Magnetic probe for detecting faults in cables having a ferromagnetic portion, associated method and associated system

Abstract

The invention relates to a magnetic probe for detecting faults in a ferromagnetic portion of a cable. The probe includes at least three magnetic circuits held by a frame and each circuit includes a core configured to extend along the cable when the probe is in use; means for generating magnetic flux in a section of the ferromagnetic portion of the cable; and an air gap located in the core to create a zero magnetic field point surrounded by a low magnetic field zone, between the core and the central axis. The probe includes at least three magnetic sensors, each being associated with one or more circuits and being located outside the core in the low magnetic field zone. The sensors are able to measure magnetic flux or a variation in magnetic flux caused by faults in the ferromagnetic portion of the cable.

Description

[0001] MAGNETIC PROBE FOR DETECTING FAULTS IN CABLES COMPRISING A FERROMAGNETIC PART, ASSOCIATED METHOD AND SYSTEM

[0002] TECHNICAL FIELD

[0003] The present application relates to the field of apparatus and methods for detecting and locating one or more faults in components comprising at least one ferromagnetic part, and more particularly relates to a magnetic probe for detecting faults in cables comprising a ferromagnetic part.

[0004] STATE OF THE ART

[0005] It is estimated that there are approximately 5 million kilometers of high-voltage lines worldwide, with an additional 200,000 kilometers added annually. To put this number into perspective, Hydro-Québec has the largest electrical grid in North America with 35,000 kilometers of high-voltage lines, which represents approximately 0.7% of the global total. A large proportion of the electrical conductors used on these high-voltage lines are ACSR (acronym for "Aluminum Conductor Steel Reinforced") or AAAC (acronym for "All Aluminum Alloy Conductors"). In the case of Hydro-Québec's network, almost exclusively ACSR conductors are used. These consist of a central steel core that provides the mechanical strength of the conductor.It generally comprises between 1 and 37 zinc-galvanized steel strands to resist corrosion and / or other external mechanical forces. Around the steel core, there are generally between 6 and 84 aluminum strands ensuring the conduction of electricity. An example of a conductor is shown in Figure 3 (PRIOR ART). Finally, ACSR conductors are produced in finished lengths of the order of kilometers and must therefore be spliced ​​using connecting sleeves, also made of steel and aluminum. Beyond about fifty years, or in the event of improper installation of the conductors, corrosion agents present in the environment can corrode the steel core and / or the connecting sleeves. Extreme weather conditions, such as, but not limited to, strong winds, ice, lightning, can damage electrical conductors, which can result in broken strands.Strand breakage is associated with a loss of mechanical strength, which can ultimately lead to the rupture of the electrical conductor, and therefore, of the high-voltage line. To avoid this situation, it is possible to perform non-destructive tests with magnetic probes that can use the principle of "Magnetic Flux Leakage" (MFL), such as the following devices or instruments: the "Magnetester", the "Intron" or the "Magnetograph". These devices or instruments include detectors for the loss of steel sections ("Loss of Metallic Area" or "LMA") and for broken strands ("Local Fault" or "LF"). However, these devices or instruments are not suitable for ACSR conductors, but rather for cables made of steel only.More specifically, these devices or apparatuses have an opening too small for most ACSR conductors or are too heavy to be easily transported, including transport by drone. In addition, existing devices and apparatuses cannot pass through the connection sleeves, which limits their characterization.

[0006] In light of the foregoing, there is therefore a need for an apparatus, method and associated system for solving at least one of the problems and / or limitations discussed above.

[0007] SUMMARY

[0008] In one aspect, a magnetic probe for detecting defects in a ferromagnetic portion of a cable is provided. The magnetic probe includes a frame, at least three magnetic circuits, and at least three magnetic sensors. The frame has a central axis and a passage for passing the cable therethrough. The at least three magnetic circuits are held by the frame, spaced apart from each other. Each circuit includes a core configured to extend along the cable when the probe is in use (i.e., at least one side of the core is substantially parallel to the cable); means for generating a magnetic flux in a section of the ferromagnetic portion of the cable; and an air gap located in the core to create a point of zero magnetic field surrounded by a low magnetic field area, between the core and the central axis.Each magnetic sensor is associated with at least one of the at least three magnetic circuits and is located outside the core, in the low magnetic field zone. The at least three magnetic sensors are capable of measuring low magnetic flux or low variation of magnetic flux caused by defects in the ferromagnetic part of the cable.

[0009] In some embodiments, the magnetic probe includes exactly three magnetic circuits and three associated magnetic sensors, equidistant from each other.

[0010] In some embodiments, two adjacent magnetic circuits are spaced 120° apart, around the central axis of the frame.

[0011] In some embodiments, the core includes a longitudinal portion extending along the cable, when the probe is in use, and two legs oriented radially toward the central axis; and the means for generating the flux includes a first magnet located in a first leg of the two legs and a second magnet located in a second leg of the two legs.

[0012] In some embodiments, the magnetic flux generated in the cable is below a magnetic saturation level of the cable when the magnetic probe is in use.

[0013] In some embodiments, the air gap of each circuit creates, produces, or generates a magnetic field leakage in the vicinity thereof and creates a point of zero magnetic field surrounded by a region of weak magnetic field. In some embodiments, the at least three magnetic sensors are ultrasensitive sensors.

[0014] In some embodiments, the at least three magnetic sensors are sensors capable of measuring a magnetic flux of less than 5 mT.

[0015] In some embodiments, the at least three magnetic sensors each have an operating range of ± 2.5 mT, and preferably an operating range minimally included between ± 1 mT.

[0016] In some embodiments, symmetrical positioning of the at least three magnetic sensors and averaging of the measurements can compensate for displacements of the cable relative to the central axis up to ±2 cm while limiting the error to 2 pT at most.

[0017] In some embodiments, the magnetic probe includes one or more control modules, each including acquisition means, processing means and calculation means for acquiring and processing signals captured by the at least three magnetic sensors, and for performing calculations from the processed signals.

[0018] In some embodiments, symmetrical positioning of the at least three magnetic sensors makes it possible to reduce or eliminate the effect produced by a displacement of the cable relative to the central axis on the measurements made when the magnetic probe is in use, the calculation means being configured to average the measurements of the at least three magnetic sensors or perform an equivalent operation.

[0019] In some embodiments, each control module includes means for recording and / or means for transmitting measurements or calculations made from the measurements.

[0020] In some embodiments, each control module is configured to calculate magnetic surface losses (MSL) and / or identify broken strands (LF) from magnetic flux values ​​or magnetic flux variations measured by at least one of the at least three magnetic sensors.

[0021] In some embodiments, each control module includes algorithmic means for reducing or eliminating the effect of a magnetic field generated by a current flowing in the cable under inspection, the cable in this case corresponding to an energized electrical conductor of a high voltage transmission line.

[0022] In some embodiments, a magnetic field originating from the cable or stray is an alternating magnetic field and the algorithmic means for reducing or eliminating the effect of the alternating magnetic field generated by a current flowing in the cable under inspection includes an algorithm for filtering a frequency component of a measured signal or for synchronizing the reading times of flux measurements with the times when the current flowing in the conductor crosses zero.

[0023] In some embodiments, each control module is configured to calculate magnetic surface losses (MSLs) from absolute measurements made by the magnetic sensors.

[0024] In some embodiments, the magnetic probe includes a linear encoder configured to contact the cable to be inspected, each monitoring module being configured to locate broken strands (LF) from differential measurements made by the magnetic sensors or from absolute measurements read at regular intervals, the intervals being determined based on position readings obtained from the linear encoder.

[0025] In some embodiments, the magnetic probe includes a sensor of the Earth's gravitational field, each control module including algorithmic means for reducing or eliminating the effect of the Earth's gravitational field on the magnetic flux measurements made by the sensors. In some embodiments, an opening of the magnetic probe corresponds to a transverse circular section around the central axis capable of receiving the cable between the at least three magnetic sensors of the magnetic probe, the ratio of the radius of the opening of the magnetic probe to the weight of the magnetic probe being of the order of 60 mm / kg. It should be noted that the opening is the circular section at the center of the magnetic probe 20, around the central axis, where the cable 22 will be located during the inspection.

[0026] In some embodiments, the at least three magnetic circuits and the at least three magnetic sensors are positioned and sized to enable inspection of cables having a ferromagnetic portion having a diameter between approximately 2 mm and approximately 50 mm.

[0027] In some embodiments, the at least three magnetic circuits and the at least three magnetic sensors are positioned and sized to enable inspection of sleeves connecting electrical conductors on high voltage transmission lines, the ferromagnetic portion including a section in the sleeves connecting the electrical conductors, and a transition zone between the conductors and the sleeves, in which the measurement of the magnetic probe allows insertion of the cable into the probe and in which the opening of the magnetic probe allows continuous measurement during relative movement between the magnetic probe and the sleeve.

[0028] In some embodiments, the at least three magnetic circuits and the at least three magnetic sensors are configured to enable inspection of the ferromagnetic core of ACSR type conductors.

[0029] In some embodiments, the frame, the at least three magnetic circuits, and the at least three sensors have a total mass of less than 2 kg, making the magnetic probe portable by drone or similar means of transportation. In some embodiments, the configuration of the passage in the frame allows the probe to be installed on a cable, by drone, without human intervention.

[0030] In some embodiments, the at least three magnetic sensors are of the fluxgate, Hall effect, or magnetoresistance type.

[0031] In some embodiments, the measurements made by the at least three magnetic sensors have a linear relationship with a geometric parameter of the ferromagnetic portion of the cable, facilitating calibration of the magnetic probe.

[0032] In some embodiments, the passage includes a fixed, permanently open gap.

[0033] In some embodiments, the core and legs each include a stack of mild steel laminations.

[0034] In some embodiments, the frame does not include an opening or closing mechanism for installing the magnetic probe onto the cable.

[0035] According to one aspect, a method for detecting defects in a ferromagnetic portion of a cable is provided. The method employs the magnetic probe as defined above.

[0036] According to one aspect, a system for detecting defects in a ferromagnetic portion of a cable is provided. The system includes a magnetic probe as defined above and transport means for moving the magnetic probe along the cable so as to collect measurements representative of potential defects in the ferromagnetic portion of the cable.

[0037] The technology and its advantages will become more apparent from the following non-limiting description of preferred embodiments of the technology, made with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE FIGURES

[0038] Figure 1 (prior art) illustrates continuous poles made of mild steel, and incorporating strong magnetic field magnets to create a magnetic field.

[0039] Figure 2 (prior art) is a representation of the “magnetester” apparatus.

[0040] Figure 3 (prior art) illustrates an example of a conductor.

[0041] Figure 4 illustrates an air gap in a magnetic circuit to create a zero magnetic field point, in accordance with one embodiment.

[0042] Figure 5 is a side view of a magnetic probe, in accordance with one embodiment.

[0043] Figure 6 is a front view of the magnetic probe of Figure 5.

[0044] Figure 7 is an example of a magnetic sensor, in accordance with one embodiment.

[0045] Figure 8 illustrates a magnetic probe, in accordance with one embodiment.

[0046] Figure 9 illustrates a magnetic probe, in accordance with one embodiment.

[0047] Figure 10 illustrates a perspective view of the magnetic probe shown in Figure 8.

[0048] Figure 11 illustrates a side view of the magnetic probe shown in Figure 9.

[0049] Figure 12 illustrates a top view of the magnetic probe shown in Figure 9. Figure 13 illustrates the magnetic probe shown in Figure 9, into which a cable has been inserted.

[0050] Figure 14 illustrates the ability of the magnetic probe to compensate for frame displacement.

[0051] Figures 15 to 25 illustrate different results that were obtained with the magnetic probe.

[0052] DETAILED DESCRIPTION

[0053] In the following description, similar components and / or features in the figures are represented by the same reference numerals. In order to avoid cluttering the figures, certain elements are not identified in all the figures if they have already been shown in previous figures. The elements shown in the figures are not necessarily to scale and the emphasis is instead on clearly illustrating the elements and structures of the various embodiments shown below.

[0054] Furthermore, although the described and illustrated embodiments include various components, and although some of these components have certain geometric configurations, it is understood that the number of components and their geometries may vary, and therefore should not be taken in their restrictive sense, and should not be interpreted in a manner that limits the scope of the present technology. It is to be understood, as will also be apparent to those skilled in the art, that other suitable components, as well as other suitable geometric configurations, may be used for the present technology and corresponding parts of the present technology.

[0055] All technical and scientific terms and expressions used in this specification have the same definitions as those generally understood by those skilled in the art of the present technology. Definitions of certain terms and expressions used are nevertheless provided below. The term "about" as used herein means "approximately," "in the region of," "around," or any other expression having a similar meaning. For example, when the term "about" is used in connection with a numerical value, it could modify it above and / or below by a predetermined variation. In some examples, the predetermined variation is about 10% from the nominal value. This term may also take into account, for example, the experimental error of a measuring device, rounding, and / or statistical deviations.Where a range of values ​​is referred to in this application, the lower and upper bounds of the range are, unless otherwise stated, always included in the definition.

[0056] The term "defect(s)", as well as any similar or equivalent term, will be used in this disclosure to refer to certain types of loss of material or physical integrity in ferromagnetic materials, such as loss of steel section ("LMA"), broken steel strands ("LF") and breakage of connection sleeves of electrical conductors (such as ACSR type electrical conductors).

[0057] The term "signal", as well as any similar or equivalent expression, represents a variation of any physical quantity. A signal can be analog or digital, and typically carries information. A signal can be continuous or discrete and have different characteristics such as, for example and without limitation, a period, an amplitude and a phase. For example, in the context of applications in electricity or involving the use of electricity, an electrical signal can be representative of a potential difference, the intensity of an electric current, the variation of the amplitude, the variation of a frequency, the variation of a phase and / or any other relevant physical quantity. It should be noted that the properties of a signal can be measured and that during a measurement, a sample represented by a data set is obtained. The data set is generally representative of the signal being measured.The “measurement time” represents the duration, generally finite, of the acquisition of a sample comprising a set of data. Following its acquisition, the signal (or the sample comprising a set of data representative of the signal) can be processed. The “processing” of a signal typically includes a method, a procedure and / or the use of technique(s) making it possible to confirm the presence (or absence) of defects, to locate the location of one or more defects if applicable, and / or to reveal certain physical characteristics relevant to the characterization of these defects. For example, generally and without being limiting, the processing of a signal can include mathematical operations or a series of operations.These operations include, but are not limited to: control, filtering, compression, transmission, noise reduction, convolution, deconvolution, prediction, identification and / or classification, in addition to other basic mathematical operations (e.g., addition, subtraction, multiplication and / or division). Thus, signal processing typically allows obtaining a property of a signal that can subsequently be associated with a physical quantity or its variation, which in turn can be associated with the presence or absence of defects in the ferromagnetic part of the cable being inspected.

[0058] Some of the following expressions (including similar, synonymous and equivalent expressions) will be used in this disclosure:

[0059] - “High precision” will mean that the error is below a threshold of 2%;

[0060] - “Fast measurement” will mean that the bandwidth is greater than 30 kHz

[0061] - “Fine resolution” will mean that the resolution is less than 1 pT;

[0062] - “Low offset” (or “offset”) will mean an offset of less than 10 pT;

[0063] - “Low noise level” will mean that the noise spectral density is less than 10 nT / Hz;

[0064] - “Accurate gain” will mean that the error associated with the gain is less than 0.05%; and - “Very low non-linearity” will mean that the linearity error is less than 0.1%.

[0065] The terms "external radiation", "external disturbances", and any other similar or equivalent term, represent electrical, magnetic or electromagnetic noise. Noise is here understood as a signal having an origin other or different from the signal associated with the faults being characterized by the techniques presented here. For example, a signal associated with noise generally has different properties than a signal from fault(s) in a ferromagnetic part of a cable.

[0066] The apparatus(es), method(s) and system(s) described herein, or at least elements thereof, may be implemented in computer programs executed on programmable computers (e.g., a microcontroller), each comprising at least one processor, a data storage system comprising, for example and without limitation, volatile and non-volatile memory elements, at least one input device and at least one output device. In some examples, the programmable computer may be a programmable logic unit, a mainframe computer, a server and a personal computer, a cloud computing system, a laptop computer, a personal data assistant, a cell phone, a smartphone, a wearable device, a tablet, a smart display device, a set-top box or a virtual reality device.Each program is preferably implemented in a high-level programming, procedural programming, or object-oriented language for communicating with a computer system. However, the programs may be implemented in assembly language or machine language. In any case, the language may be a compiled or interpreted language. Each of these computer programs is preferably stored on a storage medium or device readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage medium or device is read by the computer to perform the procedures that will be described in this disclosure. In some embodiments, the systems may be integrated with an operating system running on the programmable computer.

[0067] Context

[0068] The technique known as "Magnetic Flux Leakage", also commonly referred to as the "MFL technique", has been known for a long time. It has a multitude of applications for detecting defects in ferromagnetic materials. The basic principle of MFL is based on the formation of a magnetic circuit between a magnetic probe and a sample or object under inspection (or at least a portion of the sample or object). The magnetic probe is adapted to produce a relatively high magnetic field, or at least high enough to saturate the sample or object. In the presence of a defect, the magnetic flux changes its path locally near the defect (it leaks), causing a decrease or an increase in the field, which is detected by appropriate detectors, such as magnetic detectors.

[0069] Different commercial solutions exist, such as, but not limited to:

[0070] 1. The “Magnetester”, illustrated in Figure 2 (PRIOR ART). This device has a mass of 23 kg and a maximum aperture of 44 mm, which is equivalent to an aperture / mass ratio of 1.9 mm / kg;

[0071] 2. The “Intron”. This device has a mass of 3 kg and a maximum aperture of 24 mm, which is equivalent to an aperture / mass ratio of 8 mm / kg; and

[0072] 3. The “Magnograph 3”. This device has a mass of 13 kg and a maximum aperture of 45 mm, which is equivalent to an aperture / mass ratio of 3.5 mm / kg.

[0073] The three non-limiting examples presented above suggest a trend for this type of probe. Indeed, for commercial solutions already available, the probe aperture is correlated with the probe mass (i.e., the larger the aperture, the greater the mass), which is summarized by the aperture / mass ratio presented above for each of the devices. This trend can be explained in particular by the need to magnetically saturate the sample or object being inspected. It should be noted that approximately 80% of Hydro-Québec's 35,000 km of high-voltage lines have a diameter larger than 24 mm, limiting the commercial solutions that can be used, which also limits the conductors that can be inspected. In addition, the inspection of connection sleeves would be impossible with the examples of commercial solutions presented above.

[0074] The configuration of the magnetic circuit is very similar from one probe to another. Indeed, existing solutions include probes composed of “U” shaped poles. These poles are continuous and made of mild steel, and include strong magnetic field magnets (e.g.: NdFeB) to create the magnetic field, as shown in Figure 1 (PRIOR ART). The magnetic sensors are generally placed close to the magnetic circuit and at distinct locations in the different probes. However, regardless of the choice of location, the magnetic sensors are in the presence of a non-zero magnetic field which is produced by the magnetic probe. Therefore, this configuration of the existing solutions requires the use of a magnetic sensor with a large dynamic range (e.g., Hall effect sensor). This configuration is therefore less sensitive and less accurate than a sensor with a smaller measuring range.

[0075] Existing magnetic probes use multiple poles to eliminate or attempt to eliminate the impact of cable / conductor movement within the opening. For example, among the existing solutions presented above, the Magnetester and Intron magnetic probes use 2 poles to reduce sensitivity to cable movement along the gravitational axis. The Magnograph 3 probe uses 4 poles, which additionally reduces sensitivity to cable movement along the axis perpendicular to the gravitational axis and the cable axis. In all cases, the presence of 2 or 4 poles requires an opening and closing mechanism to install the magnetic probe around the cable to be inspected.

[0076] Magnetic probe, associated method and system

[0077] The technology described herein relates to an ultra-lightweight, large-aperture magnetic probe enabling relatively accurate detection of steel section losses (“SLAs”), broken steel strands (“BSLs”) and breaks in the connection sleeves of ACSR electrical conductors. The relatively accurate detection of these defects is possible despite the relatively low total mass of the magnetic probe. More specifically, the magnetic probe has a total mass of approximately 1.5 kg and has an aperture having a diameter of approximately 90 mm, which equates to an aperture-to-mass ratio of 60 mm / kg. These features allow the probe to be carried by drones, or similar means of transport, and to roll over the connection sleeves and high-voltage cable portion(s), which is an improvement over the existing probes that have been presented above.Indeed, the aperture / mass ratio of the magnetic probe presented here is therefore approximately 7 times better than existing solutions. In addition, the magnetic probe described here has a three-pole cylindrical symmetry which makes it possible to eliminate or at least reduce the effect of the conductor displacement on the measured signal, in addition to eliminating the opening and closing mechanism. In addition, the creation of a zero magnetic field point (zero point) on each of the poles of the magnetic probe allows the use of ultra-sensitive magnetic sensors, and therefore, a very precise measurement, which is also an improvement over existing solutions.

[0078] The technology described here outperforms currently commercially available probes in several ways in the precise application of steel cable inspection (which includes ACSR electrical conductors). As will be described in more detail below, the magnetic probe presented here measures LMA defects and relatively small LF defects with high accuracy, can be transported by drone or other similar means of transport, can be deployed without an operator to open or close its passage, and has an opening large enough to inspect splice sleeves.

[0079] As will be described in more detail below, the magnetic probe relies in particular on the introduction of an air gap to the magnetic circuit to create a zero magnetic field point ("zero point"), a three-pole symmetry and use in an unsaturated regime of the magnetic probe, as illustrated in a non-limiting manner in Figure 4.

[0080] Existing MFL magnetic probes use seamless "U"-shaped poles, in which there is no point near the poles where the magnetic field is zero. In existing technologies, it is necessary to use magnetic sensors with a large measuring range, which are generally inaccurate, in order not to saturate them. Introducing an air gap in the middle of each magnetic pole of the probe creates a magnetic field leakage in the air in the middle of the poles. This magnetic field leakage is in the opposite direction with the magnetic field in the air in the absence of an air gap. There is therefore definitely a point or region where the magnetic field is zero, the position of which depends on the geometric parameters of the probe. It then becomes possible to use the full range of a more accurate magnetic sensor if the sensor is positioned near this zero point.It therefore becomes possible, with the magnetic probe described here, to measure relatively weak, even very weak, magnetic fields, which makes it possible to reduce the total mass of the magnetic probe and to increase the aperture diameter of the magnetic probe, while maintaining an equally precise measurement of LMA and LF defects. The increase in the aperture diameter makes it possible to inspect large diameter conductors as well as connection sleeves, which was not possible with existing solutions.

[0081] The use of a three-pole symmetry configuration following cylindrical symmetry allows compensation for the displacement of the conductor on two axes. For example, the three poles can be arranged at an angle of approximately 120° between them. It should be noted that in the illustrated configuration, poles 1 and 3 are attached to pole 2, but poles 1 and 3 are not attached to each other, thus leaving a passage at the bottom of the magnetic probe. This passage (see for example element 30 in Figure 6) is adapted, positioned and dimensioned to insert the conductor without having to open and close the probe, or to resort to an opening and / or closing mechanism of the magnetic probe. It is therefore not necessary for an operator to climb close to the conductor to close and open the probe, as is currently required using existing solutions.The magnetic probe can therefore be delivered by drone, or any other similar means of transport, which allows for rapid and safer deployment, reducing exposure to high voltages, which are potentially dangerous for operators.

[0082] The principle of compensation of the conductor displacement by the magnetic probe will now be explained in more detail. In a scenario where the cable or a portion thereof approaches pole 1, the amplitude of the signal detected by the magnetic sensor associated with pole 1 will be modified, while the amplitude of the signal respectively detected by the magnetic sensors associated with poles 2 and 3 will be modified opposite pole 1. By averaging the signals over the three poles, these variations almost completely cancel each other out, which allows to at least reduce and preferably eliminate significant signal variations, despite the conductor displacement (i.e., the relative movement of the conductor with respect to the position of the magnetic sensors). It should be noted that the signal compensation or correction is only valid within a certain displacement limit, or more specifically a range of displacement values.For example, and without being limiting, for a magnetic probe having an aperture with a radius of 4.5 cm, the signal correction or compensation will be valid for a maximum displacement of approximately 2 cm. In practice, it is rare for a displacement to be greater than 2 cm. This range is therefore sufficient for the intended applications. In summary, the three-pole probe geometry makes it possible to reduce and preferably eliminate the signal variation caused by the displacement of the conductor relative to certain components of the magnetic probe, as illustrated in a non-limiting manner in Figures 13 and 14.

[0083] In several places in the literature, it is mentioned that magnetic probes operate or function in a saturated state. All existing magnetic probes intended for the inspection of steel cables appear to operate in a saturated state. The magnetic probe described here does not operate in a saturated state, which notably allows the weight of the magnetic probe to be greatly reduced. During the tests carried out, nothing suggests that saturation is necessary to make appropriate measurements. Indeed, the magnetic probe presented here allows the detection of relatively small defects in an unsaturated state thanks to the use of ultra-sensitive sensors.

[0084] Now that the magnetic probe and its operating principle have been described from a general point of view, different embodiments of the technology will now be presented, with reference to Figures 4 to 25.

[0085] An embodiment of a magnetic probe 20 for detecting defects in a ferromagnetic portion of a cable 22 is illustrated in Figure 5.

[0086] The magnetic probe 20 includes a frame 24, at least three magnetic circuits 26 and at least three magnetic sensors 28. The frame 22 has a central axis and a passage 30 for passing the cable 22 therethrough. The at least three magnetic circuits 26 (or simply the magnetic circuits 26) are held by the frame 24, spaced apart from each other. It is noted that the passage 30 allows the cable 22 to be inserted into the frame 24. Each magnetic circuit 26 includes a core 32 configured to extend along the cable 22 when the magnetic probe 20 is in use; means 34 for generating a magnetic flux in a section of the ferromagnetic portion of the cable 22; and an air gap 36 located in the core 32 for creating a point of zero magnetic field surrounded by a zone of low magnetic field, between the core 32 and the central axis of the frame 24.Each magnetic sensor 28 is associated with at least one of the at least three magnetic circuits 26 and is located outside the core 32, in the low magnetic field area. The at least three magnetic sensors 28 (or simply the magnetic sensors 28) are capable of measuring low magnetic flux or low variation of magnetic flux caused by defects in the ferromagnetic portion of the cable 22.

[0087] In some embodiments, the magnetic probe 20 includes exactly three magnetic circuits 26 and exactly three associated magnetic sensors 28, equidistant from each other. In other embodiments, the magnetic probe could include four, five, or six magnetic circuits.

[0088] In the illustrated configurations, two adjacent magnetic circuits 28 are spaced 120° apart, around the central axis of the frame 24. It should be noted that the angle depends on the number of magnetic circuits being mounted on the frame 24.

[0089] In some embodiments, the core 32 includes a longitudinal portion 38 extending along the cable 22, when the magnetic probe 20 is in use, and two legs 40 oriented radially towards the central axis of the frame 22. The means 34 for generating the flux include a first magnet 42 located in a first leg of the two legs 40 and a second magnet 44 located in a second leg of the two legs 40.

[0090] In some embodiments, the magnetic flux generated in the cable 22 is below a magnetic saturation level of the cable 22 when the magnetic probe 20 is in operation, i.e., the magnetic probe is not operated in a saturated regime.

[0091] The air gap 36 of each magnetic circuit 26 is adapted and configured to create a magnetic field leakage in the air 48 near the air gap 36 (i.e., in the air at the center of the circuit 26, and at the bottom of the core 32)), in the opposite direction to the magnetic flux generated in the air 48 in the absence of the air gap 32.

[0092] In some embodiments, the magnetic sensors 28 are ultra-sensitive sensors. For example, the magnetic sensors 28 could be sensors capable of measuring a magnetic flux of less than 5 mT. In some embodiments, the magnetic sensors 28 each have an operating range of ± 2.5 mT, and preferably an operating range minimally included between ± 1 mT. It should be noted that the magnetic probe 20 makes it possible to carry out measurements that are relatively insensitive to a drift in the gain or offset as a function of temperature.

[0093] As illustrated in some Figures, it is possible that a relative movement or displacement (eg, a radial displacement) between the magnetic probe 20 and the cable 22 must be compensated. In this regard, symmetrical positioning of the three magnetic sensors 28 and averaging the measurements taken by the latter can compensate for displacements of the cable 22 relative to the central axis of the frame 24 up to ±2 cm while limiting the error to 2 pT at most. Thus, the potentially negative effect of the relative displacement of the cable 22 relative to the magnetic probe 20 can be compensated, which allows for measurements to be carried out that are quite accurate for the intended applications.

[0094] In some embodiments, the magnetic probe 20 includes one or more control modules, each including acquisition means, processing means and calculation means for acquiring and processing signals picked up by the magnetic sensors 28. The control modules make it possible to perform calculations, including a plurality of mathematical operations from the measured and processed signals. As previously presented, a symmetrical positioning of the magnetic sensors 28 makes it possible to reduce or eliminate the effect produced by a displacement of the cable 22 relative to the central axis on the measurements made when the magnetic probe 20 is in use. The calculation means are configured to average the measurements of the magnetic sensors 28 or perform an equivalent operation. Each control module could include recording means and / or means for transmitting the measurements or calculations made from the measurements.In some embodiments, each control module is configured to calculate magnetic section or surface losses (LMA) and / or to identify broken strands (LF) from the magnetic flux values ​​or variations in the magnetic flux measured by at least one of the magnetic sensors 28. In some embodiments, each control module includes algorithmic means for reducing or eliminating the effect of a magnetic field generated by a current flowing in the cable 22 under inspection, the cable 22 corresponding in this case to an energized electrical conductor of a high-voltage transmission line.In some embodiments, a magnetic field originating from the cable or stray is an alternating magnetic field and the algorithmic means for reducing or eliminating the effect of the alternating magnetic field generated by a current flowing in the cable under inspection includes an algorithm for filtering a frequency component of a measured signal or for synchronizing the reading times of flux measurements with the times when the current flowing in the conductor crosses zero.

[0095] In some embodiments, each control module may be configured to calculate magnetic surface losses (MSLs) from absolute measurements (i.e., non-relative measurements) made by the magnetic sensors 28.

[0096] In some embodiments, the magnetic probe 20 includes a linear encoder 46 configured to be in contact with the cable to be inspected, each monitoring module being configured to locate for broken strands (LF) from differential measurements made by the magnetic sensors 28 or from absolute measurements read at regular intervals. The intervals are determined based on position readings obtained from the linear encoder 46.

[0097] In some embodiments, the magnetic probe 20 includes a sensor of the Earth's gravitational field, and each control module includes algorithmic means for reducing or eliminating the effect of the Earth's gravitational field on the magnetic flux measurements made by the sensors. In some embodiments, an opening of the magnetic probe corresponds to a transverse circular section around the central axis capable of receiving the cable between the at least three magnetic sensors of the magnetic probe, the ratio of the radius of the opening of the magnetic probe to the weight of the magnetic probe being of the order of 60 mm / kg. It should be noted that the opening is the circular section at the center of the magnetic probe 20, around the central axis, where the cable 22 will be located during the inspection.

[0098] In some embodiments, the magnetic circuits 26 and the magnetic sensors 28 are positioned and sized to allow inspection of cable 22 whose ferromagnetic portion has a diameter between approximately 2 mm and approximately 50 mm. In some implementations, the diameter could be up to 15 mm, for example in the context of LF defect detection, up to 20 mm, for example in the context of LMA defect detection and up to 30 mm, for example in the context of sleeve corrosion detection.

[0099] In some embodiments, the magnetic circuits 26 and the magnetic sensors 28 are positioned and dimensioned to allow the inspection of sleeves connecting electrical conductors on high-voltage transmission lines, the ferromagnetic portion including a section in the sleeves connecting the electrical conductors, and a transition zone between the conductors and the sleeves, in which the passage 30 of the frame 24 of the magnetic probe 20 allows continuous measurement during a relative movement between the magnetic probe and the sleeve, the relative movement here being defined when the magnetic probe 20 advances and progressively covers the sleeve, or conversely allows the sleeve to come out of the magnetic probe 20.

[0100] In some embodiments, the magnetic circuits 26 and magnetic sensors 28 are configured to enable inspection of the ferromagnetic core of ACSR conductors. For example, the magnetic circuits 26 and magnetic sensors 28 may be optimized, in their position and dimensions, to enable inspection of the ferromagnetic core of ACSR conductors, as opposed to an all-steel cable of the same diameter.

[0101] In some embodiments, the frame 24, magnetic circuits 26, and magnetic sensors 28 have a total mass of less than 2 kg, making the magnetic probe 20 portable by drone or similar means of transportation.

[0102] In some embodiments, the configuration of the passage 30 in the frame 24 allows the magnetic probe 20 to be installed on the cable 22, by drone, without human intervention, which greatly simplifies the installation of the magnetic probe 20 on the cable 22.

[0103] In some embodiments, the magnetic sensors 28 are of the “fluxgate”, Hall effect or magnetoresistance type.

[0104] In some embodiments, the measurements made by the magnetic sensors 28 have a linear relationship with a geometric parameter of the ferromagnetic portion of the cable 22, facilitating the calibration of the magnetic probe 20. The geometric parameter could be a radius, a diameter, a section or an area.

[0105] In some embodiments, passage 30 includes a fixed, permanently open gap.

[0106] In some embodiments, the core 32 and legs 40 each include a stack of mild steel laminations in a configuration that minimizes weight by optimizing the shape to concentrate and uniform the magnetic flux therein.

[0107] In some embodiments, the frame 24 does not include an opening or closing mechanism for installing the magnetic probe 20 on the cable 22. In one aspect, a method for detecting defects in a ferromagnetic portion of a cable is provided. The method employs the magnetic probe as defined above.

[0108] According to one aspect, a system for detecting defects in a ferromagnetic portion of a cable is provided. The system includes a magnetic probe as defined above and transport means for moving the magnetic probe along the cable so as to collect measurements representative of potential defects in the ferromagnetic portion of the cable.

[0109] The technology presented here is based on the combination of a large magnetic probe aperture (90 mm diameter) and a low magnetic probe weight (1.5 kg). The technology is also based on the absence of a probe opening and closing mechanism thanks to three-pole symmetry. The technology is also based on the compensation of the conductor displacement on two axes thanks to three-pole symmetry. The technology is also based on the sensitivity of the probe resulting from a strategic location for the ultra-sensitive magnetic sensors (range of ±2.5 mT) in a zero-field zone (zero point).More specifically, the magnetic probe includes the addition of an air gap in the magnetic circuit of the poles, the creation of a zero magnetic field point (zero point) near the inspected object, the use of an ultra-sensitive and low-noise detector near the zero point, the measurement of the inspected object in unsaturated regime and the use of 3-pole symmetry. This configuration makes it possible to obtain an ultra-light, ultra-sensitive magnetic probe with a large aperture and without a closing mechanism. The technology described here is particularly well suited to ACSR conductors. It could also be used for all-steel cables. Finally, the magnetic probe described here allows the detection of LMA and LF defects, in addition to being able to be transported by drone, be placed on the conductor without an operator to close it and pass through connection sleeves to inspect their defects.Non-limiting examples of results that can be obtained with the technology presented herein are illustrated in Figures 15 to 25.

[0110] Although several preferred embodiments have been described in detail above and illustrated in the accompanying drawings, the invention is not limited to these embodiments alone. It will be understood by those skilled in the art that the claims are not to be limited in scope by the preferred embodiments illustrated in the examples presented above, but are to be given the broadest interpretation consistent with the description as a whole and the appended claims.

Claims

CLAIMS 1. A magnetic probe for detecting defects in a ferromagnetic portion of a cable, the magnetic probe comprising: a frame having a central axis and a passage for passing the cable therethrough; at least three magnetic circuits held by the frame, spaced apart from each other, each circuit comprising: a core configured to extend along the cable when the probe is in use; means for generating a magnetic flux in a section of the ferromagnetic portion of the cable; an air gap located in the core to create a point of zero magnetic field surrounded by a low magnetic field zone, between the core and the central axis; at least three magnetic sensors, each associated with at least one of the circuits and located outside the core, in the low magnetic field zone, the three sensors being capable of measuring a low magnetic flux or a low variation in the magnetic flux caused by defects in the ferromagnetic portion of the cable.

2. The magnetic probe according to claim 1, comprising exactly three magnetic circuits and three associated magnetic sensors, equidistant from each other.

3. The magnetic probe according to claim 2, in which two adjacent magnetic circuits are spaced 120° apart, around the central axis of the frame.

4. The magnetic probe according to any one of claims 1 to 3, wherein: the core comprises a longitudinal portion extending along the cable, when the probe is in use, and two legs oriented radially towards the central axis; and the means for generating the flux comprise a first magnet located in a first leg of the two legs and a second magnet located in a second leg of the two legs.

5. The magnetic probe of any one of claims 1 to 4, wherein the magnetic flux generated in the cable is below a magnetic saturation level of the cable when the magnetic probe is in use.

6. The magnetic probe according to any one of claims 1 to 5, wherein the air gap of each circuit creates a magnetic field leakage at the center of the core in the opposite direction to the generated magnetic flux.

7. The magnetic probe according to any one of claims 1 to 6, wherein the at least three magnetic sensors are ultrasensitive sensors.

8. The magnetic probe according to any one of claims 1 to 7, wherein the at least three magnetic sensors are sensors capable of measuring a magnetic flux of less than 5 mT.

9. The magnetic probe according to any one of claims 1 to 8, wherein the at least three magnetic sensors each have an operating range of ± 2.5 mT, and preferably an operating range of at least ± 1 mT.

10. The magnetic probe according to claim 9, wherein a symmetrical positioning of the at least three magnetic sensors and the averaging measurements can compensate for cable displacements relative to the central axis up to ±2 cm while limiting the error to a maximum of 2 pT.

11. The magnetic probe according to any one of claims 1 to 10, comprising one or more control modules, each comprising acquisition means, processing means and calculation means for acquiring and processing signals captured by the at least three magnetic sensors, and for carrying out calculations from the processed signals.

12. The magnetic probe according to any one of claims 1 to 11, wherein a symmetrical positioning of the at least three magnetic sensors makes it possible to reduce or eliminate the effect produced by a displacement of the cable relative to the central axis on the measurements made when the magnetic probe is in use, the calculation means being configured to average the measurements of the at least three magnetic sensors or carry out an equivalent operation.

13. The magnetic probe according to claim 11, in which each control module comprises means for recording and / or means for transmitting the measurements or calculations carried out from the measurements.

14. The magnetic probe according to claim 13, wherein each control module is configured to calculate magnetic surface losses (LMA) and / or identify broken strands (LF) from the magnetic flux values ​​or variations in magnetic flux measured by at least one of the at least three magnetic sensors.

15. The magnetic probe according to claim 13 or 14, wherein each control module comprises algorithmic means for reducing or eliminating the effect of a magnetic field generated by a current flowing in the cable under inspection, the cable corresponding in this case to an energized electrical conductor of a high voltage transmission line.

16. The magnetic probe of claim 15, wherein the magnetic field is an alternating magnetic field and the algorithmic means for reducing or eliminating the effect of the alternating magnetic field generated by a current flowing in the cable under inspection comprises an algorithm for filtering a frequency component of a measured signal or for synchronizing the reading times of flux measurements with the times when the current flowing in the conductor passes through zero.

17. The magnetic probe according to claim 11, wherein each control module is configured to calculate magnetic surface losses (MSL) from absolute measurements made by the magnetic sensors.

18. The magnetic probe according to claim 11, comprising a linear encoder configured to be in contact with the cable to be inspected, each control module being configured to locate for broken strands (LF) from differential measurements made by the magnetic sensors or from absolute measurements read at regular intervals, the intervals being determined as a function of position readings obtained from the linear encoder.

19. The magnetic probe according to claim 11, comprising a sensor of the Earth's gravitational field, each control module comprising algorithmic means making it possible to reduce or eliminate the effect of the Earth's gravitational field on the magnetic flux measurements carried out by the sensors.

20. The magnetic probe according to any one of claims 1 to 19, wherein an opening of the magnetic probe corresponds to a transverse circular section around the central axis capable of receiving the cable between the at least three magnetic sensors of the magnetic probe, the ratio of the radius of the opening of the magnetic probe to the weight of the magnetic probe being of the order of 60 mm / kg.

21. The magnetic probe according to any one of claims 1 to 20, wherein the at least three magnetic circuits and the at least three magnetic sensors are positioned and sized to allow the inspection of cable whose ferromagnetic portion has a diameter of between approximately 2 mm and approximately 50 mm.

22. The magnetic probe according to any one of claims 1 to 21, wherein the at least three magnetic circuits and the at least three magnetic sensors are positioned and dimensioned to allow the inspection of sleeves connecting electrical conductors on high voltage transmission lines, the ferromagnetic part comprising a section in the sleeves connecting the electrical conductors, and a transition zone between the conductors and the sleeves, in which the passage of the magnetic probe allows continuous measurement during a relative movement between the magnetic probe and the sleeve.

23. The magnetic probe according to any one of claims 1 to 22, wherein the at least three magnetic circuits and the at least three magnetic sensors are configured to allow inspection of the ferromagnetic core of ACSR type conductors.

24. The magnetic probe according to any one of claims 1 to 23, wherein the frame, the at least three magnetic circuits and the at least three sensors have a total mass of less than 2 kg, making the magnetic probe portable by drone or similar means of transport.

25. The magnetic probe according to any one of claims 1 to 24, wherein the configuration of the passage in the frame allows the probe to be installed on a cable, by drone, without human intervention.

26. The magnetic probe according to any one of claims 1 to 25, in which the at least three magnetic sensors are of the “flux gate”, Hall effect or magnetoresistance type.

27. The magnetic probe according to any one of claims 1 to 26, wherein the measurements made by the at least three magnetic sensors have a linear relationship with a geometric parameter of the ferromagnetic part of the cable, facilitating the calibration of the magnetic probe.

28. The magnetic probe of any one of claims 1 to 27, wherein the passage comprises a fixed, permanently open gap.

29. The magnetic probe of claim 4, wherein the core and legs each comprise a stack of mild steel lamellae in a configuration that minimizes weight by optimizing the shape to concentrate and uniform the magnetic flux therein.

30. The magnetic probe of any one of claims 1 to 29, wherein the frame does not include an opening or closing mechanism for installing the magnetic probe on the cable.

31. A method for detecting defects in a ferromagnetic portion of a cable, the method employing the magnetic probe according to any one of claims 1 to 30.

32. A system for detecting defects in a ferromagnetic portion of a cable, the system comprising: a magnetic probe according to any one of claims 1 to 30; and transport means for moving the magnetic probe along the cable so as to collect measurements representative of potential defects in the ferromagnetic portion of the cable.

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