which can be combined with a mica layer. The outer flame-retardant layer is made of a siloxane polymer or a silicon dioxide-based polymer as the polymer matrix.

[0007] The common essential features of the known analogue and the claimed utility model are: the presence of a metallic functional conductive core, the use of a dielectric barrier using mica, as well as the use of materials based on silicon dioxide in the structure of the protective layers.

[0008] A disadvantage of this analogue is the fundamental impossibility of its long-term and continuous use at temperatures up to +1000°C. The presence of a polymer matrix (polyetheretherketone, whose melting point is approximately +343°C, and siloxane polymers) in the design leads to their intense thermal-oxidative degradation at temperatures above +400…+500°C. Burnout of the polymer matrix leads to a complete loss of the structural integrity of the insulating coating, which prevents the technical result provided by the claimed utility model.

[0009] The KNMS brand of heat-resistant cable (manufactured according to technical specifications TU 16-505.564-75) is designed for use in areas with extreme conditions at temperatures up to +600°C. This cable contains a pure nickel conductor, inorganic metal oxide powder insulation (magnesium oxide insulation), and an outer metal sheath made of corrosion-resistant steel.

[0010] The common essential features of the known analogue and the claimed utility model are: purpose (operation in high-temperature conditions), the presence of a metal conductive core made of pure nickel, and the use of exclusively inorganic materials to ensure dielectric properties.

[0011] A disadvantage of this analogue is the high structural rigidity caused by the use of a solid metal tube as a sheath and tightly pressed mineral powder, which complicates cable installation. Furthermore, the significant difference in the coefficients of linear thermal expansion of the nickel conductive core and the steel outer sheath when subjected to extreme temperature cycling generates high internal thermomechanical stresses. These stresses can lead to disruption of the compacted insulating powder and deterioration of the product's dielectric properties.

[0012] The closest technical solution (prototype) to the claimed utility model is a high-temperature electric cable according to utility model patent CN 202205486 U (published April 25, 2012). The design of this cable includes a stranded conductive core twisted from pure nickel, a multilayer dielectric barrier containing a modified composite mica tape, ceramic fiber, and an organosilicon varnish coating, as well as a protective metal screen in the form of a stainless steel wire braid.

[0013] The common essential features of the prototype and the claimed utility model are: purpose (high-temperature electric cable); the presence of a conductive core made of pure nickel; the presence of insulation in the form of a multilayer dielectric barrier based on mica-containing tapes; the presence of a protective metal screen in the form of a wire braid.

[0014] The technical problem, the solution of which is provided by the claimed utility model, is the need to expand the arsenal of technical means and create a flexible cable capable of long-term and continuous operation at temperatures up to +1000°C without destruction of the internal structure and loss of dielectric properties.

[0015] The specified technical problem could not be solved during the implementation of the prototype cable design for two objective reasons that prevent the technical result provided by the utility model from being achieved:

[0016] Firstly, the operating temperature of the prototype design is limited by the properties of the organosilicon varnish and the binding elements of the mica tape (+500°C). When heated to extreme temperatures (up to +1000°C), the organic components completely burn out, resulting in the formation of dry silica ash and mica flakes, which inevitably crumble, delaminate, and lose their dielectric integrity.

[0017] Secondly, the difference in the coefficients of linear thermal expansion of the conductive core material (nickel) and the protective shield material (stainless steel) when heated to +1000°C causes significant internal thermomechanical shear stresses. During thermal deformation, the rigid metal strands of the stainless steel shield press through and grind the unprotected, brittle layer of the burnt mica tape, inevitably leading to electrical breakdown and short-circuiting of the nickel core to the shield.

[0018] The claimed utility model overcomes these shortcomings by ensuring absolute temperature parity of the structural elements (by constructing both the core and screen from pure nickel, which neutralizes shear stresses) and by introducing a system for rigid spatial fixation of the inorganic dielectric barrier in the form of continuous braids made of silica or quartz threads. Dividing the insulation into two barriers interrupts microcracks, and the braids form a non-expanding, thermally stable framework that radially compacts the mica ash residue during thermal expansion of the nickel core from within. The outer quartz braid protects the fragile mica from being cut by the screen threads.

[0019] DISCLOSURE OF THE ESSENCE OF THE UTILITY MODEL

[0020] The technical problem, the solution of which is provided by the implementation of the utility model, is the need to expand the arsenal of technical means and create a cable capable of long-term and continuous operation at temperatures up to +1000°C without destruction of the internal structure.

[0021] The technical result consists in increasing the operational reliability of a high-temperature electric cable under conditions of long-term continuous exposure to temperatures up to +1000°C due to the complete elimination of internal thermomechanical shear stresses between layers and ensuring rigid spatial fixation of the inorganic dielectric barrier.

[0022] The said technical result is achieved in that in a high-temperature electric cable, including at least one metal conductive core, insulated by a multilayer dielectric barrier based on mica-containing tapes, a protective metal screen in the form of a wire braid and an outer protective coating made of inorganic fiber, according to the utility model, the conductive core and the protective metal screen are made of pure nickel, wherein the said multilayer dielectric barrier is made in the form of first and second multilayer dielectric barriers formed by concentrically superimposed layers of tapes based on phlogopite mica, wherein a first continuous fixing braid of silica or quartz threads is superimposed on the first dielectric barrier, a second continuous fixing braid of silica or quartz threads is superimposed on the second dielectric barrier,and the outer protective coating is also made in the form of a braid of silica or quartz threads.

[0023] The increase in the operational reliability of the cable is due to the combined action of the following physical, chemical and thermomechanical factors, which together ensure the achievement of the stated technical result:

[0024] Firstly, the use of chemically pure nickel for both the conductive core and the protective shield ensures absolute temperature parity between these elements. The coefficients of linear thermal expansion of the core and shield are strictly equal. When the cable is cyclically heated to +1000°C, the core and shield expand synchronously in the radial and longitudinal directions by an identical amount, completely eliminating the occurrence of destructive shear stresses typical of structures with stainless steel shields.

[0025] Secondly, at extreme temperatures, the organic binder of mica tapes burns away, leaving dry silica ash and mica flakes. The application of continuous fixing braids of silica or quartz threads, which have a virtually zero coefficient of thermal expansion, forms a rigid, non-expanding, heat-stable "exoskeleton." The nickel core, which expands when heated, exerts pressure on the mica layers from within, pressing them against the stationary quartz braids, creating a radial compaction effect (densification) of the ash residue and preventing its shedding.

[0026] Thirdly, dividing the overall dielectric layer into two independent multilayer barriers using an intermediate quartz braid physically interrupts possible through-hole microcracks formed by the burnout of the binder, which exponentially reduces the likelihood of forming a continuous current path and prevents avalanche electrical breakdown. Fourthly, the second quartz braid, located directly under the metal screen, acts as a high-strength distributing mechanical buffer that protects the fragile mica ash package from localized crushing (cutting) by intersecting metal threads of the screen during mechanical and thermal deformations.

[0027] BRIEF DESCRIPTION OF DRAWINGS

[0028] The essence of the utility model is explained by drawings, where Fig. 1 shows a cross-section of a high-temperature electric cable (basic version), and Fig. 2 shows a cross-section of a cable with additional mechanical armor.

[0029] The drawings indicate: 1 - multi-wire conductive core; 2 - first multilayer dielectric barrier; 3 - first solid fixing braid; 4 - second multilayer dielectric barrier; 5 - second solid fixing braid; 6 - protective metal screen; 7 - outer protective coating; 8 - armor in the form of a braid made of heat-resistant stainless steel wires.

[0030] IMPLEMENTATION OF A UTILITY MODEL

[0031] The claimed high-temperature electric cable is a reliable, flexible multilayer concentric structure, the cross-section of which is clearly shown in Figs. 1 and 2 of the accompanying graphic materials. The structure is formed by the following functionally interconnected elements, arranged from the center to the periphery.

[0032] The main conductive core (1) is located in the geometric center of the structure and is a multi-wire concentric twist. All wires of the conductive core are made of technically pure chemical nickel (e.g., grade NP1 according to GOST 492-2006). Chemically pure nickel was chosen, as opposed to copper-containing alloys or bimetallic structures, due to its high melting point (over 1450°C), exceptional thermodynamic stability, high resistance to high-temperature oxidation (scale formation), and the maintenance of stable electrical conductivity properties under long-term extreme temperature operating conditions.

[0033] The first multilayer dielectric barrier (2) is located concentrically and without gaps directly above the twisted conductive core (1). This barrier is formed by dense, multiple spiral windings of insulating tapes created on the basis of high-temperature phlogopite mica (a mineral of the magnesite-iron mica group), the flakes of which are pre-bonded with a heat-resistant organic or organosilicon (silicone) polymer binder on a backing made of ultra-fine glass fiber. Phlogopite mica is used due to its increased resistance to thermal dehydration and the preservation of dielectric parameters under extreme heating, compared to classic muscovite mica. The first continuous fixing braid (3) is tightly applied over the first dielectric barrier (2). It is formed by regular cross-weaving of high-temperature inorganic threads, preferably silica (with a silicon dioxide SiO2 content of at least 94%) or quartz.This braid forms the first, internal level of a rigid, spatially stable and non-expanding fixing frame (exoskeleton), tightly bandaging the underlying layers of mica.

[0034] A second multilayer dielectric barrier (4), identical to the first barrier (2), formed by spirally applied tapes based on phlogopite mica, is concentrically located on top of the first silica fixing braid (3).

[0035] A second continuous fixing braid (5), similarly made of silica or quartz inorganic fibers, is applied under high tension over the second dielectric barrier (4). This braid forms the second, outer layer of the heat-resistant fixing frame.

[0036] A protective metal shield (6) is concentrically positioned over the second retaining braid (5), constructed as a continuous, dense wire braid. In strict accordance with the claimed utility model's objective of mitigating thermomechanical stress, the wires of the protective metal shield (6) are manufactured exclusively from the same material as the wires of the central conductive core (1)—technically pure nickel. This strict identity of the metals used ensures absolute matching of the coefficients of linear thermal expansion (CLTE) of the core and outer shield of the cable assembly, eliminating the occurrence of bimetallic curvature effects.

[0037] Above the protective nickel metal shield (6), there is an outer protective coating (7), made of a dense, continuous braid of silica or quartz threads. The coating (7) provides basic electrical insulation of the shield from the external grounded environment, prevents mechanical abrasion of the structure during installation, and serves as an additional thermal barrier.

[0038] Depending on the specific operating requirements at complex industrial facilities, in the embodiment shown in Fig. 2, a mechanical armor (8) can be additionally applied over the outer protective coating (7).

[0039] The armor (8) is made in the form of a shell braid from thick heat-resistant stainless steel wires (for example, based on chromium-nickel alloys of the austenitic class), which do not form peeling scale at high temperatures and give the entire product ultimate mechanical resistance to tensile, crushing, vibration and impact loads typical of heavy metallurgy.

[0040] Industrial manufacturing technology (implementation method)

[0041] The possibility of real industrial implementation of the utility model with the achievement of the expected technical result is confirmed by the fact that for its full-scale serial production, only well-known materials, serially produced by the chemical and metallurgical industries, are used, and standardized technological processes are applied, implemented on classical cable equipment (drawing mills, cigar twisting machines, high-speed winding and braiding machines).

[0042] To empirically confirm the viability of the idea in pilot production conditions, a full-size functional sample of the claimed high-temperature electric cable with a nominal effective cross-section of the central conductive core of 1.5 mm was manufactured. 2 .

[0043] Semi-finished nickel grade NP1 was used as a precursor for the production of the conductive core (1) and metal screen (6). The central conductive core (1) was formed on a cigar-type twisting machine by concentrically twisting 21 nickel wires, each with a diameter of 0.3 mm.

[0044] The first multilayer dielectric barrier (2) was formed on an automatic tape-wrapping machine. The core (1) was spirally wrapped in a single pass using high-temperature phlogopite mica-containing tape (initial thickness 0.14 mm). The most important process parameter was the winding pitch, ensuring a stable overlap of tape turns of at least 50%. This technological solution guaranteed the presence of at least two continuous layers of mica insulation at any point in the cable cross-section, bridging any possible microcracks in the tape itself.

[0045] Next, the first fixing braid (3) was applied on a vertical braiding machine using specialized heat-resistant silica threads. The braid's surface density (continuity index) was 85-90%. This created a dense, uniform, fine-mesh textile bandage that securely compressed the mica layer.

[0046] In strict sequence, using a similar technological method, the second dielectric barrier (4), formed by the spiral winding of phlogopite tape, and the second fixing braid (5), woven from silica threads with an identical density coefficient of 85-90%, were successively applied.

[0047] The protective metal shield (6) was formed on a high-speed, 24-spool heavy-duty braiding machine. The spools were made exclusively of nickel wire (grade NP1) with a diameter of 0.3 mm, which underwent a thermal annealing step to relieve internal stress after drawing. The surface optical density of the nickel wire braid was 85%, which, according to electrical engineering standards, is absolutely sufficient to ensure reliable shielding from external high-frequency electromagnetic interference and create a path for the safe discharge of short-circuit currents to ground.

[0048] The final stage of the assembly cycle was the application of an outer protective coating (7) made of dense silica threads with a coating density coefficient of at least 90%.

[0049] Device operation under extreme dynamic conditions

[0050] The key, insurmountable technical problem of all the studied analog and prototype cables was the catastrophic loss of dielectric integrity under prolonged exposure to extreme temperatures. This occurred due to the combination of two detrimental factors: the colossal difference in the thermal expansion coefficients of the metal components and the inevitable burnout of the organic binder holding the mica flakes together. The proposed utility model effectively solves this fundamental problem through the complex interaction of the thermomechanical properties of its composite elements during dynamic operation (directly during intense heating).

[0051] The implementation and operation of the utility model are as follows. During normal cable installation in a work area with extreme temperature profiles (e.g., in close proximity to the working space of a blast furnace, in gas turbine units, or in the coolant circuits of high-temperature reactors) and the application of an operating electrical signal, the cable sheath and core temperature can reach peak values ​​of up to +1000°C.

[0052] When the thermal barrier reaches +500…+600°C, the organosilicon binder, which initially provided flexibility to the phlogopite tapes in the first (2) and second (4) barriers, undergoes complete, irreversible thermal destruction (pyrolysis burnout). The flexible mica tape is transformed into a dry, mechanically unbound, loose ash layer consisting exclusively of inorganic mineral flakes of pure phlogopite and residual silica ash. In prior-generation cables, it was at this critical stage that the insulation rapidly delaminated, crumbled, and fell out under the influence of gravity or the slightest operational vibration of the equipment.

[0053] However, in the architecture of the claimed utility model, this dry, shapeless ash packet is fixed (encapsulated) in microvolumes between the turns of the conductive nickel core (1) and the mesh of the first silica braid (3), as well as in the annular gap between two solid silica braids (3) and (5). The silica fibers used have a phenomenal melting point, significantly exceeding +1100°C, and, critically importantly, have an extremely low, near-zero coefficient of linear thermal expansion (about 0.55⋅10 -6 K -1 ). Unlike metals, silica threads practically do not lengthen or deform when heated, forming an absolutely rigid, non-expanding, static cylindrical frame.

[0054] With a further increase in temperature gradient up to the target +1000°C, the key declared technical result begins to fully manifest itself, due to the innovative use of chemically pure nickel (grade NP1) simultaneously and consistently for both the core (1) and the screen (6). It is known that the average coefficient of thermal expansion of nickel NP1 over a wide range from +20 to +1000°C is approximately 16.6⋅10 -6 K -1 .

[0055] The massive conductive core (1) undergoes a natural geometric expansion when intensively heated to +1000°C, undergoing significant radial thermal expansion. Since the expanding metal core exerts enormous thermodynamic force on the loose ash-mica layer from within, while this fragile layer is irresistibly held in place by the ultra-rigid, non-expanding silica braid (braids 3 and 5), the system achieves a unique, beneficial effect of radial thermal compaction. Dry mica flakes and ash are mechanically compressed (compacted) within a strictly enclosed annular space. The porosity of the insulating layer is significantly reduced, becoming a dense monolith, which dramatically prevents the formation of electrical breakdown paths and maintains the dielectric barrier in a fully functional, current-impermeable state.

[0056] In the design of the claimed utility model, the protective shield (6) is made of pure nickel grade NP1. Consequently, the CTE of the outer shield (6) is mathematically and physically strictly equal to the CTE of the inner core (1). When heated to any temperature delta, the core and shield synchronously expand by an absolutely identical amount, with micron precision. Zero difference in thermal elongation completely eliminates, according to the laws of physics, the occurrence of internal longitudinal shear friction stresses. The shield and core expand absolutely synchronously, as a single monometallic organism.

[0057] Additionally, the integrated second silica braid (5), located directly beneath the metal shield (6), serves as a crucial shock-absorbing, load-distributing buffer. The rigid metal wires of the expanding nickel shield now rest not on exposed, brittle annealed mica, but on high-strength silica strands, which effectively distribute localized radial pressure and prevent the metal from pushing through the insulation to the core. The physical separation of the common mica layer into the first (2) and second (4) completely independent dielectric barriers by means of the intermediate silica braid (3) prevents the radial growth of microcracks. If a defect forms in layer (2), it cannot propagate to layer (4), statistically eliminating the formation of direct through-hole channels for avalanche electrical breakdown through the entire thickness of the insulation.

[0058] Objective empirical data from thermal bench tests

[0059] To provide irrefutable, objective confirmation of the stated technical result (a significant increase in operational reliability at temperatures up to +1000°C), a series of comparative high-temperature bench tests were conducted. The tests were carried out in a certified laboratory high-vacuum muffle resistance furnace of the SNOL type. The test methodology was based on the principles of the international standards GOST IEC 60331 (Testing of electric cables under flame conditions), with engineering adaptation of the protocols for ultra-high temperatures and prolonged exposure.

[0060] To conduct a correct comparative analysis, two test samples of cable products of the same cross-section, each exactly 1 meter long, were manufactured:

[0061] Sample A (Control Prototype): The conductive core is stranded nickel. Dielectric insulation is provided by a continuous winding of phlogopite tape (4 layers in total) without the use of separating or internal inorganic braids. The outer protective metal shield is braided from 12Kh18N10T austenitic stainless steel wires.

[0062] Sample B (the claimed utility model): the design fully complies with the stated formula. Conductor core - nickel (NP1). First barrier - 2 layers of phlogopite tape. First silica fixing braid (85% continuity). Second barrier - 2 layers of phlogopite tape. Second silica fixing braid (85% continuity). Outer protective metal screen - woven from nickel (NP1).

[0063] Both test specimens were rigidly mounted on a ceramic refractory stand inside the working chamber of a muffle furnace. A test operating voltage of 300 V AC (with grounded shields) was continuously applied to the conductive conductors of the specimens. The furnace temperature controller was programmed to smoothly and linearly increase the chamber temperature from normal room temperature (+20°C) to extreme temperature (+1000°C) at a gradient rate of 10°C / min. The isothermal hold time (exposure) upon reaching exactly +1000°C, as specified in the regulations, was 180 minutes. During the test, precision measuring systems continuously recorded leakage currents through the insulation, and the moment of complete electrical breakdown (short circuit) was recorded with an accuracy of up to a second. The summary results of the laboratory thermal profiling are presented in Table 1 below.

[0064]

[0065] The obtained array of objective empirical data allows us to draw an unambiguous scientific conclusion that the replacement of the outer screen material from stainless steel to chemically pure nickel (which leads to the physical elimination of destructive shear stresses) in an inseparable combination with the introduction of a multi-layer divided exoskeleton made of silica braids (which ensures rigid spatial fixation of the ash residue), in combination, provides a multiple, radical increase in the operational reliability of cable products under conditions of long-term, continuous thermal exposure at temperatures up to +1000°C.

[0066] Based on the above, the claimed utility model completely, effectively, and demonstrably solves the technical problem posed in the application. The utility model is undoubtedly feasible for its direct and indirect purposes using standard, accessible industrial technologies, equipment, and raw materials, which irrefutably demonstrates its full compliance with the "industrial applicability" criterion of patentability.

Claims

1. A high-temperature electric cable comprising one metallic conductive core insulated by a multilayer dielectric barrier based on mica-containing tapes, a protective metallic screen in the form of a wire braid and an outer protective coating made of inorganic fibre, characterised in that the conductive core and the protective metallic screen are made of pure nickel, wherein said multilayer dielectric barrier is made in the form of first and second multilayer dielectric barriers formed by concentrically applied layers of tapes based on phlogopite mica, wherein a first continuous fixing braid made of silica or quartz threads is applied over the first dielectric barrier, a second continuous fixing braid made of silica or quartz threads is applied over the second dielectric barrier, and the outer protective coating is made in the form of a braid made of silica or quartz threads.

2. A high-temperature electric cable according to paragraph 1, characterized in that an additional armor in the form of a braid of heat-resistant stainless steel wires is applied over the outer protective coating.

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