GB2245704A - Current sensor - Google Patents
Current sensor Download PDFInfo
- Publication number
- GB2245704A GB2245704A GB9014761A GB9014761A GB2245704A GB 2245704 A GB2245704 A GB 2245704A GB 9014761 A GB9014761 A GB 9014761A GB 9014761 A GB9014761 A GB 9014761A GB 2245704 A GB2245704 A GB 2245704A
- Authority
- GB
- United Kingdom
- Prior art keywords
- fibre
- conductor
- shield
- portions
- spaced
- 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.)
- Granted
Links
- 239000000835 fiber Substances 0.000 claims abstract description 42
- 239000004020 conductor Substances 0.000 claims abstract description 33
- 230000000737 periodic effect Effects 0.000 claims abstract description 15
- 239000013307 optical fiber Substances 0.000 claims abstract description 13
- 230000003287 optical effect Effects 0.000 claims abstract description 3
- 239000003973 paint Substances 0.000 claims description 3
- 229910000859 α-Fe Inorganic materials 0.000 claims description 3
- 238000010408 sweeping Methods 0.000 claims description 2
- 238000000034 method Methods 0.000 abstract description 2
- 230000008878 coupling Effects 0.000 description 3
- 238000010168 coupling process Methods 0.000 description 3
- 238000005859 coupling reaction Methods 0.000 description 3
- 239000011324 bead Substances 0.000 description 2
- 229910001369 Brass Inorganic materials 0.000 description 1
- 208000032365 Electromagnetic interference Diseases 0.000 description 1
- 229920005439 Perspex® Polymers 0.000 description 1
- 230000008033 biological extinction Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- CPBQJMYROZQQJC-UHFFFAOYSA-N helium neon Chemical compound [He].[Ne] CPBQJMYROZQQJC-UHFFFAOYSA-N 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000004926 polymethyl methacrylate Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 230000002463 transducing effect Effects 0.000 description 1
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
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
Abstract
Apparatus for measuring a current in a conductor, comprising an optical source feeding a high birefringent optical fibre positioned adjacent to a portion of the conductor, means to apply a field produced by the current in the conductor to the fibre in a periodic manner so as to couple with the light signal therein, and means to monitor the signal when output from the fibre. One manner of applying the periodic field to the optical fibre is to provide an incomplete shield between the fibre and the conductor. An alternative method is to provide a portion of the conductor configured so as to provide spaced conductor portions each disposed at an angle to the fibre axis. <IMAGE>
Description
Current Sensor
The present invention relates to apparatus which can be used to determine the value of an electric current in a conductor.
In particular, the present invention relates to a sensor which utilises Faraday rotation of a signal in a birefringent optical fibre. Faraday rotation occurs when polarised light in an optical fibre is affected by a longitudinal field such as the magnetic field produced by the passage of a current through a conductor. The effect is to cause the input polarisation of light of in a fibre to differ from the output polarisation from the fibre, such that the magnitude of the field can be determined.
Traditionally, electric current is measured with a current transformer which makes use of magnetic induction, or the change in magnetic field, to measure the current.
However, these devices tend to be large, expensive and of bandwidth which limits the range of applications where such devices are useful or cost effective. A number of optical-fibre current sensing devices has previously been proposed in which the optical fibre acts as both the current transducing element and the information transmission medium.
The optical fibre is an electrically and chemically passive device and is therefore free from electro-magnetic interference, electrical short circuit hazards, and is suitable for long haul use in inaccessible and hostile environments such as inside a sub-station or a power station.
Such optical-fibre sensors have used low birefringent fibres, which wrap around the current-carryinging conductor.
However, the accuracy of such sensors is reduced by unintentional perturbation of the fibre. Both temperature fluctuations and asymmetrical pressure imposed on the fibre will lead to noise on the output signal, constituting a major drawback in low birefringence versions of the devices.
The present idea has arisen in an attempt to provide an optical-fibre current sensor which obviates or mitigates these problems.
In accordance with the present invention, there is provided apparatus for measuring a current in a conductor, comprising an optical source feeding a high birefringent optical fibre positioned adjacent to a portion of the conductor, means to apply a field produced by the current in the conductor to the fibre in a periodic manner so as to couple resonantly with the light signal therein, and means to monitor the signal when output from the fibre.
One manner of applying the periodic field to the optical fibre is to provide an incomplete shield between the fibre and the conductor. An alternative method is to provide a portion of the conductor configured so as to provide spaced conductor portions each disposed at an angle to the fibre axis. The periodic field is applied in order that resonant coupling should take place. Resonance occurs when the spatial period of the magnetic field is equal to the birefringence beat length of the fibre.
Where a shielding arrangement is used, the shield preferably comprises a plurality of substantially regularlyor irregularly- spaced shield portions around the fibre. The shield portions can comprise spaced ferrite rings around the fibre or spaced bands of conductive paint on the fibre.
Alternatively, the shield can comprise a shield body having a plurality of substantially regularly spaced slots therein.
Where the configured conductor arrangement is used, the spacing of the conductor portions can also be substantially regular.
In both cases, the spacing is typically close to the birefringence beat length of the fibre. Within one unit, the spacing can be varied such that the range of spacings corresponds to the range of beat lengths encountered in normal use due to temperature variation. Where the conductor portions or the slots are regularly spaced, the path of the fibre can be non-linear in order to provide a suitable range of spatial period to account for temperature variation.
The source is conveniently arranged to provide a plurality of different wave lengths at around the beat length of the fibre. This can be achieved by either sweeping or jittering a narrow band source, or alternatively by providing a wide band source.
The present invention will now be described by way of example, with reference to the accompanying drawings, in which:- Figure 1 shows a diagrammatic representation of an apparatus according to all aspects of the present invention;
Figures 2 to 4 show alternative manners of providing a periodic field on the fibre; and
Figure 5 shows the variation of coupling efficiency against current.
Referring now Figure 1, the arrangement shown therein comprises a Spectra Physics model 1051 helium neon laser with an output wavelength of 633 nm. This provides a coherent signal to a high birefringent fibre, with wavelength measurement via a Bentham Model 300 monochromator (slit width of 0.37 mm giving 1 nm resolution). The fibre is an Andrew
Corporation high birefringent fibre having an extinction ratio of 36 dB, a core of 1 micron by 2 microns and a beat length Lb of 3.8 mm. The fibre leads the signal to a periodic arrangement A via a Corman Instruments 158 WM25 1/4 wave plate, a Carl Lambrecht MGT 25A10 Glan Thompson
Polariser, a x40 Kyowa Strain free objective lens and a mode stripper.
The periodic arrangement comprises a perspex base through which the fibre is directed. 44 conductors in the form of 1.5 mm brass rods are embedded in the base and are parallel and spaced at regularly intervals of 3.88 mm. The conductors lie substantially at right angles to the line of the fibre but the angle can be varied by rotation of the arrangement with respect to the fibre. The conductors are joined in series and arranged to operate at up to 10 amps RMS on 50 Hz A/C supply and have a resistance of 0.6 ohms.After passing through the periodic structure A, the fibre passes another mode stripper, a x20 objective lens and in to a final polariser/analyser which compares the output rotation with the input rotation and provides an appropriate electrical signal enabling the calculation of the current from 0 = VNI wherein 0 = the angle of rotation relative to the input N = the number of conductor passes and'I = current.
Figures 2 to 4 show alternatives to the periodic structure A. In Figure 2, the fibre has annular ferrite beads 10 spaced apart thereon to provide a periodic shielding pattern when the fibre is laid alongside a conductor (not shown). The field between the beads is shown by the arrows.
In Figure 3, the shielding is achieved by bands of conductive paint 12, which gives the periodic variation in the H field as shown in the graph below.
Figure 4 shows a further alternative in which slots 14 are provided in bus bar 16 and the fibre F is led past the slots substantially at right angles thereto.
Coupling can be affected by temperature variation causing changes in the length of the fibre and hence in the beat length Lb. This may be overcome in several ways. The laser signal source can be swept or jittered to give various wavelengths of signal which in turn will give various beat lengths. Alternatively a broad bandwidth source such as a superluminescent diode could be used. A further alternative is to provide a range of conductor spacings or to make the fibre path curve passed the conductors in a predetermined manner.
It will be appreciated that variations can be made while remaining within the scope of the invention.
Claims (12)
1. Apparatus for measuring a current in a conductor, comprising an optical source feeding a high birefringent optical fibre positioned adjacent to a portion of the conductor, means to apply a field produced by the current in the conductor to the fibre in a periodic manner so as to couple with the light signal therein, and means to monitor the signal when output from the fibre.
2. Apparatus as claimed in claim 1, wherein the periodic field is applied to the optical fibre by means of an incomplete shield between the fibre and the conductor.
3. Apparatus as claimed in claim 1, wherein a portion of the conductor is configured so as to provide spaced conductor portions each disposed at an angle to the fibre axis to provide said periodic field.
4. Apparatus as claimed in claim 2, wherein the shield comprises a plurality of substantially regularly spaced shield portions around the fibre.
5. Apparatus as claimed in claim 4, wherein the shield portions comprise spaced ferrite rings around the fibre or spaced bands of conductive paint on the fibre.
6. Apparatus as claimed in claim 2, wherein the shield comprises a shield body having a plurality of substantially regularly spaced slots therein.
7. Apparatus as claimed in claim 3, wherein the spacings of the conductor portions are substantially regular.
8. Apparatus as claimed in claim 3 or 4, wherein a range of spacings is provided corresponding to the range of beat lengths encountered in use due to temperature variation.
9. Apparatus as claimed in claim 8, wherein the conductor portions, or shield portions are regularly spaced and the path of the fibre is non-linear with respect thereto in order to provide a range of spacings.
10. Apparatus as claimed in any preceding claim, wherein the source is arranged to provide a plurality of different wavelengths to correspond to the range of beat lengths in the fibre.
11. Apparatus as claimed in claim 10, wherein the plurality of wavelengths is achieved by sweeping or jittering a narrow band source, or by providing a wide band source.
12. Apparatus which is substantially as herein described in relation to Figure 1-5 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9014761A GB2245704B (en) | 1990-07-03 | 1990-07-03 | Current sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9014761A GB2245704B (en) | 1990-07-03 | 1990-07-03 | Current sensor |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9014761D0 GB9014761D0 (en) | 1990-08-22 |
| GB2245704A true GB2245704A (en) | 1992-01-08 |
| GB2245704B GB2245704B (en) | 1993-12-01 |
Family
ID=10678606
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9014761A Expired - Fee Related GB2245704B (en) | 1990-07-03 | 1990-07-03 | Current sensor |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2245704B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0826971A2 (en) * | 1996-08-30 | 1998-03-04 | Kabushiki Kaisha Toshiba | Optical current transformer |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2033601A (en) * | 1978-08-16 | 1980-05-21 | Max Planck Gesellschaft | Fibre optical arrangement for measuring the intensity of an electric current |
| GB2104213A (en) * | 1981-08-12 | 1983-03-02 | Giers | Electric current measurement |
| GB2168807A (en) * | 1984-12-21 | 1986-06-25 | Robin David Birch | Optical fibres and methods of manufacture thereof |
-
1990
- 1990-07-03 GB GB9014761A patent/GB2245704B/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2033601A (en) * | 1978-08-16 | 1980-05-21 | Max Planck Gesellschaft | Fibre optical arrangement for measuring the intensity of an electric current |
| GB2104213A (en) * | 1981-08-12 | 1983-03-02 | Giers | Electric current measurement |
| GB2168807A (en) * | 1984-12-21 | 1986-06-25 | Robin David Birch | Optical fibres and methods of manufacture thereof |
Non-Patent Citations (1)
| Title |
|---|
| Proc. IEE. vol.123, No.10, October 1976. A.J.Rogers.pages 957-960. * |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0826971A2 (en) * | 1996-08-30 | 1998-03-04 | Kabushiki Kaisha Toshiba | Optical current transformer |
| EP0826971A3 (en) * | 1996-08-30 | 1999-03-31 | Kabushiki Kaisha Toshiba | Optical current transformer |
| US6281672B1 (en) | 1996-08-30 | 2001-08-28 | Kabushiki Kaisha Toshiba | Optical current transformer |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9014761D0 (en) | 1990-08-22 |
| GB2245704B (en) | 1993-12-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20040703 |