Apparatus and methods for coupling to multi core armoured cables

Abstract

An apparatus and methods for coupling to a multi-core steel wire armoured cable or a multi core conductor cable 6 for measuring an electric current passing through the cable. The apparatus consists of

Description

A magnetically permeable shell around a current carrying cable reduces the magnetic field around it due to the currents within the cable, making it impractical to measure 5 anything beyond the net current in the cable running at the centre of the cable. This is what is measured by a conventional current transformer or Rogowski coil placed around the cable. Thus information in the external magnetic field about (amongst other things) differential currents and conductor positioning within the cable is lost. 10 Prior art relevant to the present invention: W02013 / 068360A1 (2013) discloses a device for measuring currents in the conductors of a sheathed cable of a poly-phase network. The invention consists in at least six magnetic field sensors arranged around a central hole. The cable to be measured pass 15   through said central hole, and the number of conductors in the cable has to be less than the number of the magnetic field sensors. The invention comprises a calculation device and a library of matrices that relate the measured fields to the currents in the conductors when the conductor configuration is known. A procedure is described to select the optimal matrix and to optimise and adapt it to the set of conductors under 20 test. W02013 / 068360A1 offers significant advantages with respect to EP0874244B1 and to the other documents discussed above: the total current is not limited to zero, the number of sensors is not constrained to be equal to the number of conductors minus 1, and allows with some limits to adapt to unexpected configurations of conductors. 25 Therefore, it is known in the art to derive currents within a non-armoured multi core cable from magnetic fields. Examples are disclosed in the patent application W02013 / 068360. The invention disclosed in this specification addresses the need to measure currents 30 within a steel wired armoured multi-core cable that is not addressed in the prior art. Summary The present specification concerns methods and apparatuses which apply magnetic fields to saturate the permeable shell, reducing its effective permeability, and allowing the magnetic fields arising from a current distribution within the cable to reach the 5 exterior. In this way, techniques to calculate the internal current distribution from external field measurements may be employed. Typical armoured cables use steel wire wound around the conductors, providing a partial permeable shell and resulting in attenuated and distorted fields due to current 10 distribution within the cable. As described herein, magnetically saturating the steel wire reduces (or effectively removes) this effect, allowing accurate and reproducible measurements of fields due to the current distribution within the cable to be made. Based on the magnetic fields, calculations of the current distribution may be performed, yielding derived parameters such as, without limitation, conductor current, 15 differential currents, phases, harmonics, time domain currents in one of more individual cores, a number and / or the geometry of cores within a multi-core steel wire armoured cable and / or a multi core cable without armour, and so forth. According to a first aspect of the invention there is provided apparatus for coupling to a 20 multi-core steel wire armoured cable. The apparatus includes one or more magnets and one or more magnetic field sensors. The apparatus is configured such that, when the apparatus is coupled to a multi-core steel wire armoured cable, a magnetic field corresponding to the one or more magnets is applied to a region of the multi-core steel wire armoured cable. The apparatus is configured such that, when the apparatus is 25 coupled to a multi-core steel wire armoured cable, each magnetic field sensor is oriented to detect components of magnetic field originating from the region of the multi-core steel wire armoured cable. The magnets maybe rare earth magnets such as Samarium cobalt (SmCo) and / or 30 Neodymium (NdFeB), and / or other non-rare earth magnets . The magnet may require protection from mechanical shock or impact, as the magnet may be brittle. The magnet may be coated in a rubber or other polymer. The magnet or magnets may be over moulded using a polymer; or assembled with a rigid polymer or 35 metal ( magnetic or no magnetic material) cover or covers that protects the surfaces of the magnet(s) that otherwise would be exposed to impact. In this way, the magnetic field from the one or more magnets saturates, or at least partly saturates, the steel wire armouring (typically in the form of wires wrapped about a circumference of the multi-core cable). Consequently, the permeability of the steel 5 wire armouring is reduced, allowing a greater fraction of magnetic fields generated by currents within the cores of the cable to couple to the magnetic field sensor(s). This may improve the accuracy and reliability of measured magnetic fields arising due to differential currents between two or more cores (or conductors) of the multi-core steel wire armoured cable. Consequently, derived quantities calculated based on said 10 measured magnetic fields may also be improved. Examples of derived quantities may include (without limitation), currents, differential currents, phases, harmonics, time domain currents in one of more individual cores, a number and / or the geometry of cores within a multi-core steel wire armoured cable, and so forth. 15 Each magnetic field sensor may be oriented to detect components of magnetic field originating from currents carried passing through one or more of the cores within the region of the multi-core steel wire armoured cable to which the magnetic field corresponding to the one or more magnets is applied. The magnetic field sensors may be configured to measure magnetic fields resulting from differential currents between 20 two or more cores of the multi-core steel wire armoured cable. A multi-core cable may alternatively be referred to a multi-conductor cable (and these terms should be interpreted interchangeably). 25 The magnetic field corresponding to the one or more magnets corresponds to the superposition of magnetic fields generated by each of the one or more magnets. The coupling may include mechanical coupling and / or connection. The coupling may include linking magnetic flux generated by, or within, the multi-core steel wire 30   armoured cable and / or cores thereof. The coupling does not include DC electrical connection. When the apparatus is coupled to the multi-core steel wire armoured cable, within the region the magnetic field corresponding to the one or more magnets may include a 35 component parallel to an axial direction of the multi-core steel wire armoured cable. The component parallel to an axial direction of the multi-core steel wire armoured cable maybe the largest component of the magnetic field at each point within the region. The component parallel to an axial direction of the multi-core steel wire armoured cable may be the largest overall component of the magnetic field. 5 At least one of the one or more magnets may include, or take the form of, a permanent magnet. Two or more of the magnets may include, or take the form of, permanent magnets. All of the one or more magnets may include, or take the form of, permanent magnets. 10 At least one of the one or more magnets may include, or take the form of, an electromagnet. Two or more of the magnets may include, or take the form of, electromagnets. All of the one or more magnets may include, or take the form of, electromagnets. 15 At least one of the one or more magnetic field sensors may include, or take the form of, a coil. Two or more of the magnetic field sensors may include, or take the form of, respective coils. All of the one or more magnetic field sensors may include, or take the form of, respective coils. Coils, maybe premade, with the cable inserted, or wound 20 around the cable in situ, or connected around the cable in situ, or placed around the cable in situ. The coils may be mounted radially, tangentially or in other axis relative to the longitudinal axis of the sensor. A mixture of coil orientations may be used, such as but not limited to radial and tangential within a single sensor. 25 At least one of the one or more magnetic field sensors may include, or take the form of, a solid state magnetic field sensor device. Each solid-state magnetic field sensor may sense magnetic fields in one, two, three or more axis. A solid state magnetic field sensor device may include, or take the form of, semiconductor type magnetic sensor, a magnetoresistive or giant magnetoresistive sensor. A solid state magnetic field sensor 30 device may include, or take the form of, a giant magnetoimpedance (GMI) sensor. A solid state magnetic field sensor device may include, or take the form of, a superconducting quantum interference detector (SQUID). A solid state magnetic field sensor device may include, or take the form of, a magneto-optical sensor. A solid state magnetic field sensor device may include, or take the form of, a fluxgate. The solid 35 state magnetic field sensor device may include, or take the form of, a chip or integrated circuit. A solid state magnetic field sensor device may include, or take the form of, a Hall sensor. Two or more of the magnetic field sensors may include, or take the form of, respective 5 solid state magnetic field sensor devices (of any type described herein). All of the one or more magnetic field sensors may include, or take the form of, respective solid state magnetic field sensor devices (of any type described herein). The magnetic field corresponding to the one or more magnets may have a magnitude of 10 at least 5 mT within the region. The magnitude of the magnetic field corresponding to the one or more magnets may be at least 12 mT within the region. The magnitude of the magnetic field corresponding to the one or more magnets may be at least 50 mT within the region. 15 The magnetic field corresponding to the one or more magnets may be time varying. A time varying magnetic field may correspond to at least some of the one or more magnets taking the form of electromagnets. The at least some electromagnets maybe driven with alternating current. The at least some electromagnets maybe energised during active periods and de-energised within inactive periods. The apparatus maybe 20 configured to compare measurements of magnetic fields between active and inactive periods in order to identify and preferably compensate for a residual screening effect of the steel wire armouring. Active and inactive periods may be sequenced according to a predetermined scheduled. Additionally or alternative, the apparatus maybe configured to energise the at least some electromagnets in response to a trigger condition, a 25 received signal and so forth. The apparatus may be configured such that the magnetic field corresponding to the one or more magnets is constant. Constant may mean that, when powered and operating correctly, the magnetic field is not time varying. A constant magnetic field may be 30 provided by permanent magnets, electromagnets energised by DC currents, or a combination of both. The apparatus may be configured to mechanically couple to the multi-core steel wire armoured cable using a magnetic force arising from application of the magnetic field to 35 the steel wire armour. The one or more magnets may be principally configured to apply magnetic field to the region to at least partially saturate the steel wire armour. However, this will always generate some magnetic force between the apparatus and the multi-core steel wire armoured cable. With suitable design choices, this magnetic force may additionally be used to secure the apparatus and a coupled multi-core steel wire armoured cable relative to one another. For example, the apparatus may be designed to 5 have a weight which is less than the magnetic force generated when a multi-core steel wire armoured cable is received within the region. The apparatus may also include a structure supporting the one or more magnets and the one or more magnetic field sensors. The structure may include a channel 10 configured to receive the multi-core steel wire armoured cable. The channel may be open, so as to receive the multi-core steel wire armoured cable. The structure may define the channel to be C-shaped or U-shaped in cross-section. The channel may be defined by first and second parts of the structure, configured to 15 close about the multi-core steel wire armoured cable when received within the channel. The first and second parts may be urged together by a spring. The first and second parts maybe urged to close about the multi-core steel wire armoured cable may magnetic forces from at least some of the one or more magnets. The first and second parts of the structure may provide a clamp. 20 The apparatus may also include a net current sensor configured to measure a net current through the multi-core steel wire armoured cable when the apparatus is coupled to the multi-core steel wire armoured cable. The net current sensor may include, or take the form of, a Rogowski coil. The net current sensor may include, or 25 take the form of, a current transformer. At least one of the one or more magnetic field sensors may include, or take the form of, a coil. Each coil may be wound around a sensing pole piece. Two or more of the magnetic field sensors may be provided by respective coils. Two or more coils 30 providing magnetic field sensors may be wound around respective portions of a single sensing pole piece. Alternatively, two or more coils providing magnetic field sensors maybe wound around respective, separate sensing pole pieces. A circumferential sensing pole piece may extend around all, or part of, a circumference 35 surrounding the multi-core steel wire armoured cable when received, and may include two or more inward radial protrusions. A coil providing a magnetic field sensor maybe wound around each inward radial protrusion. At least one of the one or more magnets may include, or take the form of, an 5 electromagnet. Each electromagnet maybe wound around a magnet pole piece. Two or more of the magnets may be provided by electromagnets. Two or more electromagnets may be wound around respective portions of a single magnet pole piece. Alternatively, two or more coils providing magnetic field sensors may be wound around respective, separate magnet pole pieces. 10 The apparatus may include a common pole piece having one or more coils providing magnetic field sensors wound around respective portions and one or more electromagnets wound around other portions. 15 The apparatus may include two or more magnet field sensors. The apparatus may include three or more magnetic field sensors. The apparatus may include four or more magnetic field sensors. The apparatus may include five or more magnetic field sensors. The apparatus may include six or more magnetic field sensors. The apparatus may include ten or more magnetic field sensors. 20 The magnetic field sensors may be equi-angularly spaced about the channel which receives the multi-core steel wire armoured cable. The one or more magnets may include, or take the form of, a first group comprising a 25 plurality of first magnets and a second group comprising a plurality of second magnets. The first and second groups maybe positioned to either side of the one of more magnetic field sensors along a direction corresponding to the axial direction of the multi-core steel wire armoured cable when coupled to the apparatus. In other words, the first and second groups of magnets bracket or sandwich the magnetic field sensors 30   along the length of a coupled / received multi-core steel wire armoured cable. The apparatus may include a pair of magnets corresponding to each magnetic field sensor. The pair of magnets may be arranged to either side of the corresponding magnetic field sensor along a direction corresponding to the axial direction of the 35 multi-core steel wire armoured cable when coupled to the apparatus. In other words, the pair of magnets bracket or sandwich the corresponding magnetic field sensor along the length of a coupled / received multi-core steel wire armoured cable. The one or more magnet field sensors may include a first set of first magnetic field 5 sensors and a second set of second magnetic field sensors. The first and second sets may be arranged to be spaced out along the axial direction of the multi-core steel wire armoured cable when it is coupled to the apparatus. In this way, differences in magnetic field measurements made using the first and 10 second sets may be used to compensate for different twisting rates between different multi-core cables, as discussed further in relation to the apparatus of the third aspect. A sensor may include the apparatus of the first aspect and a controller. The controller may be connected to the one or more magnetic field sensors and configured to 15 calculate, for some or all of the cores of a multi-core steel wire armoured cable, one or more derived quantities based on the magnetic field components measured by the magnetic field sensors. The one or more derived quantities may include (without limitation): currents in 20 individual cores, a core current may be alternating or direct current differential currents between cores, phases between cores, harmonics, time domain currents in one of more individual cores, a number and / or the geometry of cores within a multi-core steel wire armoured cable; or cores / conductors within magnetically soft conduits or pipes or cables trays, and so forth. 25 At least part of apparatus containing at least one sensor maybe moved relative to the cores or conductors of interests to provide additional data to enable improved determination of the derived quantities. The at least one sensor maybe moved between two defined positions relative to the conductors of interest to provide additional 30 magnetic field data to determine the geometry and other derived quantities of the current carrying conductors. Two or more rings of magnetic field sensors maybe axially spaced apart in addition, or alternatively one or more of the rings may be displaced from the central axis of the 35 sensor assembly thus providing additional magnetic field data to determine the geometry and other derived quantities of the current carrying conductors / cores. The array of magnetic sensors may be arranged in any predetermined geometry at the time of measurement such as a ring, a two piece clamp or clam shell shapes, or in any shape used by conventional single current probes , or a rectangular shape fixed or 5 opening (good for use with conductors arranged within a rectangular duct or cable tray section), or within an oval (fixed or opening), or with and open shapes such a “C”, or “U” shape, or a shape that returns on itself. The relative positions of the sensors must not change during the measurement process. 10 The apparatus and methods described may also be applied to a cores, cables, or conductors that are grouped together but not necessarily house in a single multi core cable. A steel wire armoured multi core cable is a subset of multi core cable. 15 The apparatus and methods described may be used to partially saturate a partial permeable steel or magnetically soft: conduits or pipes or cables containing conductors. The one or magnets and one or more the magnetic field sensors may be mounted within 20 a magnetically soft housing or channel. The magnetically soft channel provides magnetic immunity to external current carrying conductors close or adjacent to the apparatus. The channel may be made from non-magnetic material if magnets are not used. The 25 magnetic immunity is achieved using the magnetic field sensors. The controller may include one or more digital electronic processors communicatively coupled to memory. The controller may include storage holding computer program code which, when executed by the one or more digital electronic processors, causes one 30 or more of: • the controller to obtain magnetic field measurements using the one or more magnetic field sensors; • the controller to control the energisation state of one or more electromagnets; • the controller to calculate one or more derived quantities. The computer program may be an algorithm or a range of algorithms. The computer program may operate based on the same principles as the cited prior art; and / or may use a range of principles developed: to make the derived quantities immune to external magnetic fields (e.g. external 5 magnetic fields caused by adjacent current carrying conductors that are external the sensor); and / or to make the calculation of the derived quantities immune to the twist of the cores associated with multi core cables 10 A sensor may include the apparatus of the first aspect. The apparatus may be further configured to generate one or more signals based on outputs of the one or more magnetic field sensors. Each signal maybe proportional to a differential current between cores of the multi-core steel wire armoured cable when coupled to the apparatus. The sensor may also include a link corresponding to each signal, for 15 connection to a control and / or measurement system. Some or all of the links may take the form of wired links. Some or all of the links may take the form of low powered wireless links such as, for example, Bluetooth (RTM), RFID and so forth. 20 Either sensor may also include one or more voltage sensors, and the one or more derived quantities may include one or more power values. The one or more power values may include a power delivered by each core and / or a total power delivered by the multi-core steel wire armoured cable. 25 A system may include either sensor, coupled to provide input to a measurement device. The measurement device may receive one or more derived quantities from the sensor. The measurement device may receive one or more signals based on outputs of the one or more magnetic field sensors. 30 The measurement device may be a power quality analyser. A power quality analyser may also be referred to as a “power quality monitor”. The measurement device maybe a power quality logging device. A power quality 35 logging device may take the form of a power logger or an energy logger. According to a second aspect of the invention, there is provided a method including coupling apparatus according to the first aspect to a multi-core steel wire armoured cable, or coupling the apparatus incorporated by the sensor or the system to the multicore steel wire armoured cable, such that a magnetic field corresponding to the one or 5 more magnets is applied to a region of the multi-core steel wire armoured cable. The method also includes measuring, using the one or more magnetic field sensors, components of magnetic field originating from the region of the multi-core steel wire armoured cable. 10 The magnetic field corresponding to the one or more magnets may saturate a magnetic field in the steel wire armour within the region. Permeability for a magnetic material such as the steel wire armour may be defined as the gradient of magnetic flux with magnetic field, i.e.: dB ^dii 15   In which p is magnetic permeability of the steel wire armour, B is magnetic flux in Tesla, T, and H is magnetic field in amps per metre, A.m-1. The magnetic field in the steel wire armour may be considered to be saturated if permeability p is less than or equal to 20% of a peak value. The magnetic field in the 20 steel wire armour may be considered to be saturated if permeability p is less than or equal to 15% of the peak value. The magnetic field in the steel wire armour may be considered to be saturated if permeability p is less than or equal to 10% of the peak value. The magnetic field in the steel wire armour may be considered to be saturated if permeability p is less than or equal to 5% of the peak value. 25 Alternatively, the magnetic field in the steel wire armour may be considered to be saturated if the magnetic fields measured by the one or more magnetic field sensors are attenuated by no more than 10% compared to a multi-core cable which is identical to the multi-core steel wire armoured cable except that it omits the steel wire armour, 30 when identical currents are supplied via the cores of each cable in each case. The method may also include calculating, for some or all of the cores of a multi-core steel wire armoured cable, one or more derived quantities based on the magnetic field components measured by the magnetic field sensors. The one or more derived 35   quantities may include (without limitation): currents in individual cores, differential currents between cores, phases between cores, harmonics, time domain currents in one of more individual cores, a number and / or the geometry of cores within a multi-core steel wire armoured cable, and so forth. 5 The method may include features corresponding to any feature of the apparatus of the first aspect and / or sensors or system including the apparatus of the first aspect (and / or features thereof). Definitions applicable to the apparatus of the first aspect and / or sensors or system including the apparatus of the first aspect (and / or features thereof), maybe equally applicable to the method of the second aspect (and / or features thereof). 10 According to a third aspect of the invention there is provided apparatus for coupling to a multi-core cable. The apparatus includes a first set of one or more first magnetic field sensors. The apparatus also includes a second set of one or more second magnetic field sensors. The apparatus is configured such that, when the apparatus is coupled to a 15 multi-core cable, each first magnetic field sensor is oriented to detect components of magnetic field originating from a first region of the multi-core cable. The apparatus is configured such that, when the apparatus is coupled to a multi-core cable, each second magnetic field sensor is oriented to detect components of magnetic field originating from a second region of the multi-core cable. The apparatus is configured such that, 20 when the apparatus is coupled to a multi-core cable, the first region is spaced apart from the second region along a length of the multi-core cable. The apparatus of the third aspect may include features corresponding to any of the features of the apparatus of the first aspect and / or the method of the second aspect 25   (and / or features thereof). Definitions applicable to the apparatus of the first aspect and / or the method of the second aspect (and / or features thereof) maybe equally applicable to the apparatus of the third aspect (and / or features thereof). When coupled to a multi-core cable, the number and arrangement of first magnetic 30 field sensors relative to the multi-core cable may be the same as the number and arrangement of second magnetic field sensor relative to the multi-core cable. The individual cores of multi-core cables are typically twisted about one another to increase mechanical compliance of the cable overall and facilitate cable routing, 35 winding and so forth. When measurements of magnetic fields generated from the cores are used for the purpose of inferring the currents in the cores and / or the relative phases therebetween, some assumptions about the relative positions and twisting rate of the cores need to be made. However, if measuring an unknown cable, such geometric factors are not available without dismantling the cable and defeating the objective of non-invasive measurement. Using the apparatus of the third aspect, the relative 5   positions of each core will vary between the first and second sets of magnetic field sensors, whilst the current is conserved between the first and second regions. In this way, differences in magnetic field measurements made using the first and second sets maybe used to compensate for different twisting rates between different multi-core cables. For example, a measured rotation rate of the magnetic fields detected by the 10 magnetic field sensors may be related to a twist / rotation rate of cores of the multi-core cable. The apparatus of the third aspect may also include one or more magnets arranged such that, when the apparatus is coupled to the multi-core cable, a magnetic field 15 corresponding to the one or more magnets is applied to the first and second regions of the multi-core cable. The magnetic field corresponding to the one or more magnets maybe applied substantially equally to the first and second regions of the multi-core cable. 20 Substantially equally may mean that the magnetic fields in the first and second regions are approximately symmetric about a mirror plane equidistant between the first and second regions and oriented perpendicular to an axial direction of the multi-core cable when coupled. Approximately symmetric may mean that magnetic field components (for example x, y, z components) at any point in the first region differ from a reflected 25 point in the second region by no more than 10%. Brief Description of the Drawings Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 5 Figure i is a cross-sectional % view of a sensor assembly which includes 2 magnet arrays, an array of semiconductor type magnetic sensors, a housing channel, and associated electronics, connections and outputs, shown with a length of armoured multi core cable for illustrative purposes. 10 Figure 2 is a cross-sectional % view of a sensor assembly which includes 2 magnets, an array of semiconductor type magnetic sensors and a housing channel, shown with a section of armoured multi core cable for illustrative purposes. Figure 3a is a cross sectional view of a sensor assembly which includes a housing, 2 15 magnet arrays, an array of semiconductor type magnetic sensors mounted on a magnetically soft mounting ring and a housing channel. Figure 4a is a cross sectional 3 / 4 view of a sensor assembly which includes a housing, 2 magnet arrays, an array of tangential coil type magnetic sensors, a housing channel, 20 and associated electronics and outputs. Figure 5a is a cross section % view of a sensor array which includes a magnetically soft ring, a number of axial sensor coils and their associated outputs. 25 Figure 6 is an isometric view of a sensor assembly configured specifically as a polyphase electricity meter, including a sensor assembly, an associated electronics enclosure with display and service port, a load under test, phase connections from the electronics enclosure to the load under test and a length of armoured multi core cable for illustrative purposes. 30 Figure 7 is an isometric view of a sensor assembly configured specifically as a power quality analyser, including a sensor assembly, a power meter, phase connections to the device under test and a set of 3 Rogowski coils to illustrate an alternative method - an armoured multi core cable under test is not illustrated. Figures 08a and 08b are isometric axial section and isometric cross section views respectively of a sensor assembly which includes 2 magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring and a housing channel. 5 Figures 09a and 09b are isometric axial section and isometric cross section views respectively of a sensor assembly which includes 2 magnet arrays, an array of radial and tangential coil type magnetic sensors mounted on a magnetically soft mounting ring and a housing channel. 10 Figures 10a and 10b are isometric axial cross section and isometric cross section views respectively of a sensor assembly which includes 2 magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring, and a housing channel with 2 additional radial coils either side of the magnetically soft mounting ring. 15 Figure 11 is an isometric section view of a sensor assembly which includes 2 magnet arrays, two arrays of radial coil type magnetic sensors mounted on individual magnetically soft mounting rings and a housing channel. 20 Figures 12a, 12b and 12c are isometric axial cross section, cross section and isometric cross section views respectively of an open-ended sensor assembly which includes 2 magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring, a mounting channel and a housing shown with a length of armoured multi core cable set against a flat surface for illustrative purposes. 25 There are no figures 13 to 15. Figures 16a, 16b and 16c are isometric cutaway (opened), isometric (closed) and 30 isometric cross section (opened) views respectively of a ‘spring clamp’ type sensor assembly which includes 2 magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring, a mounting channel and a housing assembly with spring, shown with a length of armoured multi core cable for illustrative purposes. Figures 17a, 17b and 17c are isometric cross section, plan cutaway and isometric views respectively of a sensor assembly which includes 2 magnets, a radial sensor coil, a magnetically soft backing piece and a wired connection, shown with a length of armoured multi core cable for illustrative purposes. 5 Figures 18a, 18b, 18c, i8d and i8e are isometric (opened), isometric (closed), cross section (closed), isometric axial cross section (closed) and isometric cross section views respectively of a multiple unit sensor assembly, each individual unit of which includes 2 magnets, a radial sensor coil, a magnetically soft backing piece, hinge elements and movement limiting elements, shown with a length of armoured multi core cable for 10 illustrative purposes. Figures 19a, 19b and 19c are isometric, isometric cross section and isometric axial cross section views respectively of a sensor assembly which includes a magnetically soft cylindrical sensor body, an electromagnetic coil and an array of radial coil type 15 magnetic sensors mounted on a magnetically soft mounting ring. Figures 20a, 20b and 20c are isometric, axial cross section and cross sectional views respectively of a sensor assembly which includes an electromagnetic coil, a magnetically soft armature, a hinged and / or clipped housing and an array of radial coil type magnetic sensors, shown with a length of armoured multi core cable for illustrative 20 purposes. Figures 21a, 21b and 21c are isometric cross section, plan cutaway and isometric views respectively of a sensor assembly which includes 1 magnet, a radial sensor coil, a magnetically soft backing piece and a wired connection, shown with a length of 25 armoured multi core cable set against a flat surface for illustrative purposes. Detailed description In the following, like parts are denoted by like reference numerals. 30 Figure 1 shows a sensor assembly I comprises a magnetically soft housing ‘channel’ 1 made from laminated steel, sintered or bonded metal powder or any other suitable material, that partially or fully surrounds the armoured multi core cable under test 6. The sensor assembly is formed of one, two or more magnetically soft ‘channel’ sections of an enclosure, possibly hinged down sidelong one axis that is parallel to longitudinal 35   the axis of the sensor in order to allow the sensor to be opened and closed around a multi core steel wired armoured cable. The armoured multi core cable under test or armoured multi conductor cable under test, consisting of three phase alternating current carrying wires 8,9 & 10 armoured by a ‘cage’ of metal non-current-carrying multiple magnetically soft wires 7, built into the outer section of the cable. The sensor is closed around the cable 6, partially or completely enclosing the multi core cable 6 under 5 test. Each end of the channel has one or more magnets, 2 & 3. On one end the magnet(s) are polarised North, in that all the North poles are pointing inwards from the array, pointing towards the multi core cable under test. The opposite end all the magnetic array is polarised South, again with all poles pointing towards the multi core cable under test. These magnets 2 and 3 are concentric to the multi core cable under 10 test and produce a magnetic field running from North to South along the multi core cable under test (Fig 3a, 107). That in turn saturates the region of steel armouring of the section of cable where the sensor assembly is located. The magnetic field could also be generated partially or fully by electromagnet coils mounted with or in place of the permanent magnets. 15 Mounted within the channel 1, located between both magnetic arrays 2 and 3 is a Magnetic Field Sensor array 4. This consists of a number of magnetic field sensors 5 aligned on the same axis. The sensors all point inwards towards and concentric with the armoured multi core cable under test forming a ring of sensors around it. This version uses solid state or semiconductor type sensors such as Hall sensors or giant 20 magnetoresistive sensors mounted on a flexible pcb or flexi in close contact with the housing. The sensors 5 are located against, or adjacent or abutted to the magnetically soft housing 1. Location of the sensors 5 is such to enable the sensors to measure the magnetic field generated by currents in the cores of the cable within the region of cable saturated by the magnets 2,3. 25 Processing of the signals from the sensors is by a processor (or controller) 12 either integrated with the sensor assembly or wired separately 11 to the sensor assembly. This processor takes the form of an electronics enclosure containing a controller 12 electrically connected to the sensor assembly. The controller 12 s processes the data including may include three distinct current signals outputs, one for each of the 3 30 discrete phases 13,14,15 in the multi core cable under test. The apparatus may be used with two or three or four or five or six or more core cable. The number of outputs are arranged accordingly. The electronics unit could also include a connector or connectors for power, data, updates and other utilities and taking the form of a USB or similar 16. This sensor could also be used with non-steel wired multi core cable e.g. cables with copper wire “armour” that may also be used as a neutral or earth or with cables without any “armour” i.e. just conductive cores within a plastic sheathing. 5 Figure 2 shows ae sensor assembly II this is similar in design and operation to the sensor assembly described in Figure i. The sensor assembly II is again formed of one or two or more magnetically soft ‘channel’ sections 21 with a sensor array 25 with one or more magnetic field sensor 24 surrounding an armoured wire strands 27 of the multi 10 core cable 26, the cable having cores 28a, 28b, 28c (all included y 28) under test. In this case, instead of an array of magnets, each end of the channel has an axially magnetised ring magnet or section of a ring magnet 20 and 23. Magnets 20 and 23 are positioned either end of the channel 21. Magnets 20 and 23 are oriented in the same direction, in that the North poles are oriented in the same direction along the axis of 15 the multi core cable26 under test. Therefore, the two magnet sides facing each other in the sensor assembly II are magnetically polar opposites. These produce a magnetic field 22 running from North to South and that in turn saturates the region of steel armouring of the section of armoured multi core cable 26 under test the sensor assembly II is located. 20 Figure 3a shows a section view of a sensor assembly III that is similar to the sensor assembly described in Figure 1, including channel 102 and 103 containing magnets 105, 110,109 and 104 with poles oriented North 105,110 and South 104,109 to produce a magnetic field 107,108. 25 Sensor assembly III differs in having the flexi or pcb 112 mounted semiconductor or solid state magnetic sensors 106 and 111 and other possible others not shown mounted onto a ring 101 made from axially or radially stacked / wound laminated steel or some other soft magnetic material. The ring 101 could alternatively be made from ferrite, pressed, sintered or composite magnetic material. The ring 101 could be wide enough to 30 accommodate the magnetic sensors with separate parts to accommodate the magnet arrays 105,110,109, and 104 at each end of the channel 102 or the ring 101 could be wide enough to form the entire channel removing the need for channels 102 and 103. Figure 4a shows a sensor assembly IVa that is similar to sensor assembly I described in 35 Figure 1, including channels 1 containing magnets 49 with poles oriented North and South at opposite ends to produce a magnetic field in the armoured multi core cable under test. As detailed in Figure 1, processing of the signals from the magnetic sensors 41,42,43,44,45,46,47,48 is by a controller 50 either integrated with the sensor assembly or wired separately to the sensor assembly IVa. The controller 50 may provide 3 distinct outputs 51,52, and 53, one for each of the in the multi core cable 5   under test (not shown for clarity). The controller 50 may include a connector or connectors for power, data, updates and other utilities and taking the form of a USB or similar 54. Sensor assembly IVa differs by using a number of sensor coils 41,42, 43 44,45,46,47, and 48 mounted in a ring formation tangentially around the cable under test. The 10 sensors coils 41, 42, 43,44,45,46,47, and 48 are mounted between the magnet arrays 49a and 49b. The sensor coils 41, 42,43,44, 45,46,47, and 48 could be preplaced by solid state magnet field sensors in sensors on flexi / pcb material. Figure 5a shows a sensor assembly that is similar to sensor assembly Illa in Figure 3a 15 but the semiconductor type sensors 111 on flexi / pcb material 112, are replaced using a number of sensor coils 62 mounted in a ring formation radially around the armoured multi core cable under test (not shown) and located between the magnet arrays (for example like those shown in Figures 3a, 104,105,109,110). The coils may include pole pieces 61 made from soft magnetic material or air cores that could be mounted on 20 plastic bobbins. The coils 62 could be mounted on a magnetically soft ring 60 consisting of radially stacked / wound laminated steel or ferrite, pressed, sintered or composite magnetic material. Alternatively, the sensor array could be mounted directly into the channel section of the sensor assembly not shown but similar to (Figure 1,1). 25 Figure 6 shows a power meter assembly VI. Any version of the described sensor assemblies but configured specifically as a polyphase electricity meter with the specific advantage of non-intrusive fitting. This could be accomplished by combining the magnetic sensor assembly data derived from the sensor assembly 72 and 73 with additional monitoring of the phase voltages u, v and w. This would include a magnet 30 and sensor assembly 72,73 mounted on the armoured multi core cable under test 79 and connection 75 with a meter 74. The sensor assembly could be similar to any of the sensor assembles described shown in the prior figures or variants using alternative sensors, magnets and magnetic materials. The meter 74 includes a display for metrology readings and other relevant information 82. Flying lead 81 enables voltage 35 input from phases u,v,w to the meter 74.. The meter 74 may include a connector or connectors for power, data, updates and other utilities and taking the form of a USB or similar 83. Figure 7 show a power quality analyser VII. The sensor assembly magnetic sensor 87 to 5 be mounted on to an armoured multi core cable under test (not shown) and may be used in combination with a power meter 91 as a power quality analyser VII. Three flying leads 88,89, and 90, are connected to the individual phases at the point of connection to the load to input the voltage for each phase in to the power quality analyser. 10 This solution could be a lower cost, easier fitting alternative to using a set of 3 Rogowski coils, 84,85, or 86(shown for illustration not necessarily needed if using the sensor 87). Using Rogowski coils would require the armoured multi core cable under test to have its’ 3 phases split out from the armouring and separated to leave enough room to attach 3 individual Rogowski coils, therefore adding to cost of parts and complexity of the 15 installation - drawbacks that could be avoided using of the sensor assembly 87. Figures 08a and 08b show a sensor assembly VIII. The Sensor assembly VIII is similar to the sensor assemblies shown in Figure 1 and Figure 5 but shows in more detail a number of radial field coils 115 mounted onto a ring 114 made from axially or radially 20 stacked / wound laminated steel instead of pcb / flexi mounted semiconductor magnetic sensors between the magnet arrays 117a and 117b. The ring 114 could alternatively be made from ferrite, pressed, sintered or composite magnetic material. The ring 114 could extend into the centre of each coil 115 to form pole pieces 116, alternatively the ring 114 could be flush with the back edge of the coils (i.e. tube shaped), in other words, the coils 25   115 would have air cores with the magnetic material ring 114 behind them. Alternatively, the radial field coils 115 could be mounted in the channel 113 with no additional magnetic material mounting ring. Figures 09a and 09b show a sensor assembly IX. Sensor assembly IX has number of 30 sensor coils 121 and I22positioned in a ring formation around the multi core cable under test and located between the magnet arrays 120a and 120b. The sensor coils are made up of tangential coils 122 and axial coils 121 in the same row, possibly alternating or in any other pattern such as 2 tangential, one radial, vice-versa and so forth. These may have air coils, be integrated into a magnetic material ring 119 as shown in Figure 35   09a, having separate pole pieces (not shown) or be a combination of both air core (not shown) and integrated / separate poles(not shown) . Figures 10a and 10b show a sensor assembly X. Sensor assembly X consisting of any of magnet 128a and magnet 128b sensor coil 124 and magnetically soft material 127 similar to some configurations described in prior assemblies, but sensor assembly X 5 has the addition of one or two additional magnetic sensors 125,126 either side of the primary sensor array 124. These additional sensorsi25 and or 126 are used to detect the amount of physical twist in the multi core cable under test. The magnets 128a and 128b are not required if the cable to be tested does not have a soft magnetic sheath or armour. 10 Figures 11a and 11b show a sensor assembly XI. Sensor assembly XI consisting of any of the magnet 131 and material configurations described but having a second sensor array 130 in addition to the primary sensor array 129. Many features maybe similar to 15 sensor assembly XIII but in this case with an additional ring of sensors iso.The use of the two rings of magnetic field sensors 129 and 130 axially spaced apart is used to detect the amount of physical twist in the 3 phase wires in the armoured multi core cable under test or any multi core cable. 20 Figures 12a and 12b and 12c show a sensor assembly XII. A sensor assembly XII consisting of any of the magnet 132, magnetic sensori33, magnetically soft material 137 configurations but measurement and magnetic arrays forming an open or U shape or shape that return on itself but not forming a closed loop. The open shape of the sensor assembly XII allows conductor insertion and measurement when the armoured or non-25 armoured multi core cable under test 135 is mounted against or close to a planar surface 134. This could take the form of a hand-held device for rapid deployment application 136 or a permanent or semi-permanent device. Figures 16a, 16b & 16c b show a sensor assembly XVI. Sensor assembly XVI consisting 30 of any of the magnet 138, sensor 139, magnetically soft material 140 configurations described to date, but in the form of a clamp on device for quick attachment and to easily move from one armoured or non-armoured multi core cable 141 under test to another. Sensor assembly XVI consists of 2 channel sections 142,143 with magnets and sensors mounted in a double handled, ‘spring clamp’ type housing 145,146 with the 35 spring or springs being of compression, torsion or any other suitable type 144 and positioned to hold the sensor arrays closed shut when not being opened by squeezing the handles 145,146 together. The spring or springs 144 maybe supplemented or substituted or used in addition to a catch on the opening ends of the sensor (not shown) to ensure the sensor assembly XVI is fully closed when being used. 5 Figures 17a and 17b and 17c show a sensor assembly XVII. Sensor assembly XVII uses the same technology as detailed in Figure 1 but consisting of a pair of magnets 150,151 (alternatively 1 magnet and feature made form soft material instead) and one or more sensors 152 mounted on a magnetically soft backing piece 147. Sensor assembly XVII could consist of any of the magnet / sensor / material configurations but in a simplified, 10 single sensor / coil / magnet form, as a lower cost, easy-fit variant or possibly temporarily fixed or held against the armoured multi core cable under test 149. Sensor assembly XVII may be wired 148 to connect to sensing, monitoring, data logging or other equipment and / or could include some or all data processing electronics either built-in or remotely wired / wireless. 15 Figures 18a, 18b, 18c, i8d & i8e show a sensor assembly XVIII. A sensor array is made from individual, simplified sensors 153 as described or similar to sensor assembly XVII shown Figure 17, but the sensor assemblies XVII are chained together using integrated or separate hinge, clip or other flexible joining elements 155, into a flexible assembly to 20 provide monitoring performance closer to the sensor in Figure 1 and variants by providing more coverage around the circumference of the armoured multi core cable under test 154. The sensor array can be sprung to facilitate fast attachment and could have stops to naturally spring closed to form a circle 156, to facilitate minimising off axis inaccuracy. 25   A number of sensor modules 153 could be added or taken away to optimize the ID of the sensor depending on the requirements. As with the sensor assembly detailed in Figure 17, each sensor could be wired (Figure 17,148) to connect to sensing, monitoring, data logging or other equipment and / or could include some or all data processing electronics either built-in or remotely 30 wired / wireless. Alternatively, the individual sensor outputs could be ganged into a single electronics housing (Figure 1,12) to process data from all sensors 153 in the array. Figures 19a, 19b, & 19c show a sensor assembly XIX. A simplified, lower cost version of Figure 1 and other variants previously described. A 1-piece sensor consisting of a 35 cylindrical body 161 made from a magnetically soft material wound with an electromagnetic coil around the outside of a pole 162 and an array of sensors 163 forming a ring. The magnetic sensors can be of axial or tangential coil or semiconductor type or solid state type, either mounted on a separate magnetically soft ring, (please refer to Figure 03a, 101), or directly onto the cylindrical body 161, with or without individual poles or extensions from the ring or cylindrical body 161 forming poles. 5 Designed to be threaded onto the armoured multi core cable under test 160 as a single unit. The electronics can be integrated or separate from the sensor assembly. Sensor assembly XIX may have magnets added (not shown) if armoured cables are to be evaluated. 10 Figures 20a, 20b & 20c show a sensor assembly XX. Similar in operation to the sensors detailed in Figure 1,2 and Figure 8 but using an offset electromagnetic coil 165 to provide the magnetic field to saturate or substantially saturate the steel armouring in the armoured multi core cable under test 170. The magnetic field is brought around the armoured multi core cable under test by means of a magnetically soft armature 167, 15 onto which the electromagnetic coil 165 is axially mounted. The armature 167 extends towards and loops around the armoured multi core cable under test at both poles, either side of the sensor array, which is housed in a hinged 168 and / or clipped 169 housing to allow for fitting around the armoured multi core cable under test 170. The magnetic sensors can be of any type described in the descriptions - axial or 20 tangential coils as illustrated 166 or semiconductor types, with or without a magnetic material behind them and with or without pole pieces. Figures 21a, 21b & 21c show a sensor assembly XXL A simplified sensor similar to the sensor detailed in Figure 17 but consisting of a single magnet or magnetic field source 25   174 and sensor 175. The assembly could consist of any of the magnet / sensor / material configurations, in this example a permanent magnet and a sensor coil on a magnetically soft backing plate / mount 173. This lower cost variant could be wired 172 to connect to sensing, monitoring, data logging or other equipment and / or could include some or all data processing 30   electronics either built-in or remotely wired / wireless. Modifications It will be appreciated that various modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features 35 and / or methods which are already known in the design, manufacture and use of electrical test and measurement equipment, and / or component parts thereof, and which may be used instead of or in addition to features already described herein. Features of one embodiment maybe replaced or supplemented by features of another embodiment. 5 Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or 10 not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom

Claims

1. Apparatus for coupling to a multi-core steel wire armoured cable, comprising: one or more magnets; and5          one or more magnetic field sensors;wherein the apparatus is configured such that, when the apparatus is coupled to a multi-core steel wire armoured cable:a magnetic field corresponding to the one or more magnets is applied to a region of the multi-core steel wire armoured cable; andio                 each magnetic field sensor is oriented to detect components of magneticfield originating from the region of the multi-core steel wire armoured cable.

2. The apparatus of claim t, wherein at least one of the one or more magnets comprises a permanent magnet.

153. The apparatus of claims t or 2, wherein at least one of the one or more magnets comprises an electromagnet.

4. The apparatus of any one of claims t to 3, wherein at least one of the one or20 more magnetic field sensors comprises a coil.

5. The apparatus of any one of claims 1 to 4, wherein at least one of the one or more magnetic field sensors comprises a solid state magnetic field sensor device.25   6. The apparatus of anyone of claims lto 5, wherein the magnetic fieldcorresponding to the one or more magnets has a magnitude of at least 5 mT within the region.

7. The apparatus of any one of claims 1 to 6, configured such that the magnetic30 field corresponding to the one or more magnets is time varying.

8. The apparatus of any one of claims 1 to 6, configured such that the magnetic field corresponding to the one or more magnets is constant.26 02 249-     The apparatus of any one of claims 1 to 8, wherein the apparatus is configuredto mechanically couple to the multi-core steel wire armoured cable using a magnetic force arising from application of the magnetic field to the steel wire armour.5 to. The apparatus of any one of claims 1 to 9, comprising a structure supporting the one or more magnets and the one or more magnetic field sensors.

11. The apparatus of claim 10, wherein the structure comprises a channel configured to receive the multi-core steel wire armoured cable.1012.    The apparatus of claim 11, wherein the channel is open.

13. The apparatus of claim 11, wherein the channel is defined by first and secondparts of the structure, configured to close about the multi-core steel wire armoured 15 cable when received within the channel.

14. The apparatus of any one of claims 1 to 13, further comprising a net current sensor configured to measure a net current through the multi-core steel wire armoured cable when the apparatus is coupled to the multi-core steel wire armoured cable.2015.    The apparatus of any one of claims 1 to 14, wherein at least one of the one ormore magnetic field sensors comprises a coil, wherein each coil is wound around a sensing pole piece.25   16.    The apparatus of any one of claims 1 to 15, wherein at least one of the one ormore magnets comprises an electromagnet, wherein each electromagnet is wound around a magnet pole piece.

17. The apparatus of any one of claims 1 to 16, comprising two or more magnet field 30 sensors.

18. The apparatus of any one of claims 1 to 17, wherein the one or more magnet field sensors comprise a first set of first magnetic field sensors and a second set of second magnetic field sensors;26 02 24wherein the first and second sets are arranged to be spaced out along the axial direction of the multi-core steel wire armoured cable when it is coupled to the apparatus.5   19. A sensor comprising:the apparatus of any one of claims 1 to 18;a controller connected to the one or more magnetic field sensors and configured to calculate, for some or all of the cores of a multi-core steel wire armoured cable, one or more derived quantities based on the magnetic field components measured by the10 magnetic field sensors.

20. A sensor comprising:the apparatus of any one of claims 1 to 18, the apparatus further configured to generate one or more signals based on outputs of the one or more magnetic field15 sensors, each signal proportional to a differential current between cores of the multicore steel wire armoured cable when coupled to the apparatus;a link corresponding to each signal, for connection to a control and / or measurement system.20   21. The sensor of claims 19 or 20, further comprising one or more voltage sensors,wherein the one or more derived quantities comprise one or more power values.

22. A system comprising the sensor of any one of claims 19 to 21, coupled to provide input to a measurement device.2523. The system of claim 22, wherein the measurement device is a power quality analyzer.

24. The system of claim 22, wherein the measurement device is a power quality30 logging device.

25. A method comprising:coupling apparatus according to any one of claims 1 to 18 to a multi-core steel wire armoured cable, or coupling the apparatus of the sensor of claims 19 to 21 or the 35 system of claims 22 to 24 to the multi-core steel wire armoured cable, such that amagnetic field corresponding to the one or more magnets is applied to a region of the multi-core steel wire armoured cable;measuring, using the one or more magnetic field sensors, components of magnetic field originating from the region of the multi-core steel wire armoured cable.

526. The method of claim 25, wherein the magnetic field corresponding to the one ormore magnets saturates the steel wire armour within the region.

27. The method of claims 25 or 26, further comprising calculating, for some or all of10 the cores of a multi-core steel wire armoured cable, one or more derived quantities based on the magnetic field components measured by the magnetic field sensors.26 02 24

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