RU2573572C2 - High-frequency symmetrical fire-resistant sealed cable - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: cable comprises current-conducting strands from a round copper wire with insulation from fire-resistant organosilicic rubber, which are twisted in pairs jointly with insulating cords from water-blocking threads, on top of which a screen is laid from laminated aluminium foil with a metal layer outside and braids from copper tinned wires applied evenly above the laminated aluminium foil. Screened pairs of the cable with pair number of 2 or 4 are twisted into a core. The inner space of the cable core is filled with sealing compound and enclosed into a shell from a polymer composition that does not contain halogens.

EFFECT: increased resistance of a cable to exposure of open frame under single mechanical shock, preservation of cable operability after fire liquidation under long-term exposure of sinusoid vibration, increased ability of a cable to resist action of longitudinal hydrostatic water pressure.

2 cl, 2 dwg

Description

The invention relates to one of the branches of the electrical industry - cable technology, namely to symmetrical high-frequency sealed shielded cables for data transmission. The invention can be used in various industries where it is necessary to maintain the operability of cables under the conditions of exposure to an open flame, mechanical shock of a single action, sinusoidal vibration, longitudinal and radial hydrostatic pressure of water.

From the "prior art" is known a sealed, fire-resistant cable, including: one or more conductive conductors with rubber insulation with an additional fire-resistant barrier in the form of a winding with the overlap of one or two mica tapes, sealed with a vulcanizing dielectric composition, which fills all the voids under and between the tapes , as well as places of overlapping tapes; placeholders for interwire, insulating and inter-core voids; rubber sheath; common screen (RU 57958 U1, 01/17/2006). The fire resistance of the cable is ensured by introducing a thermal barrier with mica tapes in addition to working electrical insulation. Known cable retains the ability to transfer electrical energy when exposed to a flame during a fire. Tightness can be ensured by filling all voids in the cable with special sealing compounds having high adhesion to the structural elements of the cable.

The disadvantages of the known device are:

- the cable design does not provide high-frequency data transmission due to the lack of symmetrical isolated pairs;

- low resistance of the cable to mechanical stresses (sinusoidal vibration and mechanical shock of a single action) in a fire and after exposure.

The closest in technical essence to the claimed invention is a sealed fire-resistant cable, comprising: conductive stranded conductors with a winding of each of them with mica tape and the application of insulation from high density polyethylene; thermosetting sealing compound filling the space between all structural elements of an insulated conductive core and internal voids between insulated conductive conductors; polyvinyl chloride film belt insulation; a common screen in the form of a braid of tinned copper wires and an outer casing of polyvinyl chloride plastic compound (TU 0293-005-07537654-2008, OJSC SPO Arktika, SMPEVGO-40 [1]. The known cable ensures that the cable remains operational when exposed to a flame (800 ± 50) ° C for at least 180 minutes, as well as resistance to longitudinal and radial hydrostatic pressure up to 4 MPa (40 kgf / cm ² ).

The disadvantages of the known device are:

- the cable design does not provide high-frequency data transmission at a frequency of up to 250 MHz due to the lack of symmetrical isolated pairs;

- low resistance of the cable to mechanical stresses (sinusoidal vibration and mechanical shock of a single action) in a fire and after the end of its impact;

- reduced resistance to longitudinal and radial hydrostatic pressure up to 4 MPa (40 kgf / cm ² ) with requirements of at least 6 MPa (60 kgf / cm ² );

- the lack of the possibility of group cable laying;

- runoff of the sealing filler of the cable with its vertical laying at the maximum permissible operating temperature;

- a limited range of changes in operating temperatures of cable operation from minus 50 ° C to plus 70 ° C.

The objective of the claimed invention is to create a design of a high-frequency symmetric fire-resistant sealed cable that retains high physical and mechanical characteristics under the influence of hydrostatic longitudinal and radial pressure of 15.18 MPa (150 kgf / cm) with horizontal and vertical laying, as well as maintaining operability ( parameters of data transmission at a frequency of up to 250 MHz) of a cable in conditions of exposure to an open flame up to 850 ° C and a single mechanical shock of multiple actions tions for at least 2 hours, during cooling to a temperature of 400 ° C for 1.5 hours and after exposure to an open flame for 300 hours, when subjected to a sinusoidal vibration.

The technical result consists in increasing the resistance and strength of the cable to the effects of longitudinal and radial hydrostatic pressure of water, with the action of an open flame simultaneously with mechanical loads and maintaining high-frequency characteristics of data transmission up to 250 MHz during and after exposure to a flame.

The achievement of the technical result is ensured by a high-frequency symmetrical fire-resistant sealed cable containing conductive conductors insulated with flame-retardant insulation, a screen sealing the filling between the structural elements of the cable, and an outer sheath, while the conductive conductors are insulated with flame-retardant silicone rubber and twisted into at least two symmetrical pairs while each pair is superimposed a two-layer screen consisting of a laminated aluminum foil superimposed on aru with overlapping edges with a metal layer to the outside and braids of tinned copper wires, the sealing filling between the pair and the screen is made of fibrous water-blocking material, and between individually shielded pairs twisted into the core and the outer shell is made of low molecular weight organosilicon compound, and the shell is made of a polymer composition halogen free.

According to the claimed invention, the cable core is twisted from four individually shielded pairs.

The presence of a cord from water-blocking threads in a pair of twisted insulated conductive wires reduces the dielectric constant of the transmission medium of the electrical signal and, as a result, allows to reduce the attenuation coefficient of the pairs. The use of shielded pairs in the cable design using a continuous screen of laminated aluminum foil eliminates the penetration of the sealing filler into the pair and provides data transmission parameters at frequencies up to 250 MHz. If the compound enters the shielded pair, it can lead to a decrease of two orders of magnitude lower electrical insulation resistance of conductive conductors from silicone rubber. The resistance and strength of the cable to longitudinal and radial hydrostatic pressure of water up to 15.18 MPa (150 atm) is achieved through the use of two types of sealing materials in the design: filaments of fibrous water-blocking material and low molecular weight organosilicon compound. Water-blocking threads provide sealing of the space between the insulated conductive wires of the shielded pair, the compound fills the inner space of the core between twisted shielded pairs. Due to the adhesion of the sealing compound to the inner part of the cable sheath, extrusion of the core under the influence of hydrostatic pressure of water is excluded. Preservation of cable operability (data transfer parameters) and resistance to mechanical stress is due to the interaction of the screen in the form of a braid of tinned copper wires with silicone rubber insulation, twisted into pairs of conductive wires, when exposed to an open flame and after it ends. When combustible substances of insulation from organosilicon rubber (silicone rubber mixture) are burned out, it is converted into a brittle refractory ceramic layer, which is reinforced with a braid of tinned copper wires and the resulting reinforced ceramic insulating layer allows maintaining cable performance and data transmission parameters, both in case of fire, and after it, under the influence of mechanical loads.

The technical essence of the invention is illustrated by the following illustrations:

FIG. 1 is a cross-sectional view of a cable;

FIG. 2 is a longitudinal section view of a cable.

The cable includes conductive conductors 1 made of round copper wire, separately insulated with silicone rubber 2 (for example, UNISIL Proff PC 20-8465 silicone rubber mixture). Insulated conductive conductors are twisted in pairs together with cords of water blocking threads 3 (for example, water blocking thread GTA-20). Insulated conductors in pairs are distinguished by the color coding of adjacent insulated conductors to ensure clear identification of each pair. A screen of laminated aluminum foil 4 (for example, Alumoflex laminated aluminum foil) with overlapping edges with a metal layer to the outside and a braid of tinned copper wires 5, applied evenly over the laminated aluminum foil is superimposed on top of twisted insulated cores. Shielded cable pairs with the number of pairs 2 or 4 are twisted into the core. A sealed hull 7 of halogen-free, flame-retardant polymer material (for example, ConGuard S-6645 halogen-free polymer composition) with a sealing filler 6 (for example, two-component silicone compound PC-68 VIKSINT, consisting of a mixture based on synthetic heat-resistant low molecular weight, is applied over the core) rubber SKTN and catalyst No. 68).

Conductors 1 are made of round copper wire. An insulation 2 of fire-resistant silicone rubber is applied to each conductive core 1 by extrusion, combined with the vulcanization process on continuous vulcanization cable lines. Insulated cores 2 together with corbels of water blocking threads 3 are twisted in pairs by twisting machines. Hydrophilic water blocking threads have a high level of flexibility and excellent absorbency, which ensures a high degree of water blocking without the formation of residues of powder water blocking materials. Occupying an insignificant volume initially, when interacting with water, they increase in volume by several tens of times, forming a gel-like plug that fills all the free space between the insulated conductive veins of the shielded pair and, thus, prevents further longitudinal propagation of water in the shielded pair. GTA-20 water-blocking threads are made of polyester non-woven material with a layer of water-blocking powder and a water-soluble binder applied to it and have the following advantages: small diameter, stability of water blocking characteristics over the entire cable service life, high tensile strength, gel density, which provides reliable locking of the space between conductive insulated conductors from water penetration. A screen made of laminated aluminum foil 4 with overlapping edges, a layer of metal facing outward and a braid of tinned copper wires 5 is applied over a twisted pair. When burning combustible substances of insulation from organosilicon rubber (silicone rubber mixture), it is transformed into a brittle refractory ceramic layer, which reinforced with a braid of tinned copper wires, and the resulting reinforced ceramic insulating layer allows you to maintain cable performance and data transmission parameters under fire, so after it, with simultaneous exposure to mechanical stress.

Shielded cable pairs with the number of pairs 2 or 4 are twisted into the core. Simultaneously with the application of a sheath 7 of a halogen-free polymer material, a pre-prepared sealing compound 6 (for example, two-component silicone compound PK-68 VIKSINT consisting of a mixture based on synthetic heat-resistant low molecular weight rubber SKTN and catalyst No. 68) is fed through a dispenser into the cable core .

The resulting cable design is characterized by the following properties: maintaining operability (data transfer parameters) in a fire and after it while ensuring resistance to mechanical stress; cable resistance to withstand longitudinal hydrostatic pressure of water with a force of 15.18 MPa (150 kgf / cm ² ); non-proliferation of combustion during group laying; low smoke and gas emission; the absence of life-threatening halogen concentrations in cable combustion products.

As a result of the tests revealed the following.

The cable remains operational when exposed to an open flame with a temperature of 800 ± 50 ° C for 15 minutes, during cooling to 400 ° C for 1.5 hours and after exposure to an open flame, cooling for 300 hours when exposed to sinusoidal vibration. The data transmission parameters of the cables (attenuation coefficient, wave impedance) increase to 7% if 2% of the total length of the laid cable is damaged by open fire. Cables can work:

-when outdoor laying at an ambient temperature of -60 ° to + 70 °, in the presence of protection against direct exposure to solar radiation;

- in water, including marine, at a temperature of + 2 ° C to + 35 ° C at a depth of up to 1500 m for at least 2 hours;

- for vertical installation with unlimited level difference.

Literature

[1] TU 0293-005-07537654-2008. Cables ship pressurized fireproof. Specifications, OJSC “SPA“ Arktika ”, SMPEVGO-40, Severodvinsk, 2008, 55 l.

Claims (2)

1. A high-frequency symmetrical fire-resistant sealed cable containing conductive conductors insulated with flame-retardant insulation, a shield sealing the filling between the structural elements of the cable, and an outer sheath, characterized in that the conductive conductors are insulated with flame-retardant silicone rubber and twisted into at least two symmetrical pairs while each pair is superimposed a two-layer screen consisting of a laminated aluminum foil superimposed on a pair with overlapping metal edges with a layer to the outside, and braids from tinned copper wires, the sealing filling between the pair and the screen is made of fibrous water-blocking material, and between individually shielded pairs twisted into the core and the outer shell - from a low molecular weight organosilicon compound, and the shell is made of a polymer composition that does not contain halogen free. 2. A high-frequency symmetrical fire-resistant sealed cable according to claim 1, characterized in that the core is twisted of four individually shielded pairs.

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