FR2902273A1 - Electrical heating cable for thawing and clearing snow from e.g. airport track, has positive temperature coefficient polymer composition layer surrounding central element and contacting conducting surfaces, where element has heater wire - Google Patents

Abstract

The cable (1) has an insulating layer/sheath (3) surrounding a core (2) that has a central element (4). The core includes two electrical conductors (5, 6) which are arranged in the element, so that a part of a conducting surface of the conductors coincides with an outer surface of the central element. A positive temperature coefficient polymer composition layer (8) surrounds the element and contacts the conducting surfaces, where the element includes a resistant heater wire (7). A metal shield is positioned between the insulating layer and a thermo-chrome type protection sheath. Independent claims are also included for the following: (1) an electrical heating device comprising a control system (2) a method for implementing an electrical heating device.

Description

1 Electric heating cable with low starting current This

  The invention relates to an electric heating cable, more particularly having a low starting current, and a heating device incorporating such a cable.

  It typically, but not exclusively, applies to thawing or snow removal of structures such as airport runways, house roofs, pipelines, and thermal regulation of ducts and pipelines. EP-0 880 302 proposes a heating cable comprising an extruded polymer core element, two bare conductors arranged in grooves of said central element and flush with the surface thereof, a layer of a semiconductor polymer in contact with said conductors and arranged on said central element. When the two conductors are connected to a current source, the current flows from one to the other through the semiconductor polymer layer. Said semiconductor polymer, polymer loaded with a conductive filler, has a positive temperature coefficient (PTC). In this, the increase in the temperature of said polymer is associated with an increase in its resistivity: the polymer tends to expand much more than the charges present, which has the effect of separating the particles from the charge. conductor, thus reducing the heating power of the heating cable. The CTP effect thus allows self-regulation of the cable and limits any problem of overheating by preventing the passage of current on either side of the conductors. However, this type of self-regulating cable is not suitable for use at temperatures below -20 C or cable lengths exceeding sixty meters. Indeed, when they are put into operation, these cables induce a high electrical consumption, more particularly a current of 2

  high starting, especially since the cable is long and / or the cable is used at negative temperatures. The PTC composition expands under the effect of the starting current and the conductive fillers component reorganize causing a change in its PTC behavior. Said starting current thus deteriorates the intrinsic properties of the cable, in particular its mechanical properties and resistivity. The invention aims to solve the problems of the prior art by providing an electric heating cable easy to implement and having a low starting current when using said cable. To this end, the subject of the invention is an electric heating cable comprising a core and an insulating layer surrounding said core, said core comprising a central polymer element, two electrical conductors arranged in said central element so that part of their conductive surface is flush with the outer surface of the central element, and a layer of a positive temperature coefficient (PTC) polymer composition surrounding the central element and in contact with said conductive surfaces, said central element comprising in addition to a resistant heating wire. Thanks to the invention, the resistant heating wire is used to heat the self-regulating cable before the said cable is put into operation. The self-regulating cable thus does not undergo a starting current deteriorating its intrinsic properties, and in particular avoids any over-consumption of power when it is turned on. In a particular embodiment of the invention, each electrical conductor is individually surrounded by a layer of a PTC polymer composition. The said PTC effect polymer layer is substantially of the same polymer base as the insulating sheath to facilitate adhesion between the individual CTP layers of the two conductors, the CTP layer surrounding the central element and the insulating sheath. According to one characteristic of the invention, the cable further comprises a protective sheath covering said insulating layer. This protective sheath protects the cable against abrasion phenomena and chemical and thermal aggressions.

  In a particular example, the protective sheath is of the thermo-chromium type, that is to say that said sheath changes color depending on the temperature of the cable. According to another characteristic of the invention, the cable further comprises a metal screen positioned between the insulating layer and the protective sheath. This screen is used to mechanically protect the cable and can be connected to the protective earth to increase the user's safety of the cable. The invention also relates to an electric heating device 15 comprising a cable according to the invention, a first end of a first electrical conductor is electrically connected to a first end of the heating resistive wire, and the second end of the first electrical conductor is connected. to a neutral conductor, the device comprising a control system for establishing a power-up of either the second end of the heating resistive wire, or an end of the second electrical conductor, or the second end of the heating resistive wire and an end of the second electrical conductor. When the control system of the device energizes only the second end of the resistive heating wire, the device is in resistive mode. When the control system of the device only energizes the end of the second electrical conductor, the device is in self-regulating mode. The invention also relates to a method for implementing the device according to the invention comprising the following steps:

  voltage only the second end of the heating resistive wire to preheat said cable using the control system, and when the temperature of the cable reaches a temperature sufficient to prevent damage to the cable by too much starting current, turn on the power only the end of the second electrical conductor using the control system, while disconnecting the second end of the heating resistive wire from the voltage. Thanks to the method according to the invention, the strong starting currents are avoided in the self-regulating cable and said cable can thus be used at very low temperatures, especially below -20 C and with a length of cable that can clearly exceed 60m. Initially, the cable is heated by the heating resistive wire, to bring the cable to a sufficient starting temperature to prevent deterioration of the PTC compositions by the starting current, then the cable switches to mode self-regulating using the control system. Other features and advantages of the present invention will appear in light of the examples which follow with reference to the annotated drawings, said examples and drawings being given for illustrative and not limiting. Figure 1 shows a schematic sectional view of an electric heating cable according to the invention. FIG. 2 represents a schematic sectional view of a particular embodiment of an electric heating cable according to the invention.

  FIG. 3 represents a schematic electrical device in resistive mode of an electric heating cable according to the invention. FIG. 4 represents a schematic electrical device in self-regulating mode of an electric heating cable according to the invention.

  FIG. 5 represents a schematic production line for manufacturing an electric heating cable according to the invention. As shown in FIG. 1, the electric heating cable 1 according to the invention has a substantially circular section. Advantageously, the manufacture and installation of the electric heating cable, in particular in cylindrical ducts, are facilitated by said circular section. Said electric heating cable 1 comprises a core 2 surrounded by an insulating layer 3.

  The core 2 comprises a central element 4 made of extruded polymer, two electrical conductors 5, 6 and a heating resistive wire 7. The central element 4, of good thermal resistance, is for example a crosslinked polyethylene, Teflon or a perfluoroacrylate. The two electrical conductors 5, 6, made of copper, are respectively arranged inside grooves 5 ', 6' provided in said central element 4. Said conductors 5, 6 are installed in these grooves 5 ', 6' so a portion of their conductive surfaces is flush with the outer surface of the central element 4. These conductors 5, 6 are diametrically opposed in the central element 4. The resistive alloy heating resistive wire 7 is located in the center 4. The resistive alloy is, for example, an alloy of either copper and nickel, or chromium and nickel, or iron, chromium and aluminum, or either copper and manganese. The electrical conductors 5, 6 and the heating resistive wire 7 extend inside the electric heating cable 1 parallel to the longitudinal axis of said cable. The core 2 further comprises a layer 8 of a CTP polymer composition surrounding the central element 4 and being in contact with the conductive surfaces of the electrical conductors 5,6. The CTP polymers are, for example, polyolefin-type filled, such as polyethylene, polypropylene, copolymers of ethylene and vinyl acetate or copolymers of ethylene and propylene. These charges are one or more conductive charges of the carbon black type. The insulating layer 3, extruded on the core 2, is a charged polymer well known to those skilled in the art, which has good thermal conductivity, such as for example polyethylene, loaded with alumina, boron nitride or aluminum nitride. According to another embodiment, as shown in FIG. 2, each electrical conductor 5, 6 is individually surrounded by a layer 8 'of PTC effect polymer. The insulating sheath 3 is surrounded by a metal screen 9 to mechanically reinforce the electric heating cable 1 according to the invention. This metal screen 9 is for example of the type of aluminum tape or copper and / or braided copper wire. This metal screen 9 is surrounded by a protective sheath 10 which may be based on polyolefin, with good thermal conductivity. The protective sheath 10 may be of the thermochromic type. 7

  The base polyolefin is, for example, loaded with an inorganic filler such as VO 2, Ag 2 Hg 4, Cu 2 Hg 4, liquid crystals or leuco derivatives such as fuchsin or nitroblue tetrazolium. The electric heating cables according to the invention are mainly used in electric heating devices and are of the single-phase type. In single-phase systems, the cable has two electrical conductors, one electrical conductor of which is connected to one power source and the other of which is connected to a neutral conductor. When the two conductors are connected to a current source, the current flows from one to the other through the semiconductor polymer layer and generates heat in the cable. FIG. 3 represents an electrical device incorporating an electric heating cable according to the invention, of the single-phase type. The two electrical conductors 5, 6 are electrically equivalent to a multitude of resistors 11 in parallel, while the resistive heating wire 7 is electrically equivalent to a plurality of resistors 12 in series. A first end 5b of a first electrical conductor 5 is electrically connected by a conductor wire 13 at a first end 7b of the heating resistive wire 7, the second end 5a of the first electrical conductor 5 being connected to a neutral conductor 14. A system control 15, of the electric switch or thermostat type, makes it possible to energize the second end 7a of the resistant heating wire 7. The device is then in resistive mode. When the device reaches a temperature sufficient to allow the use of the cable in self-regulating mode, the control system 15 also energizes the heating resistant wire 7, the end 7a is no longer connected to the control system 15, but the second electrical conductor 6 at its end 6a, as shown in FIG.

  The devices according to the invention make it possible to use circuit breakers (not shown) with lower amperages and thus guarantee a better stability of the electrical network as well as optimized security and at a lower cost.

  The various components of the electric heating cable, according to Figure 1, are assembled on a production line as shown schematically in Figure 5. The substantially circular section of the cable according to the invention allows a simple and fast manufacture of said cable by extrusion.

  The production line comprises a series of extruders 16, 18, 19 placed one after the other and a die 17. The central element 4 is first extruded on the heating resistive wire 7 via the extruder 16. The two electrical conductors 5, 6 are respectively provided by two coils 20, 21 and pass through the die 17, said electrical conductors 5, 6 being inserted into the grooves 5 ', 6' provided in the element 4. Once the assembly of the central element 4 with firstly the heating resistive wire 7 and secondly the two electrical conductors 5, 6 carried out, the layer 8 of PTC effect polymer is applied to the using the following extruder 18 to form the core 2. The insulating layer 3 is extruded with the extruder 19 to be applied to the PTC polymer layer 8. The cable 1 according to the invention thus formed is wound on a spool 22, rotating in the plane perpendicular to the axis of the production line to give the assembly a spiral effect. Before application of the insulating layer 3, the materials of the assembly may optionally be crosslinked. In another example of manufacture, the extruders 18, 19, 30 allowing the application of the layer 8 of PTC effect polymer and of the insulating layer 3, can be replaced by a two-layer extruder. 9

  The production of the cables according to the invention can be done continuously, as described above, or in a discontinuous manner, with all the possible combinations between the extrusion and spinning steps. The present invention is not limited to the implementation example which has just been described and relates in general to all the cables that can be envisaged from the general indications provided in the disclosure of the invention. In particular, the individual layers surrounding the electrical conductors may be of semiconductor material with very low resistivity.

  Furthermore, the heat resistant wire may also be copper or aluminum.

Claims (7)

  An electric heating cable (1) comprising a core (2) and an insulating layer (3) surrounding said core (2), said core (2) comprising: a central polymer element (4), two electrical conductors (5, 6) arranged in said central member (4) so that a portion of their conductive surface is flush with the outer surface of the core member (4), and a layer (8) of a temperature coefficient polymer composition positive (CTP) surrounding the central element (4) and being in contact with said conductive surfaces, characterized in that said central element (4) further comprises a heating resistive wire (7).   2. Cable according to claim 1, characterized in that each electrical conductor (5, 6) is individually surrounded by a layer (8 ') of the PTC polymer composition.   3. Cable according to claim 1 or 2, characterized in that the cable further comprises a protective sheath (10) surrounding the insulating layer (3).   4. Cable according to claim 3, characterized in that the protective sheath (10) is of the thermochromic type.   5. Cable according to claim 3 or 4, characterized in that the cable further comprises a metal screen (9) positioned between the insulating layer (3) and the protective sheath (10).   6. Electric heating device comprising a cable according to any one of claims 1 to 5 characterized in that: - a first end (5b) of a first electrical conductor (5) is electrically connected to a first end (7b) heating resistive wire (7), and - the second end (5a) of the first electrical conductor (5) is connected to a neutral conductor (14), the device comprising a control system (15) for establishing a power-up - either the second end (7a) of the heating resistive wire (7), - either one end (6a) of the second electrical conductor (6), or - or the second end (7a) of the heating resistive wire ( 7) and an end (6a) of the second electrical conductor (6).   7. A method of operating the electric heating device according to claim 6, comprising the following steps: - only power on the second end (7a) of the heating resistive wire (7) to preheat said cable (1) to the using the control system (15), and - when the temperature of the cable (1) reaches a temperature sufficient to prevent the cable from being damaged by too much starting current, only energize the end (6a) of the second conductor electric (6) using the control system (15), while disconnecting the second end (7a) of the heating resistive wire (7) from the voltage.