RU73117U1 - FIRE SAFE CABLE - Google Patents

Abstract

The utility model relates to the field of electrical engineering and defines the design of a fireproof cable for fixed installation in power circuits, control, monitoring and signaling circuits.

The cable contains one or more conductive conductors and fireproof combined insulation made by the method of combined tape winding with two tapes. The first of these tapes is glass mica; the second is made of rubber based on boron-siloxane rubber and is laid on top of each glass mica tape. Tapes are laid in one direction to reduce air gaps. The number of sequentially applied tapes is determined by the required electrical strength of the cable.

To ensure a radial uniform electric field in the insulation, semiconducting shields are provided along the conductive core and fireproof combined insulation.

3 points of the formula; 1 illustration.

Description

The utility model relates to the field of electrical engineering, namely, to the designs of fireproof (fireproof, fireproof) cables intended for operation in power circuits, control and monitoring circuits for stationary installation. We define a fireproof cable (FRHF cable - flame resistant, halogen free) - as a product that complies with the IEC-60331-21 standard, which defines the minimum uninterrupted transmission of electrical energy at a flame temperature of 750 ° C for 90 minutes.

Several approaches are known in the design and manufacture of fireproof cable insulation. In the first of them (Privezentsev V.A., Grodnev I.I., Kholodny S.D. Fundamentals of cable technology. Textbook for high schools. - M .: Energy, 1975. - 471 p.) Insulation is made from mineral components , for example, glass and mica or ceramic powder with the addition of plasticized silicone resin. The disadvantage of these analogues is the significant complexity and low productivity of the cable manufacturing process, the toxicity of the insulation components used.

In the analogue of the patent for a utility model of the Russian Federation No. 58777 (Chadov OA Fire-resistant cable. Patent for a utility model of the Russian Federation No. 58777 dated 2006.06.21), two-layer (graded) combined insulation was used. Conductors in this design are insulated by extrusion of a composite material, which in normal working condition (in the absence of a flame) provides electrical insulation strength and its flexibility. In _{case of} fire, this material turns into ceramic with a volume resistance of ρ _v ≥10 ¹¹ Ohm · cm, avoiding short circuiting between the conductors. On top of the composite material layer, an insulation layer of polymer halogen-free plastic compound is applied, which burns out in case of fire. It is also a container for composite material during the entire time the cable operates in normal mode. The contribution of the second layer of insulation to ensuring electrical strength is not needed. The disadvantage of this analogue is the use as a structural material of an expensive crosslinkable thermochemical or radiation method of a polyethylene composition, the redundancy of the second insulating layer in terms of ensuring the electric strength of the cable.

In the analogue of the patent for a utility model of the Russian Federation No. 58777 (Korovin N.G., Korovin M.G., Savushkin I.V. Fire-resistant electrical cable. Patent for

Utility Model of the Russian Federation No. 47131 dated 2005.02.08) an additional fire-resistant barrier made of a composite material for belt insulation, made in the form of an extruded continuous concentric layer, which at high temperature (fire) turns into ceramic. As a fire-resistant barrier, one or two glass-mica tapes coated with silicone grease can be additionally applied. The disadvantage of the analogue in this embodiment is the complexity, cost of construction and the complexity of the manufacturing process. The barrier does not protect the layer of cross-linked polyethylene from combustion, after which a cavity is formed between the two layers of the composite material, filled with either a conductive material and a gas or silicon oxide powder. The cable design becomes mechanically unstable. Similarly to the last model, but without silicone grease, power cables of grades, for example, PPGNG-FRHF, PvPGNG-FRHF, are produced in the Russian Federation (Appendix to the journal “Cables and wires”. - 2007. - No. 2. - P. 10).

The prototype of this utility model is a fire-resistant electrical cable according to the patent for utility model No. 47131 (Korovin NG, Korovin MG, Savushkin IV. Fire-resistant electrical cable. Patent for utility model of the Russian Federation No. 47131 dated 2005.02.08) . The insulation of the prototype cable is two-layer. Layer on TPG - fireproof; made by winding with glass mica tapes laid in one direction with an overlap of at least 48%. Each layer is coated by smearing with an organosilicon material based on polymethylsiloxane liquids or oligomeric compounds in the form of a non-drying paste, which increases the resistance of mica tape to mechanical stress and increases the dielectric strength in the initial state. The second layer of insulation is made of a polymer crosslinkable composition that acts as the main insulation during long-term operation of the cable in the absence of fire. The disadvantage of the prototype is the complexity of the manufacturing process for the manufacture of cable insulation, including incompatible operations: tape winding, lubrication and extrusion. Dusting with paste cannot provide a uniform coating of glass-mica tape and cannot exclude its extrusion during winding. In addition, after the combustion of the polyethylene layer, the cable structure becomes mechanically unstable.

When creating a utility model for this application, the task was to create a design of a fireproof cable in which due to the new relative positioning of the insulation elements, the introduction of its new elements and the use of new materials, the electrical strength in normal and emergency (in the process

fire) operating modes up to an operating voltage of 10 kV, mechanical stability of the cable structure in normal and emergency operation modes is increased, and it is possible to combine the technological processes of applying insulation in order to increase productivity and reduce the cost of the cable.

The problem is achieved in that in a fireproof electric cable, which includes one or more conductive conductors, fireproof combined insulation, a shield made of copper wires superimposed on an electrically conductive polymer tape, filling (in the case of several conductors), a protective cover consisting of an inner sheath, armor and the outer shell, semiconductor screens are made along the conductive core and fireproof combined insulation, the insulation of each conductive core is made with two tapes using entwined tape winding. The first of these tapes - glass mica is laid on a semiconductor screen along the TPG down with a layer of mica, the second, made of rubber, which is made to improve adhesion based on borsiloxane rubber (or rubber with additives of organic compounds with polar groups - polyester resins) - on top of the glass mica tape . The number of sequentially applied tapes is determined by the required electrical strength of the cable.

The advantage of the proposed fireproof cable option is that the electric strength of the cable is ensured by both components of the combined insulation: in normal operation, a glass mica tape laid with a mica layer on a semiconducting layer in accordance with the TJ, plus non-vulcanized borsiloxane rubber; in emergency mode - glass mica tape plus silicon oxide (non-conductive organosilicon ash), as a result of the combustion of borsiloxane rubber when the temperature rises to 750 ° C. At temperatures below the burning temperature of the rubber, insulation is carried out with glass mica tapes and vulcanized borsiloxane rubber. The long-term electric strength of this cable increases in the normal mode, as compared with the prototype, the air gap between the glass-mica tapes is excluded, which is the least durable with respect to electrical sliding discharges at the insulator-air interface. The dielectric-air interface is replaced in this design by the dielectric-insulator interface, since the borsiloxane rubbers have increased autoadhesion to the glass fabric of the glass mica tape. In addition, when winding, rubber bands are stretched by 20-50%, providing mechanical strengthening of the glass mica tape even at room temperature under the influence of pressure from tension. Bonding quality with increasing temperature

increasing. As a result, an almost monolithic two-layer insulation is formed. The gain in dielectric strength is determined by the ratio of the dielectric constant (ε) of rubber and air, equal to about 3.

The proposed utility model in the case of a single-core cable is shown schematically in FIG.

In Fig. Depicted: 1 - conductive core; 2 - semiconducting screen for a conductive core; 3 - fireproof combined insulation; 4 - semiconducting screen for fireproof insulation; 5 - screen made of copper wires (with conductive polymer tape); 6 - a protective cover (inner shell, armor and outer shell).

Example

The cable conductor round or sector (item 1 in Fig.) Is made of 1 or 2 classes of flexibility from copper or aluminum. Semiconducting screens according to TPG (pos. 2 in Fig.) And insulation (pos. 4 in Fig.) With a thickness of 0.2-0.8 mm are made of semiconducting rubber tape or semiconducting crepe paper with a specific volumetric electrical resistance ρ _v ≤100 Ohm Cm (20 ° C). Semiconducting shunts shunt air inclusions on the conductors and copper screen and provide a radial uniform electric field favorable for cable insulation.

The main fire-resistant material of combined insulation is Elmicatex 54509 glass-mica tape TU 3492-023-50157149-00 (item 3 in Fig.), Which is a layered composition consisting of mica paper and glass fiber fabric, impregnated and glued together organosilicon binder. The tape thickness is 0.12 ± 0.015 mm. Dielectric constant (with a binder content of 15% by weight) ε≈5.2; dielectric strength E _CR = 12 MV / m Mechanical properties allow the use of high-speed (up to 3000 rpm) insulating machines. Silicone resin glues mica with fiberglass, providing additional electrical strength, and at high temperatures in fire conditions forms an inorganic polymer that holds the mica barrier after the destruction of fiberglass.

Borsiloxane rubber (self-adhesive insulating tape made of borsiloxane rubber), from which the tapes of the second component of the combined fireproof insulation are made (pos. 3 in Fig.), Are obtained by introducing Borsiloxane polymer in the amount of B: Si = (1: 100) ÷ (1: 200). Wherein

rubber has the following electrical characteristics: dielectric strength E _pr = 20-25 MV / m (which is more than for glass mica tape); ε = 2.7-4.5; ρ _v ≥2 · 10 ¹² Ohm · m; tanδ (50 Hz) = (3-20) · 10 ^-3 .

Both insulation components are superimposed in a single pass on a single insulating machine. The last layer of silicone tape is double the thickness (of two tapes).

To exclude the mutual influence of the conductive conductors on each other and to protect against external electromagnetic fields, each isolated conductors are shielded with a copper wire screen (braid; item 5 in Fig.). To coordinate the conductivity of the semiconducting and copper screens, an electrically conductive polymer tape was laid between them (pos. 5 in Fig.).

The cable sheath consists of a substrate (inner shell), armor and an outer shell (item 6 in FIG.). The inner and outer shells (item 6 in FIG.) Are made of plastic compound by extrusion. The armor (pos. 6 in Fig.) Is made of two steel strips 0.3 mm thick.

When calculating the thickness of the combined insulation, we take into account that the glass mica insulation in the worst case (in case of fire) must withstand the full operating voltage - we will not take into account the additional effect of the contribution to the insulation resistance of silicon oxide. Glass-mica insulation is counted on the full, maximum possible operating voltage of 10 kV. The maximum working electric field strength E _{slave is} determined taking into account a possible increase in voltage in the cable network (k ₁ = 1.15), overvoltage (k ₂ = 2.5), the spread of electrical insulation strength (k ₃ = 1.4) and a possible decrease dielectric strength during prolonged application of voltage (k ₄ = 1,2). Then, at E _pr = 12 MV / m for glass mica tape E _slave ≈ 2.48 MV / m. The thickness of the glass mica insulation is determined for a cable with a conductive core section of 240 mm ² (TJ radius r = 8.74 mm; taking into account the thickness of the semiconducting screen along the core, the inner insulation radius is 9 mm). Outer radius and the thickness of the glass mica insulation will be equal to δ≈5.1 mm. The number of layers of glass mica and rubber tapes with a thickness of 0.12 mm is taken equal to 43. The last layer of silicone tape is doubled (from two tapes). The total thickness of the insulation (glass mica and rubber tapes) Δ≈10.4 mm.

Claims (3)

1. Fireproof electrical cable containing one or more conductive cores, fireproof combined insulation, screen, filling and protective cover, characterized in that the insulation of each conductive core is made by two tapes by the method of combined tape winding, the lower of these tapes is glass-mica, the second made of rubber based on borsiloxane rubber, placed on top of glass mica tape. 2. Fireproof electric cable according to claim 1, characterized in that the semiconducting screens are made according to the conductive core and the fireproof combined insulation. 3. Fireproof electrical cable according to claim 1, characterized in that the number of sequentially applied strips is determined by the necessary electrical strength of the cable.