Symmetrical fire-resistant cable

IPC classes for russian patent Symmetrical fire-resistant cable (RU 2370839):

H01B7/295 -

H01B11/02 - Cables with twisted pairs or quads (transposing, crossing, or twisting at joints H04B; balancing of earth capacitance H04B)

Another patents in same IPC classes:

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Symmetrical fire-resistant cable / 2370839
Invention is related to cable technology, to symmetrical fire-resistant cables for transfer of high-frequency signals in communication systems, industrial automation and systems of fire protection alarms in nuclear power plants, in particular inside containment. Cable comprises at least one symmetrical pair of current-conducting strands insulated by fire-resistant organosilicic rubber and polyimide film, covering each of insulated strands, and separating them with single layer. At the same time film fixes insulated strands between each other, providing permanent symmetry of pair along cable length.

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Balanced unshielded 25-paired cable of category 5e of bunch structure with improved characteristics / 2462777
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Non-combustible cable composition / 2382427
Invention relates to the cable industry, and more specifically to preparation of a non-combustible composition meant for fire protection of electrical cables, as well as for protecting cables from corrosion and mechanical damage. In order to provide good operational characteristics and technological effectiveness, the non-combustible cable composition contains 25-70 wt % metal hydroxides as antipyrene, 20-60 wt % thermoplastic binder, as well as 1-20 wt % resin and 1-20 wt % plasticisers as an additive.

Low-fume self-extinguishing cable and flame retardant composition containing natural magnesium hydroxide / 2394115
Self-extinguishing cable contains conductor and flame-retardant coating containing polymer matrix and particles of natural magnesium hydroxide of medium diametre of particles d₅₀, equal to 0.5-5.0 mcm, and average diametre of pores less or equal to 0.35 mcm. Average diametre of particles d₅₀ is determined on assumption, that 50 vol. % particles of natural magnesium hydroxide have diametre bigger, than the said value, while 50 vol. % particles of natural magnesium hydroxide have diametre less, than the said value.

Electric cable resistant to distribution of electric arc / 2467421
This invention relates to electric cables, which may be used in aviation, for instance, on board of a plane. A cable comprises the following components: an electric conductor, surrounded with the first layer, comprising at least one winding of mice tape, besides, the specified mica tape comprises mica particles applied onto a substrate by means of a polymer binder; the second layer comprising at least one winding of a polyimide tape; and the third layer comprising at least one winding of a polytetrafluoroethylene (PTFE) tape; besides, the first layer is exposed to thermal treatment under temperature of at least 400°C; and at the same time the ratio R of the weight per unit of PTFE length to the sum of weights per unit of the polymer binder and polyimide length is such that: R is more or equal to 2, when the section of the electric conductor is not more than 0.2 mm², and is preferably in the range between 0.1 mm² and 0.2 mm²; R is more or equal to 4, when the section of the electric conductor is strictly more than 0.2 mm² and strictly less than 0.6 mm²; R is more or equal to 6, when the section of the electric conductor is equal to 0.6 mm²; and R is more or equal to 12, when the section of the electric conductor is strictly more than 0.6 mm², and preferably not more than 3 mm².

FIELD: electric engineering.

SUBSTANCE: invention is related to cable technology, to symmetrical fire-resistant cables for transfer of high-frequency signals in communication systems, industrial automation and systems of fire protection alarms in nuclear power plants, in particular inside containment. Cable comprises at least one symmetrical pair of current-conducting strands insulated by fire-resistant organosilicic rubber and polyimide film, covering each of insulated strands, and separating them with single layer. At the same time film fixes insulated strands between each other, providing permanent symmetry of pair along cable length.

EFFECT: increased reliability, higher service life of fire-resistant symmetrical cable under conditions of operation inside containment of nuclear power plants, with provision of minimum level of losses and preservation of rated parametres.

2 dwg

The invention relates to a cable technology, in particular to the balanced fire-resistant cables for transmission of analog and digital signals. The following cables are used to organize data lines in communication systems, industrial automation systems and fire alarm systems at nuclear power plants, in particular, inside the trays.

The main problem faced by the developers of the cable - a constructive implementation of the latter and the correct choice of materials. The latter must preserve the original chemical composition, structure and properties after exposure to ionizing radiation, that is, to have the necessary radiation resistance.

The level of fire safety is flame retardant cables, flame retardance, low smoke generation. All of the above must be combined with the provision of a minimum level of loss attenuation factor and the required set of normalized electrical parameters: capacitance, impedance, capacitive asymmetry pairs and other

The domestic industry are produced in accordance with K-320-2002 [1] fire resistant cables for transmission of electrical signals and distribution of electric power in stationary electrical installations in operation inside the trays nuclear power plants.

Cabalistical the conductors, over each of which imposed the winding of the mica tape. On top of the windings superimposed insulating layer made of nerasprostraneniia combustion of polymeric material. When the fire polymeric layer burn, but the cable keeps working for at least 90 minutes (standard), because the presence of a layer of mica between the electric conductors prevents them from short circuits.

The disadvantages of these cables is due, firstly, difficulties overlay winding of the mica tape on the wires with a small diameter, such as vein data cables with a diameter of less than 1 mm. secondly, used as insulation, halogen-free polymer composition has a high dielectric loss, which does not allow to use it for high-frequency cables.

Known flame retardant balanced cables produced by the company "Fabbrica Trentina Conduttori" according to German standard DIN VDE 0815 with core diameter of 0.6 and 0.8 mm [2]. As insulation is used flame-retardant silicone rubber, which made it possible to apply data cables for communication and data transmission circuits with the required level of fire resistance, in particular, in the address system fire alarm system. The use of fire-resistant silicone rubber ensures that the cable is exposed to fire for the required 90-180 minutes But in any available source of information does not contain data that would be that the cables during operation are (under certain conditions) additional impact - ionizing radiation. However, it is known that the dose that causes a significant (up to 50%) changes in the mechanical properties of the flame-retardant silicone rubber equal to (4÷5·10⁵) Gr. The value of the integral of the absorbed dose over the lifetime of the cable (40 years) without regard to possible accidents may be at least 3.6·10⁵Gr. This allows us to conclude that these cables can work under conditions of ionizing radiation, but the issue of increasing the life and work cables during emergency situations can be very problematic.

Constructive design of cables, well-known structures [2], contains polymer film located over twisted pair or bundle pairs (and not in isolation of each core), which is not designed for additional protection silicone rubber from ionizing radiation, and this goal was not persecuted by the developers of the famous cables.

The problem to which the invention is directed, is the creation of fire symmetric cable with the required characteristics, providing long life (30-50 years), including heightened the radiation radiation. The main problem faced by the developers of these cables, and design implementation of recent and correct the choice of materials. The latter must preserve the original chemical composition, structure and properties after exposure to ionizing radiation, that is, to have the necessary radiation resistance. In addition, they must possess the necessary resistance to flame, fire propagation and smoke emission. All of the above must be provided with a minimum level of loss - attenuation factor and with the necessary set of normalized electrical parameters - capacitance, impedance, capacitive asymmetry pairs and other

Recently the working conditions of electrical insulating materials, have become more severe. This is because the significantly increased demands on the reliability of electrical devices, including cables, to a very large extent determined by the reliability of their electrical insulation. In some cases, insulating materials have to work in conditions of exposure to chemical agents, ionizing radiation. For cables (as for other electrical devices) set the parameters characterizing the reliability and durability of their work. These include a parameter such as services (for example, 30-50 years). All these parameters depend on the properties and quality of used electrical insulating materials.

Insulating materials used in the solution of the task that faced the applicants have provided the cable with the desired characteristics. In this regard, these materials will be considered first.

As a rule, all insulating materials having the required dielectric properties are synthetic. In particular, the most important high-molecular compounds, such as organic polymers, such as polyimide, polyethylene terephthalate and materials such as fire resistant silicone rubber, the basic structure of which is a chain of atoms of silicon and oxygen with rare crosslinking. This circumstance is due to its inherent, to some extent, inorganic in nature. Due to its special chemical structure of silicone rubber is characterized by a number of properties that allow it to occupy a special place among rubber elastic materials.

For cables essential electrical characteristics used as insulation materials, in particular fire-resistant silicone rubber. The main parameters characterizing the electrical properties cramps the new insulation, are volume resistivity and dielectric strength. In addition, an important characteristic of the cable is resistant to flame and resistance to the spread of combustion. To ensure durability of silicone rubber to the action of fire in fire-retardant formulations introduced ceremonial. For a range of cable products, this issue is of significant operational value, as often at short circuits in the electrical network or in case of fire in the premises cables are the source of the fire.

Signs of aging rubber are the loss of elastic properties, deterioration of the electrical and mechanical parameters and other basic characteristics. Over time, the outer layer of rubber insulation gradually hardens, cracks and in a certain period of time the insulation becomes brittle, and can break down. All this is a consequence of the oxidative degradation process is contained in the rubber of the rubber under the influence of radiation, oxygen, ozone, light, heat, and other factors. Ozone is exposed to the rubber, which are neotectonic rubbers. Flame retardant silicone rubber is resistant to weathering, ozone and oxygen, because it is based on ozonostoyky. But long-term life of the cables exposed to ionizing radiation the aging process is accelerated. Thus, the loss of health need to pass three stages of aging: the appearance of the first crack, decreased elasticity (relative elongation) to 50% and lose its elasticity.

In addition, the known electrically insulating organic polymer film is thin and flexible material that may be wound into a roll in various widths. Due to the high electrical and mechanical properties at small thickness of the films have found wide application in the electrical industry, including cable technology. Organic polymer film can be divided into two large groups, with different electrophysical properties: non-polar films are characterized by a low value of ε=(2,0÷2,5) and a small value of the loss angle (tgδ=10^-4), and therefore they can be used in high-frequency technology. Polar films have higher values of ε(3 to 10÷5) and tgδ (10^-3÷10^-2). Electric strength of the polar films, as a rule, higher than that of non-polar.

Polyimide films are among the most heat of organic polymers. At 500°C film twice stronger than the films made of polyethylene at 20°C. the Degradation occurs only at temperatures Wyse°C. The film does not melt or soften to 800°C. the Polyimide film has high mechanical properties. A distinctive feature of the film is a high radiation resistance. The film retains sufficient elasticity after exposure to gamma radiation 4,16·10⁷Gr and 50% of its original elongation after irradiation by the electron flow 6-10 Gr. Long-term working temperature of the film 220°C.

The combination of high mechanical, electrical properties and radiation resistance, and heat resistance at a small thickness of 30-60 μm has allowed films find wide application in the electrical industry, including cable technology. You should pay attention to the fact that the radiation resistance of polymeric materials, primarily determined by the change of their mechanical properties. The change in electrical properties is, in many cases, the consequence of the change of mechanical properties. Electrical properties of electrical insulating materials relatively little change depending on the absorbed dose, if the material is not irreversible changes in the structure. The beginning of change in these properties corresponds to the onset of the irreversible changes in the structure, which is largely accompanied by changes in the mechanical properties of the material. Therefore, the radiation resistance of electroid the calculations material, determined by the change in mechanical properties is more significant.

Detailed description of the properties used insulating materials can be justified by the fact that this cable is designed to work in a wide range of operational impacts within the trays. In addition, it should be noted that a permanent stay cables in the pressure zone of the nuclear power station (compared to normal operating conditions) is complicated not only by constant exposure to radiation during normal operation of the reactor, but also a set of special effects, characteristic for emergency operation modes. To such influences, in particular, include: temperature, pressure, ambient humidity, ionizing radiation, solutions of chemical reagents. Regardless of this cable must be able to perform its functions.

Due to the specifics of operating their design must ensure that the fire resistance and radiation resistance in combination with low losses (attenuation factor) and with the necessary set of electrical parameters (capacitance, impedance, capacitive asymmetry pairs).

Increasing the radiation resistance of silicon rubber is achieved by protecting the insulation from the free access of oxygen is, contributing to the destruction of the rubber during its operation. As a protective insulation layer conductive wires used polyimide film, which is higher than that of silicone rubber, radiation resistance and is impervious to oxygen molecules. However, if we impose on each core symmetric pair of film and then twist these wires in pairs, the contact places lived to be at least a double layer of film (two conductors). To ensure the specified electrical parameters (capacitance and impedance) at a fixed size of cable you will need to reduce the thickness of the layer of silicon rubber, which is unacceptable. Reducing the thickness of the rubber in isolation symmetric pair cable will reduce its resistance. In addition, the increase in the mass used polyimide film mergelina space leads to an increase in dielectric losses in the cable, growth attenuation factor.

So, the expected technical effect of the invention is the creation of cable design, which provides fire resistance and radiation resistance in combination with the minimum achievable level of losses (attenuation factor) and the necessary set of electrical parameters. The review of all application materials have allowed the detection of the th set of essential features, which are causally linked to the technical result.

Fire symmetric cable containing sequentially spaced core comprising at least one symmetrical pair of insulated silicon rubber conductive wires and a polymer film on top of the core, are located below the screen and the protective shell of nerasprostraneniia combustion of polymeric material. The film used a polyimide film, which in cross-section of the cable has an S-shaped configuration having two cavities formed by a single layer of film around the perimeter of the isolation conductive wires of the pair. Each lived isolated pair is located inside one of the cavities and veins are connected to the specified film that ensures stability of the symmetry pair.

We must once again return to the consideration of essential features and to determine the technical result is behind these signs. Radiation-resistant film is a polyimide film and its structural performance, and the relationship with insulated silicone rubber cords produce a result. So, the film has an S-shaped configuration formed of one layer. Thus, the problem associated with the dual layer film in places of contact of the two lived (which leads to neo is the need to reduce the thickness of the rubber and, as a consequence, to reduce the resistance of the cable), are excluded.

The purpose of the symmetric cables for data transmission is the transmission of high-frequency signals from the transmitting device to the receiver. Thus the attenuation of the transmitted signal depends, in particular, from the dielectric losses in the insulation, as well as losses due to reflections and phase distortion of the signal-dependent capacitive asymmetry shielded pair. Also a significant characteristic S-shaped configuration of the film around the perimeter formed by one layer, suggests that the mass fraction of isolation with high value tgδ in the cable is reduced. Therefore, decreased dielectric losses in the cable. This leads, as already mentioned, the decrease of the coefficient of attenuation in the cable. S-shaped configuration has two cavities and each of them is located (along the length of the cable) one insulated lived. Bonded tendons between the pellicle, ensuring that the constancy of symmetry of the pair, which, in turn, leads to the reduction of losses due to reflections and phase distortions of the signal.

In conclusion, you need to stay on the polyimide film. Film in the claimed invention, performing the required safety functions, closes the surface of the silicone rubber single layer. However, the AFL is stvie extremely low gas permeability, one layer is sufficient to protect the rubber from exposure to atmospheric oxygen. Its high radiation resistance provides this protection and the integrity of the cable throughout its life cycle when operating in conditions of high radiation. Thus, all the essential features identified in the analysis of the invention, allowed to say that behind them previously identified technical result.

The invention is illustrated by the photograph of the layout of the cable core, shown in figure 1, where two insulated conductive wires twisted with imitating polyimide film tape, to illustrate the formation of a single layer of S-shaped configuration of the film of the structural element of the cable. To illustrate the construction of the cable used colored plastic tape, as in reality, the polyimide film is thin and transparent, and so the pictures would not be visible. As can be seen from figure 1, the specified element closes the surface of insulation and holds the insulated cores. Figure 2 shows a cross-sectional drawing of the claimed cable 1 - conductor 2 - insulation from heat resistant silicone rubber 3 - layer polyimide, 4 - symmetric pair, 5 - screen and 6 - shell nerasprostraneniia retardant polymer material.

An example of a specific realizationality can be represented by a symmetrical design of fire-resistant cables for nuclear power plants KSB brand _NG-FRHF 1×2×0,8, which contains single-wire copper conductive wires with a diameter of 0.8 mm, insulated fire-resistant silicon rubber stamps Elastosil R 503/75 (Germany). Insulated conductive wires are twisted in pairs with a polyimide film thickness of 50 μm. Over the film superimposed shield of aluminum foil, laminated polyethylene terephthalate film, the contact conductor of tinned copper wire. On top of the screen overlay sheath of halogen-free nerasprostraneniia retardant polymer material brand D - 898 R by "ondor compounds" (Germany). The cable has a normalized wave impedance of 100 Ohms and the attenuation coefficient at a frequency of 1 MHz of 2.16 dB/100 m

Literature

[1] TUK-320-2002 "control Cables, flame retardant and fire resistant, insulation and sheath of polymer compositions, halogen-free", JSC research Institute KP, Moscow, 2002, 26 S.

[2] Security cable. The company's catalog "Fabbrica Trentina Conduttori", Italy.

Fire symmetric cable containing sequentially spaced core comprising at least one symmetrical pair of insulated fire resistant silicone rubber conductive wires and a polymer film on top of the core are the screen and the protective shell of nerasprostraneniia combustion of polymeric material, wherein t is m, as the film used polyimide, which in cross section has an S - shaped configuration around the perimeter formed by one layer and having two cavities, each lived isolated pair is located inside one of the cavities, and the wires bonded between a specified film that ensures stability of the symmetry pair.