Apparatus for centring a cable through a rogowski coil

Abstract

An apparatus for centring a cable through a Rogowski coil 110 comprises a housing 102 and a cable enclosure 104 disposed within the housing and extending from an interior surface 106 of the housing. T

Description

A Rogowski coil is used for measuring a current through a cable or wire. The most 10 accurate measurements are obtained when the cable or wire is centred through the Rogowski coil. As the cable moves or shifts away from the centre of the coil, the accuracy of the measurement decreases. CN 1096.13316 A describes an approach for centring cables of different diameters 15 within a Rogowski coil, in which a flexible skeleton is attached to the inside of the Rogowski coil. Different cable or wire centring mechanisms can be attached to the flexible skeleton to retain the cable within a centre of the Rogowski coil. It is desirable to provide an apparatus for centring a cable through a Rogowski coil 20 which is simpler and easier to manufacture than previous designs. Summary Disclosed herein is an apparatus for centring a cable through a Rogowski coil. The apparatus (also called a unit or module) is configured for use with an electrical device. 25 An apparatus or unit comprises a housing. A cable enclosure is disposed within the housing and extending from an interior surface of the housing, the cable enclosure defining a channei which is configured to accommodate a cable, the cable configured for connection to the electrical device. A Rogowski coil is arranged within the housing 30 and disposed around a portion of the cable enclosure, the Rogowski coil configured to monitor a current through the cable. The cable enclosure comprises at least three flexible portions, the at least three flexible portions separated from each other and distributed evenly around a circumference of the channel, 35 The housing can also be termed herein an exterior housing, and the cable enclosure can also be termed herein a cable housing. The apparatus (or unit) comprises the exterior housing and the cable housing, where the cable housing is disposed within the exterior housing and extending from an interior surface of the exterior housing, the cable housing defining a channel which is configured to accommodate a cable. By providing at least three flexible portions which are separated from each other and distributed evenly around a circumference of the channel, the apparatus can accommodate cables of different sizes (diameters). The flexible arrangement can centre these different size cables within the Rogowski coil, providing an even application of force around the cable to retain the cable in the centre and help ensure the cable doesn't tilt as it passes through the Rogowski coil. Optionally, the flexible portions can be resilient through form / and or material, so as to hold or retain the cable in a repeatable manner. An apparatus for centring a cable can therefore be provided. Moreover, by separating the mechanism for centring the cable from the Rogowski coil, a standard Rogowski coil can be used to monitor the current through the cable, which can reduce costs and simplify manufacturing. In some implementations, the channel and Rogowski coil are arranged to be coaxial with one another. This co-axia! alignment can help ensure that the cable is arranged in a centre of the coil and simplify manufacturing of the unit or apparatus. In some examples, the cable enclosure comprises a rigid portion coupled to, or formed integral with, the interior surface of the housing, the at least three flexible portions extending from the rigid portion. This can provide increased structural rigidity at one end of the cable enclosure, which can increase the strength of the cable enclosure. The rigid portion may have no openings or apertures. In other examples, the at least three flexible portions are coupled to, or formed integral with, the interior surface of the housing. This can increase the flexibility of the cable enclosure, helping accommodate cables of different diameters. In some implementations, the at least three flexible portions are configured to taper from a first diameter of the cable enclosure proximate the interior surface to a second diameter proximate the Rogowski coil, the second diameter smaller than the first diameter. These tapering flexible portions can act as flexible springs, accommodating different diameters of cables and keeping the cable centred while still allowing a degree of play / movement to help facilitate insertion of the cable into the unit. The first diameter can represent the maximum cable diameter that can be accommodated, and the second diameter can represent the minimum cable diameter that can be accommodated. In some examples, the at least three flexible portions are configured to flare at an end of the cable enclosure distal from the interior surface. This flaring can help prevent tilting of the cable on exit from (i.e. at the end of) the cable enclosure. In some examples, the flared end is configured to engage with a component of the unit / apparatus to help retain the cable enclosure in a centre of the Rogowski coil. In some specific examples the Rogowski coil is arranged on a printed circuit board, PCB, and the end of the cable enclosure distal from the interior surface is configured to engage with the PCB. The end may be flared, or not. The reaction force between the end of the cable enclosure and the PCB can help retain the cable enclosure in the centre of the coil, by way of the reaction force from the PCB. In some implementations, the at least three flexible portions each comprise a protrusion extending into the channel, the protrusions arranged proximate to the Rogowski coil. The protrusions can help ensure the cable is centred within the coil, while still allowing a degree of play / movement to help facilitate insertion of cables of different diameters into the unit. The at least three flexible portions can be formed from plastic and / or metal. The choice of material can be made depending on the strength requirements for the cable enclosure, which may depend in part on a diameter of cable to be accommodated and a rigidity of the cable, etc. In some examples the cable enclosure is a first cable enclosure and the Rogowski coil is a first Rogowski coil, the unit further comprising second and third cable enclosures and second and third Rogowski coils respectively disposed around a portion of the second and third cable enclosures. In this way, the current can be monitored across multiple cables, such as in the case of three phase power, within a single apparatus or unit. Optionally, the first, second and third Rogowski coils can be arranged on a same PCB within the housing. Also disclosed herein is a system, comprising: an electrical device; and a unit as described above, wherein a cable is disposed in the channel and connected to the electrical device such that the unit can monitor a current through the electrical device. In some examples, the housing is configured to engage with the electrical device to couple the unit to the electrical device. In some examples, the electrical device is a circuit breaker, optionally a miniature circuit breaker. In some examples, the unit further comprises a communication module disposed within the housing. Optionally, the communication module is configured to communicate the monitored current to a remote device. In some examples, the unit further comprises a power supply. In this way, the unit can be installed at remote locations for monitoring of the current through the electrical device. The features described above can be provided in any suitable combination. Different implementations and examples can be combined. Features described with reference to the unit may be implemented within the system, and vice versa, as appropriate. List of Figures The detailed description is with reference to the following figures. FIG. 1A shows a schematic side view of a unit as described herein, and FIG. IB shows a top view of the unit of FIG. 1A. FIG. 2A shows a schematic side view of an example implementation of the unit of FIG. 1A, and FIG. 2B shows another example implementation of the unit of FIG. 1A. FIG, 3A shows a perspective view of an example implementation of the unit of FIG. 1A, FIG. 3B shows a schematic side view of an exampie cable enclosure of FIG. 3A, and FIG. 3C shows another perspective view of the unit of FIG. 3A. FIG. 4A shows a perspective view of another example implementation of the unit of FIG. 1A, and FIG. 4B shows a schematic top view of an example cable enclosure of FIG. 4A. FIG, 5 shows a schematic view of a system comprising a unit as described herein. Like reference numerals refer to like features. Detailed Description With reference to FIG. 1A and FIG. IB, there is described a unit (also called herein an apparatus or module) configured to monitor a current through an electrical device using a Rogowski coil. The unit 100 comprises a housing 102. The housing 102 can be considered as an exterior housing of the unit. A cable housing or cable enclosure 104 is disposed within the housing 102. The cable enclosure 104 extends from an interior surface 106 of the housing 102. The cable enclosure 104 defines a channel 120 (not shown here, see FIG. 4B) which is configured to accommodate a cable 108. The cable 108 is configured for connection to the electrical device (not shown). A Rogowski coil 110 is arranged within the housing 102 and disposed around a portion of the cable enclosure 104. The Rogowski coil 110 is configured to monitor a current through the cable 108. In this way, current through the electrical device can be monitored at the unit 100. As illustrated further in FIG. IB, the cable enclosure 104 is formed of, or comprises, at least three flexible portions 104a, 104b ... 104n, the at least three flexible portions separated from each other and distributed evenly around a circumference (C) of the channel defined by the cable enclosure. In other words, the flexible portions are evenly distributed around an axis and the central portion through which the axis extends forms a channel into which a cable can be inserted. This provides a symmetric application of force along or around the circumference of the channel, better ensuring centring of cabie 108. The flexible portions can optionally be formed to be resilient, with the resiliency provided through form / and or material of the flexible portions, so as to hold or retain the cable in a repeatable manner. This may enable the cable to removed and reinserted into the unit a plurality of times. In such arrangements, the flexible portions may be termed resilient portions, or resiliency deformable portions. Optionally, in some specific arrangements, the flexible portions can be configured to deform elastically when the cable is inserted. In other arrangements, the flexibility of the portions can be sufficient to hold or retain the cable, and the portions may not be formed to be resilient or elastic. Provided there are at least three flexible portions, which arrangement provides an even application of force around the cable 108 to retain or hold the cable within the cable enclosure 104, it will be understood that there can be any suitable number of flexible portions provided, as required by the strength, size and flexibility of the cable to be accommodated. For example, cable enclosures 104 with fewer, wider flexible portions may be stiffer than cable enclosures with more, but narrower, flexible portions; wider flexible portions may be stronger than narrower flexible portions. The specific, size, shape, number and arrangement of the flexible portions 104n can be selected or determined for a given application or use case. It is known that the most accurate current measurements are obtained when a cable or wire is centred through a Rogowski coil. As the cable moves or shifts away from the centre of the coil, the accuracy of the measurement decreases. The cable enclosure 104 described herein is configured to assist in centring the cable 108 within the Rogowski coil 110. The inserted cable is retained at least in part by the cable enclosure 104, enabling the cable to be centred through the Rogowski coil by the action of the cable enclosure. The channel and Rogowski coil 110 can advantageously be arranged to be coaxial with one another. This co-axiai alignment can help ensure that the cable is arranged in a centre of the coil and simplify manufacturing of the unit or apparatus. Moreover, the cable enclosure can operate to centre cables of different sizes or diameters within a single design. In particular, by providing a cable enclosure comprising at least three flexible portions 104a, 104b ... 104n, which are separated from each other and distributed evenly around a circumference of the channel, the unit 100 can accommodate cables of different sizes (diameters) by allowing for radial movement. The flexible (optionally, resilient or resiliently deformable) arrangement can centre these different size cables within the Rogowski coil 110, providing an even application of force around the cable to retain the cable in the centre and help ensure the cable 108 doesn't tilt as it passes through the Rogowski coil. In addition, by separating the mechanism for centring the cable from the Rogowski coil, a standard Rogowski coil can be used to monitor the current through the cable, which can reduce costs and simplify manufacturing. A unit centring a cable through a Rogowski coil which is simpler and easier to manufacture than previous designs can therefore be provided. Some example implementations of the cable enclosure 104 are now described with reference to FIG. 2A and FIG. 2B. In some examples, as shown in FIG. 2A, the cable enclosure 104 comprises a rigid portion 104' coupled to, or formed integral with, the interior surface 106 of the housing, the at least three flexible portions 104a ... 104n extending from the rigid portion 104'. In other words, the gap or spacing (G, see FIG. 3C) separating the individual flexible portions 104n may not extend all the way to the interior surface 106 of the housing. This rigid portion 104' can provide increased structural rigidity at one end of the cable enclosure 104, which can increase the overall strength of the cable enclosure. The length and shape of the cuts / gap G between the flexibie portions 104n can vary based on a strength requirement for the cable enclosure. The rigid portion may have no openings or apertures,, as shown in FIG. 2A, or may have one or more openings or apertures. In other exampies, as shown in FIG. 23, the at ieast three flexible portions 104n are coupled to, or formed integral with, the interior surface 106 of the housing. This can increase the flexibility of the cable enclosure, helping to better accommodate cables of different diameters. The length and shape of the cuts / gap G between the flexible portions 104n can vary based on a strength requirement for the cable enclosure. These flexible portions can in some examples comprise finger-like structures. In some examples, the flexible finger-structure portions can be formed as, or be combined with, leaf springs to provide additional retaining forces to the cable 108. These finger-structure portions can optionally be configured to be resilient or resiliency deformable through form and / or material. Strength of the cable enclosure can also be adjusted through the use of the materials used to form the flexible portions. For example, the at ieast three flexible portions can be formed from plastic, which can facilitate cheap manufacture and a lightweight unit. Additionally or alternatively, the at ieast three flexible portions can be formed from metal, which can increase strength of the flexible portions 104n and can be stiffer than the plastic, providing a higher retaining force to the cable 108. The choice and combination of material(s) can be made depending on the strength requirements for the cable enclosure, which may depend in part on a diameter of cable to be accommodated and a rigidity of the cable, etc. For example, the cable enclosure may be formed from ail metal, all plastic, or a combination of the two. Other materials may also be used. With reference to FIG. 3A, FIG. 3B and FIG. 3C, a specific implementation of a cable enclosure 104 is now described. FIG, 3A shows three cable enclosures, 104-1, 104-2, 104-3, but it will be understood that any suitable number of cable enclosures (e.g. one, two, or more than three) may be provided. The flexible portions 104n of the cable enclosure 104-1 comprise finger-link structures. In this specific example, as described further with reference to FIG. 3B, the at least three flexibie portions are each configured to taper from a first diameter DI of the cable enclosure 104 proximate the interior surface 106 to a second diameter DI proximate the Rogowski coil (not shown), the second diameter smaller than the first diameter. These tapering flexible portions can act as flexible springs, accommodating different diameters of cables and keeping the cable centred while still allowing a degree of play / movement to help facilitate insertion of the cable into the unit. The first diameter DI can represent the maximum cable diameter that can be accommodated, and the second diameter can represent the minimum D2 cable diameter that can be accommodated. In the case of the largest cable 108, the flexible fingers will expand to accommodate the cable, and the cable may be in contact with the flexible portions along most or all of the length of the cable enclosure 104; in the case of the smallest cable 108, the smaller diameter D2 will retain the cable 108 and ensure centring of the cable in the region proximate the Rogowski coil. These flexible portions can bend without breaking, retaining or holding the cable through said internal reaction force to said bending. In some specific examples, these flexible portions may be configured to be resilient (i.e. will return to the original shape when the cable is removed), and the cable can be held or retained through a biasing force of the resiliently deformabiy portions. In this specific example, the at least three flexible portions are each configured to flare, or bend, at or near an end 114 of the cable enclosure 104-1 distal from the interior surface 106. The flared or bent portion can have a diameter D3, as shown in FIG. 3B. The diameter D3 will be understood to be greater than diameter D2, but may be more than or less than, or equal to, diameter DI (as required for a given application). This flaring or bending can help prevent tilting of the cable on exit from (i.e. at the end of) the cable enclosure 104-1. In some examples, the flared end is configured to engage with a component of the unit / apparatus 100 to help retain the cable enclosure in a centre of the Rogowski coil. In in this specific example, as shown in FIG. 3C, the Rogowski coil 110 (details of which are not shown) is arranged on a printed circuit board 116, or PCB 116. The end 114 of the cable enclosure 104-1 distal from the interior surface 106 is configured to engage with the PCB 116. In other examples, the end 114 can be configured to engage with a component of the unit (optionally part of the housing, or optionally a PCB 116 as in FIG. 3C) but the end 114 is not flared (and in some examples, the cable enclosure may not be tapered). In either instance, the reaction force between the end 114 of the cable enclosure 104-1 and the component can help retain the cable enclosure in the centre of the Rogowski coil, by way of the reaction force from the component. This arrangement can improve centring of the cable disposed or arranged in the cable enclosure and reduce or prevent movement of the cable enclosure. The arrangement can also provide increased structure to the cable enclosure, facilitating use of the unit 100 with larger or stiffer cables. With reference to FIG. 4A and FIG. 4B, another specific implementation of a cable enclosure 104 is now described. FIG. 4A shows three cable enclosures, 104-1, 104-2, 104-3, but it will be understood that any suitable number of cable enclosures (e.g. one, two, or more than three) may be provided. The flexible portions 104n of the cable enclosure 104-1 of this example are straight, i.e. not flared and / or tapered as in FIG. 3B. In other words, the cable enclosure can have a cylindrical, or substantially cylindrical, cross section (as shown in FIG. 4B). In this example, as shown in FIG. 4B, there are three flexible portions, 104a, 104b, 104c, each separated from each other by an equal distance, cut or gap G. The flexible portions are distributed evenly around a circumference C of the channel 120 defined in a centre of the cable enclosure 104-1. However, any suitable number of flexible portions may be provided, as required by the application. A length and shape of the gaps / cuts can vary based on a strength requirement for the cable enclosure. In this example, the at least three flexible portions 104a, 104b, 104c each comprise a projection or protrusion 118 extending into the channel 120. The projections or protrusions 118 are arranged at, or formed, in a region of the cable enclosure proximate to the Rogowski coil (not shown). In some examples, the protrusions 118 can be formed or arranged in a same plane as the Rogowski coil (where the plane is perpendicular to the axis of the channel 120). Although not shown here, the protrusions 118 can also be implemented in combination with the tapered and / or flared flexible portions described above. The protrusions 118 can help ensure the cable is centred within the coil, while still allowing a degree of play / movement within the body of the enclosure 104-1 itself; this flexibility / movement can help facilitate insertion of cables of different diameters into the unit, whilst at the same time providing a stiffer cable enclosure than the arrangement of e.g. FIG. 3A. The protrusions 118 can be formed from, or coupled to, the flexible portions 104a, 104b, 104c. Any suitable size or shape of protrusion 118 can be used. A length and shape of the protrusions / projections 118 can vary based on a strength requirement for the cable enclosure and / or a size of the cable 108 to be accommodated. These flexible portions can bend without breaking, retaining or holding the cable through said internal reaction force to said bending. In some specific examples, these flexible portions may be configured to be resilient (i.e. will return to the original shape when the cable is removed); and the cable can be held or retained through a biasing force of the resiliency deformably portions. In some examples (not shown), an end 114 of the cable enclosure 104-1 is configured to engage with a component of the unit / apparatus 100 to help retain the cable enclosure in a centre of the Rogowski coil. In particular, the end 114 of the cable enclosure 104-1 distal from the interior surface 106 is configured to engage with the component (which may be a PCB 116, part of the housing 102, or other component). The reaction force between the end 114 of the cable enclosure 104-1 and the component can help retain the cable enclosure in the centre of the Rogowski coil, by way of the reaction force from the component. This arrangement can improve centring of the cable disposed or arranged in the cable enclosure and reduce or prevent movement of the cable enclosure. The arrangement can also provide increased structure to the cable enclosure, facilitating use of the unit 100 with larger or stiffer cables. In both FIG. 3A and FIG. 4A, the unit is shown to comprise a first cable enclosure 104-1 and second and third cable enclosures 104-2, 104-3. Although not shown, the unit can further comprise Rogowski coiis respectively disposed around a portion of each of the first, second and third cable enclosures. In this way, the current can be monitored across multiple cables 108, such as in the case of three phase power, within a single apparatus or unit. Optionally, the first, second and third Rogowski coils can be arranged on a same PCB 116 within the housing 102. In other examples, the Rogowski coils can be implemented separately from one another. With reference to FIG. 5, there is provided a system 500. The system comprises an electrical device 530 and a unit .100. The unit 100 can be any implementation of the unit 100 as described herein. The unit 100 can also be termed a power monitoring device, and such a unit can be used with electrical devices 530, such as circuit breakers, optionally miniature circuit breakers or MCBs, to monitor the current, voltage, power or other parameters and communicate this data to a remote device. The unit can be considered as an add-on device which is mounted to the electrical device 530, such as an MCB. In some examples, the housing 102 of the unit 100 is configured to engage with the electrical device 530 to couple the unit to the electrical device. A cable 108 is disposed in the channel formed by the cable enclosure 104 of the unit (not shown) and is connected to the electrical device 530 such that the unit can monitor a current through the electrical device using the Rogowski coil 110 disposed within the unit (not shown). The cable wiil pass through the power monitoring device or unit 100 and be connected to the electrical device 530. A Rogowski coil, optionally a printed Rogowski coil, can be implemented in the power monitoring device or unit. The cable enclosure can help ensure that the cable 108 passes through the centre of the coil for accurate measurements of the current. Voltage pins (not shown) can be connected for voitage monitoring. In some implementations, the Rogowski coil is arranged or printed onto a PCB in the housing to monitor current and the voltage pins are connected to PCB for voltage monitoring. In some examples, the unit 100 further comprises a communication module 540 disposed within the housing 102. Optionally, the communication module 540 configured to communicate the monitored current to a remote device (not shown). The communication can be by any suitable wired or wireless connections. In some examples, the unit further comprises a power supply 550 within the housing 102. In this way, the unit 100 can be installed at remote locations for monitoring of the current through the electrical device 530. The use of the unit 100 described herein can allow the accuracy of current measurement using a Rogowski coii, and thus the monitoring of current through an electrical device 530, to be improved. This is achieved by helping to centre the cable within the coil in an efficient, repeatable and reliable manner. Moreover, a range of different cable sizes can be accommodated using the same enclosure design. The unit may therefore improve measurements using a Rogowski coil and be simpler and cheaper to manufacture than previous designs.

Claims

1. A unit (100) for use with an electrical device, the unit (100) comprising:a housing (102);a cable enclosure (104) disposed within the housing (102) and extending from an interior surface (106) of the housing (102), the cable enclosure (104) defining a channel (120) which is configured to accommodate a cable (108), the cable (108) configured for connection to the electrical device;a Rogowski coil (110) arranged within the housing (102) and disposed around a portion of the cable enclosure (104), the Rogowski coil (110) configured to monitor a current through the cable (108),wherein the cable enclosure (104) comprises at least three flexible portions (104a, 104b ... 104n), the at least three flexible portions (104a, 104b ... 104n) separated from each other and distributed evenly around a circumference (C) of the channel (120).

2. The unit (100) of claim 1, wherein the channel (120) and Rogowski coil (110) are arranged to be coaxial with one another.

3. The unit (100) of claim 1 or claim 2, wherein the cable enclosure (104) comprises a rigid portion (104') coupled to, or formed integral with, the interior surface (106) of the housing (102), the at least three flexible portions (104a, 104b ... 104n) extending from the rigid portion (104’).

4. The unit (100) of claim 1 or claim 2, wherein the at least three flexible portions (104a, 104b ... 104n) are coupled to, or formed integral with, the interior surface (106) of the housing (102).

5. The unit (100) of any preceding claim, wherein the at least three flexible portions (104a, 104b ... 104n) are configured to taper from a first diameter (DI) of the cable enclosure (104) proximate the interior surface (106) to a second diameter (D2) proximate the Rogowski coil (110), the second diameter (D2) smaller than the first diameter (DI).

6. The unit (100) of claim 5, wherein the at least three flexible portions (104a, 104b ... 104n) are configured to flare at an end of the cable enclosure (104) distal from the interior surface (106).

7. The unit (100) of any preceding ciaim, wherein the at least three flexible portions (104a, 104b ... 104n) each comprise a protrusion (118) extending into the channel (120), the protrusions (118) arranged proximate to the Rogowski cod (110).

8. The unit (100) of any preceding claim, wherein the at ieast three flexible portions (104a, 104b ... 104n) are formed from plastic and / or metal.

9. The unit (100) of any preceding claim, wherein the Rogowski coil (110) is arranged on a printed circuit board (116), PCB, wherein an end (114) of the cable enclosure (104) distal from the interior surface (106) is configured to engage with the PCB (116).

10. The unit (100) of any preceding claim, wherein the cable enclosure (104) is a first cable enclosure (104-1) and the Rogowski coii (110) is a first Rogowski coii, the unit further comprising second and third cable enclosures (104-2, 104-3) and second and third Rogowski coils respectively disposed around a portion of the second and third cable enclosures.

11. The unit (100) of claim 10, wherein the first, second and third Rogowski coils are arranged on a same PCB (116).

12. A system (500), comprising:an electrical device (530); andthe unit (100) of any preceding claim, wherein a cable (108) is disposed in the channel and connected to the electrical device (530) such that the unit (100) can monitor a current through the electrical device (530).

13. The system of claim 13, wherein the housing (102) is configured to engage with the electrical device (530) to couple the unit to the electrical device.

14. The system of claim 12 or claim 13, wherein the electrical device (530) is a circuit breaker, optionally a miniature circuit breaker.

15. The system of any of claims 12 to 14, wherein the unit (100) further comprises a communication module (540) disposed within the housing (102), the communication module (540) configured to communicate the monitored current to a remote device.14

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