GB2332784A

GB2332784A - Current measuring arrangement

Info

Publication number: GB2332784A
Application number: GB9827029A
Authority: GB
Inventors: David Alan Ward
Original assignee: ROCOIL Ltd
Current assignee: ROCOIL Ltd
Priority date: 1997-12-13
Filing date: 1998-12-10
Publication date: 1999-06-30
Anticipated expiration: 2018-12-10
Also published as: GB2332784B; GB9827029D0; GB9726306D0

Abstract

An alternating current measuring device and method comprises a conductive coil 2 formed on a flexible material. The said coil 2 is then wrapped in or on a support structure 32 which secures the coil 2 in a required position. Also disclosed is an alternating current measuring device comprising a support structure which is placed around a conductor and a coil is wrapped on or in the said support with at least one end of the coil being engaged by the support. The support structure may include slots such that the support can be arranged substantially around a conductor of interest 26. One or both ends of a coil may be arranged to be secured within the support structure. The above arrangements may provide a re-usable Rogowski coil arrangement which can be readily and accurately located and formed around a conductor to provide accurate current measurements.

Description

Measuring Device The invention which is the subject of this application relates to devices for use in measuring the alternating current passing along a conductor, and in particular to measuring devices known as Rogowski Coils.

There are several known methods for measuring alternating current, one of which is using an iron-cored current transformer, which is typically large and bulky and therefore inflexible in use, and another method is to use a transducer in the form of a toroidal coil wound usually on a non-magnetic former which, in order for the measurements to be accurate, requires the device to be carefully manufactured. This device is known as a Rogowski Coil.

One known type of Rogowski coil consists of a coil of conducting material wound round a former, which can be flexible, and the device is then wrapped around a conductor for which the alternating current measurement is required. Devices of this type are disclosed in patent no.GB2088568.

The ability to render the use of Rogowski coils in many areas and on conductors of many shapes by using a flexible former allows the same to be used to measure alternating current in conductors which are of an awkward shape or where there is insufficient space for a conventional measuring device to be used. The coils operate by sensing the magnetic field caused by the current in the conductor and can provide a highly accurate measurement without the need for electrical contact to be made with the conductor and are therefore non-invasive devices. The coil acts as a mutual inductance coupled to the conductor being measured and the voltage output is proportional to the rate of change of the current. The voltage output can be integrated electronically to produce an output that reproduces the current waveform and thus can be used to measure currents ranging from the milliampere range to several million amperes.

The coils are conventionally manufactured to suit the conductor to be measured and in one embodiment can be wrapped on cores or spindles of material with an aperture passing therethrough and through which passes the conductor to be measured. One key feature which is required for the coils in whichever form is that the ends of the coil should be in line or joined together in a manner which leaves as small a gap as possible therebetween so that a uniform and hence accurate measurement is achieved. Where a gap is unavoidable an additional small coil or coils can be used to provide compensation.

One known problem with Rogowski coil devices is the requirement for the same to be fitted into position in a uniform and accurate manner in order to ensure that the measurements obtained are accurate and this requirement has meant that the use of these coils is frequently limited to special or "one-off" measuring requirements.

The aim of the present invention is provide a measuring device which utilises a Rogowski coil format and provides the same as part of the device in a manner which allows the device to be adaptable in use, allows the same to be used on a number of differing conductors repetitively and ensures that for each use the coil is correctly positioned on the device without the need for a skilled person to fit the same in position.

In a first aspect of the invention there is provided a measuring device comprising a coil formed of an elongate former of flexible material around which is wound a conducting material and, connected thereto, output wires to allow a measurement signal to be transmitted, said coil adapted to be wrapped in a configuration with a support and wherein said coil is selectively locatable with the said support.

In one embodiment at least one of the ends of said coil is selectively locatable with a location point on said support. In one embodiment when a gap or offset is present between the ends of the coil on the support an additional coil or coils can be connected to provide compensation for the measurement obtained.

In one embodiment the coil is wrapped around a support in the form of a core.

In an alternative embodiment the support is hollow and the coil is housed in the hollow cavity. In this embodiment the coil has a resilient characteristic which tends to force the coil into contact with the inner wall of the support. The support may be provided with a slot to allow the same to be fitted over the conductor to be measured and end pieces can in one embodiment be provided to be fitted onto the support to ensure that the conductor is located in the correct position in relation to the coil. In one embodiment one of the end pieces can be attached to an end of the support before the coil is placed into the support.

In one embodiment each of the ends of the coil are selectively locatable in respective spaced location points on said core and preferably the ends are interchangeable between said location points in repeated use.

The ability to locate each end of the coil ensures that, in use, the ends of the coil are held in the same position upon each use and said location points are provided to ensure the optimum location of each end to ensure that accurate measurements are obtained.

In one embodiment the former has a wire along its centre. Output wires are secured to, or adjacent to, one end of the coil and former and the opposing end of the coil is short circuited to the centre wire.

Typically, when the support is in the form of a core, the core is provided with a slot along the length thereof, or is provided in at least two parts, to allow the same to be placed substantially around the conductor which is to be measured and to ensure that the conductor is held in the correct position along the length of the core. In a preferred embodiment the core is injection moulded from plastics material into the required size and format to suit the proposed use for the same.

It is envisaged that each end of the coil is provided with a location portion which is provided to be engageable with location points on the support thereby ensuring that the ends of the coil are fixed in known positions in use and, in one preferred format, the ends of the coil are fixed so that the ends abut a common line along the length of the support.

The location portions can take one or a combination of different forms including, adhesives for a permanent installation, Velcro to allow removable location, rings or loops which can be attached to the ends of the coil which engage with pegs or hooks mounted on the surface of the support, the ends of the coil can be soldered or welded or otherwise electrically connected to electrical contacts already mounted on the support, a location portion can be attached to the end of the coil which locates in a hole in the support or in the slot provided to allow the support to be mounted over the conductor. Any other suitable location means can of course be used.

In a further aspect of the device there is provided a measuring device for measuring the alternating current in a conductor, said device including a support to be placed substantially around said conductor, and a coil to be wrapped around or within said support and wherein at least one or both of the ends of said coil are selectively engagable with the said support to secure the coil in position wrapped around or within the support for use.

In a yet further aspect of the invention there is provided a method for forming a measuring device for electrical measurement of a conductor, said method comprising placing a support onto and substantially around the conductor to be measured, wrapping a coil, comprising a flexible former with windings of conductive material therearound, around or within the support to pass around said conductor, maintaining the coil in position on the support and connecting the coil to output means to allow signals indicative of the measurement to be transmitted from the coil.

In one alternative embodiment one of the ends of the coil is permanently attached to the support and it is only the opposing end of the coil which is required to be located in position.

Once the device has been used to provide the required measurement at least one end of the coil is disconnected from the support, the coil unwound, the support removed from the conductor whereupon it can then be placed on the next conductor to be measured and the method steps repeated and so on for further conductors. In each case as the position of the ends of the coil are fixed so the device can be relied upon to provide accurate readings each time and thus the device provides the advantage of being reusable in that it can be moved relatively easily between conductors to be measured and the accuracy of the measurements obtained are ensured by the ability to control the position of the coil relative to the support and hence the conductor.

It is envisaged that the device of the invention is particularly suited for use in measuring relatively small alternating currents but this does not limit the scope of the invention.

Specific embodiments of the invention will now be described with reference to the accompanying drawings wherein; Figure 1 illustrates a coil according to the invention in a first form, Figure 2 illustrates the coil of Figure 1 with output wires attached and with location portions threaded on but not yet fixed in place, Figures 3A and 3B illustrate the coil of Figure 1 in a preferred form for use; Figures 4A and 4B illustrates the core of the invention in one embodiment; Figures 5A and 5B illustrate the core in end elevation and sectional elevation along Line A-A respectively; Figures 6A-C illustrate views of a location portion for the coil; and Figures 7A-B illustrate an alternative embodiment of the invention.

Referring firstly to Figure 1 there is illustrated a coil 2 according to the invention, said coil including a former ( not shown) around which is wound a wire 4 of conducting material. Another wire passes axially down the former to utilise the coil 2 as part of the device of the invention, solder portions 6 are applied at each end and at a known distance apart so that the coil can be wound onto the core which is described hereonin. Turning now to Figure 2, location portions 9 are threaded onto respective ends of the coil as shown and one end 8 of the coil is short circuited by applying a wire 10 to connect the centre conductor to the portion of solder 6 and, at the other end 13, output leads 12, 14 are connected to allow signals of the electrical measurements to be transmitted to associated measuring apparatus with one lead 12 attached to the portion of solder 6 and the other to the centre conductor.

The location points 9 are then moved to the ends of the coil 2 as shown in Figure 3 and the output leads 12, 14 threaded through an aperture provided in the location point as shown. Finally, the location portions are secured in position and in line with the solder portions 6 thereby ensuring the correct configuration of the coil when wrapped around the core to which it is to be fitted.

A support of the device is shown in one embodiment in the form of a core 16 in Figures 4A and B and in this case is in the form of a one piece bobbin 18 which is provided with an axial slot 20 which passes from the outer wall 22 to beyond the centre line 24 of the same and this allows the core to be placed onto a conductor 26 which is to be measured. The slot 20 also acts to provide location points 28, 30 for locating portions 9 fitted to the coil which is wrapped around the central body portion 32 as is shown in Figures 5A and B where the device is shown in a formed, in use, condition to measure the conductor 26. The location portions 9 are shown secured in the slot 20 and this holds the coil 2 in the wrapped condition, as shown, around the body 32 of the core.

Figures 6A-C illustrate a location portion 9 in more detail and illustrates the manner in which the provision of the recessed portion 34 allows the positions of the ends 8, 13 of the coil 2 to be secured in position and in line along a common line along the core. Each location portion is provided with an aperture 36 to allow the same to be threaded onto the coil and one portion has a smaller aperture 38 to allow the output leads 12, 14 to be threaded therethrough.. A corner portion 40 of the same can also be cut away to allow the location portions to be more easily inserted into the slot 20 in use and also locates the bobbin centrally on the conductor.

Figures 7A -B illustrate an alternative embodiment of the invention in which the support is provided in the form of a hollow body 116 which defines a hollow cavity 117 in which the coil 102 is wrapped as shown and in a similar form to that shown when the coil 2 is wrapped around the support in the form of the core. In this case the coil has a resilience which tends to force the same against the inner wall 119 of the support and so retain the same in position. An end piece 121 is also provided which can be placed in position to enclose the coil within the cavity for use. Typically both the support 116 and end piece 121 are provided with a slot 120 which allows the same to be placed onto a conductor and with the conductor held along the centre axis of the device for measurement.

Thus, to use the device of the invention as herein described, the conductor to be measured is placed into the slot 20,120 of the support to the appropriate position for measurement. When the support is a core 16 one end of the coil is then attached to one end of the core 16 by placing a location portion 9 into the slot and the coil is then wrapped around the body portion of the core until the second end of the coil lies adjacent the slot whereupon the second location portion 9 is placed into the slot 20 to secure the coil in place in the required position. When the support is hollow 116 the coil is retained in the correct position and the output leads can then be connected to the associated measurement apparatus. Once the measurement is completed the coil is unwound and the conductor can be removed whereupon the device can be placed on the next conductor to be measured and so on.

Thus it will be appreciated that the device according to the invention can be used in many different embodiments, shapes and sizes to suit the types of conductors to be measured and can be used repetitively while ensuring that the configuration of the coil relative to the conductor is the same on each use thereby allowing accurate measurements to be obtained.

Claims

Claims 1. A measuring device comprising a coil formed of an elongate former of flexible material around which is wound a conducting material and, connected thereto, output wires to allow a measurement signal to be transmitted, said coil adapted to be wrapped in a configuration with a support and wherein said coil is selectively locatable with the said support.
2. A measuring device according to claim 1 wherein at least one of the ends of said coil is selectively locatable with a location point on said support.
3. A measuring device according to claim 1 wherein the coil is wrapped around a support in the form of a core.
4. A measuring device according to claim 1 wherein the support is hollow and the coil is housed in the hollow cavity.
5. A measuring device according to claim 4 wherein the coil has a resilient characteristic which tends to force the coil into contact with the inner wall of the support.
6. A measuring device according to claims 3-4 wherein an end piece or end pieces are provided to be fitted onto the support to ensure that the conductor is located in the correct position in relation to the coil.
7. A measuring device according to any of the preceding claims wherein the support is slotted to allow the same to be fitted over the conductor to be measured.
8. A measuring device according to any of the preceding claims wherein each of the ends of the coil are selectively locatable in respective spaced location points on said support and preferably the ends are interchangeable between said location points in repeated use.
9. A measuring device according to claim 8 wherein the ends of the coil are held in the same position upon each use and said location points are provided to ensure the optimum location of each end to ensure that accurate measurements are obtained.
10. A measuring device according to claim 9 wherein the ends of the coil are fixed so that the ends abut a common line along the length of the support.
11. A measuring device according to claims 8-10 wherein the location portions can take one or a combination of different forms including, adhesives for a permanent installation, Velcro to allow removable location, rings or loops which can be attached to the ends of the coil which engage with pegs or hooks mounted on the surface of the support, the ends of the coil can be soldered or welded or otherwise electrically connected to electrical contacts already mounted on the support, a location portion can be attached to the end of the coil which locates in a hole in the support or in the slot provided to allow the support to be mounted over the conductor.
12. A measuring device according to any of the preceding claims wherein when a gap or offset is present between the ends of the coil an additional coil or coils can be connected to provide compensation for the measurement obtained.
13. A measuring device according to claim 1 wherein the coil former has a wire along its centre and output wires are secured to, or adjacent to, one end of the coil and former and the opposing end of the coil is short circuited to the centre wire.
14.A measuring device according to claim 1 wherein the support is provided in at least two parts, to allow the same to be placed substantially around the conductor which is to be measured and to ensure that the conductor is held in the correct position along the length of the support.
15.A measuring device for measuring the alternating current in a conductor, said device including a support to be placed substantially around said conductor, and a coil to be wrapped around or within said support and wherein at least one or both of the ends of said coil are selectively engageable with the said support to secure the coil in position wrapped around or within the support for use.
16. A method for forming a measuring device for electrical measurement of a conductor, said method comprising placing a support onto and substantially around the conductor to be measured, wrapping a coil, comprising a flexible former with windings of conductive material therearound, around or within the support to pass around said conductor, maintaining the coil in position on the support and connecting the coil to output means to allow signals indicative of the measurement to be transmitted from the coil.
17. A method according to claim 16 wherein one of the ends of the coil is permanentlv attached to the support and it is only the opposing end of the coil which is required to be located in position.
1 8. A method according to claim 1 6 wherein once the device has been used to provide the required measurement the coil is unwound, the support removed from the conductor whereupon it can then be placed on the next conductor to be measured and the method steps repeated and so on for further conductors.
19. A method according to claim 18 wherein the position of the ends of the coil are fixed for each use.
20.A measuring device as hereinbefore described with reference to the accompanying drawings.
21.A method of measuring a characteristic of a conductor as hereinbefore described with reference to the accompanying drawings.