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    • 专利摘要:
    METHOD OF MEASURING THE LENGTH OF AN ELECTRICAL CABLE, E, ELECTRICAL CABLE The present invention relates to a method of measuring the length of an electrical cable, the method comprising: providing an electrical cable having a cable length and including a neutral axis cable, and a fiber unit that extends longitudinally along the cable and that includes an optical fiber arranged substantially along the neutral axis, in which the optical fiber is mechanically coupled with the cable, injecting an optical signal into the optical fiber: detecting backscattered light from the optical fiber in response to said optical signal, analyzing the backscattered light detected as a function of time in order to determine the length of the optical fiber, and deriving the cable length from the length of the optical fiber.
    公开号:BR112013013140B1
    申请号:R112013013140-3
    申请日:2010-11-29
    公开日:2021-01-26
    发明作者:Bernd Knuepfer；Davide Sarchi
    申请人:Prysmian S.P.A.；
    IPC主号:
    专利说明:

    [0001] [1] The present invention is directed to a method for measuring the length of an electrical cable.
    [0002] [2] The length of a cable can play a critical role in the transmission of the signals carried by it. WO 2010/126467 discloses a method for indicating the length of the input cable for serial digital interface signals. The method comprises measuring a differential that varies between first (+1 V) and second (-1 V) values approximately linearly in proportion to a characteristic of a signal at one end of the cable, and translating the measured differential voltage into a length measurement cable.
    [0003] [3] WO 2010/092256 describes a device for measuring the length of a moving cable provided with markings, which are fixed at predetermined intervals along the cable. The device comprises electronic detection means, which are suitable for automatically detecting, on the moving cable, each local change in the transverse geometry linked to the presence of a marking.
    [0004] [4] Profiling operations in oil and gas wells in general require accurate determination of the location of the profiling tool in the well borehole. One way of achieving determination of the accurate location of the profiling tool during profiling operations involves monitoring the length of the hole below the cable or the inline support of the profiling tool paid in or coiled out of the borehole through drilling works. cable removal. The length monitoring can be performed using a calibrated counting wheel which is precisely matched to the diameter of the line or cable loaded on the drum / cable reel of the withdrawal jobs to generate a distance from the travel signal to the cable length released or wound. US 6,745,487 describes a length of bore cable below that measures the apparatus comprising three main components: a rotating distance measurement assembly; a rotation-to-length calibration assembly, and a processor unit.
    [0005] [5] Cable length sensors from a cable that is wrapped around a cable drum have been used. In general, the cable is clamped at one end and is pre-tensioned through a return element. As the diameter of the cable drum is known, the withdrawal of cable length can be determined by means of the sensor through an evaluation unit, which is usually external. US 2008/0141548 refers to a cable length sensor in which the return device is arranged in a coupling and housing means for coupling the return device to the turning direction of the cable drum is provided. Fixing means, which can be actuated from outside the housing and which serve to fix the current position of the return device, in particular the at least slightly pre-tensioned start position of the return device, is associated with the housing .
    [0006] [6] In some applications, consumers may be charged for cable and installation through the total length purchased or installed. In such cases, it may be useful to measure the cable length after installation without having to measure it in advance. US 2006/181283 discloses a cable diagnostic mechanism that uses time domain reflectometry (TDR) to detect and identify cable faults, perform cable length estimations, identify cable topology, identify load and irregular impedance in paired metallic cable, such as coaxial and twisted pair cables.
    [0007] [7] As the measurement made using TDR is performed on electrical conductors, when the conductors are twisted around the cable axis - a very common configuration - the length of the conductor is greater than the length of the cable, and the difference is not known with satisfactory accuracy as the accumulation step is not exactly controlled.
    [0008] [8] WO 08/073033 describes a system for monitoring the bending and deformation of a power cable connected to a mobile off-shore platform by measuring the tension in optical fibers attached to or incorporated into the power cable. A bend in the power cable will cause deformation in the optical fiber and this deformation will alter the optical properties of the fiber. The change in optical properties can be measured using the optical time domain reflectometer (OTDR) or optical frequency domain reflectometer (OFDR).
    [0009] [9] GB 2368921 discloses a borehole cable having spaced ends that include a first end and a second end, a hollow metal tube that extends from the first end to the second end thereof, and at least one fiber optics arranged loosely inside the hollow metal tube and extending from the first end to the second end thereof. At least one optical fiber has at least one vibrating Bragg network.
    [0010] [10] EP 0203249 discloses a medium voltage power cable (from 6 to 60 kV) that includes at least one temperature and / or voltage sensor optical fiber.
    [0011] [11] Typically, electrical cables are distributed to consumers wound around coils along with information on the nominal length of the wound cable. In some applications, such as for use in a borehole environment, it may be important to know the “actual” length of the released cable in order to define the route of the cable throughout the release. Apparently negligible lengths, such as 1 meter or less, especially when they are missing, can lead to inconvenience.
    [0012] [12] The Depositor noted that, in some cases, consumers may order a cable that is provided with splice connectors, which therefore need to be provided at the factory before distribution of the cable. The preparation at the factory of the cable ends for field splices has a great advantage of reducing the splicing procedure in the field, and that it works in a controlled (clean) environment with higher quality results. In this case, if the cable length section between subsequent cable connectors does not match the required length section in the environment of use, the cable section may result and be either too short or too long to be connected to the existing splice locations along the cable route. Especially in the case of cable sections containing multiple cable lengths, it may not be straightforward to cut and adjust the cable length sections.
    [0013] [13] In some other cases, consumers may wish to control the cable length after cable distribution.
    [0014] [14] The Depositor noted that measuring cable length using a mechanical device that moves along the cable length may not be practical when the cable release follows a complex route and / or the cable length is relatively large, for example, exceeding 1 km.
    [0015] [15] The Depositor considered that the use of methods that measure the differential voltage variation that results from connecting the input cable to an input port or methods that detect reflected electrical pulses. However, such methods involve electrical measurement along one or more electrical conductors within the cable, which are, in typical cable configurations, helically wound around the central longitudinal axis of the cable. This implies that the length of the measured electrical conductors is generally greater than the length of the cable that includes them. This introduces an uncertainty in the determined cable length. The inaccuracy of the determined length value is at an absolute higher the greater the cable length.
    [0016] [16] The Depositor noted that in electrical cables provided with at least one optical fiber, the cable length can be measured by optical techniques that detect the transmitted and / or reflected light along the optical fiber. In addition, the Depositor noted that if the electrical cable is provided with an optical fiber loosely inserted in a module that extends longitudinally, such fiber usually has a length of excess fiber with respect to the length of the cable, which introduces inaccuracy in the correspondence between the measured length and the actual cable length. Inaccuracy can also stem from the fact that the fiber optic module is typically tensioned along with electrical cable conductors. Fiber gaps introduce inaccuracies in measurements, also in the case of geometric construction of the cable, they are known as common manufacturing process tolerances (for example, for a loose polybutylene terephthalate tube containing twelve SZ tensioned optical fibers) allow a measurement optical fiber length of no more than about 0.5%. For example, at a cable accuracy of 4 km in length the measurement can be about 20 m, a value that in some applications may be unacceptable.
    [0017] [17] The Depositor recognized that if the electrical cable is provided with a fiber optic unit arranged substantially along the neutral axis of the electrical cable and mechanically coupled to the electrical cable, it is possible to precisely measure the length of the electrical cable by measuring the optical fiber length comprised in the optical fiber unit by an optical backscattering technique.
    [0018] [18] In general terms and according to one aspect, the present invention relates to a method of measuring the length of an electrical cable, the method which comprises providing an electrical cable having a cable length and which includes: a neutral axis cable, and a fiber unit which extends longitudinally along the cable and which includes an optical fiber arranged substantially along the neutral axis, in which the optical fiber is mechanically coupled with the cable. The method additionally comprises: injecting an optical signal into the optical fiber, which detects backscattered light from the optical fiber in response to said optical signal; analyze the backscattered light detected as a function of time in order to determine the length of the optical fiber, and derive the cable length from the length of the optical fiber.
    [0019] [19] By "neutral axis" is meant a longitudinal axis of the cable which, through the cable bend, does not undergo compression or elongation stress.
    [0020] [20] In some preferred modalities, ensuring mechanical coupling, and in particular mechanical congruence, between the electrical cable and the optical fiber of the optical fiber unit attached to the cable, movements and deformations, the latter caused, for example, by loads of tension, thermal tension and the like, of the electrical cable during release and / or operation are at least partially transferred to the optical fiber coupled to the cable thus maintaining a substantially constant relationship between the cable length, Lc, and the length of the cable. optical fiber attached to the cable, Lp. In particular, in the preferred embodiments, no fluctuation in length of the optical fiber coupled to the cable occurs regardless of variations in the length of the electrical cable.
    [0021] [21] By "mechanical congruence" is meant the capacity of two or more parts of movement substantially as a whole, with the same geometric elongation (positive or negative). The mechanical congruence between the optical fiber attached to the cable and the cable allows to obtain a cable capable of providing a reliable assessment of its length by detecting the length of the optical fiber attached to the cable.
    [0022] [22] According to some preferred embodiments of the invention, the optical fiber unit coupled to the cable is incorporated into a mechanical coupling filler, which mechanically couples the fiber unit with the longitudinal structural element of the cable.
    [0023] [23] By configuring the fiber optic unit in accordance with the general teaching of the present invention, the measurement length of the optical fiber coupled to the cable substantially corresponds to the length of the electrical cable. The fiber length can be determined by the OTDR with an accuracy of about one meter for electrical cables less than 5 km in length.
    [0024] [24] Preferably, the optical fiber attached to the cable is surrounded by a protective sheath to improve the mechanical resistance to lateral loads, said protective sheath directly contacts the optionally buffered optical fiber of the optical fiber unit attached to the cable. Preferably, the protective sheath comprises a fiber-reinforced composite.
    [0025] [25] Preferably, the mechanical coupling filler is the basis of an elastomeric material, more preferably in a thermoset elastomer.
    [0026] [26] Preferably, the method according to the invention employs OTDR or OFDR to measure the length of the optical fiber attached to the cable and thus to determine the length of the electrical cable.
    [0027] [27] Within the present description, the term “longitudinal structural element” indicates a component of the electrical cable, which extends substantially longitudinally along the cable length, which supports the main portion of the cable load, thus defining the neutral axis the cable. Typically, in a cable consisting of insulated conductors, covered by one or more polymeric sheaths, the longitudinal structure element is the cable conductor (or possibly the assembly of cable conductors). In case one or more resistance members are provided, in addition to the conductor or conductors, the longitudinal structural element is the assembly of such resistance members and cable conductors, which together define the neutral cable axis.
    [0028] [28] The term “core” indicates a semi-finished structure of the electrical cable that comprises at least one electrical conductive element, such as an electrical conductor and, typically, at least one layer of insulation surrounding the electrical conductor. In typical configurations, electrical conductors comprise a plurality of stranded conductor wires.
    [0029] [29] The method according to the present invention can be applied from low to high voltage electrical cables. Brief description of the drawings
    [0030] [30] The present invention will now be described more fully below with reference to the accompanying drawings, in which some, but not all of the embodiments of the invention are shown. Drawings that illustrate the modalities are schematic representations that are not to scale.
    [0031] [31] For the purpose of this description and the appended claims, except where otherwise indicated, all figures expressing amounts, quantities, percentages, and so on, should not be understood as being modified in all cases by the term “ about". In addition, the ranges include the maximum and minimum points disclosed and include any intermediate ranges in them, which may or may not be specifically listed here.
    [0032] [32] FIG. 1 is a schematic cross-sectional view of the electrical cable according to an embodiment of the invention.
    [0033] [33] FIG. 2a is a schematic perspective view of a longitudinal structural member unit coupled to the cable used in an electrical cable of the present invention.
    [0034] [34] FIG. 2b is a schematic perspective view of a longitudinal structural member unit attached to the cable shown in Fig. 2a.
    [0035] [35] FIG. 3 is a schematic cross-sectional view of an electrical cable, according to an additional embodiment of the present invention.
    [0036] [36] FIG. 4 is a schematic cross-sectional view of an electrical cable, in accordance with yet another additional embodiment of the present invention.
    [0037] [37] FIG. 5 is a schematic cross-sectional view of an electrical flat cable, according to an additional embodiment of the present invention.
    [0038] [38] FIG. 6 is a schematic diagram illustrating the principles of operation of an optical backscatter technique on an electrical cable according to an embodiment of the invention.
    [0039] [39] FIG. 7 is a graph of an exemplary OTDR trace measured using the method according to an embodiment of the present invention. Detailed Description
    [0040] [40] Figure 1 illustrates a cross-sectional view of an electrical cable, according to an embodiment of the present invention. the cable 1 is a round cable comprising three cores 2 arranged radially around a central longitudinal axis Z of the cable. Cores 2 can provide three-phase power transmission. Cable 1 can be a low or medium voltage power cable, where the low voltage indicates a voltage of up to 1 kV and the average voltage indicates a voltage from 1 kV to 60 kV. Each core 2 comprises an electrical conductor 12, for example, a copper conductor formed by a bundle of bare or tinned copper electrical wires braided together according to conventional methods. In the radial external position with respect to each electrical conductor 12, an internal semiconductor layer 13, an insulation layer 16, and an external semiconductor layer 17 are sequentially provided. The inner semiconductor layer 13, the insulation layer 16, and the outer semiconductor layer 17 are made of polymer-based materials that can be extruded on top of each other or coextruded in the conductor 12. The insulation layer 16 can be, for example, cross-linked propylene ethylene rubber (EPR); the inner and outer semiconductor layers 12 and 17 can, for example, be made of EPR, ethylene / propylene / diene terpolymers (EPDM) or a mixture thereof, loaded with an appropriate amount of a conductive filler, which can be typically black of carbon.
    [0041] [41] Alternatively, whenever operating conditions permit this, both the insulation layer and the semiconductor layers can be made of thermoplastic compounds, such as polypropylene-based compounds.
    [0042] [42] In some applications, the cable core 2 comprises at least one layer of wire mesh 22 in a radially external position with respect to the external semiconductor layer 17.
    [0043] [43] It should be understood that the description above of cores 2 represents only one of the possible structures of the cores included in the electrical cable, which in general can be phase cores for grounding or power transmission, cores for carrying out control signals or cores that perform both control and energy signals.
    [0044] [44] According to the functionality of the invention, the electrical cable 1 comprises a fiber optic unit coupled to the cable 5 arranged substantially along the central longitudinal axis Z of the electrical cable, which is substantially the neutral axis of the cable. The fiber optic unit coupled to the cable 5 is mechanically coupled with the longitudinal structural element in the cable, that is, with the cores 2.
    [0045] [45] The fiber optic unit attached to the cable 5 is mechanically congruent with the longitudinal structural element in the cable in such a way that it remains in coaxial alignment with the central longitudinal axis and a substantially constant relationship between the cable length and the length of the cable. optical fiber attached to the cable is maintained. To this end, in some preferred embodiments, the fiber optic unit coupled to the cable 5 is incorporated into a mechanical coupling filler 6 that mechanically couples the fiber optic unit coupled to the cable with the longitudinal structural element of the electrical cable. Preferably, the mechanical coupling filler mechanically couples the fiber optic unit coupled to the cable with each circumferentially arranged core integrated into the electrical cable.
    [0046] [46] In addition to cores 2 for the transmission of control and / or energy signals, electrical cable 1 comprises at least one earthing conductor 7. In the embodiment shown in Fig. 1, the cable comprises two earthing conductors 7, for example example, in the form of a bundle of stranded bare or tinned copper electrical wires. Especially for medium voltage applications, the bundle of electrical wires from the earth conductors can be surrounded by a semiconductor layer (not shown in the figures). The earth conductors 7 are arranged radially external with respect to the fiber optic unit coupled to the cable 5 and are braided together with the cores 2 along a longitudinal direction of the cable. In particular, cores 2 and earth conductors 7 are helically wound around the center of the central longitudinal axis Z of the cable, according to conventional methods.
    [0047] [47] In the embodiment shown in Fig. 1, cable 1 comprises an optical fiber element 3 that includes a plurality of optical fibers, for example, from 6 to 24 fibers, for the transmission of control, voice, video and other data signals. A single optical fiber or a pair of fibers can be inserted into a loose tube plug construction in longitudinally extending modules 19, preferably made of a flexible material such as polybutylene terephthalate (PBT) or ethylene tetrafluoroethylene (ETFE). In the illustrated example, the modules containing the fibers are SZ helically wound around a member of longitudinal resistance 18, being, for example, a glass fiber, an aramid filament or a carbon fiber. The fiber optic element 3 can be attached together with the cores 2 and the earth conductors 7. In general, if the cable construction allows this, the earth conductors and the fiber optic element can be arranged in the external interstices formed by the cores 2.
    [0048] [48] The cores 2 and, if present, the core conductors 7 and / or the fiber optic element 3, are relatively referred to as the longitudinal structural element of the electrical cable.
    [0049] [49] As the heat bending can induce an elongation in an optical fiber arranged within the electrical cable, through the arrangement of the coaxial optical fiber unit with the central longitudinal axis of the electrical cable, the optical fiber unit is not damaged by the bending of the cable for any radius of curvature not being less than the radius of curvature, ρmin, which corresponds to the minimum radius at which the cable can be bent without permanent damage. It was observed that the fiber optic unit attached to the cable is generally undamaged through the cable bend at radii of curvature not less than ρmin when the longitudinal deformation induced by the bend is less than the deformation applied to the fiber in a test of deformation of typically 1 or 2%. The ρmin values specified for heavy-duty cables, especially for applications in mobile equipment, can be relatively small, for example, 250 mm. In order to improve the bending resistance of the optical fiber attached to the cable, preferably the optical fiber attached to the cable is arranged within a relatively small radial distance from the central longitudinal axis of the electrical cable, for example, not greater than 5 mm .
    [0050] [50] In some preferred embodiments, the optical fiber attached to the cable is arranged along the cable length within a distance from the neutral axis of not more than 0.02 ρmin and preferably not more than 0.01 ρmin.
    [0051] [51] Preferably, the optical fiber attached to the cable is arranged along the cable length within a distance from the neutral axis that should be as small as possible, taking into account the cable size, the minimum cable bending radius ( either on a coil or when released in the field) and the accuracy required for length measurement. For example, a displacement from the neutral axis of less than 5 mm is acceptable for most applications.
    [0052] [52] Preferably, the contact between the mechanical coupling filler and the at least one longitudinal structural element should not show significant slip at least in a stressed condition. In many cases of interest, a substantial absence of slippage between the fiber optic unit and the element (s) implies an adhesion with the friction or connection between them. A mechanical coupling between two elements that cause substantially the same deformation as a result of no significant slippage between the elements, is referred to here as mechanical congruence.
    [0053] [53] In the modality illustrated in Fig. 1, the geometric configuration of the mechanically coupled filler 6 is such that the filler contacts a plurality of longitudinal structural elements positioned in the radial external position in relation to the optical fiber unit coupled to the cable 5, also when the cable is in a substantially unstressed condition.
    [0054] [54] Based on the geometric construction of the electric cable and the number of longitudinal structural elements integrated in the cable, the mechanically coupled filler 6 of Fig. 1 has an approximately clover shape.
    [0055] [55] Preferably, the mechanically coupled filler 6 is made of a material that has elastic properties to react to the maximum deformation for which the cable exhibits an elastic behavior without permanent deformation of the filler (that is, the reversibility of the deformation). The mechanically coupled filler material is selected to properly stretch along the cable that undergoes elongation and to substantially recover deformation when external stress loads are removed, at least for stress loads that correspond to the maximum allowable strain, beyond which irreversible and permanent deformation of the cable occurs.
    [0056] [56] The mechanically coupled filler 6 can be the basis of a polymeric material, advantageously extruded around the fiber optic unit coupled to the cable 5. Thermoset elastomers having an elastic behavior within a relatively large range of deformation, for example, exceeding 1% have been found to be particularly suitable for the cable of the invention. Advantageously, thermoset elastomers are observed to adhere with high friction to the surfaces of the longitudinal structural elements. For example, it has been noted that thermoset elastomers provide strong adhesion to the semiconductor materials that typically surround the cores of some electrical cables, while exhibiting a non-damaging friction to the semiconductor outer surface of the cores. A reliable deformation transfer having at least a derivable or predicable relationship between the deformation experienced in a longitudinal structural element of the cable and the deformation measured in the sensor was observed to occur.
    [0057] [57] Advantageously, the mechanically coupled filler material is resistant to the heat treatments that can occur during cable manufacture, such as when curing the outer sheath of the electric cable, typically carried out at approximately 200 ° C.
    [0058] [58] Preferably, the mechanically coupled filler comprises a thermoset elastomer reticulated by means of vapor pressure, electron beam irradiation, immersion or silane crosslinking systems. In general, the mechanically coupled filler is preferably made of elastomers having an elastic modulus between 0.01 and 0.7 Gpa.
    [0059] [59] For example, the mechanically coupled filler is selected from the group consisting of ethylene propylene diene rubber (EPDM), ethylene propylene rubber (EPR), nitrile butadiene rubber (NBR).
    [0060] [60] Although thermoset elastomers are preferred because of their temperature resistance adhesion properties and high elasticity range, the use of thermoplastic elastomers is not excluded. Examples of thermoplastic elastomers include three-block copolymers of styrene - diene - styrene; thermoplastic polyester elastomers and thermoplastic polyurethane elastomers, and polyolefin rubbers (polyolefin mixtures).
    [0061] [61] In some embodiments, the mechanically coupled filler 6 can be electrically conductive.
    [0062] [62] Areas of interstices 11 are filled with the polymeric filler such as an EPR base compound. An outer jacket 14 is provided, for example, through extrusion. To increase the resistance of the electrical cable to mechanical stresses, the outer jacket 14 is preferably made of a cured polymeric material, preferably based on a thermoset reinforced working elastomer, such as high density polyethylene (HDPE), polychloroprene, polyurethane or compound based on NBR.
    [0063] [63] Optionally, to increase the torsion resistance of the electrical cable, a shield 15 in the form, for example, of braids or double spiral of reinforcement filaments, such as metal or polyester filaments, for example, made of Kevlar® ( aromatic polyamide), is provided.
    [0064] [64] Figures 2a and 2b illustrate a partial perspective view and a cross section, respectively, of a fiber optic unit coupled to the cable 5 integrated in the electrical cable of Fig. 1, according to a preferred embodiment of the present invention. The optical fiber coupled to the cable 5 comprises an optical fiber 9 which is substantially arranged along the Z axis, which is the neutral axis of the cable, when the optical fiber coupled to the cable is integrated into the cable. The fiber 9 of the optical fiber coupled to the cable 5 is an optical fiber, namely a silica-based optical fiber, with the typical nominal diameter of 125 μm, covered by a primary coating, which is surrounded by a secondary coating, which typically contacts adherently to the primary coating, where the primary and secondary coating form a coating system. The outer diameter of the (coated) optical fiber can be 250 +/- 10 µm or 200 +/- 10 µm. Single layer coating systems can also be used. Preferably, optical fiber 9 is a single-mode optical fiber, although a multi-mode optical fiber can also be used.
    [0065] [65] In some modalities, where the method is to measure the length of a heavy duty cable, the optical fiber of the fiber optic unit attached to the cable has improved bending performance, which exhibits low bending losses. In some modalities, optical fiber is compliant with the G.657 ITU-T recommendations.
    [0066] [66] In one embodiment, the fiber coating system attached to the cable is coated with a coating system as disclosed in EP 1 497 686, which has been observed to provide the optical fiber without breaking when subjected to repeated stretching that exceeds 2 %.
    [0067] [67] In some preferred embodiments, the optical fiber 9 is buffered sealed with a layer of buffer 10 that surrounds the coating system to improve the mechanical protection of the optical fiber, for example, against microduck losses. The Depositor understood that the uniform adhesion of the buffer layer to the optical fiber, namely to the fiber coating system, is particularly important to ensure the congruence between the optical fiber and the mechanical coupling filler.
    [0068] [68] For example, buffer layer 10 is extruded or applied over 250 μm coated fiber, which increases the outside diameter up to 600 to 1000 μm, with typical values from 800 to 900 pm. preferably, the buffer layer is made of a material that has elastic properties that allow the sealed buffered optical fiber to support elongations up to and including 2%.
    [0069] [69] Advantageously, the buffer layer is selected in order to adhere to the fiber optic coating system essentially without crimping, slipping or disconnection. Preferably, the buffer layer is based on a thermally resistant material capable of exhibiting sufficient thermal resistance to withstand the heat treatments that occur during the manufacture of the cable.
    [0070] [70] Preferably, the buffer layer is made of a radiation-curable acrylate polymer.
    [0071] [71] For example, the sealing plug is made of a UV-curable acrylate polymer as described in WO 2005/035461, or of a polymeric matrix loaded with a flame retardant filler as described in WO 2008/037291 .
    [0072] [72] An adhesion promoting layer can be provided between the fiber optic coating system and the sealing buffer layer.
    [0073] [73] A protective sheath 8, designed to improve resistance to lateral compressions, can advantageously be provided to surround the optionally sealed buffered optical fiber of Figs. 2a and 2b.
    [0074] [74] In round cables, such as the one illustrated in Fig. 1, lateral compressions in the transverse directions to the longitudinal cable direction, typically occur in radially inward directions.
    [0075] [75] The fiber optic unit attached to the cable can be used as a pulling member in the extrusion step of the mechanical coupling filler during the cable manufacturing process. For this purpose, it has been observed that it is important that the fiber optic unit material attached to the cable does not soften during the extrusion process of the mechanically coupled filler, in order to guarantee a uniform pulling force. The presence of a protective sheath 8 and an appropriate selection of the material that forms said sheath can advantageously provide the fiber optic unit coupled to the cable with a sufficient tensile strength both to improve the resistance to lateral compression and to allow the fiber unit optics attached to the cable act as a pulling force member in the electrical cable manufacturing process.
    [0076] [76] When mechanical congruence between the optical fiber and the mechanically coupled filler is desired, the protective sheath material is preferably selected in order to provide strong and relatively uniform adhesion with the optionally buffered optical fiber.
    [0077] [77] Preferably, the protective sheath 8 is made of a fiber-reinforced composite, where the fibers may be carbon fiber, graphite, boron, or glass (non-optical). In one embodiment, the protective sheath 8 is a glass-reinforced polymer (GRP), in which the polymer is reinforced by glass fibers incorporated into the polymer. It has been observed that advantageously relatively high tensile rigidity of the optical fiber unit coupled to the cable is achieved by the presence of reinforcement fibers released parallel to the longitudinal axis of the optical fiber, thus preventing the lateral compression from being misinterpreted as tensile deformation. The protective sheath 8 may be protruding into the buffer layer 10 and is in direct contact with it. Preferably, the polymer incorporating the reinforcement fibers are crosslinked resins, in particular UV curable crosslinked resins or thermoregulating crosslinked resins, which in general provide compressive strength. The cross-linked resins can be unsaturated polyesters, epoxies, or vinyl esters.
    [0078] [78] Optionally, the outer surface of the protective sheath, which is surrounded by the mechanical coupling filler in which the fiber optic unit attached to the cable is incorporated, comprises a plurality of grooves or cuts or is treated to form a rough surface to increase the adhesion of the protective sheath with the mechanical coupling filler. Alternatively, or in addition, an adhesion-promoting layer can optionally be provided in the protective sheath.
    [0079] [79] To improve the flexibility of the fiber optic unit attached to the cable, the thickness of the protective sheath, when made of polymer-based material, is preferably comprised between 500 and 1000 μm. For example, the protective sheath is a layer of GRP that increases the outer diameter of the buffered optical fiber up to 1.8 to 2.5 mm.
    [0080] [80] It is preferred that the protective sheath that surrounds the optical fiber of the sensor prevents shrinkage of the fiber at temperatures used in the manufacturing process, and in particular in the curing process of some cable components, such as the inner and outer sheaths. High temperature graded retinal retinas that withstand the curing temperature are selected, for example, high temperature Polystal® from Polystal Composites GmbH.
    [0081] [81] In preferred embodiments described above, the fiber optic unit attached to the cable comprises a layered fiber optic fiber (ie, protective plug-sealed sheath) that exhibits elastic properties and is incorporated into a mechanical coupling filler with elastic properties. However, since the structure composed of the fiber optic unit attached to the cable and the mechanical coupling filler is able to recover the elongation in the reversible elastic regime of the cable, at least one of the layers selected from the group consisting of the layer of buffer surrounding the coated fiber, the protective sheath and the mechanical coupling filler can exhibit non-elastic behavior and in particular plastic behavior. In particular, the at least one layer can be made of a plastic material, namely a material that has the ability to deform in response to mechanical forces without fracture, at least until a certain threshold value of the external forces is not exceeded. In general terms, the elastic response is obtained if: (1) a layer made of substantially plastic material is congruent with at least one layer made of elastic material, and (2) the axial stiffness of the layer made of plastic is less than that axial stiffness of the at least one layer made of elastic material which the layer of plastic material is in contact with. Axial stiffness, typically measured in N, is the product of Young's modulus and the cross-sectional area of the layer element. In this way, the layer made of substantially plastic material stretches along the elastic material in which it adheres or contacts with friction during the elongation of the cable and is pulled back to its original position by the elastic material, provided that sufficient adhesion force exists. between the two layers.
    [0082] [82] For example, the protective sheath of the fiber-optic unit attached to the cable is a fiber-reinforced thermoplastic polymer having the Young's module of 72,400 MPa, while the mechanical coupling filler is a thermoset elastomer having the Young's module of 671 MPa. The cross-sectional area of the protective sheath is 3.4 mm2 and the cross-sectional area of the mechanical coupling filler is 75 mm2, providing an axial stiffness of 250 kN for the protective sheath and 50 kN for the coupling filler mechanical. If a fiber-reinforced thermoplastic polymer has good adhesion to the deformation transfer filler and the underlying layers, such as the buffer layer, the thermoplastic polymer takes the mechanical coupling filler together, even if the cross-sectional area of it is much smaller. It should be noted that this must also be true if the mechanical coupling filler is made of a thermoplastic polymer, provided that the conditions above (1) and (2) are met, and where the layer with elastic properties is the surrounded buffer layer through the protective sheath.
    [0083] [83] In one embodiment, under the assumption that conditions (1) and (2) are met, the mechanical coupling filler is selected from the group consisting of: polyester with Young's modulus from from 1 to 5 Gpa, polyamide with Young's modulus from 2 to 4 Gpa, polyvinyl chloride (PVC) with Young's modulus from 0.003 to 0.01 Gpa, low density polyethylene with Young's modulus from 0.1 to 0.3 Gpa, and high density polyethylene with Young's modulus from 0.4 to 1.2 Gpa. Preferably, cross-linked polymeric materials are employed.
    [0084] [84] According to another modality, in order to provide the fiber optic unit attached to the cable with improved resistance to lateral loads and pull resistance, the protective sheath of the fiber optic unit attached to the cable can be a metal tube that surrounds the optionally buffered fiber optic buffer layer (modality not shown in the figures). In this case, the metallic tube contains a gel or gel-like material, optionally under pressure, capable of providing the desired mechanical congruence between the metallic tube and the optical fiber contained therein. In a preferred embodiment, the metal tube is made of steel.
    [0085] [85] Preferably, only one in the group consisting of the buffer layer surrounding the coated fiber, the protective sheath and the mechanically coupled filler is made of a material with plastic properties.
    [0086] [86] Although in some preferred embodiments the fiber optic unit attached to the cable comprises a buffer layer in order to improve the strength and elasticity of the fiber optic unit attached to the cable, as in the construction shown in Figs. 2a and 2b, it should be understood that the fiber optic unit coupled to the cable may comprise an optical fiber coated with a coating system directly surrounded by a protective sheath.
    [0087] [87] The electrical cable 1 may comprise a temperature sensor comprising an optical fiber 24 to measure the internal temperature of the cable 1. The optical fiber 24 of the temperature sensor is in a loose plug construction. In particular, in the embodiment illustrated in the figure, the optical fiber 24 positioned loosely within a module 19 that longitudinally encompasses the fiber, the module 19 being comprised in the optical fiber element 3. The longitudinally extending module 19 contains optical fiber length of excess per unit of fiber optic tube length 24. The excess fiber length (EFL) is defined by the following ratio:
    [0088] [88] The optical fiber 24 of the temperature sensor can be a single-mode fiber and the temperature is measured using Brillouin backscattering techniques. However, the use of a multi-mode optical fiber can be visualized for temperature detection. In the latter case, temperature measurement can be performed using known techniques based on Raman scattering. In the embodiment of Fig. 1, the optical fiber 24 is wound helically with respect to a central longitudinal axis along the cable. For example, optical fiber 24 is twisted around a longitudinal member. In the case of an electrical cable comprising an optical fiber element comprising more than one optical fiber, two fibers can be helically wound around each other along a longitudinal direction, one of the two fibers being used as a fiber optics of the temperature sensor.
    [0089] [89] Mechanical coupling, and in particular mechanical congruence, between the fiber optic unit attached to the cable and the cable can occur only when at least one of the longitudinal structural elements is subject to a tensile load and comes in contact with the filler mechanical coupling. For example, mechanical coupling occurs when the longitudinal structural elements undergo stress loads that correspond to elongations of at least 0.1%.
    [0090] [90] Figure 3 is a cross-sectional view of an electrical cable, according to an additional embodiment of the present invention. The same numbers are used to identify similar components that have the same or similar functions to the elements of Fig. 1. While the mode of Fig. 1 includes a mechanical coupling filler that contacts the longitudinal structural elements of the cable even in the absence of loads of tension, in the modality shown in Fig. 3, the deformation transfer filler does not contact, at least not completely, the surface of the longitudinal structural elements when the cable is in a substantially unstressed condition, for example, the original condition of the cable , prior to installation or use on mobile equipment. In particular, the electrical cable 30 comprises a fiber optic unit coupled to the cable 5 surrounded by a mechanical coupling filler 25, which is preferably directly extruded onto the fiber optic unit coupled to the cable, for example, with reference to Figs. 2a and 2b, on the outer surface of the protective sheath 8. The mechanical coupling filler 25 may have a circular cross section. For example, the protective sheath 8 has a thickness of from 2 to 7 mm. The interstitial space 26 between the mechanical coupling filler 25 and the radially external longitudinal structural elements, namely cores 2, and, if present, earth conductors 7 and fiber optic element 3, can be filled by the same material as the polymeric filler 27 surrounding the longitudinal structural elements, for example, an EPR-based compound.
    [0091] [91] Because of its size, the fiber optic unit attached to the cable 5 buffered with the mechanical coupling filler 25 and the longitudinal structural elements of the cable, the mobility of the fiber optic unit attached to the cable also depending on the viscosity of the cable. stuff that fills the interstitial space. The cable is configured in such a way that the extent of mobility of the fiber unit within the cable does not affect the accuracy of the length measurement. Through the application of a tensioning force, the longitudinal structural elements tend to compress radially inwards, thereby reducing the radial distance to the longitudinal axis along which the fiber optic unit coupled to the cable is arranged. When the value of the tensile force through which the cable passes is above a certain threshold, the longitudinal structural elements are pressed radially inward and establish contact with the mechanical coupling filler 25. On the contrary, when the cable extends in any longitudinal position of the cable length below that threshold, the optical fiber of the fiber optic unit coupled to the cable 5 follows the cable movement with a delay due to the relatively poor adhesion with the longitudinal structural elements of the cable. Preferably, the threshold in tensile strength is 0.1%.
    [0092] [92] The material properties of the mechanical coupling filler 25 are those described above with reference to Fig. 1.
    [0093] [93] Figure 4 is a cross-sectional view of an electrical cable, in accordance with an additional embodiment of the present invention. Some numbers are used to identify similar components having the same function or different functions to the elements of Figs. 1. The electric cable 40 comprises four longitudinal structural elements, namely three energy cores 43 and an earth conductor 44, being arranged radially external with respect to the fiber optic unit coupled to the cable 5, which may have the construction described with reference to the Figs. 2a and 2b. the energy cores 43 and the earth conductor 44 each comprise a conductor 45, for example, in the form of a bundle of bare or tinned copper electrical wires, surrounded by a polymeric insulating layer 46. The mechanical coupling filler 47 incorporates the fiber optic unit attached to the cable 5 and fills the interstices between the fiber optic unit attached to the cable and the longitudinal structural elements. The properties and geometric shape of the mechanical coupling filler 47 are such that the mechanical coupling, and in particular the mechanical congruence, exist between the longitudinal structural elements 43 and 44 and the optical fiber unit coupled to the cable 5, also in a condition untensioned cable. Cable 40 can be a 1 kV power cable, such as for vertical winding applications.
    [0094] [94] Figure 5 shows a schematic cross-sectional view of a three-phase electrical flat cable 60, such as for applications in well pump systems, it includes two outer cores 61 and 63 and a central core 62. Each core 61 , 62, and 63 comprises a respective electrical conductor 61a, 62a and 63a, each electrical conductor being preferably surrounded by a respective semiconductor or insulating layer 61b, 62b and 63b. The cores are positioned substantially parallel and adjacent to each other, centered along a common axis 69 parallel to the X direction, transverse to the longitudinal cable axis. In the embodiment of Fig. 5, axis 69 is the midline of the cable cross section in the plane (X, Y). An optical fiber unit coupled to the cable 5 comprising an optical fiber is arranged within the central core 62, in particular along the longitudinal axis of the electrical conductor 62a. A plurality of wires 65 are helically wound around the fiber optic unit 5 through the gripping process generally known in the gripping technique. The fiber optic unit coupled to cable 5 may have the structure described with reference to Figs. 2a and 2b. A mechanical coupling filler is not required in the present cable construction because of the compatibility of the stranded wires around the fiber optic unit. Electric conductors 61a and 63a may comprise a bundle of a plurality of wires 65, for example 6, 12 or 18, helically wound around a central wire 65a, which may have the cross-sectional area of the surrounding ones.
    [0095] [95] In some embodiments, the core 62 is arranged in such a way that the central longitudinal axis of the core, along which the optical fiber unit 5 is arranged, crosses the middle axis 69, since it is the axis of symmetry of the cable cross section along the Y axis and a neutral axis of the cable 60. The fiber optic unit coupled to the cable 5 is arranged within the neutral region for folding the thickness d, defined between two planes 69a and 69b parallel to the midline 69, each being distant d / 2 from 69 on the Y axis. For flat cables with typical values of ρmin of 500 mm, and the thickness d can vary from 5 to 10 mm.
    [0096] [96] The flat cable 60 additionally comprises the outer shield 68 arranged in an external position with respect to the cores and which includes them longitudinally. The outer shield 68 has two substantially flat sides 68a parallel to the X axis and two opposite side sides 68b that surround a portion of two outer cores 61 and 63. The outer shield 68 is preferably a steel or stainless steel or steel tape shield. a copper and nickel alloy.
    [0097] [97] The electrical cable 60 has a plurality of interstitial spaces 65, which are defined by the spaces between the cores and the outer shield 68. The resistance members 67 are arranged in interstitial spaces between the outer cores and the central core, in two common planes parallel to the X axis. the resistance members 67 have a circular cross section and can be made of steel, glass or reinforced polymers.
    [0098] [98] The free space between the cores and the resistance members is filled with an inner sheath 64, made, for example, of polymeric compound loaded with mineral filler, preferably directly in the longitudinal structural elements of the flat cable.
    [0099] [99] A cable comprising a single conductor (not shown) may include a fiber optic unit attached to the cable according to the invention in an arrangement similar to that illustrated for core 62 of Figure 5. Such a cable typically has a global circular cross section.
    [0100] - um núcleo de cabo que compreende uma pluralidade de fios condutores trançados, - um eixo neutro de cabo, e - uma unidade de fibra óptica acoplada ao cabo que se estende longitudinalmente ao longo do cabo e que inclui uma fibra óptica acoplada ao cabo arranjada substancialmente ao longo do eixo neutro, em que a fibra óptica acoplada ao cabo é acoplada mecanicamente com o cabo; em que:a pluralidade de fios é trançada em torno da unidade de fibra óptica;a unidade de fibra óptica acoplada ao cabo é acoplada mecanicamente com pelo menos um da pluralidade de fios.[100] According to one aspect, the present invention relates to an electrical cable which comprises: - a cable core comprising a plurality of stranded conductor wires, - a neutral cable shaft, and - a fiber optic unit attached to the cable which extends longitudinally along the cable and which includes an optical fiber attached to the cable arranged substantially along the neutral axis, wherein the optical fiber attached to the cable is mechanically coupled with the cable; on what: the plurality of wires is braided around the fiber optic unit; the fiber optic unit coupled to the cable is mechanically coupled to at least one of the plurality of wires.
    [0101] [101] At least part of the plurality of wires directly surround the fiber optic unit attached to the cable. Preferably, the fiber optic unit is mechanically coupled with at least part of the plurality of wires that directly surround the fiber optic unit.
    [0102] [102] According to a feature of the present invention, electrical cables according to the invention are monitored to determine the length of the cable using optical backscattering techniques, such as optical time domain reflectometry (OTDR), reflectometry of photon counting optical time domain or optical frequency domain reflectometry (OFDR). According to generally known measurement techniques, an optical signal (probe) generated by a laser is launched at a first end of the optical fiber integrated in the electrical cable. In OTDR the optical probe signal is a pulsed wave signal, in OFDR it is a continuous wave modulated in frequency. The backscattered optical return signal from the optical fiber is measured by a detection circuit.
    [0103] [103] In the event that a fiber cycle is formed by joining a first optical fiber with a second optical fiber, the optical signal is sent to the first optical fiber and the cable length is determined by the length of the first optical fiber measured up to the connector or splice with the second optical fiber, subtracting the braid length used for splitting the optical fiber.
    [0104] [104] In OTDR, a measurement of the portion of light reflected back from the fiber as a function of light arrival time is performed to produce an OTDR trace made by the measured optical energy of the reflected back reflected light signal against the time. The OTDR trace is determined by the light reflected back and guided back to the fiber caused by the Rayleigh scattering that occurs in the fiberglass material due to its inhomogeneities and the Fresnel reflection that occur at interfaces with different index materials refractive (like air) appearing in the OTDR trace as a discontinuity in the measured optical energy. By comparing the amount of light scattered back at different times, OTDR can determine connection and fiber positions along the fiber and losses. If a second fiber end, opposite the first fiber end, has a face that is sharply cut orthogonally to the longitudinal axis of the fiber, strong reflection occurs in a cable position that corresponds to that second fiber end and a peak that is visible in the OTDR trace. A fiber end face orthogonal to the fiber axis can be achieved by means of a commercially available fiber cutter.
    [0105] [105] The time between the pulse launch and the receipt of the backscattered pulse is proportional to the distance along the fiber to the backscatter source. The time T required by the laser pulse to travel the length of fiber Lf in the frontal direction and return back to the point of pulse injection into the fiber (for example, first fiber end) is described by the following equation: 2Lf / T = with neff (2) where c is the speed of light in a vacuum (2.99792458x108 m / s) and neff is the group refractive index of the optical fiber.
    [0106] [106] The neff group refractive index is the ratio of the speed of light in a vacuum to the speed of light in the fiber for a pulse of light at a given frequency (or wavelength). In many cases of interest, the neff uncertainty is the main factor that determines the accuracy of length, as neff is usually quoted for 1 in 103 (ie 3 digits) while the best available measurements are 1 in 104 (ie 4 digits). The neff value for the optical fiber coupled to the cable is determined by using Eq. (1) on a calibration optical fiber made of the same type, possibly removed from the same preform, and of known fiber length.
    [0107] [107] In optical frequency domain reflectometry (OFDR) with frequency scanning (OFDR-FS), a signal injected into a fiber is a continuous frequency modulated optical wave (not a pulse as in OTDR). The optical radiation generated by the highly coherent laser diode is slowly and linearly scanned around the central frequency and coupled to a Michelson fiber interferometer. The reference arm is terminated by a mirror and the test arm is attached to the fiber under test. The time delay between the signals from the reflector on the reference arm and the backscattered signal from an arbitrary element dx at position x on the test arm is τ = 2 x / Vg, where Vg is the group velocity in the nucleus fiber. For coherent detection, both signals are mixed in the detector. During the time delay τ the optical frequency scanned linearly changes by Ω = τ [dω / dt]. This subtraction frequency component can be seen in the detector signal using the optical spectrum analyzer. Its frequency Ω determines the x position in the fiber and its amplitude is proportional to the local backscatter coefficient and the optical energy, which is proportional to the exp factor (-2ax) and which describes the attenuation of the front and rear signal at distance x. performing the Fourier transform of the detector signal in a low frequency spectrum analyzer, one can simultaneously observe the backscattered waves from all points along the fiber under test. They correspond directly to the frequency axes Ω of the analyzer.
    [0108] [108] Figure 6 is a schematic block diagram that illustrates a measurement system that uses an OTDR-based backscatter technique, according to an embodiment of the invention. a sampling device 70 is used to inject optical signals into an electrical cable 73 and to analyze the backscattered optical signal received from the cable. For this purpose the sampling apparatus comprises an optical source, such as a laser, and a detection circuit capable of detecting the scattered light signal. For example, the sampling device is an OTDR module E8136MR SM marketed by JDSU.
    [0109] [109] The electrical cable 73 comprises a fiber optic unit coupled to cable 71 in mechanical sealing coupling with at least one longitudinal structural element, which extends along the longitudinal direction of cable Z (only the optical fiber coupled to the cable is represented schematically in the figure). The electrical cable 73, and in particular the arrangement of the optical fiber 71 within the cable, can have a structure like any of those described in the following embodiments. The fiber optic unit coupled to the cable 71 is located along the central longitudinal axis of the cable and has mechanical congruence with at least one of the longitudinal structural elements of the cable.
    [0110] [110] The sampling device 70 sends an optical signal from an output 78 to an optical cable section 74, that is, the “launch cable”, which comprises a “launch” optical fiber connected to a proximal end of the optical fiber 71. The terms “proximal” and “distal” for the fiber ends are referred to in relation to the sampling device, or at least for the optical connection to the sampling device. However, these terms are intended to indicate only a relative position and / or are used to facilitate the description of the drawings, but they should not be interpreted as having an absolute meaning. The non-permanent connection between the cable section 74 of the measuring device 70 to the optical fiber 71 can be made by conventional means, for example, through an optical connector 77, for example, a splice connector.
    [0111] [111] The presence of an optical connector is seen by the light that travels as a discontinuity that produces a modification of the OTDR trace. In particular, optical connector 77 determines a change in the OTRD trace, such as a peak in the reflected optical energy back. An optical connector 76 is positioned at the distal end of the optical fiber 71. A splice connector can be used to optically couple the optical fiber attached to the cable to an additional optical fiber (not shown) arranged in a loose plug construction, which can be used for temperature measurement. In such an embodiment, the optical fiber 71 and the additional optical fiber are joined in one cycle. A fusion splice between the two fibers is recorded in the OTDR trace as a disturbance, usually as a sharp decrease in the optical energy of the reflected light signal.
    [0112] [112] Alternatively, the distal end of the optical fiber 71 can be cut to form a sharp end cut orthogonally to the longitudinal axis of the fiber. Both the presence of the connector 76 at the distal end of the fiber coupled to the cable or a cut end of the fiber generates a change in the OTDR trace, such as a peak of optical energy due to the reflection of light from the face of the distal end. It should be noted that non-orthogonal angled cut end faces can be used as fiber end faces, although angled end faces in generate weaker reflection light signals compared to orthogonal end faces. The distance between the peaks of optical energy generated by the optical connectors 77 and 76 gives rise to the fiber length. More generally, the distance between the discontinuities in the OTDR trace on the end faces of the optical fiber coupled to the cable provides the fiber length, Lf. By configuring the optical fiber unit in accordance with the teaching of the present invention, the measured length of the optical fiber coupled to the cable corresponds to the length of the electrical cable. The fiber length can be determined by the OTDR with an accuracy of about one meter for electrical cables of less than 5 km in length, in particular from 0.1 km to 100 km.
    [0113] [113] The sampling device 70 detects and analyzes the OTDR trace as a function of the distance from the proximal end of the launching optical fiber 74 to the distal end of the optical fiber coupled to the cable 71. Within the trace analysis, the sampling device records the distance between two or more recognized events, detected as disturbance of the linear evolution of the trace. The determination and location of the event of its nature (for example, splice, connector, fiber cracks, bending, fiber end) can be implemented as an automatic tool in the sampling device.
    [0114] [114] Figure 7 is a graph of an exemplary measurement of the OTDR trace on an electrical cable according to an embodiment of the invention. In the abscissa, the detection time of the reflected reflected light returned was converted into distance, d (in km), from the proximal end of the launch fiber, taken as d = 0. The launch fiber was connected to the optical fiber coupled to the cable inside the electrical cable and the connection point is visible as a sharp peak at about d = 1 km. In the example, the electrical cable, as well as the optical fiber, is joined in two intermediate positions along the cable length, as shown in the graph with triangles. The sharp discontinuity at the end of the optical fiber coupled to the cable originated from the peak of reflection at the distal end of the fiber. Near the distal end, the presence of a connector causes a disturbance of the line, indicated in the graph with a triangle. The length, Lf, of the optical fiber is determined by the difference between the position on the graph between the proximal end and the distal end of the optical fiber coupled to the cable. In the example, Lf = 4.54 km, which corresponds to the length of the electrical cable.
    [0115] [115] Using an OFDR technique to measure the length of an electrical cable in accordance with the present invention can allow an accuracy of a few mm to be obtained for cable lengths exceeding 0.1 km.
    权利要求:
    Claims (13)
    [0001]
    Method of measuring the length of an electrical cable, the method comprising: provide an electrical cable (1, 30, 40, 73) having a cable length and a central longitudinal axis (Z) defining a neutral cable axis which, after cable bending, is not subjected to compression or elongation tension, the cable including: - a longitudinal structural element (2, 7; 43, 44) including at least one electrical conductor (12, 7, 45), and - a fiber unit (5) which extends longitudinally along the cable and which includes an optical fiber (9, 71) having a fiber length and arranged along the central longitudinal axis (Z), wherein the optical fiber ( 9, 71) is mechanically coupled with the cable; inject an optical signal into the optical fiber; detecting backscattered light from the optical fiber in response to said optical signal; analyze the backscattered light detected as a function of time in order to determine the fiber length, and derive the cable length from the fiber length, characterized by the fact that the optical fiber unit (5) is incorporated in a mechanical coupling filler (6; 25; 47) that mechanically couples the optical fiber unit with the longitudinal structural element (2, 7; 43, 44) , the optical fiber unit being congruent with the longitudinal structural element in such a way that the optical fiber unit remains in coaxial alignment with the central longitudinal axis (Z) and a constant relationship between the cable length and the fiber length is maintained .
    [0002]
    Method according to claim 1, characterized in that the length of the optical fiber corresponds to the length of the cable.
    [0003]
    Method according to claim 1, characterized by the fact that the optical fiber (9) is provided in a sealed configuration in the optical fiber unit (5).
    [0004]
    Method according to claim 1, characterized in that the mechanical coupling filler (6) is the base of an elastomer material, more preferably in a thermoset elastomer.
    [0005]
    Method according to claim 1, characterized in that the mechanical coupling filler (6) contacts the longitudinal structural element in at least one tensioned condition of the cable.
    [0006]
    Method according to claim 1, characterized in that the cable (1; 30; 40; 73) comprises a plurality of longitudinal structural elements (2, 7; 43, 44) and the mechanical coupling filler (6) contacts the plurality of longitudinal structural elements positioned in an external radial position with respect to the optical fiber unit (5).
    [0007]
    Method according to claim 1, characterized in that the optical fiber unit (5) comprises a protective sheath (8) that surrounds the optical fiber (9) and in which the mechanical coupling filler (6; 25; 47 ) surrounds and is congruent with the protective sheath.
    [0008]
    Method according to claim 7, characterized in that the fiber optic unit additionally comprises a sealed buffer layer (10) that surrounds the optical fiber (9) and is congruent with the protective sheath.
    [0009]
    Method according to any one of claims 1 to 8, characterized by the fact that the optical fiber (9, 71) has a proximal end and a distal end and that analyzing backscattered light comprises: analyze changes in backscattered light; based on changes in the scattered light signal determine the position of the proximal end and the distal end of the fiber, and calculate the fiber length from the difference between the position of the proximal end and the position of the distal end of the optical fiber.
    [0010]
    Method according to claim 9, characterized by the fact that it comprises: provide a cleaved distal end of the optical fiber (71), injecting an optical signal at the proximal end of the optical fiber, detecting the scattered light emitted from the proximal end of the optical end (71), and identify a reflection peak that corresponds to the position of the distal end of the optical fiber.
    [0011]
    Method according to any one of claims 1 to 10, characterized by the fact that analyzing the scattered light comprises using an optical time domain reflectometer (70).
    [0012]
    Flat electrical cable (60) having a central longitudinal axis and comprising: - two external cable cores (61, 63) and a central cable core (62) positioned parallel, adjacent to each other and centered along a common axis (69) of a cable cross section, the common axis (69 ) being parallel to a direction (X) transverse to the central longitudinal axis, each core (61, 62, 63) comprising a plurality of twisted conductive wires (65), - a neutral cable shaft, and - an optical fiber unit (5) coupled to the cable that extends longitudinally along the cable (60) and which includes an optical fiber (9) arranged along the neutral axis, characterized by the fact that the optical fiber is mechanically coupled with the cable; and the neutral axis of the cable is the central longitudinal axis and the common axis (69) is the middle axis of the cable cross section so that the central longitudinal axis of the central cable core (62) crosses the middle axis, the plurality of wires (65) of the central core are braided around the optical fiber unit (5); and the optical fiber unit is arranged within the central core (62) along the central longitudinal axis and is mechanically coupled with at least one of the plurality of conductive wires (65).
    [0013]
    Cable according to claim 12, characterized in that the cable (60) is a three-phase cable.
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    同族专利:
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    RU2547143C2|2015-04-10|
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    CN103314415A|2013-09-18|
    WO2012073260A1|2012-06-07|
    EP2647016A1|2013-10-09|
    US20140049786A1|2014-02-20|
    BR112013013140A2|2020-08-11|
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    法律状态:
    2020-08-18| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-12-01| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-01-26| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 10 (DEZ) ANOS CONTADOS A PARTIR DE 26/01/2021, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    PCT/IT2010/000475|WO2012073260A1|2010-11-29|2010-11-29|Method for measuring the length of an electric cable that uses an optical fibre element as a sensor|
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