Apparatus and methods for coupling to multi core cables

Abstract

Apparatus and methods for coupling to a multi-core steel wire armoured cable or a multi core cable are described. The apparatus may include one or more magnets and one or more magnetic field sensors and / or may include two or more arrays of one more sensor to enable the twisting of the multiple conductors or cores to be accommodated. 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 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.

Description

[0001] Apparatus and methods for coupling to multi core cables

[0002] Field of the Invention

[0003] This invention relates to apparatus and methods for non-contact measurements of currents within multi-core cables. In some examples the multi-core cables may be armoured. In some examples, the multi-core cables may be used for supply of net current.

[0004] Background 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 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.

[0005] Prior art relevant to the present invention:

[0006] 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 passes 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 test. WO 2013 / 068360 Ai offers significant advantages with respect to documents such as EP o 874 244 Bl : 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.

[0007] 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 WO 2013 / 068360 A1. The invention disclosed in this specification addresses the need to measure currents within a steel wired armoured multi-core cable that is not addressed in the prior art.

[0008] Single conductor current sensors based on Gauss law and the magnetic field from the current, such as current transformers and Rogowski coil units have been the mainstay of electrical measurements. They rely on Faraday’s law, require a sensor to be placed around each conductor, and give accurate readings of the net current enclosed, independent of materials used in the cable, magnetic or otherwise. Systems to measure multiple conductors simultaneously in the same cable have been demonstrated. However, conventionally this has required separating out each conductor and measure current in each - CT, Rogowski, shunt and so forth. Sensing currents in multiple conductors within the same cable, without separating out the conductors, have been discussed in US 5,473,244 A, US 7,755,347 Bl and EP o 874 244 A2

[0009] Summary

[0010] The present specification concerns, in part, methods and apparatuses which apply magnetic fields to saturate the permeable shell of an armoured multi-core cable, reducing its effective permeability, and allowing the magnetic, fields arising from a current distribution within the cable to reach the exterior. In this way, techniques to calculate the internal current distribution from external field measurements may be employed.

[0011] 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 distribution within the cable, As described herein, m agnetically 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.

[0012] Based on the magnetic fields, calculations of the current distribution may be performed, yielding derived parameters such as, without limitation, conductor current, 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 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 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 may be rare earth magnets such as Samarium cobalt (SmCo) and / or Neodymium (NdFeB), and / or other non-rare earth magnets .

[0013] 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 metal ( magnetic or not magnetic material) cover or covers that protects the surfaces of the magnet(s) that otherwise would be exposed to impact.

[0014] 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 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 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.

[0015] 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 m ulti-core steel w ire 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 tw o or more cores of the m ulti-core steel w ire armoured cable.

[0016] A multi-core cable may alternatively be referred to a multi -conductor cable (and these terms should be interpreted interchangeably) .

[0017] 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 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 component parallel to an axial direction of the multi-core steel wire armoured cable.

[0018] The component parallel to an axial direction of the multi-core steel wire armoured cable may be 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.

[0019] 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.

[0020] At least one of the one or more magnets may include, or take the form of, an electromagnet. Tw o 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.

[0021] 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 m ay include, or take the form of, respective coils. Coils, may be premade, with the cable inserted, or wound 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. Coils may be wound around a core of permeable material. Coils may be so called “air core” coils, which do not include a core of permeable material. An “air core” coil may be wound about a supporting structure form of non-permeable material such as plastic, glass and so forth.

[0022] 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 axes. A solid state magnetic field sensor device may include, or take the form of, semiconductor type magnetic sensor, a magnetoresistive sensor, a giant magnetoresistive sensor or an anisotropic magnetoresistance sensor. A solid state magnetic field sensor 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 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.

[0023] Two or more of the magnetic field sensors may include, or take the form of, respective 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).

[0024] The magnetic field corresponding to the one or more magnets may have a magnitude of 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.

[0025] 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 may be driven with alternating current. The at least some electromagnets may be energised during active periods and de-energised within inactive periods. The apparatus maybe 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 alternatively, the apparatus may be configured to energise the at least some electromagnets in response to a trigger condition, a 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 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 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 have a weight which is less than the magnetic force generated when a multi-core steel wire armoured cable is received within the region.

[0026] 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 configured to receive the multi-core steel wire armoured cable. In other words, the structure may be a channel-defining-structure. A cross-section of the channel may have a shape which is circular or an arc of a circle, A cross-section of the channel may- have a shape w'hich is non-circular and which does not correspond to an arc of a circle. The channel may be open, so as to receive the multi-core steel wire armoured cable.

[0027] The structure may define the channel to be C-shaped or U-shaped in cross-section. Cross-sections may be taken in a plane perpendicular to a direction corresponding to an axial direction of the channel along which the multi-core steel wire armoured cable will be received when coupled to the apparatus.

[0028] The channel may be defined by first and second parts of the structure, configured to close about the multi-core steel wire armoured cable when received within the channel.

[0029] The first and second parts may be urged together by a spring. The first and second parts may- be urged to close about the multi-core steel wire armoured cable by magnetic forces from at least some of the one or more magnets. The first and second parts of the structure may provide a clamp. Once closed about the multi-core steel wire armoured cable, the first and second parts may be secured together by a latch, a catch or similar fastening means.

[0030] The structure may include, or take the form of, two or more parts configured to close or wrap about the multi-core steel wire armoured cable to define the channel. The two or more parts may be urged together by springs. Once closed about the multi-core steel wire armoured cable, the two or more parts may be secured together by one or more latches, catches, or similar fastening means.

[0031] 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 take the form of, a current transformer. The one or more magnetic field sensors may be disposed within a transformer coil of the current transformer.

[0032] 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 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 may be wound around respective, separate sensing pole pieces.

[0033] A circumferential sensing pole piece may extend around all, or part of, a circumference surrounding the multi-core steel ware armoured cable when received, and may include two or more inward radial protrusions. A coil providing a magnetic field sensor may be wound around each inward radial protrusion.

[0034] At least one of the one or more magnets may include, or take the form of, an electromagnet. Each electromagnet may be 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. 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.

[0035] The apparatus may include two or more magnetic 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.

[0036] The magnetic field sensors may be equi-angularly spaced about the channel which receives the multi-core steel wire armoured cable.

[0037] The one or more magnets may include, or take the form of, a first group comprising a plurality of first magnets and a second group comprising a plurality of second magnets. The first and second groups may be 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 may bracket or sandwich the magnetic field sensors 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. Each 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 multi-core steel wire armoured cable when coupled to the apparatus. In other words, each pair of magnets may bracket or sandwich the corresponding magnetic field sensor along the length of a coupled / received multi-core steel wire armoured cable.

[0038] The one or more magnet field sensors may include a first set of first magnetic field 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.

[0039] In this way, differences in magnetic field measurements made using the first and 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.

[0040] 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 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 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.

[0041] At least part of apparatus containing at least one sensor may be 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 may be moved between two defined positions relative to the conductors of i nterest to provide additional magnetic field data to determine the geometry and other derived quantities of the current carrying conductors. Two or more rings of magnetic field sensors may be axially spaced apart. Additionally or alternatively, one or more of the rings may be displaced from the central axis of the 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 any7shape used by conventional single current probes, or a rectangular shape fixed or 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.

[0042] The apparatus and methods described may also be applied to cores, cables, or conductors that are grouped together but not necessarily housed in a single multi core cable.

[0043] A steel wire armoured multi core cable is a subset of multi core cables.

[0044] The apparatus and methods described may be used to partially saturate a partially 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 a magnetically soft housing or channel-defining-structure. The magnetically soft channel -defining-structure provides magnetic immunity to external current cartying conductors close or adjacent to the apparatus.

[0045] The channel-defining-structure maybe made from non-magnetic (i.e. non-permeable) material if magnets are not used. The channel-defining-structure may be made from non-magnetic (i.e. non-permeable) material if magnets are used. The channeldefining-structure may be made from magnetic (i.e. permeable) material if magnets are used.

[0046] The magnetic immunity may be achieved using the magnetic field sensors. For example, by using the known relative positions and orientations of the magnetic field sensors to distinguish magnetic field sources internal to the multi-core cable from external magnetic field sources.

[0047] 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 or more of:

[0048] » the controller to obtain magnetic field measurements using the one or more magnetic field sensors;

[0049] ® the controller to control the energisation state of one or more electromagnets;

[0050] • the controller to calculate one or more derived quantities.

[0051] 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 magnetic fields caused by adjacent current cartying conductors that are external to the sensor); and / or to make the calculation of the derived quantities immune to the twist of the cores associated with multi core cables A sensor may include the apparatus of the first aspect. The apparatus may be further configured to generate one or more sign als based on outputs of the one or more magnetic field sensors. Each signal may be proportional to a differential current between cores of the multi-core steel wire armoured cable when coupled to the apparatus. Each signal m ay be proportional to the individual core currents of the individual cores of the multi core cable. The sensor may also include a link corresponding to each signal, for connection to a control and / or measurement system.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] The measurement device may be a power quality analyser. A power quality analyser may also be referred to as a “power quality monitor”.

[0056] The measurement device may be a power quality logging device. A power quality logging device may take the form of a power logger or an energy logger.

[0057] 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 multi- core steel wire armoured cable, such that a magnetic field corresponding to the one or 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. The magnetic field corresponding to the one or more magnets may saturate a magnetic field in the steel wire armour within the region. The magnetic field corresponding to one or more magnets may magnetically saturate (fully or partially) the steel wire armour within the region.

[0058] 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.:

[0059] In which μ 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.

[0060] The magnetic field in the steel wire armour may be considered to be saturated if permeability μ is less than or equal to 20% of a peak value. The magnetic field in the steel wire armour may be considered to be saturated if permeability μ 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 μ 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 μ is less than or equal to 5% of the peak value. 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, when identical currents are supplied via the cores of each cable in each case.

[0061] 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 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.

[0062] 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), may be equally applicable to the method of the second aspect (and / or features thereof). 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 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, 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.

[0063] 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 (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) may be equally applicable to the apparatus of the third aspect (and / or features thereof).

[0064] When coupled to a multi-core cable, the number and arrangement of first magnetic field sensors relative to the multi-core cable may be the same as the number and arrangement of second magnetic field sensors relative to the multi-core cable.

[0065] The individual cores of multi-core cables are typically Wasted about one another to increase mechanical compliance of the cable overall and facilitate cable routing, 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 Wasting 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 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 may be 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 magnetic field sensors may be related to a twist / rotation rate of cores of the multi-core cable.

[0066] 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 corresponding to the one or more magnets is applied to the first and second regions of the multi-core cable.

[0067] The magnetic field corresponding to the one or more magnets may be applied substantially equally to the first and second regions of the multi-core cable. 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 point in the second region by no more than 10%.

[0068] According to a fourth aspect of the invention, there is provided an apparatus for coupling to a multi-core cable, including a current transformer coil and one or more magnetic field sensors. The apparatus is configured such that, when the apparatus is coupled to a multi-core cable, a region of the multi-core cable passes through the current transformer coil. The apparatus is configured such that, when the apparatus is coupled to a multi-core cable, the one or more magnetic field sensors are disposed at least partly between a core of the current transformer coil and the multi-core cable. At least one of the magnetic field sensors is oriented to detect components of magnetic field originating from the region of the multi-core cable.

[0069] The current transformer coil may also be referred to as a “CT” coil. The current transformer coil may be configured to measure a net current flowing through the multicore cable. The one or more magnetic field sensors may be arranged and configured to measure, for some or all of the cores of the multi-core cable, one or more derived quantities based on the magnetic field components measured by the magnetic field sensors. The derived quantities may include any or all of the derived quantities specified in relation to the apparatus according to the first aspect and / or the method according to the second aspect.

[0070] The apparatus according to the fourth aspect may include features corresponding to any features of the apparatus(es) according to the first and / or third aspect. Definitions applicable to the apparatus(es) according to the first and / or third aspects (or features thereof) may be equally applicable to the apparatus according to the fourth aspect (or features thereof). The current transformer coil may be shorted via a resistance. The resistance may sometimes be termed a “shunt resistor”, a “load resistor” or a “burden resistance”. The resistance may be between o.1 Ω and too Ω. Preferably, the resistance may be between 1 Ω and to Ω. The voltage measured across the “burden resistance” is proportional to the net current of the multicore con ductor passing through the current transformer coil.

[0071] The one or more magnetic field sensors may be disposed at least partly within the interior diameter of the current transformer coil. The core of the current transformer coil may include, or take the form of, permeable material. The permeable material may be soft iron. The current transformer coil may be directly wound about the core of permeable material. The current transformer coil may be wound about a bobbin (or similar support), and one or more regions of permeable material may be received into the bobbin (or similar support). For example, the current transformer coil may be wound about a bobbin having a through-hole, and the core of permeable material may be inserted into the through-hole so as to be disposed within the current transformer coil.

[0072] The bobbin may be flexible and / or segmented. In this way, the current transformer coil may be wound about the bobbin in a flat configuration, and the bobbin may subsequently be curved and / or folded to form an annular shape (or a portion thereof).

[0073] The current transformer coil may include, or take the form of, two or more sub-coils. The two or more sub-coils may be connected together. Two, a subset, or all of the sub- coils may be connected in series. Two, a subset, or all of the sub-coils may be connected in parallel. The apparatus may be configured such that the region of a multi-core cable received through the current transformer coil is oriented in an axial direction. The current transformer coil may extend in the axial direction on both sides of the one or more magnetic field sensors. The core of the current transformer coil may extend in the axial direction on both sides of the one or more magnetic field sensors.

[0074] The current transformer coil may extend in the axial direction for a length which is greater than or equal to half an interior diameter of the current transformer coil. The current transformer coil may extend in the axial direction for a length which is greater than or equal to the interior diameter of the current transformer coil. The current transformer coil may extend in the axial direction for a length which is greater than or equal to twice the interior diameter of the current transformer coil. The one or more magnetic field sensors may be disposed half-way along the length of the current transformer coil in the axial direction.

[0075] At least one of the one or more magnetic field sensors may include, or take the form of, a sensor coil. Each sensor coil may be wound around a sensing pole piece. Each sensor coil may be would around a portion or protrusion of the core of the current transformer coil. Two or more of the magnetic field sensors may include, or take the form of, respective sensor coils. All of the one or more magnetic field sensors may include, or take the form of, respective sensor coils. Sensor coils, may be premade, with the multicore cable inserted, or wound around the multi-core cable in situ, or connected around the multi-core cable in situ, or placed around the multi-core cable in situ. The sensor coils may be mounted radially, tangentially or in other axis relative to the longitudinal axis of the apparatus (along which the multi-core cable is configured to be received). A mixture of sensor coil orientations may be used, such as but not limited to radial and tangential within a single apparatus. Sensor coils may be wound around a core of permeable material. Sensor coils may be so called “air core” coils, which do not include a core of permeable material. An “air core” sensor coil may be wound about a supporting structure formed of non-permeable material such as plastic, glass and so forth. Sensor coils may be wound about a bobbin. The bobbin may be common with the current transformer coil. At least one of the one or more magnetic field sensors m ay 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 axes. A solid state magnetic field sensor device may include, or take the form of, semiconductor type magnetic sensor, a magnetoresistive sensor, a giant magnetoresistive sensor or an anisotropic magnetoresistance sensor. A solid state magnetic field sensor 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 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.

[0076] Two or more of the magnetic field sensors may include, or take the form of, respective 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).

[0077] The apparatus may include a structure supporting the current transformer coil and the one or more magnetic field sensors. The structure may include, or take the form of, a bobbin about which that current transformer coil and / or one or more sensor coils are wound. When one or more magnets are included in the apparatus, the structure may also support the one or more magnets.

[0078] The structure may include a channel configured to receive the multi-core cable. In other words, the structure may take the form of a channel-defining-structure.

[0079] A cross-section of the channel may have a shape which is circular or an arc of a circle.

[0080] A cross-section of the channel may have has a shape which is non-circular and which does not correspond to an arc of a circle.

[0081] The channel may be open. The open channel may receive the multi-core cable. The structure may define the channel to turn back on itself in cross-section. The structure may define the channel to be C-shaped or U-shaped in cross-section. Cross-sections may be taken in a plane perpendicular to a direction corresponding to an axial direction of the channel along which the multi-core cable will be received when coupled to the apparatus.

[0082] The channel may be defined by first and second parts of the structure, which may be configured to close about the multi-core cable when received within the channel. The first and second parts may be urged together by a spring. The first and second parts of the structure may provide a clamp. Once closed about the multi-core cable, the first and second parts may be secured together by a latch, a catch or similar fastening means.

[0083] The structure may include two or more parts configured to close or wrap about the multi-core cable to define the channel. The two or more parts may be urged together by springs. Once dosed about the multi-core cable, the two or more parts may be secured together by one or more latches, catches, or similar fastening means. The structure may be segmented, with the two or more parts joined together with flexible material, or using hinges aligned with the axial direction.

[0084] The apparatus may include two or more magnetic field sensors. The apparatus may also include one or more magnets. The apparatus may be configured such that, when the apparatus is coupled to the multi-core cable, a magnetic field corresponding to the one or more magnets is applied to the region of multi-core cable which passes through the current transformer coil. In this way, the apparatus according to the fourth aspect may be applied to steel-wire armoured multi-core cables in the same way as the apparatus according to the first aspect, and to obtain the same effects and advantages.

[0085] The one or more magnet field sensors may include a first set of first magnetic field sensors and a second set of second magnetic field sensors. The first and second sets of magnetic field sensors may be arranged to be spaced out along the axial direction of the multi-core cable when it is coupled to the apparatus.

[0086] A sensor may include the apparatus according to the fourth aspect. The sensor may also include a controller connected to the one or more magnetic field sensors. The controller may be configured to calculate, for some or all of the cores of a multi-core cable, one or more derived quantities based on the magnetic field components measured by the magnetic field sensors.

[0087] The controller may be further configured to calculate a net current through the multi- core cable based on measurements using the current transformer coil.

[0088] The one or more derived quantities may include (without limitation): currents in 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 cable; or cores / conductors within magnetically soft conduits or pipes or cables trays, and so forth.

[0089] A sensor may include the apparatus according to the fourth 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 cable when coupled to the apparatus. Alternatively, each signal may be proportional to the individual core currents of the individual cores of the multi core cable. The sensor may also include a link corresponding to each signal, for connection to a control and / or measurement system. The apparatus incorporated in the sensor may be further configured to generate a net current signal based on an output from the current transformer coil.

[0090] The sensor may also include one or more voltage sensors. The one or more derived quantities may include one or more power values. The sensor may be configured to use the one or more voltage sensor to correctly allocate phases to the cores of the multi-core cable.

[0091] Using the current transformer coil, the sensor may be powered by a net current passing through the multi-core cable,

[0092] A system may include a sensor described hereinbefore, coupled to provide input to a measurement device. The measurement device may be a power quality analyzer. The measurement device may be a power quality logging device. The measurement device may be an energy meter. The measurement device may be an electricity meter. According to a fifth aspect of the invention, there is provided a method including coupling apparatus according to according to the fourth aspect (or a sensor / system incorporating the apparatus) to the multi-core cable, such that a region of the multicore cable passes through the current transformer coil. 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 cable,

[0093] The method according to the fifth aspect may include features corresponding to any features of the apparatus(es) according to the first, third and / or fourth aspects. Definitions applicable to the apparatus(es) according to the first, third and / or fourth aspects (or features thereof) may be equally applicable to the method according to the fifth aspect (or features thereof).

[0094] The method may also include measuring a net current passing through the multi-core cable using the current transformer coil.

[0095] According to a sixth aspect of the invention, there is provided an apparatus for coupling to a multi-core cable, including a Rogowski coil and one or more magnetic field sensors. The apparatus is configured such that, when the apparatus is coupled to a multi-core cable, a region of the multi-core cable passes through the Rogowski coil, or the Rogowski coil is wrapped about the region of the multi-core cable. At least one of the magnetic field sensors is disposed adjacent to the Rogowski coil, and oriented to detect components of magnetic field originating from the region of the multi-core cable. At least one of the one or more magnetic field sensors may be disposed inside, or at least partly inside, an inner diameter of the Rogowski coil. In other words, between the Rogowski coil and the multi-core cable in use. At least one of the one or more magnetic field sensors may be disposed outside the Rogowski coil. In other words, separated from the multi-core cable by the Rogowski coil. At least one of the one or more magnetic field sensors may be disposed adjacent to the Rogowski coil along an axial direction.

[0096] The apparatus according to the sixth aspect may include features corresponding to any features of the apparatus(es) according to the first, third and / or fourth aspects. Definitions applicable to the apparatus! es) according to the first, third and / or fourth aspects (or features thereof) may be equally applicable to the apparatus according to the sixth aspect (or features thereof).

[0097] Brief Description of the Drawings

[0098] Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional 3 / 4 view of a sensor assembly which includes two magnet arrays, an array of semiconductor type magnetic sensors, a housing channel-defining- structure, and associated electronics, connections and outputs, shown with a length of armoured multi core cable for illustrative purposes. Figure 2 is a cross-sectional 3 / 4 view of a sensor assembly which includes two magnets, an array of semicon ductor type magnetic sensors and a housing channel-defining- structure, shown with a section of armoured multi core cable for illustrative purposes.

[0099] Figure 3 is a cross sectional view of a sensor assembly which includes a housing, two magnet arrays, an array of semiconductor type magnetic sensors mounted on a magnetically soft mounting ring and a housing channel-defining-structure.

[0100] Figure 4 is a cross sectional 3 / 4 view of a sensor assembly which includes a housing, two magnet arrays, an array of tangential coil type magnetic sensors, a housing channel- defining-structure, and associated electronics and outputs.

[0101] Figure 5 is a cross section 3 / 4 view of a sensor array which includes a magnetically soft ring, a number of axial sensor coils and their associated outputs. 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.

[0102] 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 three Rogowski coils to illustrate an alternative method - an armoured multi core cable under test is not illustrated. Figures 8A and 8B are isometric axial section and isometric cross section views respectively of a sensor assembly which includes two magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring and a housing channel -defining-structure.

[0103] Figures 9A and 9B are isometric axial section and isometric cross section views respectively of a sensor assembly which includes two magnet arrays, an array of radial and tangential coil type magnetic sensors mounted on a magnetically soft mounting ring and a housing channel-defining-structure.

[0104] Figures 10A and 10B are isometric axial cross section and isometric cross section views respectively of a sensor assembly which includes two magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring, and a h ousi ng channel-defin ing-structure with two additional radial coils either side of the magnetically soft mounting ring.

[0105] Figure 11 is an isometric section view of a sensor assembly which includes two magnet arrays, two arrays of radial coil type magnetic sensors mounted on individual magnetically soft mounting rings and a housing channel-defining-structure.

[0106] Figures 12A, 12B and 12C are isometric axial cross section, side elevation and isometric cross section views respectively of an open-ended sensor assembly which includes two magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring, a mounting channel-defining-structure and a housing shown with a length of armoured multi core cable set against a flat surface for illustrative purposes.

[0107] Figures 13A, 13B and 13C are isometric cutaway (opened), isometric (closed) and isometric cross section (opened) views respectively of a ‘spring clamp’ type sensor assembly which includes two magnet arrays, an array of radial coil type magnetic sensors mounted on a magnetically soft mounting ring, a mounting channel-defining- structure and a housing assembly with spring, shown with a length of armoured multi core cable for illustrative purposes.

[0108] Figures 14B, 14B and 14C are isometric cross section, plan cutaway and isometric views respectively of a sensor assembly which includes two 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.

[0109] Figures 15A, 15B, 15C, 15D and 15E are isometric (opened), isometric (closed), side elevation (closed), isometric axial cross section (closed) and isometric cross section views respectively of a m ultiple unit sensor assembly, each individual unit of which includes two magnets, a radial sensor coil, a magnetically soft backing piece, hinge elements and movement limiting elements, show n with a length of armoured multi core cable for illustrative purposes.

[0110] Figures 16A, 16B and 16C 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 magnetic sensors mounted on a magnetically soft mounting ring.

[0111] Figures 17A, 17B and 17C 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 purposes.

[0112] Figures 18A, 18B and 18C are isometric cross section , plan cutaway and isometric views respectively of a sensor assembly which includes one magnet, a radial sensor coil, a magnetically soft backing piece and a wired connection, shown with a length of armoured multi core cable set against a flat surface for illustrative purposes.

[0113] Figure 19 show's experimentally measured currents in a three-conductor multi-core cable using a sensor assembly as shown in Figures 8A and 8B, compared to a measuremen t made by separating out one of the conductors and using a conventional current clamp probe.

[0114] Figure 20 show's errors obtained from analysis of data as shown in Figure 19, for a range of applied currents. Figures 21 and 22 show' comparable data for Figure 19, for current signals having harmonic components up to the eleventh harmonic. Figures 21 and 22 show experimentally determined currents obtained using the same arrangement as Figure 19, for current signals comprising a superposition of sinusoids at a base frequency and the 31stharmonic thereof.

[0115] Figures 24A and 24B are isometric axial cross section and isometric cross section views respectively of a sensor assembly which is a modification of the sensor assembly shown in Figures 9A and 9B. Figures 25A and 25B are isometric and axial cut-away views of a sensor assembly including a two channel-defining-structures which together form a ring. An array of solid state magnetic field sensors are arranged around an interior surface of the ring.

[0116] Figures 26A, 26B, 26C and 26D show respectively axial cut-away, axial side, isometric and plan views of a sensor assembly including a set of radial sensor coils disposed within a channel-defining-structure in the form of two demi-cylinders of permeable material. Magnets / magnet arrays are included at both ends, and end caps of permeable material help to complete the magnetic circuit exterior to the sensed volume.

[0117] Figures 27A, 27B and 27C show respectively plan, axial side, and isometric views of a bobbin arrangement used in the sensor assembly of Figures 26A to 26D.

[0118] Figures 28A, 28B and 28C show respectively plan, axial side, and isometric views of magnets used in the sensor assembly of Figures 26A to 26D.

[0119] Figures 29A, 29B and 29C show respectively plan, axial side, and isometric views of outer cores used in the sensor assembly of Figures 26A to 26D. Figures 30 A, 30B and 30C show respectively plan, axial side, and isometric views of end caps used in the sensor assembly of Figures 26A to 26D.

[0120] Figures 31A and 31B show respectively isometric axial section and axial cut-away views of a sensor assembly including two magnet arrays and an array of tangential coil type magnetic sensors mounted on ch annel -defining-structure. Figures 32A, 32B, 32C and 32D show respectively an isometric view of a closed sensor array, an isometric view of the open sensor array, a plan view of the closed sensor array, and a plan view of the closed sensor array. The sensor array includes an array of tangential coil type magnetic sensors mounted on a pair of channel-defining-structures forming an ovoid shape in cross-section.

[0121] Figures 33A, 33B, 33C and 32D show respectively an isometric view of a closed sensor array, an isometric view of the open sensor array, a plan view of the closed sensor array, and a plan view of the closed sensor array. The sensor array includes an array of solid state type magnetic sensors mounted on a pair of channel-defining-structures forming an ovoid shape in cross-section.

[0122] Figures 34A, 34B, 34C, 34D and 34E show respectively isometric, isometric axial section, axial cut-away, plan, and plan section views of a sensor assembly incl uding two magnet arrays and an array of radial coil type magnetic sensors supported within the permeable core of a current transformer. The radial coil type magnetic sensors are disposed about protrusions of the current transformer core.

[0123] Figures 35A and 35B show respectively isometric axial section and plan section views of a sensor assembly including two magnet arrays and an array of radial coil type magnetic sensors supported within the permeable core of a current transformer. The radial coil type magnetic sensors are air cored.

[0124] Figures 36A and 36B show respectively an isometric view of a flat bobbin assembly and an isometric view of the same bobbin assembly re-arranged into a curved configuration.

[0125] Figure 36C shows an isometric view of a demi-cylindrical core section for threading through the bobbin assembly in the curved configuration.

[0126] Figures 37A and 37B show respectively plan and isometric views of a sensor assembly having an array of solid state type magnetic sensors disposed just inside a transformer coil wound about a ring-shaped core of permeable material.

[0127] Figures 38A and 38B show respectively plan and isometric views of a sensor assembly having an array of solid state type magnetic sensors disposed inside the windings of a transformer coil wound about a ring-shaped core of permeable material. Figures 39A, 39B, 39C and 39D show respectively an isometric view of a closed sensor array, an isometric view of the open sensor array, a plan view of the closed sensor array, and a plan view of the closed sensor array. The sensor array includes an array of solid state type magnetic, sensors mounted on a pair of channel -defining-structures forming an ovoid shape in cross-section. The channel-defining-structures are formed of permeable material and serve as the core for a current transformer coil.

[0128] Figures 40A and 40B show respectively an isometric and axial side view of a sensor array receiving a multi-core cable. The sensor array includes a Rogowski coil adjacent to an array of radial coil type magnetic sensors.

[0129] Detailed description

[0130] In the following, like parts are denoted by like reference numerals. Figure 1 shows a first sensor assembly I comprises a magnetically soft housing ‘channel-defining-structure’ 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 6 under test. The first sensory’ assembly I is an apparatus for coupling to a multi-core steel wire armoured cable, but may also be used with an unarmoured multi-core cable. The first sensor assembly 1 is formed of one, two or more magnetically soft ‘channel-defining- structure’ sections of an enclosure, possibly hinged down sidelong one axis that is parallel to longitudinal the axis of the first sensor assembly I in order to allow the sensor to be opened and closed around a multi core steel wired armoured cable 6. The armoured multi-core cable 6 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-cariying multiple magnetically soft wires 7, built into the outer section of the multi-core cable 6. The first sensor assembly I is closed around the multi-core cable 6, partially or completely enclosing the multi-core cable 6 under test.

[0131] Each end of the channel-defining-structure 1 has one or more magnets, 2 & 3 (or arrays of magnets). On one end the magnet(s) 2 are polarised North, in that all the North poles are pointing inwards from the array, pointing towards the multi-core cable 6 under test. At the opposite end all the magnet(s) 3 (for example forming a magnetic array) is (are) polarised South, again with all poles pointing towards the multi-core cable 6 under test. These magnets 2 and 3 are concentric to the multi-core cable 6 under test and produce a magnetic field running from North to South along the multicore cable 6 under test (see also Figure 3, label 107). That in turn saturates the region of steel armouring 7 of the section of multi-core cable 6 where the first sensor assembly 1 is located. The magnetic field could also be generated partially or fully by electromagnet coils mounted with or in place of the permanent magnets 2, 3.

[0132] Mounted within the channel of the channel-defining-structure 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 magnetic field sensors 5 all point inwards towards and concentric with the armoured multi-core cable 6 under test forming a ring of magnetic field sensors 5 around it. The first sensor assembly I uses solid state or semiconductor type sensors such as Hall sensors or giant magnetoresistive sensors mounted on a flexible pcb or flexi in close contact with the housing 1 (or “channel-defining-structure”). The magnetic field sensors 5 are located against, or adjacent or abutted to the magnetically soft housing 1. Location of the magnetic field sensors 5 is such as to enable the magnetic field sensors 5 to measure the magnetic field(s) generated by currents in the cores 8, 9, 10 of the multi-core cable 6 within the region of cable saturated by the magnets 2,3. Processing of the signals from the magnetic field sensors 5 is by a processor (or controller) 12 either integrated with the first sensor assembly I or wared separately 11 to the first sensor assembly I. This processor takes the form of an electronics enclosure containing a controller 12 electrically connected to the first sensor assembly I. The controller 12 processing the data may generate three distinct current signals outputs, one for each of the 3 discrete phases 13,14,15 in the multi-core cable 6 under test. The apparatus in the form of the first sensor assembly I may be used with two or three or four or five or six or more core cable. The number of outputs 13, 14, 15 are arranged accordingly. The electronics unit 12 (or “controller”) could also include a con nector or connectors 16 for power, data, updates and other utilities and taking the form of a USB or similar.

[0133] This first sensor assembly I 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. Figure 2 shows a second sensor assembly II this is similar in design and operation to the first sensor assembly I described in relation to Figure 1. The second sensor assembly II is again formed of one or two or more magnetically soft ‘channel-defining- structure’ sections 21 wit h a sensor array 25 with one or more magnetic field sensors 24 surrounding an armoured wire strands 27 of the multi-core cable 26, the multi-core cable 26 having cores 28a, 28b, 28c under test. In this case, instead of an array of magnets 2, 3, each end of the channel-defining-structure 21 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-defining-structure 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 the m ulti-core cable 26 under test. Therefore, the two magnet 20, 23 sides facing each other in the second 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 27 of the section of armoured m ulti-core cable 26 under test where the second sensor assembly II is located.

[0134] Figure 3 shows a section view of a third sensor assembly III that is similar to the first sensor assembly I described in relation to Figure 1, including channel-defining- structures 102 and 103 containing magnets 105, 110, 109 and 104 with poles oriented North 105, 110 (directed radially outwards) and South 104, 109 (directed radially outwards) to produce a magnetic field 107, 108.

[0135] Third 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 (shown dispersed between 106 and ill in Figure 3) 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 accommodate the magnetic sensors 106, 111 with separate parts to accommodate the magnets or arrays 105, 110 , 109, and 104 at each end of the channel-defining-structure 102, or the ring 101 could be wide enough to form the entire channel removing the need for channel-defining-structures 102 and 103.

[0136] Figure 4 shows a fourth sensor assembly IV that is similar to the first sensor assembly I described in relation to Figure 1, including channel-defining-structure 1 containing magnets (or arrays of magnets) 49a, 49b with poles oriented North and South at opposite ends to produce a magnetic field in the armoured multi-core cable 6 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 fourth sensor assembly IV or wired separately to the fourth sensor assembly IV. The controller 50 may provide 3 distinct outputs 51, 52, and 53, one for each of the cores 8, 9, to in the multi-core cable 6 under test (not shown in Figure 4 for clarity)- The controller 50 may include a connector or connectors for powder, data, updates and other utilities and taking the form of a USB or similar 54. The fourth sensor assembly IV differs from the first sensor assembly I by using a number of magnetic sensors in the form of sensor coils 41, 42, 4344, 45, 46, 47, and 48 mounted in a ring formation tangentially around the multi-core cable 6 under test. The sensor coils 41, 42, 43, 44, 45, 46, 47, and 48 are mounted between the magnets (or arrays of magnets) 49a and 49b. The sensor coils 41, 42, 43, 44, 45, 46, 47, and 48 could be replaced by solid state magnet field sensors in sensors on flexi / pcb material.

[0137] Figure 5 shows a fifth sensor assembly V that is similar to the third sensor assembly III shown in Figure 3, 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 6 under test (not shown in Figure 5) and located between the magnet arrays (for example like those show n in Figures 3, 104, 105, 109, 110 ). The sensor coils 62 are read using connections 63, which may be twisted wire pairs as shown, or which may be co-axial cables (or similar) for improved rejection of interfering signals. The sensor coils 62 may include pole pieces 61 made from soft magnetic material or air cores that could be mounted on supports such as plastic bobbins. The sensor 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 fifth sensor array V could be mounted directly into the channel formed by the channel-defining-structure of the sensor assembly not shown but similar to (Figure 1).

[0138] Figure 6 shows a sixth sensor assembly VI in the form of a power meter. Any version of the described first I to fifth V sensor assemblies may be used, 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 (provided in first 72 and second 73 halves which as shown are secured about the multi-core cable 79 under test) with additional monitoring of the phase voltages u, v and w (shown by indicia 71 in Figure 6). This would include a magnet and sensor assembly 72, 73 mounted on the armoured multicore cable 79 under test and connection 75 with a meter 74. The sensor assembly 72, 73 could be similar to (or the same as) any of the first I to fifth V sensor assemblies described and shown in the prior figures (Figures 1 to 5) 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 input from phases u,v,w to the meter 74. Firing lead 81 includes three wares 80, each of which is connected to an exposed length 76 of a respective core 77 leading into housing 70. The armour strands 78 are stripped back to allow con nection of flying lead 81. The voltage input from phases u,v,w may help top correctly assign currents measured from the armoured multi-core cable 79 under test to the correct core of the cable 79. The meter 74 may include a con nector or connectors for power, data, updates and other utilities and taking the form of a USB or similar 83.

[0139] Figure 7 show a seventh sensor assembly VII in the form of a power quality analyser. The sensor assembly magnetic sensor 87 is to be mounted on to an armoured multicore cable under test 6 (not shown in Figure 7) 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 (for example exposed lengths 76 as shown in Figure 6) to input the voltage for each phase (u, v, w ) in to the power quality analyser VII. This solution could be a lower cost, easier fitting alternative to using a set of three Rogowski coils, 84, 85, or 86 (shown for illustration, not necessarily needed if using the sensor 87). Using Rogowski coils 84, 85, 86 would require the armoured multi-core cable 6 under test to have its’ three phases (for example cores 8, 9, 10) split out from the armouring (for example wires 7) and separated to leave enough room to attach the individual Rogowski coils 84, 85, 86, therefore adding to cost of parts and complexity of the installation - drawbacks that could be avoided using of the sensor assembly 87.

[0140] In a modification (not shown) of the seventh sensor assembly VII, the output of the magnetic sensor assembly 87 may be split into three outputs (not shown) which simul ate the respective outputs of three current transformers, or three Rogowski coils (similar to 84,85,86), applied to the individual cores 8, 9, 10 (when divided from the multi-core cable). In this way, such three outputs (not shown) of the magnetic sensor assembly 87 can be connected to an existing power meter or power quality analyser designed for input from a trio of Rogowski coils (similar to 84,85,86) or current transformers.

[0141] Figures 8A and 8B show an eighth sensor assembly VIII. The eighth sensor assembly

[0142] VIII is similar to the sensor assemblies I, V show n in Figure 1 and Figure 5 but shows in more detail a number of radial field coils 115 (magnetic sensors) mounted onto a ring 114 made from axially or radially stacked / wound laminated steel instead of pcb / flexi mounted semiconductor magnetic sensors between the magnet arrays 117a and 117b.

[0143] 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 radial field coil 115 to form pole pieces 116, alternatively the ring 114 could be flush with the back edge of the coils 115 (i.e. tube shaped), in other words, the coils 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 -defining-structure 113 with no additional magnetic material mounting ring.

[0144] Figures 9A and 9B show a ninth sensor assembly IX. The ninth sensor assembly IX has a number of radial 121 and tangential 122 sensor coils positioned in a ring formation around the multi-core cable 6 under test (not shown in Figures 9A and 9B) and located between the magnet arrays 120a and 120b. The sensor coils 121, 122 and magnet arrays 120a, 120b are support by channel-defining-structure 118. The sensor coils are made up of tangential coils 122 and radial 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, may be integrated into a magnetic material ring 119 as shown in Figure 9A (the ring 119 having protrusions extending radially to provide pole pieces / cores), having separate pole pieces (not shown) or be a combination of both air core (not shown) and integrated / separate poles(not shown).

[0145] Figures 10A and 10B show a tenth sensor assembly X. Tenth sensor assembly X consisting of any of magnets 128a and magnet 128b (or arrays) sensor coils 124 and magnetically soft material 127 similar to some configurations described in prior assemblies, but the tenth sensor assembly X has the addition of one or two additional magnetic sensors 125, 126 (or arrays) either side of the primary sensor array 124. These additional sensors 125 and / or 126 are used to detect the amount of physical twist in the multi-core cable 6 under test (not shown in Figures 10A and 10B). The magnets 128a and 128b are not required if the cable to be tested does not have a soft magnetic sheath or armour. The ring of magnetically soft material 127 is sandwiched by the channeldefining-structure 123 along the axial direction, and magnets 128a, 128b and additional magnetic sensors 125, 126 are supported by channel-defining-structure 123. Magnetic sensors 124 are supported by (or integrally formed with) the ring of m agnetically soft material 127.

[0146] Figure 11 show? an eleventh sensor assembly XI. The eleventh sensor assembly XI consisting of any of the magnet 131a, 131b and material configurations described herein but having a secondary (or second) sensor array 130 in addition to the primary (or first) sensor array 129. Many features may be similar to sensor assembly VIII but in this case with an additional ring of sensors 130. 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 three phase wires (for example cores 8, 9, 10) in the armoured multi-core cable 6 under test, or any multi-core cable including unarmoured multi-core cables.

[0147] Figures 12A and 12B and 12C show a twelfth sensor assembly XII. The twelve sensor assembly XII consisting of any of the magnet 132a, 132b, magnetic sensor 133, and magnetically soft material 137 configurations described herein, but measurement

[0148] (magnetic sensor 133 )and magnetic 132a, 132b arrays form an open or U shape, or comparable shape that returns on itself without forming a closed loop. The open shape of the twelfth sensor assembly XII allows conductor (for example multi-core cable 6) insertion and measurement when the armoured or non- 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 136 for rapid deployment application or a permanent or semi-permanent device.

[0149] Figures 13A, 13B & 13C b show' a thirteenth sensor assembly XIII. The thirteenth sensor assembly XIII consisting of any of the magnet 138a, 138b (or arrays), magnetic sensor

[0150] 139, magnetically soft material (channel-defining-structure) 140 configurations described herein, 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. The thirteenth sensor assembly XIII consists of two channel-defining- structure sections 142, 143 with magnets 138a, 138b and magnetic sensors 139 mounted in a double handled, ‘spring clamp’ type housing 145, 146 with the spring or springs 144 being of compression, torsion or any other suitable type and positioned to hold the sensor arrays (i.e. channel-defining-structure sections 142, 143) closed shut when not being opened by squeezing the handles 145, 146 together. The spring or springs 144 may be supplemented or substituted, or used in addition to a catch (not shown) on the opening ends of the sensor (i.e. channel-defining-structure sections 142, 143) to ensure the thirteenth sensor assembly XIII is fully closed when being used.

[0151] Figures 14A and 14B and 14C show a fourteenth sensor assembly XIV. The fourteenth sensor assembly XIV uses the same technology as detailed in the first sensor assembly I shown in Figure 1, but consisting of a pair of magnets 150, 151 (alternatively 1 magnet and feature made from soft material instead) and one or more magnetic sensors 152 mounted on a magnetically soft backing piece 147 (or “structure”). The fourteenth sensor assembly XIV could consist of any of the magnet / sensor / material configurations described herein, but in a simplified, 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.

[0152] The fourteenth sensor assembly XIV 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.

[0153] Figures 15A, 15B, 15C, 15D & 15E show a fifteenth sensor assembly XV. The fifteenth sensor array XV is made from individual, simplified sensors 153 as described or similar to the fourteenth sensor assembly XIV shown Figures i4Ato 14C, but the individual, simplified sensors 153 (for example fourteenth sensor assemblies XIV) are chained together using integrated or separate hinge, clip or other flexible joining elements 155, into a flexible assembly to provide monitoring performance closer to the first sensor assembly I shown in Figure 1 and variants by providing more coverage around the circumference of the armoured multi-core cable under test 154. Each simplified sensor 153 includes magnets 157, 158 and magnetic sensor 159. The fifteenth sensor assembly

[0154] XV (or 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.

[0155] A number of individual sensor modules 153 (simplified sensors) could be added or taken away to optimize the internal diameter (ID) of the sen sor depending on the requirements. As with the fourteenth sensor assembly XIV detailed in Figure 14, each sensor could be wired (Figure 14B, 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. 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 fifteenth sensor array XV

[0156] In a modification (not shown), the fifteenth sensor assembly XV (or array), may include more or fewer than the six simplified sensors 153 illustrated in Figures 15A to 15E.

[0157] Moreover, the modified fifteenth sensor assembly XV (or array) may be configured to use only the number of may have additional or lesser number of segments and may use the number of simplified sensors 153 necessary to wrap around a given multi-core cable 154. In some implementations of such a modified fifteenth sensor assembly XV (or array), an operator may specify the number of simplified sensors 153 to use, for example by providing input to a controller (not shown), or by actuating switches or similar elements provided on each individual simplified sensor 153. Additionally or alternatively, a controller (not shown) may automatically determine the number of active simplified sensors 153, for example by analysing the signals received from each. Inactive (or surplus) simplified sensors 153 will be continue to wrap around / hang away from the cable 154 and may be ignored. The relative angles of each simplified sensor 153 is easily derived from the number of active sensors.

[0158] In a further modification, the simplified sensors 153 may be connectable / dis- connectable from one another. For example using clips, connectors and so forth for mechanical and / or electrical connections between the simplified sensors 153. In this way, the operator may easily add or remove simplified sensors 153 to obtain the right size. The number of simplified sensors 153 connected together may be automatically detected, in a particularly simple example by adding additional connections in each simplified sensor 153 with a resistor in series for each, so that the total resistance may be used to automatically determine the number of simplified sensors 153 in use. The relative angles of each simplified sensor 153 is easily derived from the number of active sensors. Figures 16A, 16B, & 16C show a sixteenth sensor assembly XVI. The sixteenth sensor assembly XVI is a simplified, lower cost version of the first sensor assembly I show n in Figure 1, and / or other variants previously described. The sixteenth sensor assembly

[0159] XVI is a 1 -piece sensor consisting of a cylindrical body 161 (channel-defining-structure) made from a magnetically soft material wound with an electromagnetic coil around the outside of a pole 162 and an array of magnetic sensors 163 forming a ring. The magnetic sensors 163 can be of radial coil (as shown) or tangential coil or semiconductor type or solid state type, either mounted on a separate magnetically soft ring, (please refer to Figure 3, 101), or directly onto the cylindrical body 161 , with or without individual poles or extensions from the ring or cylindrical body 161 forming poles. Designed to be threaded onto the armoured or unarmoured multi-core cable under test 160 as a single unit. The electronics can be integrated or separate from the sixteenth sensor assembly

[0160] XVI. The sixteenth sensor assembly XVI may have magnets added (not shown) if armoured cables are to be evaluated.

[0161] Figures 17A, 17B & 17C show a seventeenth sensor assembly XVII. Similar in operation to the sensor assemblies I, II, VIII detailed in Figures 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, onto which the electromagnetic coil 165 is axially mounted (or directly wound). The armature 167 extends towards and loops around the armoured multi-core cable 170 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 tangential coils as illustrated 166 or semiconductor types, with or without a magnetic material behind them and with or without pole pieces.

[0162] Figures 18A, 18B & 18C show an eighteenth sensor assembly XVIII. The eighteenth sensor assembly XVIII is a simplified sensor similar to the fourteenth sensor assembly XIV detailed in relation to Figures 14A to 14C, but consisting of a single magnet or magnetic field source 174 and magnetic sensor 175. The eighteenth sensor assembly XVIII could consist of any of the magnet / sensor / material configurations described herein, in this example a permanent magnet and a sensor coil on a magnetically soft backing plate / mount 173 (or “structure”) are used. The eighteenth sensor assembly XVIII may be pressed, held or coupled against armoured or unarmoured multi-core cable 171 under test (for example, held in place by magnet or magnetic field source 174 when the multi-core cable 171 is armoured with steel).

[0163] This lower cost variant (eighteenth sensor assembly XVIII) could be coupled by wired connection 172 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.

[0164] Referring also to Figures 19 and 20, linearity of sensor assemblies described herein was evaluated. An example of the eighth sensor assembly VIII was applied to a 3-core steelwire armoured multi-core cable of diameter 30 mm. The internal diameter of the channel of the eighth sensor assembly VIII was 42 mm. Figure 19 shows the currents measured for each of the three cores (solid, dashed and chained lines) using the example of the eighth sensor assembly VIII. The dotted line shows the current measured using a conventional current clamp applied directly to the second core, separated out from the multi-core cable and steel-wire armour at a point offset from the example of the eighth sensor assembly VIII. The agreement may be observed to be very accurate, despite the presence of the steel wire armouring. The current range of the eighth sensor assembly VIII used was approximately from 40 mA up to 500 A. The eighth sensor assembly VIII was tested from 25 in A up to 80 A, and the measured % error is plotted in Figure 20.

[0165] Referring also to Figure 21 and 22, similar data to Figure 20 is shown for the case of signals having higher harmonic components. In particular, core 1 had a square wave applied, wirilst cores 2 and 3 had triangular waveforms applied. All the waveforms included components up to the 11thharmonic. The solid, dashed and chained lines show the first, second and third core currents measured using the example of the eighth sensor assembly VIII . In Figure 21, the dotted line shows the measurements obtained using a conventional current clamp probe applied to core 2 when separated from the multi-core cable and steel wire armouring at a position offset from the example of the eighth sensor assembly VIII. Figure 22 is the same, except that the conventional current clamp probe was applied to core 1 instead of core 2. In both Figures 21 and 22, good agreement is obtained between the example of the eighth sensor assembly VIII and the conventional measurements (w hich required physical disassembly of the multicore cable components) even through the steel wire armouring. Referring also to Figure 23, similar data to Figures 20, 21 and 22 is shown for the case of three phase current having a signal formed from a base sinusoid at 20 A amplitude, superposed with the 31stharmonic at 2 A amplitude. In this case, the dotted line representing the conventional current clamp measurement was obtained from core 2.

[0166] Even at the 31stharmonic, good agreement with the conventional measurement approach (which has the disadvantage of requiring the physical disassembly of the multi-core cable) was obtained using the example of the eighth sensor assembly VIII. Figures 24A and 24B show a nineteenth sensor assembly XIX. The nineteenth sensor assembly XIX is the same as the ninth sensor assembly IX, except that the ring 119b of magnetic material and tangential sensor coils 122b have been reconfigured in a way which may improve efficiency. In particular, the tangential sensor coils 122 of the ninth sensor assembly IX are disposed entirely within an inner radius of channel-defining- structure 118, and to accommodate this the magnetic material ring 119 of the ninth sensor assembly IX includes “kinks” corresponding to each of the tangential sensor coils 122, in which the ring 119 diverts radially inwards to pass through the windings of the tangential sensor coils 122. This may be disadvantageous in terms of diversions of flux paths within the ring 119. Compared to this, in the nineteenth sensor assembly XIX the ring of magnetic material 119b has a simpler shape without the “kinks”. The tangential sensor coils 122b wound partly around the ring 119b, with the coils arranged partly inside and partly outside the channel defining structure 118. In this way, tangential flux may follow uninterrupted circular paths about the ring 119b. The radial sensor coils 121 remain w ound about inw ard radial protrusions of the ring 119b in the same way as for the ninth sensor assembly IX, and may be wound directly about the protrusions, or may be wound about a bobbin which is received over the protrusion.

[0167] Figures 25A and 25B show a twentieth sensor assembly XX. The twentieth sensor assembly XX is similar to the first to third sensor assemblies I, II, III, except that the twentieth sensor assembly XX is formed to be substantially more compact along the length of the multi-core cable, which may be an armoured or unarmoured multi-core cable 160. The twentieth sensor assembly XX has first 180 and second 181 channeldefining-structures which are joined together about an armoured or unarmoured multicore cable 160. The first 180 and second 181 channel-defining-structures may be formed of magnetic material (for example silicon steel), but do not need to be. The inner surfaces of channel -defining-structures 180, 181 support solid state magnetic sensors 182, either directly or via a flexi or pcb. The longitudinal ends of the channeldefining-structures 180, 181 include respective lips 183a, 183b, 184a, 184b which extend radially inwards for a distance at least equal to a height of the solid state magnetic sensors 182. The twentieth sensor assembly XX is illustrated with six solid state magnetic sensors 182 arranged at 60 degree intervals about the circumference to form a hexagonal arrangements, however, more or fewer solid state magnetic sensors 182 may be used and / or the angular spacing may be different or irregular.

[0168] The twentieth sensor assembly XX may be used as illustrated for unarmoured multi- core cables 160. For use with armoured multi-core cables 6, magnets (not shown in Figures 25A and 25B) should be added. This may be discrete or ring-like, and may be received on the interior surfaces of channel-defining-structures 180, 181 and / or lips 183a, 183b, 184a, 184b. In some examples, the lips 183a, 183b, 184a, 184b could be formed using ring-like magnets.

[0169] Referring also to Figures 26 A to 30C, a twenty first sensor assembly XXI is shown. The twenty first sensor assembly XXI is similar to the eighth sensor assembly VIII, with the components specifically designed for a compact, efficient and yet cost-effective fabrication.

[0170] Figures 26A to 26D show the assembled twenty first sensor assembly XXL Figures 27A to 27C show a bobbin arrangement 185 in the form of a semi-circular support 186 from which three bobbins 187 extend radially inwards. Preferably, the bobbins 187 are integrally formed with the semi-circular support 186, using injection molded plastic. Alternatively, the bobbins 187 may be formed separately and attached to the semicircular support 186. The bobbins 187 are spaced from one another by 60 degrees about the semicircular support 186 (with about 30 degrees separation to either end). Each half of the twenty first sensor assembly XXI includes a bobbin arrangement 185, so that overall a ring is formed about a multi-core cable 6, 160. A radial sensor coil 188 is wound about each bobbin 187. For example, each radial sensor coil 189 may by formed from 300 turns of 0.25 mm diameter enamelled copper wire. Although illustrated as air-coil in Figures 26A to 26D, in some examples magnetic core materials may be inserted into the through-holes of each bobbin 187 (before or after winding the sensor coils 188). The bobbin arrangements 185 with sensor coil 188 windings formed are received into first 189a and second 189b outer cores (shown separately in Figures 29A to 29C). Each outer core 189a, 189b is a half-cylinder formed of magnetic material suitable for a transformer, for example wound silicon steel tape. The first 189a and second 189b outer cores are preferably formed by splitting a wound silicon steel tape cylinder in half. A pair of magnets 190a, 190b are also received within each outer core half 189a, 189b. A single magnet 190 is shown in Figures 28A to 28C. The magnets 190a, 190 b may be magnetised ferrite, form example grade C5 as used in a loudspeaker. The magnets 190a, 190b may be magnetised to provide the magnetic field substantially along the longitudinal axis as in the second sensor assembly II, or may have opposite radial polarisations as in the first sensor assembly I. Each outer core 189a, 189b is terminated at both ends by a pair of identical end caps 191, formed for example using silicon steel (or other material suitable for transformer cores). Each end cap 190 has the shape of a semi-circle having a semi-circular cut-out with a diameter which defines the maximum size of multi-core cable 6, 160 w-hich can be accommodated.

[0171] The two halves of the twenty first sensor assembly XXI are placed together about a multi-core cable 6, 160 and secured together. For example the two halves may be hinged on one side and a latch or similar securing mechanism may be provided on the other side.

[0172] When intended for use with an unarmoured multi-core cable, the magnets 190a, 190b may be omitted. Referring also to Figure 31A and 31B, a twenty second sensor assembly XXII is shown. The twenty second sensor assembly XXII is the same as the fourth sensor assembly IV, except that a specific design of tangential sensor coils 41b to 48b is shown in place of the schematic cylindrical sensor coils 41 to 48 shown in Figure 4. Tangential sensor coils 41b to 48b are wound onto respective bobbins, and supported inside the channel- defining-structure 1. Tangential sensor coils 41b to 48b may be air-cored, or may have magnetic material inserted through the coils before or after winding. The specific shape shown for the tangential sensor coils 41b to 48b, which is flattened in the radial direction and extended along the longitudinal axis (rounded rectangular) may help to increase the total area of sensor coils 41b to 48b, without reducing the diameter of cable 6 which may be received (by comparison to cylindrical sensor coils). When intended for use with an unarmoured multi-core cable, the magnets 49a, 49b may be omitted.

[0173] Whether the channel is designed to close about a multi-core cable or to remain open, the first to twenty second sensor assemblies I, ..., XXII have been illustrated to define a circular channel (or portion thereof). However, the invention is not limited to sensor assemblies which are circular (or a portion thereof) in cross-section (perpendicular to the longitudinal axis of a received multi-core cable). For example, referring also to Figures 32A to 32D, a twenty third sensor assembly XXIII is shown. The twenty third sensor assembly XXIII is similar to the twentieth sensor assembly XX, except that lips 183, 184 are omitted, tangential sensor coils 192 are used instead of solid state magnetic field sensors 182, and that the first 180b and second 181b channel-defining-structures are not semi-circular. Instead, each channel- defining-structure 180b, 181b defines half an ovoid (or “egg-shaped”) shape in cross- section (or end-on view).

[0174] As another example, referring also to Figures 33A to 33D, a twenty fourth sensor assembly XXIV is shown. The twenty fourth sensor assembly XXVI is identical to the twenty third sensor assembly XXIII, except that solid state magnetic field sensors 182 are used instead of tangential sensor coils 192. The twenty fourth sensor assembly XXVI may alternatively be viewed as being the same as the twentieth sensor assembly XX, except that lips 183, 184 are omitted and that the first 180b and second 181b half- ovoid channel-defining-structures are used.

[0175] In analogous manner, any of the first to twenty second sensor assemblies I, ..., XXII may be modified to have a non-circular shape in cross-section (or end-on view).

[0176] Sensor assemblies incorporating current transformers When performing measurements from multi-core cables, whether armoured or unarmoured, if there is a net current in the multi-core cable, this may cause saturation of magnetic field sensors and / or any components of the channel -defin ing-structure(s) which include permeable materials. As described hereinafter, such issues may be mitigated (or even avoided) by basing a sensor on a current transformer (CT), of sufficient inner aperture to pass the multi-core cable (armoured or unarmoured), and having a current rating suited to the expected net, or zero sequence current in the multi-core cable.

[0177] Referring also to Figure 34A to 34E, a twenty-fifth sensor assembly XXV is shown. The twenty-fifth sensor assembly XXV is similar to the eighth sensor assembly VIII, except that instead of h aving a separate ring 114 and channel-defining-structure 113, the twenty-fifth sensor assembly XXV instead has a channel -defining-structure 193 in the form of a single piece (or preferably two halves) of permeable material which also provides the core for the windings of a current transformer coil 194. The current transformer coil 194 is provided in the form of eight sub-windings 194a to 194h, which are connected together and placed in series with a burden resistance 195.

[0178] The core 193 of the current transformer coil 194 includes protrusions 196 extending radially inwards about which radial sensor coils 115 are wound or over which the radial sensor coils 115 are received (for example, pre-wound onto a plastic bobbin). The core 193 of the current transformer coil 194 is preferably made of a material suitable for a current transformer, for example silicon steel.

[0179] The magnets 117a, 117b may be included when it is desired to measure armoured or unarmoured multi-core cables, but the magnets 117a, 117b may be omitted if the twenty-fifth sensor assembly XXX is only intended for use with unarmoured multi-core cables. When the magnets 117a, 117b are include (as shown in Figures 34Ato 34E), the core 193 of the current transformer coil 194 may also include end or “lip” protrusions 197a, 197b at either end along the longitudinal axis and coinciding with magnets 117a, 117b. The end protrusions 197a, 197b help to connect the return flux path between magnets 117a and 117b.

[0180] The twenty-fifth sensor assembly XXV may be formed in two halves to provide a clampon sensor, or it may be of the thread-through type (i.e. threading the multi-core cable through the current transformer coil 194.

[0181] Radial fields going into the inside of the core 193 of the curren t transformer coil 194 are measured by the radial sensor coils 115. Solid state magnetic field sensors and / or tangential sensor coils may be used in addition to, or instead of, the radial sensor coils 115- The magnetic field sensors, whether radial / tangential sensor coils, solid state magnetic field sensors, or any other magnetic field sensors suitable to sense dipole moment generated by unbalanced currents in the multi-core cable (or symmetric or antisymmetric currents), may be placed between the core of the current transformer coil and the multi-core cable, or places so that the core of the current transformer coil is between the magnetic field sensors and the multi-core cable the core 193 of the current transformer coil 194. Preferably the magnetic field sensors (such as the illustrated radial sensor coils 115 or equivalents) are placed at least partly within the core 193 to obtain shielding from external magnetic fields as explained hereinafter. However, other effects, such as stopping the core 193 of the current transformer coil from being saturated by net current in the multi-core cable, may be obtained whether the magnetic. field sensors are disposed between the core of the current transformer coil and the m ulti-core cable, or disposed so that the core of the current transformer coil is between the magnetic field sensors and the multi-core cable.

[0182] The current transformer coil 194 and core 193 provide four functions:

[0183] 1) A measurement of the net, or common mode, or zero sequence current in the cable (from the voltage across the burden resistance).

[0184] 2) Partial magnetic screening of the dipole sensin g magnetic sensors (radial sensor coils 115 as illustrated) by the core 193 of the current transformer from magnetic fields caused by currents in cables not passing through the sensor (or other sources of magnetic field). The degree of screening is largely driven by the aspect ratio of the core 193. A longer core 193 (compared to its internal diameter) is expected to provide more effective screening than a short, large internal diameter core 193.

[0185] 3) The core 193 of the current transformer increases the sensitivity of the dipole sensing magnetic sensors (radial sensor coils 115 as illustrated) by providing a low reluctance flux path around the outside part of the dipole field sensing magnetic circuit.

[0186] 4) To prevent the core 193 being saturated by the net current in the multi-core cable. It is important to note that the use of a current transformer coil 194 for functions 2) and 3), as compared to just a tube of permeable material (for instance the core 23 without the secondary winding 194) is preferable. This is because as the current transformer coil 194 winding, combined with its approximate short circuit provided by the burden resistance 195 provides a balancing current to the net current in the multicore cable. This prevents the core 193 being saturated by the net current in the multi- core cable (function 4)). This would easily happen otherwise with a high permeability core 193 - as would be required to provide the best screening of external magnetic fields; resulting in the core 193 getting hot, voltage steps being imposed on the multicore cable net current as the core 193 saturates, modulation of the sensitivity of the dipole field sensing magnetic sensors (radial sensor coils 115 as illustrated), and also interference induced into the dipole sensing magnetic sensors (radial sensor coils 115 as ill ustrated) from different parts of the core 193 saturating at different times.

[0187] The level of screening provided by a long core 193 is approximately the core 193 permeability times core 193 thickness / diameter. For example, this may provide a 1000 times improvement for a core 193 w hich is 10mm thick, has a 100mm external diameter (hence an 80mm internal diameter) and 10,000 relative permeability. Such a large core 193 would saturate (2 Tesla) with a net current of 50 A passing though the sensor. For shorter, high permeability cores 193, the screening improvement ratio will be limited by geometry (related to length / internal diameter).

[0188] Although the twenty-fifth sensor assembly XXV is illustrated using radial sensing coils 115, these may be replaced with any other magnetic field sensor suitable for detecting dipole components, for example tangential sensing coils and / or solid state magnetic field sensors described herein, or combinations thereof.

[0189] When measurements from armoured multi-core cables 6 are not required, the magnets 117a, 117b may be omitted. When the magnets 117a, 117b are omitted, the protrusions 197a, 197b may be omitted, or they may be retained to help define the aperture / channel for receiving the multi-core cable.

[0190] Unless evidently incompatible, any optional features, modifications and / or applications of the first I to twenty fourth XXIV sensor assemblies are equally applicable to the twenty-fifth sensor assembly XXV. Any of the first I to twenty fourth XXIV sensor assemblies described hereinbefore may be modified to include a current transformer coil 24, for example by replacing the respective channel -defining-structure with a suitably shaped core and then adding current transformer coil 24 windings. The extent of screening obtained will depend on the aspect ratio (length to diameter) as explained, and may be improved by changing this aspect ratio. When modified in this way to include a current transformer coil 24, any of the first I to twenty fourth XXIV sensor assemblies may have any included magnets omitted if measurement of armoured multi-core cables is not required. Such modified first I to twenty fourth XXIV sensor assemblies will still obtain, to greater of lesser extents, the advantages / functions 1), 2) and 3) described in relation to the twenty-fifth sensor assembly XXV.

[0191] Referring also to Figures 35A and 35B, a twenty sixth sensor assembly XXVI is shown.

[0192] The twenty sixth sensor assembly XXVI is the same as the twenty fifth sensor assembly XXV, except that the core 23 does not include protrusions 196, such that the radial sensor coils 115 are air-cored.

[0193] If the end protrusions 197a, 197b are also omitted, then the twenty sixth sensor assembly XXVI may be produced in a particularly straightforward fashion, as illustrated with reference also to Figures 36A to 36C. Figure 35A shows a bobbin assembly 198 for forming the sensor coils 115 and current transformer coil 194 of the twenty sixth sensor assembly XXVI. The bobbin assembly 198 includes first, tangential bobbins 199 interspersed with second, radial bobbins 200. The radial bobbins 200 extend perpendicular to (and are integrally formed with) supporting plates 201. The tangential bobbins 199 and supporting plates 201 are connected by thin, flexible articulation sections 202. Each tangential bobbin 199 includes a respective rectangular through-hole 203, and each radial bobbin 200 includes a respective rectangular through-hole 204.

[0194] The radial sensor coils 115 are made on the radial bobbins 200 with a pair of first and second bobbin assemblies 198 in the flat state (illustrated in Figure 36A). Four of the sub-windings 194a to 194d of the current transformer coil 194 are made on the tangential bobbins 199 of the first bobbin assembly 198, w hilst the remaining subwindings 194e to 194I1 are made on the tangential bobbins 199 of the second bobbin assembly 198. Referring in particular to Figure 36B, each of the first and second bobbin assemblies 198 is curved as illustrated, by bending flexible articulation sections 202, and a demi- cylindrical core section 205 is threaded th rough the through-holes 203 of the tangential bobbins 199. Once done for both halves, magnets 117a, 117b may be added if required, along with any end-caps (not shown), and the halves assembled to finish the twenty sixth sensor assembly XXVI (for example the halves may be hinged on one side and securable with a latch or comparable mechanism(s) on the other side).

[0195] If it is desired that the sensing coils 115 have permeable cores, permeable materials formed to the right shape may be inserted into the through-holes 204 of the radial bobbins before or after winding the radial sensor coils 115.

[0196] The bobbin assembly 198 may be modified to accommodate solid state magnetic field sensors, which may be mounted to the supporting plates 201 directly or via flexi / PCB prior to folding the bobbin assembly 198 and inserting the demi-cylindrical core section

[0197] 205. Similarly, the orientation of second bobbins 200 may be changed from radial to tangential (or may alternate) to allowing forming other magnetic field sensor configurations. Referring also to Figures 37A and 37B, a twenty seventh sensor assembly XXVII is shown. The twenty seventh sensor assembly XXVII includes an annular transformer core 206 with a continuous helical transformer coil 207 wound thereabout. Ends 208 of the transformer coil are connected via a burden resistance (not shown in Figures 36A and 36B) to form a current transformer. Twelve (the number may be varied) solid state magnetic field sensors 209 are supported on a substrate 210 such as a flexi / PCB disposed just within the inner diameter of the transformer coil 207.

[0198] The twenty seventh sensor assembly XXVII functions in the same way as already described in relation to the twenty fifth XXV and / or twenty sixth XXVI sensor assemblies, though the twenty seventh sensor assembly XXVII will have relatively reduced screening owing to the shorter length parallel to the longitudinal direction of receiving the multi-core cable.

[0199] For use with an armoured multi-core cable, magnets may be added to the twenty seventh sensor assembly XXVII. Referring also to Figures 38A and 38B, a twenty eighth sensor assembly XXVIII is shown. The twenty eighth sensor assembly XXVIII is the same as the twenty seventh sensor assembly XXVII, except that the substrate 210 is supported on an interior diameter of the annular core 206, and the solid state magnetic field sensors 209 are contained within the coils of the continuous helical transformer coil 207.

[0200] For use with an armoured multi-core cable, magnets may be added to the twenty eighth sensor assembly XXVIII. Sensor assemblies including a current transformer are also not limited to circular shapes in cross-section / viewed end on. For example, referring also to Figures 39A to 39D, a twenty ninth sensor assembly XXIX is shown .

[0201] The twenty ninth sensor assembly XXIX is similar to the twenty fourth sensor assembly XXIV, with the addition of a transformer coil sub-windings 211 about the first 180b and second 181b channel-defining-structures, w hich are also formed of permeable material and form a core for a transformer coil realised by connecting together the transformer coil sub-windings 211. The transformer coil sub-windings 211 are also connected in series with a burden resistance (not shown) to form a current transformer. The first 180b and second 181b channel-defining-structures are hinged on one side to allow a multi-core cable to be received through the transformer coil formed by connection of the sub-windings 211. The other side may then be closed and preferably secured, for example by a latch or comparable mechanism. Alternatively, a spring or similar biasing means may be included to urge the unhinged ends of the first 180b and second 181b channel-defining-structures together.

[0202] For use with an armoured multi-core cable, magnets may be added to the twenty ninth sensor assembly XXIX. Referring also to Figures 40A and 40B, a thirtieth sensor assembly XXX is shown. The thirtieth sensor assembly XXX includes a Rogowski coil 212 and a number of magnetic field sensors 213. For the sake of illustration in Figures 40A and 40B, the magnetic field sensors 213 are shown as air-cored radial sensor coils, but only type of magnetic sensor described herein may be used including, but not limited to, solid state magnetic field sensors, radial sensor coils (with an air core or a core of permeable material), tangential sensor coils (with an air core or a core of permeable material), and so forth. The Rogowski coil 212 and the number of magnetic field sensors 213 are supported by a channel-defining-structure, which is not shown in Figures 40A and 40B, but which may be configured as described in relation to the sensor assemblies described hereinbefore.

[0203] The thirtieth sensor assembly XXX is configured such that, when the apparatus is coupled to a multi-core cable 214 (for example three cores as illustrated), a region of the multi-core cable 214 passes through the Rogowski coil 212. At least one of the magnetic field sensors 213 is disposed adjacent to the Rogowski coil, and oriented to detect components of magnetic field originating from the region of the multi-core cable 214.

[0204] Preferably, the magnetic field sensors 213 encircle the multi-core cable 214 to allow sensing of the dipole fields and measurement of derived quantities as described hereinbefore in relation to the first I to twenty ninth XXIX sensor assemblies. The Rogowski coil 212 is used to measure the net current.

[0205] Alternatively, in some examples the Rogowski coil 212 may be flexible (to allow wrapping about the region of the multi-core cable 214. In this case, the Rogowski coil 212 and the magnetic field sensors 213 may be supported by a flexible or articulated structure.

[0206] Having the Rogowski coil 212 and magnetic field sensors 213 disposed closely adjacent to one another allows for direct comparisons to be made between the measurements.

[0207] For example, the net current measurement from the Rogowski coil 212 may be used as a check on the individual core currents inferred using the magnetic field sensors 213.

[0208] The precise location of the magnetic field sensors 213 relative to the Rogowski coil 212 is not limited to the situation shown in Figures 40A and 40B, with the magnetic field sensors 213 disposed adjacent to the Rogowski coil 212 along an axial direction of the multi-core cable 214 (in use). For example, at least one of the one or more magnetic field sensors 213 may be disposed inside, or at least partly inside, the Rogowski coil 212.

[0209] In other words, between the Rogowski coil 212 and the multi-core cable 214 in use.

[0210] Alternatively, at least one of the one or more magnetic field sensors may be disposed outside the Rogowski coil 212. In other words, separated from the multi-core cable 214 by the Rogowski coil 212. Although the multi-core cable 214 shown is unarmoured, for use with an armoured multi-core cable, magnets may be added to the thirtieth sensor assembly XXX.

[0211] Modifications It will be appreciated that various modifications may be made to the embodimen ts hereinbefore described. Such modifications may involve equivalent and other features 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 may be replaced or supplemented by features of another embodiment.

[0212] 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 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

Claims1. Apparatus for coupling to a multi-core steel wire armoured cable, comprising: one or more magnets; and 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; and each magnetic field sensor is oriented to detect components of magnetic field originating from the region of the multi-core steel wire armoured cable.

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

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

4. The apparatus of any one of claims i to 3, wherein at least one of the one or 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.

6. The apparatus of any one of claims 1 to 5, wherein the magnetic field corresponding 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 magnetic 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.

9. The apparatus of any one of claims 1 to 8, wherein the apparatus is configured to 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. io. 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.

12. The apparatus of claim 11, wherein a cross-section of the channel has a shape which is circular or an arc of a circle.

13. The apparatus of claim 12, wherein a cross-section of the channel has a shape which is non-circular and does not correspond to an arc of a circle.

14. The apparatus of any one of claims 11 to 13, wherein the channel is open.

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

16. The apparatus of any one of claims 11 to 13, wherein the structure comprises two or more parts configured to close or wrap about the multi-core steel wire armoured cable to define the channel.

17. The apparatus of any one of claims 1 to 16, 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.

18. The apparatus of any one of claims 1 to 17, wherein at least one of the one or more magnetic field sensors comprises a coil, wherein each coil is wound around a sensing pole piece.19- The apparatus of any one of claims i to 18, wherein at least one of the one or more magnets comprises an electromagnet, wherein each electromagnet is wound around a magnet pole piece.

20. The apparatus of any one of claims 1 to 19, comprising two or more magnetic field sensors.

21. The apparatus of any one of claims 1 to 20, 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; wherein 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.

22. A sensor comprising: the apparatus of any one of claims 1 to 21; 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 the magnetic field sensors.

23. A sensor comprising : the apparatus of any one of claims 1 to 21, the apparatus further configured to generate one or more signals based on outputs of the one or more magnetic field 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.

24. The sensor of claims 22 or 23, further comprising one or more voltage sensors, wherein the one or more derived quantities comprise one or more power values.

25. A system comprising the sensor of any one of claims 22 to 24, coupled to provide input to a measurement device.

26. The system of claim 25, wherein the measurement device is a power quality analyzer.

27. The system of claim 25, wherein the measurement device is a power quality logging device.

28. A method comprising: coupling apparatus according to any one of claims 1 to 21 to a multi-core steel wire armoured cable, or coupling the apparatus of the sensor of claims 22 to 24 or the system of claims 25 to 27 to the multi-core steel wire armoured cable, such that a magnetic 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.

29. The method of claim 28, wherein the magnetic field corresponding to the one or more magnets saturates the steel wire armour within the region.

30. The method of claims 28 or 29, further comprising 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.

31. Apparatus for coupling to a multi-core cable, comprising: a first set of one or more first magnetic field sensors; a second set of one or more second magnetic field sensors; wherein the apparatus is configured such that, when the apparatus is coupled to a 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; each second magnetic field sensor is oriented to detect components of magnetic field originating from a second region of the multi-core cable; wherein the first region is spaced apart from the second region along a length of the multi-core cable.

32. The apparatus of claim 31, further comprising one or more magnets arranged such that, when the apparatus is coupled to the multi-core cable, a magnetic fieldcorresponding to the one or more magnets is applied to the first and second regions of the multi-core cable.

33. Apparatus for coupling to a multi-core cable, comprising: a current transformer coil; one or more magnetic field sensors; wherein the apparatus is configured such that, when the apparatus is coupled to a multi-core cable: a region of the multi-core cable passes through the current transformer coil; the one or more magnetic field sensors are disposed at least partly between a core of the current transformer coil and the multi-core cable, and wherein at least one of the magnetic field sensors is oriented to detect components of magnetic field originating from the region of the multi-core cable.

34. Apparatus according to claims 33 or 34, wherein the core of the current transformer coil comprises permeable material.

35. Apparatus according to claims 33 or 34, wherein the current transformer coil comprises two or more sub-coils.

36. Apparatus according to any one of claims 33 to 35, wherein the apparatus is configured such that the region of a multi-core cable received through the current transformer coil is oriented in an axial direction; wherein the current transformer coil extends in the axial direction on both sides of the one or more magnetic field sensors.

37. Apparatus according to claim 36, wherein the current transformer coil extends in the axial direction for a length which is greater than or equal to half an interior diameter of the current transformer coil.

38. The apparatus of any one of claims 33 to 37, wherein at least one of the one or more magnetic field sensors comprises a sensor coil.39- The apparatus of any one of claims 33 to 38, wherein at least one of the one or more magnetic field sensors comprises a solid state magnetic field sensor device.

40. The apparatus of any one of claims 33 to 39, comprising a structure supporting the current transformer coil and the one or more magnetic field sensors.

41. The apparatus of claim 40, wherein the structure comprises a channel configured to receive the multi-core cable.

42. The apparatus of claim 41, wherein a cross-section of the channel has a shape which is circular or an arc of a circle.

43. The apparatus of claim 41, wherein a cross-section of the channel has a shape which is non-circular and does not correspond to an arc of a circle.

44. The apparatus of any one of claims 41 to 43, wherein the channel is open.

45. The apparatus of any one of claims 41 to 44, wherein the channel is defined by first and second parts of the structure, configured to close about the multi-core cable when received within the channel.

46. The apparatus of any one of claims 41 to 44, wherein the structure comprises two or more parts configured to close or wrap about the multi-core cable to define the channel.

47. The apparatus of any one of claims 33 to 46, comprising two or more magnetic field sensors.

48. Apparatus according to any one of claims 33 to 47, further comprising one or more magnets; wherein the apparatus is configured such that, when the apparatus is coupled to the multi-core cable, a magnetic field corresponding to the one or more magnets is applied to the region of multi-core cable which passes through the current transformer coil.49- The apparatus of any one of claims 33 to 48, 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; wherein the first and second sets are arranged to be spaced out along the axial direction of the multi-core cable when it is coupled to the apparatus.

50. A sensor comprising: the apparatus of any one of claims 33 to 49; 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 cable, one or more derived quantities based on the magnetic field components measured by the magnetic field sensors. 51- The sensor of claim 50, wherein the controller is further configured to calculate a net current through the multi-core cable based on measurements using the current transformer coil.

52. A sensor comprising: the apparatus of any one of claims 33 to 49, the apparatus further configured to generate one or more signals based on outputs of the one or more magnetic field sensors, each signal proportional to a differential current between cores of the multicore cable when coupled to the apparatus; a link corresponding to each signal, for connection to a control and / or measurement system.

53. The sensor of claim 52, wherein the apparatus is further configured to generate a net current signal based on an output from the current transformer coil.

54. The sensor of any one of claims 50 to 53, further comprising one or more voltage sensors, wherein the one or more derived quantities comprise one or more power values.

55. The sensor of claim 54, configured to use the one or more voltage sensor to correctly allocate phases to the cores of the multi-core cable.

56. A system comprising the sensor of any one of claims 50 to 55, coupled to provide input to a measurement device.

57. A method comprising: coupling apparatus according to any one of claims 33 to 49 to a multi-core cable, or coupling the apparatus of the sensor of claims 50 to 55 or the system of claim 56 to the multi-core cable, such that a region of the multi-core cable passes through the current transformer coil; measuring, using the one or more magnetic field sensors, components of magnetic field originating from the region of the multi-core cable.

58. The method of claim 57, further comprising measuring a net current passing through the multi-core cable using the current transformer coil. 59- Apparatus for coupling to a multi-core cable, comprising: a Rogowski coil; one or more magnetic field sensors; wherein the apparatus is configured such that, when the apparatus is coupled to a multi-core cable: a region of the multi-core cable passes through the Rogowski coil, or theRogowski coil is wrapped about the region of the multi-core cable; at least one of the magnetic field sensors is disposed adjacent to the Rogowski coil, and oriented to detect components of magnetic field originating from the region of the multi-core cable.

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