GB2345148A - Electric current sensors - Google Patents
Electric current sensors Download PDFInfo
- Publication number
- GB2345148A GB2345148A GB9828191A GB9828191A GB2345148A GB 2345148 A GB2345148 A GB 2345148A GB 9828191 A GB9828191 A GB 9828191A GB 9828191 A GB9828191 A GB 9828191A GB 2345148 A GB2345148 A GB 2345148A
- Authority
- GB
- United Kingdom
- Prior art keywords
- magnetic
- conductor
- gap
- magnetic conductor
- magnetic field
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
- G01R15/245—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect
- G01R15/246—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect based on the Faraday, i.e. linear magneto-optic, effect
Abstract
A magnetic conductor in the form of a ring 1 surrounds a current-carrying conductor 2. A magneto-optic Faraday effect sensor 5 is positioned within a gap 4 within the ring and senses the magnetic field generated by the current flowing in the conductor 2. In an alternative arrangement, the magnetic conductor comprises two ring segments, and the distance between the segments and the current-carrying conductor 2 is measured by an optical time-of-flight sensor. The ends of the magnetic conductor 1 which define the gap may be flat or concave, and the magnetic conductor 1 may be tapered in the vicinity of the gap 4. Suitable materials for the magnetic conductor include iron, ferrite, dielectrics, metal glasses, and a polymer, such as silicon rubber, in which is dispersed powdered dielectric material, such as ferrite. The magnetic material of the magnetic conductor may be retained within a tube of non-magnetic material.
Description
2345148 ELECTRIC CURRENT SENSORS
The present invention relates to apparatus and methods for sensing electric current flowing in electrical conductors, such as high-voltage electric transmission lines, by measuring the magnetic field generated by that current.
There are two known types of such current sensor. In the first type, based on Ampre's law, a determination is made of the amount of magnetic flux associated with the electric current which passes through a loop of known area. The amount of flux is determined by measuring the electric current induced in an electrical conducting ring, such as a Rogowski loop or other suitable secondary winding in a transformer configuration, located at the boundary of the loop. A Rogowski loop comprises a plurality of turns arranged in a toroid such that each turn encircles lines of magnetic flux. In the second type, the magnetic field is measured at a specific position near the electrical conductor.
The first type has the advantage that the precise positioning of the sensor loop is not critical: provided the conducting ring surrounds the electrical conductor, the magnetic field can be determined accurately from a knowledge of the area within the ring, and the result will not be influenced by stray magnetic fields which do not pass through the loop. However, since induced electric current is measured, it is necessary for an electrically conductive loop to be positioned near the main electrical conductor, with the consequential risk of arcing. In addition, the sensing arrangement is limited to measuring alternating current.
The second type of sensor suffers from the disadvantages that (i) an accurate knowledge of the distance between the current-carrying conductor and the magnetic field sensor is required, since the magnetic field varies inversely with the distance from the electrical conductor, and (ii) the magnetic field sensor is sensitive not only to the magnetic field caused by the electric current being measured but also to the magnetic fields caused by other electric currents in the vicinity. There is thus a technical prejudice against the use of the second type of sensor, especially in high-voltage applications, such as power generation, transformation, transmission and distribution.
2 It would be desirable to provide a sensing arrangement which overcomes, or at least mitigates, the above problems.
In accordance with a first aspect of the present invention, there is provided apparatus for measuring the electric current flowing in an electric conductor, the apparatus comprising: a curved magnetic conductor; means for mounting the magnetic conductor in relation to the electric conductor such that the curve of the magnetic conductor substantially follows the curve of the magnetic field generated by the electric current, the magnetic conductor being shaped so as to define a gap; and a magnetic field sensor located within the gap, the arrangement being such that the output of the magnetic field sensor is a measure of the electric current flowing in the electric conductor.
In such an arrangement the magnetic field sensor is sensitive to the field within the gap but relatively insensitive to stray fields.
The magnetic conductor preferably has a substantially circular crosssection.
In a first embodiment, the magnetic conductor is in the form of a complete ring apart from said gap.
In a second embodiment, the magnetic conductor comprises two parts, one at each side of said gap, in which case means are preferably provided for measuring the distance between the magnetic conductor and the electric conductor, such as an electromagnetic radiation, e.g. optical, time-offlight sensor. Such a sensor has the advantage of not being susceptible to adverse weather conditions, since it relies on the speed of light.
The ends of the magnetic conductor which define the gap may be shaped so as to yield a substantially homogeneous magnetic field within the gap.
The ends of the magnetic conductor which define the gap may alternatively be substantially flat.
3 The ends of the magnetic conductor which define the gap are preferably shaped so as to concentrate the magnetic field. For example, the ends may be concave and/or the end regions of the conductor tapered.
The magnetic field sensor may comprise any suitable sensor, such as an inductive-coil sensor, but preferably comprises a magneto-optic sensor, such as a Faraday-effect sensor. Such a sensor can be completely isolated electrically from the electrical conductor and is therefore safe. Furthermore, such a sensor has a large bandwidth and is therefore suitable for measuring high-frequency alternating magnetic fields derived from high-frequency alternating current.
Light is advantageously passed to and from the magnetic field sensor via optic fibres.
Alternatively, the magneto-optic sensor may comprise an optic fibre Bragg grating sensor.
The magnetic conductor may comprise any material having a high magnetic permeability, such as iron. However, since iron is relatively dense, it is preferred that the magnetic conductor comprise a low-density material such as a ferrite. A major advantage of ferrite materials in the present invention is the relatively low density, while maintaining a high value of relative permeability. Suitable values for relative permeability lie within the range 100 to 10,000.
Furthermore, since iron is an electrical conductor, there is the risk of arcing when the apparatus is used to measure current in high-voltage transmission lines. It is therefore preferred to use a dielectric material, such as a ferrite, for the magnetic conductor.
For example, the magnetic conductor may comprise metallic glass or a polymeric material, such as silicon rubber, in which is dispersed and/or dissolved powdered magnetic material, such as a ferrite powder.
Furthermore, the magnetic conductor may comprise magnetic material within a non-magnetic tubular container made of, for example, a polymeric material. In this case, the magnetic material may itself constitute magnetic powder dispersed or 4 dissolved in another polymeric material, such as silicon rubber. The powder can be added to the rubber, which is then left to harden.
In accordance with a second aspect of the present invention, there is provided a method of measuring the electric current flowing in an electric conductor, the method comprising disposing a curved magnetic conductor in relation to the electrical conductor such that the curve of the magnetic conductor substantially follows the curve of the magnetic field generated by the electric current, the magnetic conductor being shaped so as to define a gap; locating within said gap a magnetic field sensor; and generating an output from the magnetic field sensor which is a measure of the electric current flowing in the electric conductor.
Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, wherein:
Figure 1 illustrates a first embodiment of the present invention; Figure 2 illustrates a second embodiment of the present invention; Figure 3(a) illustrates a circuit arrangement for a distance measuring sensor for use with the present invention; Figure 3(b) illustrates an alternative circuit configuration to that of Figure 3(a); Figure 4 illustrates waveforms of signals generated in the circuit arrangements of Figures 3(a) and 3(b); and Figures 5(a) to 5(c) illustrate in partial cross-section three different shapes of the ends of a magnetic conductor for use with either of the two embodiments shown in Figures I and 2; Referring to Figure 1, an electric current sensing arrangement in accordance with the first embodiment comprises a magnetic conductor in the form of a substantially circular ferrite ring I of circular cross-section positioned coaxially around a currentcarrying conductor 2. The ring I is supported on the ground by a support structure 3. The ring has a gap 4 at its lowest point in which a Faraday magneto-optic sensor 5 is positioned. The magnetic conductor 1 serves to guide the magnetic field generated by the electric current to the Faraday sensor 5 in the gap. Light from a light source 6 is passed via a first optic fibre 7 to a polariser 8, and the resulting plane-polarised light is supplied to the Faraday sensor 5. The magnetic field within the gap 4 causes a change in the plane of polarisation of the light by an angle which is proportional to the magnetic field. This phenomenon is known as the Faraday effect. Light leaving the Faraday sensor 5 is passed via a second polariser 9 to a second optic fibre 10, and the angle by which the plane is changed is sensed by measuring the quantity of light received by a photodetector 11.
In a second embodiment, shown in Figure 2, the magnetic conductor is in the form of two ring segments l a, l b which are positioned so as to define a gap in which is positioned a Faraday sensor, as in the arrangement of Figure 1.
In this case, since the magnetic conductor 1 a, 1 b does not form a complete ring around the electric conductor 2, it may be necessary to measure the distance between the magnetic conductor la, lb and the current-carrying conductor 2. An optical distance sensor 12 is provided for this purpose, which is shown in greater detail in Figures 3(a) and 3(b).
Referring to Figure 3(a), the sensor 12 comprises a light source 13, such as a light-emitting diode or laser diode which is supplied with a squarewave signal SW from a square-wave signal generator 14. The square-wave signal SW is also supplied to a phase shifter 15, the output SW of which is supplied to the first input of a phasesensitive detector 16. Light reflected from the current-can-ying conductor 2 is received by a photodetector 17, such as a photodiode, the output signal SW of which is supplied to the second input of the phase-sensitive detector 16. The phase-sensitive detector 16 generates an output signal the magnitude of which is proportional to the phase difference between the signals SW and SW supplied to the first and second inputs respectively. The output signal is fed back to a control input of the phase shifter 15 which introduces a phase shift into the square-wave signal SW which is dependent on the magnitude of the output signal, thus forming a phase-locked loop 18. The output signal from the phase-locked loop 18 is supplied via an electrical filter 19 to an 11.11' 6 amplifier 20, the output signal of which is a measure of the distance between the magnetic conductor 1; 1 a, 1 b and the current-carrying conductor 2.
In an alternative arrangement, as shown in Figure 3(b), both signals SW and SW are supplied to the respective inputs of the phase shifter 15, and the feedback path is eliminated. In this case, the signal SW is the output signal from the detector after amplification in an amplifier 2 1.
Typical waveforms of the two signals supplied to the first and second inputs of the phase-sensitive detector 16 are illustrated in Figure 4. It can be seen that the photodetector output signal SW lags in relation to the square-wave generator output signal SW by an amount to, which is the time taken for the light from the light source 13 to reach the light detector 17 after reflection at the current-carrying conductor 2. The distance r is then given by:
r = c. to / 2, where c is the speed of light. From a knowledge of the distance r, it is then possible to calculate the current flowing in the electrical conductor.
The shape of the two ends of the magnetic conductor I; la, lb may be flat, as shown in Figure 5(a), or may be such as to concentrate the magnetic flux into a relatively small region so as to enhance the sensitivity of the magneto-optic sensor 5. This can be achieved by shaping the end face of the magnetic conductor, as shown in Figure 5(b) and/or by profiling the parts of the magnetic conductor 1; la, lb adjacent the gap 4.
Although the invention has been described with reference to preferred embodiments thereof, many modifications may be made without departing from the scope of the invention. For example, the magnetic field sensor need not be based on the
Faraday effect, but could alternatively comprise any other suitable magnetic field sensor, such as simple inductive coils, Rogowski coils or a Hall-effect sensor.
In addition, the efferent optic fibre 7 could be a polarising optic fibre (PZ optic fibre). Alternatively, the light source 6 could be a laser diode, which has the property of emitting plane-polarised light, and the efferent optic fibre 7 connecting the laser diode to the Faraday sensor 5 could be a polarisation-maintaining optic fibre (PM optic fibre), 7 which has the property of transmitting light in a single polarisation state. In this case, the PM fibre is oriented so that the plane of polarisation of the emitted light coincides with one of the two PM fibre polarisation directions. In either case, there is no need for a separate polariser 8. Furthermore, the afferent optic fibre 10 may be a PZ optic fibre, in which case there is no need for a separate second polariser 9, since the PZ fibre acts as an analysing polariser. Alternatively, the afferent optic fibre 10 could be a PM optic fibre, which has the property of transmitting light in two plane-polarised states. In this case, a second polariser is required, for single-channel detection, or, alternatively, the second polariser 10 is replaced with a polarising beam splitter which directs light of the 10 two polarisation states to two respective photodetectors in a dual-channel arrangement.
8
Claims (30)
1. Apparatus for measuring the electric current flowing in an electric conductor, the apparatus comprising:
a curved magnetic conductor; means for mounting the magnetic conductor in relation to the electric conductor such that the curve of the magnetic conductor substantially follows the curve of the magnetic field generated by the electric current, the magnetic conductor being shaped so as to define a gap; and a magnetic field sensor located within the gap, the arrangement being such that the output of the magnetic field sensor is a measure of the electric current flowing in the electric conductor.
2. Apparatus as claimed in claim 1, wherein said magnetic conductor has a substantially circular cross-section.
3. Apparatus as claimed in claim 1 or claim 2, wherein said magnetic conductor is in the form of a complete ring apart frorn said gap.
4. Apparatus as claimed in claim 1 or claim 2, wherein said magnetic conductor comprises two parts, one at each side of said gap.
5. Apparatus as claimed in claim 4, wherein each of said two parts is of substantially the same length.
6. Apparatus as claimed in claim 4 or claim 5, further comprising means for measuring the distance between the magnetic conductor and the electric conductor.
7. Apparatus as claimed in claim 6, wherein said distance measuring means comprises an electromagnetic radiation time-of-flight sensor.
8. Apparatus as claimed in any preceding claim, wherein said ends of the magnetic conductor which define the gap are shaped so as to yield a substantially homogeneous magnetic field within the gap.
9 9. Apparatus as claimed in any one of claims I to 7, wherein said ends of the magnetic conductor which define the gap are substantially flat.
10. Apparatus as claimed in any one of claims I to 7, wherein said ends of the magnetic conductor which define the gap are shaped so as to concentrate the magnetic field within the gap.
11. Apparatus as claimed in claim 10, wherein said ends of the magnetic conductor are concave.
12. Apparatus as claimed in claim 10 or claim 11, wherein said ends of the magnetic conductor are tapered.
13. Apparatus as claimed in any preceding claim, wherein said magnetic field sensor comprises an inductive-coil sensor.
14. Apparatus as claimed in any preceding claim, wherein said magnetic field sensor comprises a magneto-optic sensor.
15. Apparatus as claimed in claim 14, wherein said magnetic field sensor comprises a Faraday-effect sensor.
16. Apparatus as claimed in any one of claims 13 to 15, wherein light passes to and from the magnetic field sensor using optic fibres.
IT Apparatus as claimed in claim 14, wherein said magneto-optic sensor comprises an optic fibre Bragg grating sensor.
18. Apparatus as claimed in any preceding claim, wherein said magnetic conductor comprises iron.
19. Apparatus as claimed in any one of claims I to 16, wherein said magnetic conductor comprises a dielectric material.
20. Apparatus as claimed in any one of claims I to 16, wherein said magnetic conductor comprises ferrite.
21. Apparatus as claimed in any one of claims 1 to 16, wherein said magnetic conductor comprises metallic glass.
22. Apparatus as claimed in any one of claims 1 to 16, wherein said magnetic conductor comprises polymeric material in which is dispersed powdered magnetic material.
23. Apparatus as claimed in claim 22, wherein said powdered material is a ferrite.
24. Apparatus as claimed in claim 22 or claim 23, wherein said polymeric material comprises silicon rubber.
25. Apparatus as claimed in any preceding claim, wherein said magnetic conductor comprises magnetic material within a non-magnetic tubular container.
26. Apparatus as claimed in claim 25, wherein said tubular container comprises a polymeric material.
27. Apparatus as claimed in any preceding claim, wherein the magnetic conductor comprises magnetic material having a relative permeability within the range 100 to 10,000.
28. A method of measuring the electric current flowing in an electric conductor, the method comprising:
disposing a curved magnetic conductor in relation to the electric conductor such that the curve of the magnetic conductor substantially follows the curve of the magnetic field generated by the electric current, the magnetic conductor being shaped so as to define a gap; locating within said gap a magnetic field sensor; and generating an output from the magnetic field sensor which is a measure of the electric current flowing in the electric conductor.
29. Apparatus for measuring the electric current flowing in an electric conductor substantially as hereinbefore described with reference to the accompanying drawings.
11
30. A method of measuring the electric current flowing in an electric conductor substantially as hereinbefore described with reference to the accompanying drawings.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9828191A GB2345148A (en) | 1998-12-21 | 1998-12-21 | Electric current sensors |
| AU17919/00A AU1791900A (en) | 1998-12-21 | 1999-12-21 | Electric current sensors |
| PCT/IB1999/002080 WO2000037948A1 (en) | 1998-12-21 | 1999-12-21 | Electric current sensors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9828191A GB2345148A (en) | 1998-12-21 | 1998-12-21 | Electric current sensors |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9828191D0 GB9828191D0 (en) | 1999-02-17 |
| GB2345148A true GB2345148A (en) | 2000-06-28 |
Family
ID=10844699
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9828191A Withdrawn GB2345148A (en) | 1998-12-21 | 1998-12-21 | Electric current sensors |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU1791900A (en) |
| GB (1) | GB2345148A (en) |
| WO (1) | WO2000037948A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102021111412A1 (en) | 2021-05-03 | 2022-11-03 | Phoenix Contact Gmbh & Co. Kg | Current measuring system for measuring a current flowing through an electrical current conductor and a corresponding method |
| LU102798B1 (en) | 2021-05-03 | 2022-11-03 | Phoenix Contact Gmbh & Co | Current measuring system for measuring a current flowing through an electrical current conductor and a corresponding method |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2015174A (en) * | 1978-02-22 | 1979-09-05 | Gen Electric Co Ltd | Current Transducer |
| EP0242560A1 (en) * | 1986-04-25 | 1987-10-28 | VDO Adolf Schindling AG | Arrangement for the contactless measuring of an electric current in a conductor |
| JPS6385377A (en) * | 1986-09-30 | 1988-04-15 | Toshiba Corp | Apparatus for evaluating semiconductor memory |
| US4894608A (en) * | 1987-07-22 | 1990-01-16 | Square D Company | Electric current sensor using the faraday effect |
| GB2228337A (en) * | 1989-02-18 | 1990-08-22 | Diehl Gmbh & Co | Hall-effect apparatus for measuring direct current |
| EP0521250A2 (en) * | 1991-07-03 | 1993-01-07 | Landis & Gyr Business Support AG | Current measuring transducer using a magnetic field sensor |
| US5438256A (en) * | 1992-07-06 | 1995-08-01 | Gec Alsthom T & D Sa | Apparatus and method for measurement from the ground for high voltage overhead lines |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH03216558A (en) * | 1990-01-23 | 1991-09-24 | Tokin Corp | Photocurrent sensor |
| JPH07333254A (en) * | 1994-06-13 | 1995-12-22 | Yaskawa Electric Corp | Optical current sensor |
| JPH08304469A (en) * | 1995-04-28 | 1996-11-22 | Toshiba Corp | Current sensor |
-
1998
- 1998-12-21 GB GB9828191A patent/GB2345148A/en not_active Withdrawn
-
1999
- 1999-12-21 AU AU17919/00A patent/AU1791900A/en not_active Abandoned
- 1999-12-21 WO PCT/IB1999/002080 patent/WO2000037948A1/en active Application Filing
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2015174A (en) * | 1978-02-22 | 1979-09-05 | Gen Electric Co Ltd | Current Transducer |
| EP0242560A1 (en) * | 1986-04-25 | 1987-10-28 | VDO Adolf Schindling AG | Arrangement for the contactless measuring of an electric current in a conductor |
| JPS6385377A (en) * | 1986-09-30 | 1988-04-15 | Toshiba Corp | Apparatus for evaluating semiconductor memory |
| US4894608A (en) * | 1987-07-22 | 1990-01-16 | Square D Company | Electric current sensor using the faraday effect |
| GB2228337A (en) * | 1989-02-18 | 1990-08-22 | Diehl Gmbh & Co | Hall-effect apparatus for measuring direct current |
| EP0521250A2 (en) * | 1991-07-03 | 1993-01-07 | Landis & Gyr Business Support AG | Current measuring transducer using a magnetic field sensor |
| US5438256A (en) * | 1992-07-06 | 1995-08-01 | Gec Alsthom T & D Sa | Apparatus and method for measurement from the ground for high voltage overhead lines |
Non-Patent Citations (1)
| Title |
|---|
| Patent Abstracts of Japan & JP 63 085 377 A * |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2000037948A1 (en) | 2000-06-29 |
| GB9828191D0 (en) | 1999-02-17 |
| AU1791900A (en) | 2000-07-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |