Coaxial three-phase heating cable. RU patent 2516219.

FIELD: electricity.

SUBSTANCE: invention is related to electrical heating cables and namely to designs of coaxial three-phase heating cables intended for heating of objects with different shape, size and purpose. The cable has three cores 1, 2 and 3, each core is covered with an external heat and electric insulating sheath 4, it has an inner 5 and outer 6 conductors interconnected in series and placed coaxially with an annular gap between them filled with the inner heat and electric insulating sheath 8, and a common protective jacket 9. Cable strands are identical and twisted. The jacket 9 has three layers, the lower layer 10 and the upper layer 11 are made of the heat and electric insulating material while the middle layer is made in the form of a metal wire braid 12, which can be earthed PE at the point of the cable connection to the electric mains and the point of in-series connection 7 of the inner 5 and outer 6 conductors. The outer conductors 6 of each core are interconnected at the final point and form an artificial earthing point.

EFFECT: improving electrical and fire safety of the cable, flexibility in any direction, linear heat power, reliability, service life, reducing power consumption and expanding the scope of application.

2 cl, 1 dwg

The invention relates to the electrical heating cables, namely, to designs of coaxial cables, heating phase, which are intended for heating of objects of different forms, sizes and purposes (anti-icing cable systems for roofs roofs, heated floors in residential and administrative buildings, various pipelines, roads, airports, stadiums, the soil in greenhouses etc) and can be used in various branches of industry, construction, transport, public utilities and agriculture, etc.

Famous cable heating, includes one Central oriented along the entire length of the cable conductor, enclosed in termoelectrotraning the shell, placed a metal braid, connected to the protective earth, and external termoelectrotraning shell [1]

Cables specified type found wide practical the use, simple and adaptable to production, have sufficient security and flexibility. However, they require increased electricity costs, as one of the Central oriented guide is not possible to consider it is useful to use different physical effects and field produced by the flow of electric current in the conductors.

The nearest technical the decision to declared is the coaxial cable heating phase, including three cores, each covered foreign sealed thermoelectromotive shell, has the inner and outer conductors, consistently connected among themselves and coaxially placed the ring the gap between them, and internal termoelectrotraning shell filling this ring gap, and General protective shell, which concluded the three strands [2].

Individual wires of the cable are located in one plane and parallel to each other, and the protective sheath is made of flat sealed thermoelectromotive material. Internal conductors of cable wires connected to phase tyres, and the outer - to the zero bus. To improve electrical safety in emergency situations outer conductors may be in the same electrical panel additionally connected to protective earth ground.

Such an implementation, cable allows you to close the electromagnetic field within the conductors of cable cores, amplify them, and most fully to use the resulting proximity effect that gives the cable significant advantages over widely used cables, heating [1], ensuring, first of all, a significant reduction in the energy intensity of the process of heating. But during tests and trial operation of this cable identified a number of shortcomings, significantly reducing its technical-economic effectiveness and scope. These disadvantages include the following:

- insufficient electrical and fire safety during operation in hazardous and especially dangerous conditions (roofs and roofs of buildings, cellars, road and other), as the grounding of the cable has only one end;

- performance of cable flat predetermines its limited flexibility in the plane of the location lived, which significantly narrows the scope of its application, especially when the heating surfaces of complex forms, which require the laying of the heating cable snake with a small step of installation, and makes its installation;

- in the absence of symmetry currents in certain phases of the network is not ensured balanced load in various veins cable, which reduces possible linear thermal capacity, reliability, service life of cables and increase energy consumption;

- execution of General protective shell single layer of thermoelectromotive material at a given flexibility cable in all directions in space also reduces its reliability and service life.

The objective of the invention is to increase the technical and economic indicators of the cable and the expansion of the application area.

The achieved technical result consists in increasing the electric and fire safety of cable, flexibility in any direction, linear thermal capacity, reliability, durability, decrease of power consumption and extend the scope of application.

This technical result is achieved by the fact that the heating cable coaxial three-phase, with three veins, each covered foreign sealed thermoelectromotive shell and has inner and outer conductors, United sequentially between themselves and coaxially placed with an annular gap between them, internal termoelectrotraning shell filling this ring gap, and General protective shell, which concluded the three veins, veins are twisted among themselves and identical, General protective shell has three layers, the bottom and top of which is made of tight thermoelectromotive material, and the middle layer is in the form of metal wire braid, with the possibility of ground in the place of connection of the cable to the electrical network and the location of the serial connection of inner and outer conductors lived, and outer conductors each conductor connected to the end point and form of artificial zero point, not electrically connected with a zero wire electrical network.

In addition, the cross-sectional shape of the bottom layer total containment with external parties is limited to metal wire braid middle layer, and the inside - closed curve corresponding to the form of the cross-section of twisting the wires of the cable.

Specified in an independent claim of the invention is a collection of characteristics included significant features, each of which is indispensable, and all together are sufficient to obtain a technical result.

Only the performance of each core of the cable with the inner and outer conductors, consistently interconnected and coaxially placed with an annular gap between them, filled internal thermoelectromotive shell, coated external hermetic thermoelectromotive shell provides under certain annular gap [2] the effect of proximity, i.e. alternating current in the outer conductor will not pass on external the surface of a conductor, and on its inner surface. Simultaneously, the impact of the skin effect (surface effect) on the effective penetration depth AC or conditional equivalent depth of penetration of the electromagnetic field, which is greatly reduced. This raises the electromagnetic field is closed in the annular gap between coaxial conductors and heating is accomplished not only by resistance, but, first of all, due to this field. Heated inner thermoelectromotive shell filling specified annular gap is much more electromagnetic field, and not by the heat transfer from conductors. This improves technical and economic indicators of coaxial cables, heating compared with applicable heating cables, veins which have one Central oriented along the entire length of the conductor.

Twisting the wires of the cable allows you to ensure it is given the same flexibility in either direction along the entire length of the cable, which expands the area of its application due to the possibility of use for heating surfaces of complex volumetric forms, and facilitates its mounting. In addition, it increases the total thermal power cable, as it increases the length lived on one linear meter cable length.

All three cable's core, which is the single-phase coaxial heating cables are identical, that is made of the same design parameters of the same materials. The result in all the veins of the influence of the proximity effect and skin effect will be the same. This predetermines the possibility of providing symmetry current in all the cable wires.

The mutual containment of three-layer cable, the lower and the upper layer which is made of tight thermoelectromotive material, and the middle layer is a metal wire braid, increases the strength of the casing of the cable without prejudice to its flexibility, while reducing the harmful effects of atmospheric precipitation, temperature and random shock and other mechanical loads. This increases the electrical and fire safety of cable, reliability and service life, especially when operating in hazardous conditions.

The implementation of the bottom layer total containment with cross-sectional shape, with limited external side of a wire braid middle layer, and the inside - closed curve corresponding to the form of the cross-section of twisting the wires of the cable, allows you to fill in emptiness in the twist. This guarantees the preservation of the mutual position of cable cores during its curves and, therefore, retains its advantages not only for rectangular parts of the installation.

The drawing shows the proposed cable with slits on the introduction coupling (the upper part of the drawing) and end fitting (bottom drawing).

The cable consists of three lived 1, 2 and 3, which is the single-phase identical coaxial heating cables, that is made of the same design parameters and of the same materials. Each lived covered external hermetic thermoelectromotive shell 4, has an internal 5 and outer 6 conductors. Inner conductor 5 can be completed with one or multi-wire from low-carbon steel galvanized wire. Outer conductor 6 - as a braid with density not less than 85% of the steel wires. Conductors 5 and 6 within each core consistently connected among themselves in the end fitting, for example, moulding junction 7 in copper or brass sleeve filled epoxy coated heat-shrinkable polyethylene pipe (not shown), and coaxially placed with an annular gap between them, filled internal thermoelectromotive shell 8.

Strands 1, 2 and 3 of cable twisted among themselves with the step of twisting 150-200 mm and imprisoned in General protective shell 9. Such a pitch when applicable diameters lived from 5.5 to 8.5 mm ensures the necessary flexibility of the cable with the simultaneous closure of electromagnetic fields inside a co-axial clearance between the inner and outer conductors lived. When a smaller or larger pitch interaction of electromagnetic fields is reduced and increase losses of electricity.

Shell 9 has three layers, the lower top 10 and 11 of which are made of tight thermoelectromotive material, and the middle layer is in the form of metal wire braid 12 with density not less than 85% and grounding PE cable was connected to the electricity network and the location of the serial connection 7 internal 5 and 6 outdoor conductors lived. Outer conductors 6 each conductor connected to the end point and form of artificial zero point N A,B,C, not electrically connected with a zero wire electrical network (not shown). The shape of the cross section of the lower layer 10 total containment 9 from outer side is limited to metal wire braid 12 middle layer, and the inside - closed curve corresponding to the form of the cross-section of twisting the wires of the cable. Shell 4, 8 and layers 10 and 11 shell 9 can be made of heat-resistant PVC, polyethylene, fluoroplastic, optical fiber or other similar materials.

Cable works as follows.

Cable connection to the network is made known in accordance with the applicable Regulations for electrical installation (PUE).

In the introductory coupling with the free end lived 1, 2 and 3 cable is part of the insulation. Then use the terminal clamps in a sealed raspahni box (on drawing does not show) internal conductors 5 each conductor is connected to the phases A, B and C electrical network, and the ends of all external conductors 6 of these veins are combined in a common artificial zero point N A,B,C , which is isolated to not have contact with the zero point of the network. In all his veins, which have the same design parameters and made from the same material, is installed automatically symmetry currents. Metal wire braid 12 middle layer total containment 9 connect with the conductor PE protective ground the electrical network.

In the end fitting the ends of the inner conductors 5 each lived connect with the beginning of external conductors 6, and metal wire braid 12 connect with the conductor PE protective ground the electrical network.

When the supply voltage alternating currents in the internal 5 and 6 external conductors flow in each strand 1, 2 and 3 toward each other. Therefore there is a proximity effect in these guides is a redistribution of density currents in conductive their cross-sections. Alternating current in the outer conductor 6 will be held not on outer surfaces of conductors, and on their inner surfaces. Simultaneously, the impact of the skin effect (surface effect) on the effective penetration of the electromagnetic field, which is due to this effect further reduced in several times. Arising electromagnetic field is closed in the annular gap between coaxial conductors that provides heating not only at the expense of electric resistance, but, first of all, due to this field. Heated inner thermoelectromotive shell 8, filling the specified annular gap is much more electromagnetic field that enables more efficient heat transfer to the outer surface of conductors 6. Taken together, all this improves technical and economic indicators of work of the cable.

The first point PE ground metal wire braid 12 domestic Explorer 5 each core (the upper part of the drawing) electric potential is practically equal to the potential phase electric network. The second point grounding in place 7 series connection of internal 5 and 6 outdoor conductors of cable cores on the surface of outer conductors occurs same potential as on the surface of the inner conductor wires, that is, practically the same as in the first grounding point. In a few tens of centimeters electric current in the result of joint influence of the proximity effect and skin effect goes deep into the body of external conductors 6 and on their surface remains completely secure potential of the order of a few tens of millivolts.

Work cable supported known automatically by sensors, such as temperature, humidity and precipitation patterns associated with the microprocessor and the Executive body (magnetic contactor, contactor, etc.).

Sources of information

1. Cable heating system "CEILHIT". Instructions for installation and operation. 2000, p.1-3.

2. RF patent №2236769 C2, CL H05B 3/56 with the priority from 25.07.2002 (prototype).

1. The heating cable coaxial three-phase, with three veins, each covered foreign sealed thermoelectromotive shell, has the inner and outer conductors, consistently connected among themselves and coaxially placed with an annular gap between them, and internal termoelectrotraning shell filling this ring gap, and General protective shell, which concluded the three strands notable what veins are twisted among themselves and identical, General protective shell has three layers, the lower and the upper made of tight thermoelectromotive material, and the middle layer is in the form of metal wire braid, with the possibility of ground in the place of connection of the cable to electricity network and the location of the serial connection of inner and outer conductors lived, and outer conductors each conductor connected to the end point and form of artificial zero point, not electrically connected with a zero wire electrical network.

2. Cable according to claim 1, characterized in that the shape of the cross section of the lower layer total containment with external parties is limited to metal wire braid middle layer, and the inside - closed curve corresponding to the form of the cross-section of twisting the wires of the cable.