DE102005003200B4 - Circuit for measuring electrical currents in electrical conductors with optical fibers - Google Patents

Abstract

Circuit arrangement for measuring electrical currents in electrical conductors with optical waveguides, containing as a measuring part
A light source for generating a polarized measuring light,
A polarizer connected to the light source by means of an optical waveguide,
An optical fiber measuring coil wound with a number of turns N around an electrical conductor leading to the current i to be measured,
An analyzer to which the optical fiber measuring coil is guided,
A light receiver with an evaluation device, the light receiver being associated with the analyzer,
characterized,
the light source (2) is connected obliquely at an angle φ to the following polarizer (3) which is favored for the z-direction, and a first coupler (9) is connected between the polarizer (3) and the optical waveguide measuring coil (5) ) and between the optical waveguide measuring coil (5) and the analyzer (7), a second coupler (10) are arranged, wherein the coupler (9, 10) associated with a measuring part (11) directed in parallel, both sides of the reflection-free compensation part (16). ..

Description

• – eine Lichtquelle zum Erzeugen eines polarisierten Messlichts,
• – einen Polarisator, der mit der Lichtquelle verbunden ist,
• – eine Lichtwellenleiter-Messspule, die mit einer Windungszahl N um einen den zu messenden Strom i führenden elektrischen Leiter gewickelt ist,
• – einen Analysator, an den die Lichtwellenleiter-Messspule geführt ist, und
• – einen Lichtempfänger mit einer Auswerteeinrichtung, wobei der Lichtempfänger dem Analysator zugeordnet ist.

The invention relates to a circuit arrangement for measuring electrical currents in electrical conductors with optical waveguides, containing as a measuring part

• A light source for generating a polarized measuring light,
• A polarizer connected to the light source,
• An optical fiber measuring coil wound with a number of turns N around an electrical conductor leading to the current i to be measured,
• An analyzer to which the optical fiber measuring coil is guided, and
• - A light receiver with an evaluation, wherein the light receiver is associated with the analyzer.

Such a circuit arrangement with optical waveguides for measuring electrical currents in an electrical conductor is in the document US Pat. No. 3,605,013 described. The circuit arrangement consists essentially of a laser diode, a polarizer, an analyzer and a light receiver with a connected evaluation device, wherein between the laser diode and the light receiver, a fiber optic optical waveguide connects the intermediate components together. The optical waveguide connecting the polarizer and the analyzer spirally surrounds the electrical conductor with at least one turn as an optical waveguide measuring coil.

spreads linearly polarized light of the laser diode in the optical waveguide out, so the polarization remains. When in the electrical conductor Electricity flows, a magnetic field is generated. The magnetic field rotates the polarization plane of the linearly polarized light due to the Faraday effect. The bigger the Value of the electric current, the larger the magnetic field and the longer the path in the optical fiber is the stronger the rotation of the polarization plane. Consequently, from the rotation angle α of Polarization level of the value of the electric current i determined become.

• – einer Lichtquelle zum Erzeugen eines polarisierten Messlichts,
• – einer Messspule aus einer optischen Faser mit vielen Windungen, die um einen elektrischen Leiter gewickelt sind, in dem der zu messende elektrische Strom i fließt, wobei die Windungen derart angeordnet sind, dass das von der Lichtquelle emittierte polarisierte Licht um den Leiter im Kreis geführt wird, so dass die Polarisationsebene des polarisierten Messlichts durch das von dem elektrischen Strom erzeugte Magnetfeld gedreht wird, und
• – Messmittel zur Bestimmung des elektrischen Stromes durch Erfassen des Drehwinkels α der Polarisationsebene,

wobei die optische Messspule ein mit der Lichtquelle verbundenes Eingangsende und ein mit dem Messmittel verbundenes Ausgangsende aufweist,
wobei das Eingangsende und das Ausgangsende auf eine solche Art und Weise angeordnet sind, dass ein durch Betrachten der beiden Enden von der Mitte des Leiters erhaltener Winkel nicht mehr als 1% von 2πn ist, und wobei das Eingangsende und das Ausgangsende in einem einzigen, aus einem magnetischen Material hergestellten Element enthalten ist.It is an optical current sensor in the document EP 0 826 971 B1 described, which is provided with

• A light source for generating a polarized measuring light,
• - A measuring coil of a multi-turn optical fiber, which are wound around an electrical conductor in which the electrical current to be measured i flows, wherein the windings are arranged such that the polarized light emitted from the light source is circulated around the conductor is rotated so that the polarization plane of the polarized measuring light is rotated by the magnetic field generated by the electric current, and
• Measuring means for determining the electric current by detecting the angle of rotation α of the polarization plane,

the optical measuring coil having an input end connected to the light source and an output end connected to the measuring means,
wherein the input end and the output end are arranged in such a manner that an angle obtained by observing the both ends from the center of the conductor is not more than 1% of 2πn, and wherein the input end and the output end are in a single, off contained element made of a magnetic material.

there The optical fiber and the light source are connected to each other by a first optical coupling element while the optical fiber and the measuring means to each other through a second optical coupling system are connected.

One Problem is that the first and the second optical Coupling systems are contained in one element.

Further, a method and apparatus for measuring disturbance oscillations with fiber optic coils that conduct circularly polarized light are disclosed US 4,922,095 described. A circularly polarized light source propagates light in a fiber optic sensing coil in a noise sensitive environment and in a fiber optic reference coil in a constant environment. The light from both coils is evaluated by a polarization device to register the degree of polarization rotation to allow determination of the frequency and amplitude of the disturbance vibration.

One Problem is that with it no continuous electrical Electricity can be measured.

It is a fiber optic magnetic field sensor for determining electrical currents in the document DE 37 26 411 A1 described in which the magnetic field-dependent Faraday rotation of the plane of polarization of a linearly polarized light beam propagating in an optical waveguide is measured. However, the Faraday rotation caused by the magnetic field is superimposed with linear and circular birefringence properties of the optical waveguide, which make it difficult to measure the Faraday rotation and, in addition, are still dependent on environmental influences.

To belongs an arrangement with heterodyne reception and reciprocal light path, the a measurement of the Faraday rotation without being influenced by linear and almost without interference from circular birefringence components of the optical waveguide allows.

One Problem is that several photodiodes with in practice find different properties use.

• – wenigstens zwei, dem Stromleiter zugeordnete Faraday-Elemente,
• – Mittel zum Einkoppeln von linear polarisiertem Messlicht in ein erstes der Faraday-Elemente,
• – optische Verbindungsmittel, über die das erste Faraday-Element mit einem zweiten der Faraday-Elemente optisch in Reihe geschaltet ist und die das durch das erste Faraday-Element gelaufene Messlicht in einen ersten Teil und wenigstens einen weiteren Teil aufteilen,
• – einer ersten Auswerteeinheit zum Auswerten der Faraday-Drehung der Polarisationsebene von dem ersten, nur durch das erste Faraday-Element wenigstens einmal gelaufenen Teil des linear polarisierten Messlichts als Maß für einen Strom aus einem ersten Messbereich,
• – für jeden weiteren Messbereich jeweils einer Auswerteeinheit zum Auswerten der Faraday-Drehung der Polarisationsebene von jeweils einem durch das erste Faraday-Element und wenigstens ein weiteres Faraday-Element wenigstens einmal gelaufenen, weiteren Teil des Messlichts als Maß für einen Strom aus diesem weiteren Messbereich.

Another arrangement for measuring electrical currents from at least two measuring ranges in a current conductor is in the document EP 0 776 477 B1 described. The arrangement has the following components:

• At least two Faraday elements associated with the conductor,
• Means for coupling linearly polarized measuring light into a first of the Faraday elements,
• Optical connecting means, via which the first Faraday element is optically connected in series with a second one of the Faraday elements and which divide the measuring light passed through the first Faraday element into a first part and at least one further part,
• A first evaluation unit for evaluating the Faraday rotation of the polarization plane from the first part of the linearly polarized measurement light which has passed at least once only by the first Faraday element as a measure of a current from a first measurement range,
• For each further measuring range, in each case one evaluation unit for evaluating the Faraday rotation of the polarization plane of a further part of the measuring light which has passed at least once through the first Faraday element and at least one further Faraday element as a measure of a current from this further measuring range.

One The problem is that several photodiodes are used.

on the other hand provides the measurement of electrical currents at any potential at insertion the known circuit arrangement in the electrical circuit a fundamental Problem of metrology dar.

The The problem is that the known circuit arrangements for measuring the electric current only by a complex signal processing and then only approximately with the disadvantages that the fluctuating birefringence itself in the approximation is included in the measured value or the relationship between measured value and measurand nonlinear is, have.

Of the Invention is based on the object, a circuit arrangement for Measurement of electrical currents specify in electrical conductors with optical fibers, the like is suitably designed that in a simple manner in the isolated Measurement of electrical currents without intervention in the electrical circuit of the measured variable fluctuating birefringence and temperature fluctuations compensated become.

• – eine Lichtquelle zum Erzeugen eines polarisierten Messlichts,
• – einen Polarisator, der mit der Lichtquelle mittels eines Lichtwellenleiters verbunden ist,
• – eine Lichtwellenleiter-Messspule, die mit einer Windungszahl N um den zu messenden Strom i führenden elektrischen Leiter gewickelt ist,
• – einen Analysator, an den die Lichtwellenleiter-Messspule geführt ist, und
• – einen Lichtempfänger mit einer Auswerteeinrichtung, wobei der Lichtempfänger dem Analysator zugeordnet ist,

wobei gemäß dem Kennzeichenteil des Patentanspruchs 1 die Lichtquelle schräg unter einem Winkel φ an den nachfolgenden Polarisator, der für die z-Richtung favorisiert ist, angeschlossen ist sowie zwischen dem Polarisator und der Lichtwellenleiter-Messspule ein erster Koppler und zwischen der Lichtwellenleiter-Messspule und dem Analysator ein zweiter Koppler angeordnet sind, wobei die Koppler einem zum Messteil parallel gerichteten, beidendseitig reflexionsfreien Kompensationsteil zugeordnet sind, in dem sich zwischen den Kopplern eine Lichtwellenleiter-Kompensationsspule, die mit einer zweiten Windungszahl N₀ um einen zweiten elektrischen Leiter gewickelt ist, der einen Strom i₀ führt, angekoppelt befindet, wobei die Koppler jeweils zur Gegenseite der Ankopplung der Lichtwellenleiter-Kompensationsspule reflexionsfreie Abschlüsse aufweisen, wobei dem zweiten elektrischen Leiter eine Auswerteeinrichtung zugeordnet ist, die mit dem Lichtempfänger des Analysators in Verbindung steht und einen Messwert i_R des Stromes i₀ erzeugt, so dass ein Messwert i_F des Stromes i aus der Gleichung

in der Auswerteeinrichtung ermittelbar ist, wobei der am Ende des optischen Teils angeordnete Analysator die x-Komponente D_x und die y-Komponente D_y der elektrischen Verschiebungsflussdichte unterdrückt und nur bei deren z-Komponente einen Photostrom i_ph liefert, der einen Regelkreis steuert, der der Lichtwellenleiter-Kompensationsspule zugeordnet ist, wobei der Strom i durch den elektrischen Leiter eine Führungsgröße – gemessen als Messwert i_F – und der Strom i₀ durch den zweiten elektrischen Leiter eine Regelgröße – gemessen als Messwert i_R – darstellen.The object is achieved with a circuit arrangement according to the first claim. The circuit arrangement for measuring electrical currents i in electrical conductors with optical waveguides contains as a measuring part

• A light source for generating a polarized measuring light,
• A polarizer connected to the light source by means of an optical waveguide,
• An optical fiber measuring coil wound with a number of turns N around the electric current to be measured i,
• An analyzer to which the optical fiber measuring coil is guided, and
• A light receiver with an evaluation device, the light receiver being associated with the analyzer,

wherein according to the characterizing part of claim 1, the light source is obliquely connected at an angle φ to the subsequent polarizer, which is favored for the z-direction, and between the polarizer and the optical fiber measuring coil, a first coupler and between the optical fiber measuring coil and the Analyzer, a second coupler are arranged, wherein the couplers are assigned to a parallel measuring part, both sides end reflection-free compensation part, in which between the couplers, an optical fiber compensation coil, which is wound with a second winding number N ₀ to a second electrical conductor, the one Current i ₀ leads coupled, the coupler each have to the opposite side of the coupling of the optical fiber compensation coil reflection-free terminations, wherein the second electrical conductor is associated with an evaluation that st with the light receiver of the analyzer in conjunction eht and a measured value i _{R of} the current i _{0 is} generated, so that a measured value i _{F of} the current i from the equation

can be determined in the evaluation device, wherein the analyzer arranged at the end of the optical part suppresses the x-component D _x and the y-component D _{y of} the electrical shift flux density and supplies only at its z-component a photocurrent i _ph which controls a control loop, is associated with the optical waveguide compensation coil, wherein the current i through the electrical conductor, a reference variable - measured as measured value i _F - and the current i ₀ through the second electrical conductor a controlled variable - measured as measured value i _R - represent.

The Light source may preferably be a laser diode.

At the input port of the polarizer, an input signal of the polarizer has an electrical shift _{flux density} with the components D _xin , D _yin parallel to the associated input _port as well as the component D _zin perpendicular to the parallel components D _xin , D _yin .

Of the Polarizer has a first Jones matrix J according to the equation

At the output port of the polarizer, an output signal has an electrical displacement _{flux density} with the components D _xout , D _yout , D ' _{zout of} the polarizer, where D' _{zout represents} the z component of the shift _{flux density} at the output of the polarizer.

The two couplers each have two input ports and two output ports on, with each associated input / output gates opposite to each other in the optical wave direction and the input / output ports are equally spaced from each other.

The first coupler is preferably a three dB coupler with Θ ₁ = π / 4, where Θ _{1 represents} an associated first coupling angle.

The second coupler is a three dB coupler with Θ ₂ = π / 4, where Θ _{2 represents} an associated second coupling angle.

The output signal at the output port of the polarizer corresponds to the input signal for the first three dB coupler with the first coupling angle Θ ₁ = π / 4.

All Components of the output signals can each be used as a function represent the z component.

There are at the second input port of the first coupler a reflection-free first termination and the first output port of the first coupler, the optical fiber measuring coil, a second Jones matrix J = J (α) and a first z-component transfer function T _z = T. _z (α) in dependence on the first rotation angle α of the polarization plane of the undeflected light wave and the number of turns N are connected.

To the second output port is wound around the second electrical conductor Lichtwellenlei connected, the second winding number N ₀ , a third Jones matrix J ₀ = J ₀ (α ₀ ) and a second z-component transfer function T _z0 = T _z0 (α ₀ ) in response to the second rotation angle α ₀ are assigned to the polarization plane of the deflected light wave.

The optical waveguide measuring coil and the optical waveguide compensation coil are connected to the second three-dB coupler with the second coupling angle Θ ₂ = π / 4, which has a reflection-free second termination to the input side, opposite second input port of the second coupler as a second output port.

Connected to the first output port of the second coupler as the analyzer is a z-component analyzer, which generates the components of the electrical displacement flux density D _xin , D _yin generated by the laser diode via the polarizer, the first coupler, the optical fiber coils and the second Coupler are transmitted, suppressed and converts only the z component of the electrical displacement _{flux density} D _zout in the associated light receiver in the photocurrent i _ph .

The following equation exists between the z-component D ' _zout or the z-component D _zin and the z-component D _{zout of} the electrical displacement _{flux density} . D ' zout = ½ D zout (III).

For the entire z-component transfer function T _zges , the equation applies: T CGUs = D zout / D zin (IV), where also the equation T CGUs = ½ cosΘ 1 T z cos 2 - ½ sinΘ 1 T z0 sinΘ 2 (V) applies.

The Evaluation device may include an integrator of a control loop.

The integrator receiving the photocurrent i _ph (t) can be designed in such a way that the permanent control deviation, ie the difference between the rotational angles α (t) -α ₀ (t), approaches _zero as a function of the settling time t with t approaches infinity, and on the output side, the integrator supplies the measured value i _{R of} the current i ₀ , in order to determine therefrom the measured value i _{F of} the current i.

liegt ein optischer Transformator vor, wobei in den beiden Lichtwellenleiter-Spulen der Faraday-Effekt zur Drehung der Polarisationsebenen der in den Lichtwellenleiter-Spulen laufenden Lichtwellen um den jeweiligen Drehwinkel α, α₀ vorhanden ist und die sich ausbildenden Drehwinkel α, α₀ stromproportional dem Messwert i_F bzw. dem Messwert i_R entsprechend den Proportionalitäten α ~ i und α₀ ~ i₀ sind.According to the equation

is an optical transformer, wherein in the two optical fiber coils of the Faraday effect for rotating the polarization planes of the current in the optical fiber coils light waves around the respective rotation angle α, α _{0 is} present and the forming angle of rotation α, α ₀ current proportional to the Measured value i _F or the measured value i _R corresponding to the proportionalities α ~ i and α ₀ ~ i ₀ .

The circuit arrangement is thus according to the invention of an oblique excitation of the circuit arrangement by a laser diode, the oblique excitation through the φ by the predetermined angle dimensioned closed coupling point for generating a z-component D _z as a longitudinal component of the electrical displacement flux density of the emitted light wave leads. The z-component D _{z of} the electrical displacement flux density is favored by the definition of an x, y, z-coordinate system in which the z-coordinate is optionally determined as a longitudinal coordinate. Finally, only the z-component transfer function is used for the optical part of the circuit.

The circuit arrangement essentially provides, in addition to the fiber optic optical waveguide measuring coil, a fiber optic optical waveguide compensation coil. The arranged in the end of the optical part of the circuit analyzer in the form of the z-component analyzer suppresses the x-component D _x and the y-component D _{y of} the electrical shift flux density and provides only for the z-component of a photocurrent i _ph . The photocurrent i _ph controls a control loop, which is cut to size the optical waveguide compensation coil and supplies the measured value i _R.

at the circuit arrangement according to the invention is therefore essential that only the z component of the electrical Displacement flux density Since ultimately finds use. Consequently Here is a simple scalar compensation condition. Other solutions are difficult to fulfill, because these then on the compensation of all four matrix elements based on the Jones matrix.

When Faraday effect is called the phenomenon in which the vibration plane linearly polarized light passing through a magnetic field is turned. The angle of rotation - the Faraday angle - is proportional to the scalar product of the magnetization and the propagation vector of the light as well as the length of the magnetic field.

A Jones matrix is a two-dimensional matrix, which is used for representation the polarization of plane electromagnetic waves is used. The Jones formalism is particularly suitable for the analysis of optical systems in which a polarized light beam goes through a cascade of optical components.

Thereby, that only the generated z-components of the electrical displacement flux density ultimately find use arises for the fiber optic circuitry a simple scalar compensation condition.

The Invention allows a simple structure of a circuit arrangement, which also for the isolated Current measurement is used.

The inventive circuit arrangement is suitable both for measuring very small currents in the mA range and for Measurement of very high currents in the kA range and is also in a big one Frequency range can be used.

The Current measurement is without insertion the circuit arrangement in the electrical circuit on any, in particular to high voltage potential possible, with appropriate retrofit conditions already existing plants can be carried out.

Compared to the usual classical converters or transformers saves space and it does not need oil or other critical materials for insulation. This results in an environmentally friendly and explosion-proof circuit arrangement for measuring electrical currents.

further developments and advantageous embodiments of the invention are in further dependent claims specified.

The Invention is based on an embodiment closer by means of several drawings explained.

It demonstrate:

1 a schematic representation of a circuit arrangement for measuring electrical currents in electrical conductors with optical fiber coils and an associated x, y, z coordinate system in 1a .

2 a diagram of an integrator with optical fiber compensation coil, wherein the wound of the optical fiber compensation coil electrical conductor is connected to ground on one side, and a formula in 2a and

3 a circuit diagram of an integrator with a "floating" fiber optic compensation coil, wherein the wound of the optical fiber compensation coil electrical conductor is connected to the output of a second operational amplifier, and a formula in 3a ,

• – eine Lichtquelle 2 zum Erzeugen eines polarisierten Messlichts,
• – einen Polarisator 3, der mit der Lichtquelle 2 mittels eines Lichtwellenleiters 4 verbunden ist,
• – eine Lichtwellenleiter-Messspule 5, die mit einer ersten Windungszahl N um einen den zu messenden Strom i führenden ersten elektrischen Leiter 6 gewickelt ist,
• – einen Analysator 7, an den die Lichtwellenleiter-Messspule 5 geführt ist, und
• – einen Lichtempfänger mit einer Auswerteeinrichtung 8, wobei der Lichtempfänger dem Analysator 7 zugeordnet ist.

In 1 is a schematic representation of a circuit arrangement 1 for measuring electrical currents i in an electrical conductor 6 shown. The circuit arrangement 1 contains as a measuring part 11

• - a light source 2 for generating a polarized measuring light,
• - a polarizer 3 that with the light source 2 by means of an optical waveguide 4 connected is,
• - An optical fiber measuring coil 5 having a first number of turns N around a first electrical conductor leading to the current i to be measured 6 is wrapped
• - an analyzer 7 to which the optical fiber measuring coil 5 is guided, and
• - A light receiver with an evaluation 8th wherein the light receiver is the analyzer 7 assigned.

in der zugehörigen Auswerteeinrichtung 8 ermittelbar ist, wobei der am Ende des optischen Teils 11, 16 der Schaltungsanordnung 1 angeordnete Analysator 7 die x-Komponente D_x und die y-Komponente D_y der elektrischen Verschiebungsflussdichte unterdrückt und nur für deren z-Komponente einen Photostrom i_ph liefert, der einen Regelkreis steuert, der der Lichtwellenleiter-Kompensationsspule 12 zugeordnet ist, wobei der Strom i durch den ersten elektrischen Leiter 6 eine Führungsgröße – gemessen als Messwert i_F – und der Strom i₀ durch den zweiten elektrischen Leiter 15 eine Regelgröße – gemessen als Messwert i_R – darstellen.According to the invention, the light source 2 obliquely at an angle φ to the following polarizer 3 , which is favored for the z-direction, connected as well as between the polarizer 3 and the optical fiber measuring coil 5 a first coupler 9 and between the optical fiber measuring coil 5 and the analyzer 7 a second coupler 10 arranged, the couplers 9 . 10 one to the measuring part 11 parallel-directional compensation part free from reflection on both sides 16 are assigned, in which between the two couplers 9 . 10 an optical fiber compensation coil 12 having a second winding number N ₀ around a second electrical conductor 15 is wound, which carries a current i ₀ , coupled, the couplers 9 . 10 in each case to the opposite side of the coupling of the optical waveguide compensation coil 12 reflection-free terminations 13 . 14 have, wherein the second electrical conductor 15 an evaluation device 8th associated with the light receiver of the analyzer 7 is connected and generates a measured value i _{R of} the current i ₀ , so that a measured value i _{F of} the current i from the equation

in the associated evaluation device 8th can be determined, wherein the at the end of the optical part 11 . 16 the circuit arrangement 1 arranged analyzer 7 suppresses the x-component D _x and the y-component D _{y of} the electrical displacement flux density and provides only for the z-component of a photocurrent i _ph , which controls a control loop, that of the optical fiber compensation coil 12 is assigned, wherein the current i through the first electrical conductor 6 a reference variable - measured as measured value i _F - and the current i ₀ through the second electrical conductor 15 represent a controlled variable - measured as measured value i _R -.

The light source 2 may be a laser diode.

At the entrance gate 17 of the polarizer 3 For example, an input signal has an electrical shift flux density with the associated input port 17 parallel components D _xin , D _yin and the D _xin , D _yin vertical component D _zin on.

The polarizer 3 has a first Jones matrix J according to the equation

At the exit gate 18 of the polarizer 3 An output signal has an electrical displacement _{flux density} with the components D _xout , D _yout , D ' _{zout of} the polarizer 3 on, according to equation D ' zout = ½ D zout (III) where D _{zout is} the final z-component of the electrical displacement _{flux density} D ' _zout in the associated light receiver of the z-component analyzer.

The couplers 9 . 10 each have two entrance gates 19 . 21 and two exit gates 20 . 22 on, with each associated input / output gates 19 . 20 in the lightwave direction and the input / output ports 19 . 21 ; 20 . 22 are equally spaced in parallelism to each other.

The first coupler 9 may preferably be a three dB coupler with Θ ₁ = π / 4, where Θ _{1 represents} a first coupling angle.

This corresponds to the output signal at the output gate 18 of the polarizer 3 the input signal for the first three dB coupler 9 with the first coupling angle Θ ₁ = π / 4.

It is the second entrance gate 21 of the first coupler 9 a first anechoic conclusion 13 and to the first exit gate 20 of the first coupler 9 an electrical conductor which guides the current i to be measured as a reference variable 6 wound optical waveguide - the optical fiber measuring coil 5 - Connected to a second Jones matrix J = J (α), a first z-component transfer function T _z = T _z (α) and the first number of turns M are assigned.

To the second exit gate 22 of the first coupler 9 is the one around the second electrical conductor 15 wound optical waveguide compensation coil 12 connected, the second winding number N ₀ , a third Jones matrix J ₀ = J ₀ (α ₀ ) and a second z-component transfer function T _z0 = T _z0 (α ₀ ) are assigned.

The on the optical fiber compensation coil 12 Related control circuit operates on the basis of an integrating operational amplifier principle.

The second coupler 10 is a three-dB coupler with Θ ₂ = π / 4, where Θ _{2 represents} a second coupling angle.

Generally holds that the coupling angle Θ = σ L, where σ is the coupling coefficient and L represent the coupling length.

The fiber optic measuring coil 5 and the optical fiber compensation coil 12 are on the input side to the second DreidB coupler 10 connected to the second coupling angle Θ ₂ = π / 4, the second output gate 26 a reflection-free second degree 14 to its entrance, opposite entrance gate 24 has.

• – Gleiche Länge L,
• – gleiche Hauptbrechzahlen n_x, n_y,
• – gleiche Verdetkonstante V,
• – gleiche Doppelbrechung δ und
• – unterschiedliche Windungszahlen N, N₀.

Preferably, the optical fiber measuring coil 5 and the optical fiber compensation coil 12 have the following parameters:

• - same length L,
• - same main refractive indices n _x , n _y ,
• The same Verdetkonstante V,
• - same birefringence δ and
• - Different numbers of turns N, N ₀ .

The two couplers 9 and 10 can preferably be set to the same coupling angle Θ ₁ = π / 4 and Θ ₂ = π / 4.

For the entire z-component transfer function T _zges , the equation applies: T CGUs = D zout / D zin (IV), wherein also taking into account the z-component transfer function T _{z of} the measuring part 11 and considering a z-component transfer function T _{z0 of} the compensation part 16 the equation T CGUs = ½ cosΘ 1 T z cos 2 - ½ sinΘ 1 T z0 sinΘ 2 (V) applies.

The optical couplers 9 . 10 in 1 have the following functions:
The first coupler 9 evaluates all components of the input signal either with the cosine function or the sine function as a function of the set coupling angle Θ ₁ . So that the input polarization at the outputs - the output gates 20 . 22 - the first coupler 9 it has to stay the same as the second coupler 10 be polarization preserving. The second coupler 10 carries the signals out of the fiber optic coils 5 . 12 and evaluates with sine function or cosine function as a function of the set second coupling angle Θ ₂ together for evaluation in the z-component analyzer 7 , With the two couplers 9 . 10 is also the minus sign in the difference of the total z-component transfer function T _zges by exploiting the properties of the imaginary unit j in the sine functions of the coupler transfer functions between the individual ports of the coupler 9 . 10 set.

Furthermore, to the first exit gate 25 of the second coupler 10 the z-component analyzer 7 connected to that of the laser diode 2 generated components of the electrical displacement _{flux density} D _xin , D _yin , via the polarizer 3 , the first coupler 9 , the fiber optic coils 5 . 12 and the second coupler 10 be suppressed, whereby only the z-component of the electrical displacement _{flux density} D _{zout is converted} in the associated light receiver in the photocurrent i _ph .

The evaluation device 8th may preferably represent an integrator.

The associated control loop works in its stability behavior on the basis of "Harmoni balance with transients, where finally the measured value i _R in the compensation section 16 measured in the steady state.

In 2 is the integrator 8th the compensation coil 12 assigned to the unilaterally connected to ground second electrical conductor 15 umwindet. The integrator 8th in 2 consists essentially of a first operational amplifier 28 one in between its inverting input 33 and his exit 31 parallel connected capacitor 29 and one at its exit 31 connected, in series downstream resistance 30 , The resistance 30 stands with the optical fiber compensation coil 12 associated second electrical conductor 15 in connection, which rests on ground. At the exit 31 of the first operational amplifier 28 the measuring voltage u _{Mess is} tapped.

Using the same reference numerals is in 3 an integrator 8th present, its associated second electrical conductor 15 unlike 2 not to ground, but to the exit 34 a second operational amplifier 32 is fed so that a "floating" fiber optic compensation coil 12 is present. The inputs of the second operational amplifier 32 are its inverting input 35 that with the output of the resistor 30 connected, and its non-inverting input 36 which rests against the earth.

With both integrators 8th can after the 2a . 3a from the resistance value R, the capacitor value C and the time profile of the photocurrent i _ph (t), the measured value i _{R of} the current i ₀ according to the equation i 0 = 1 / RC ∫ i ph (t) dt + c (VI) be determined.

In addition, the photocurrent is i _ph (t) in the z-component analyzer 7 proportional to the difference between the two angles of rotation α, α ₀ according to the relationship: i ph (t) ~ [α (t) - α 0 (T)] 2 ,

The integrator receiving the photocurrent i _ph (t) 8th is thus designed such that the permanent control deviation, ie the difference of the rotation angle α (t) -α ₀ (t) as a function of the settling time t with t towards infinity, approaches zero and the integrator on the output side the measured value i _{R of} the current i _{0 in} order to determine the measured value i _{F of} the current i from this.

liegt in der Schaltungsanordnung 1 ein optischer Transformator vor, wobei der Faraday-Effekt zur Drehung der Polarisationsebenen der in der Messspule 5 und der Kompensationsspule 12 getrennt laufenden Lichtwellen um die Faraday-Winkel α, α₀ – als erster Drehwinkel α und zweiter Drehwinkel α₀ bezeichnet – vorhanden ist und die sich ausbildenden Drehwinkel α, α₀ stromproportional dem Messwert i_F im Messteil 11 bzw. dem Messwert i_R im Kompensationsteil 16 entsprechend den Proportionalitäten α ~ i und α₀ ~ i₀ sind.According to the equation

lies in the circuit arrangement 1 an optical transformer, wherein the Faraday effect for rotating the polarization planes of the in the measuring coil 5 and the compensation coil 12 separated current light waves by the Faraday angle α, α ₀ - as the first rotation angle α and second rotation angle α ₀ - is present - and the forming rotation angle α, α ₀ current proportional to the measured value i _F in the measuring section 11 or the measured value i _R in the compensation part 16 corresponding to the proportionalities α ~ i and α ₀ ~ i ₀ .

In the following, the operation of the circuit arrangement according to the invention 1 for measuring electrical currents i in an electrical conductor 6 explained with optical waveguides: Essential for the starting position is an oblique excitation of the circuit arrangement 1 through a laser diode 2 and thus the generation of the z-component D _z as a longitudinal component of the electrical displacement flux density. The oblique excitation is by a closed Einkoppelstelle 27 reached, in which at a certain angle φ the light source 2 and the polarizer 3 Axially related to each other.

This results in a continuous and final use of the first z-component transfer function T _{z of} the measuring coil 5 for the optical measuring part 11 the circuit arrangement 1 ,

The second scalar z-component transfer function T _z0 is the compensation part 16 assigned.

This exploitation of the compensation principle for the two scalar z-components ten transfer functions T _z , T _{z0 of} the measuring part 11 and the compensation part 16 the circuit arrangement 1 ,

This is a simple stable control loop with the switched integrator 8th used for the substantial elimination of the remaining control deviation α (t) -α ₀ (t) with t → ∞.

The circuit arrangement 1 can be adjusted by the exact adjustment of the angle φ of the oblique excitation relatively easily. The measured values i _R are available under the given conditions after a settling time t of less than 1 s.

By taking into account the Faraday effect for current-proportional rotation of the polarization planes in the similar optical waveguide coils - the optical fiber measuring coil 5 and the optical fiber compensation coil 12 - Separate current light waves, the rotation of the polarization planes along the z-direction is compared.

In this case, a simple linear relationship between the measured value i _{F of} the current i and the measured value i _{R of} the current i ₀ by the proportionality factor - the number of turns N / N ₀ - of the two associated optical fiber coils 5 . 12 taught.

gegeben ist.This also means that the invention enables the circuit arrangement 1 eliminates all adverse effects, such as the birefringence of similar optical fibers and thus a linear relationship between the current i and the current i ₀ by the number of turns in the form

given is.

1

circuitry

2

light source

3

polarizer

4

first optical fiber

5

Fiber optic measuring coil

6

first electrical conductor

7

analyzer

8th

evaluation

9

first coupler

10

second coupler

11

measuring unit

12

Optical fiber compensating coil

13

first graduation

14

second graduation

15

second electrical conductor

16

compensation part

17

front gate of the polarizer

18

output gate of the polarizer

19

first Entrance gate of the first coupler

20

first Output gate of the first coupler

21

second Entrance gate of the first coupler

22

second Output gate of the first coupler

23

first Entrance gate of the second coupler

24

second Entrance gate of the second coupler

25

first Output gate of the second coupler

26

second Output gate of the second coupler

27

coupling point

28

first operational amplifiers

29

capacitor

30

resistance

31

output

32

second operational amplifiers

33

inverting entrance

34

output

35

inverting entrance

36

inverting entrance

i

electricity in the first electrical conductor

i _f

reading of the current i

J

first Jones matrix

J (α)

second Jones matrix

T _z (α)

first z-component transfer function

T _zges

all z-component transfer function

N

first number of turns

N ₀

second number of turns

i ₀

electricity in the second electrical conductor

i _f

Measured value of the current i ₀

J ₀ (α ₀ )

third Jones matrix

T _z0 (α ₀ )

second z-component transfer function

α

first angle of rotation

α ₀

second angle of rotation

Θ ₁

first coupling angle

Θ ₂

second coupling angle

φ

angle

R

resistance

C

capacitor value

U _Mess

measuring voltage

_ph

photocurrent

t

Time

Claims (21)

Circuit arrangement for measuring electrical currents in electrical conductors with optical waveguides, comprising as measuring part - a light source for generating a polarized measuring light, - a polarizer which is connected to the light source by means of an optical waveguide, - an optical waveguide measuring coil having a number of turns N to a the electrical conductor to be measured is wound, an analyzer, to which the optical waveguide measuring coil is guided, a light receiver with an evaluation device, wherein the light receiver is associated with the analyzer, characterized in that the light source ( 2 ) obliquely at an angle φ to the following polarizer ( 3 ), which is favored for the z-direction, is connected and between the polarizer ( 3 ) and the optical fiber measuring coil ( 5 ) a first coupler ( 9 ) and between the optical fiber measuring coil ( 5 ) and the analyzer ( 7 ) a second coupler ( 10 ), the couplers ( 9 . 10 ) one to the measuring part ( 11 ) parallel directed, on both sides reflection-free compensation part ( 16 ), in which between the couplers ( 9 . 10 ) an optical fiber compensation coil ( 12 ) having a second number of turns N ₀ around a second electrical conductor ( 15 ), which carries a current i ₀ , is coupled, the couplers ( 9 . 10 ) each to the opposite side to the coupling of the optical fiber compensation coil ( 12 ) reflection-free statements ( 13 . 14 ), wherein the second electrical conductor ( 15 ) an evaluation device ( 8th ) associated with the light receiver of the analyzer ( 7 ) and generates a measured value i _{R of} the current i ₀ , so that the measured value i _{F of} the current i from the equation

in the evaluation device ( 8th ) can be determined, wherein the at the end of the optical part ( 11 . 16 ) analyzer ( 7 ) suppresses the x-component D _x and the y-component D _{y of} the electrical displacement flux density and provides only at the z-component of a photocurrent i _ph , which controls a control loop of the optical fiber compensation coil ( 12 ), wherein the current i through the electrical conductor ( 6 ) a reference variable - measured as measured value i _F - and the current i ₀ through the second electrical conductor ( 15 ) represent a controlled variable - measured as measured value i _R -. Circuit arrangement according to Claim 1, characterized in that the light source ( 2 ) is a laser diode. Circuit arrangement according to claim 1 or 2, characterized in that at the entrance gate ( 17 ) of the polarizer ( 3 ) an input signal an electrical displacement flux density with the associated input gate ( 17 ) parallel components D _xin , D _yin and the component D _zin , which is perpendicular to the parallel components D _xin , D _yin . Circuit arrangement according to any preceding claim, characterized in that the polarizer ( 3 ) a first Jones matrix J according to the equation

has. Circuit arrangement according to one of the preceding claims, characterized in that at the output gate ( 18 ) of the polarizer ( 3 ) an output signal an electrical displacement _{flux density} with the components D _xout , D _yout , D ' _{zout of} the polarizer ( 3 ), wherein according to equation D ' zout = ½ D zout (III) where D _{zout is} the final z-component of the electrical displacement _{flux density} D ' _zout in the associated light receiver of the z-component analyzer ( 7 ). Circuit arrangement according to one of the preceding claims, characterized in that the couplers ( 9 . 10 ) two entrance gates ( 19 . 21 ) and two exit gates ( 20 . 22 ), wherein the respectively assigned input / output gates ( 19 . 20 ) in the optical wave direction and the input / output ports ( 19 . 21 ; 20 . 22 ) are equally spaced in parallelism with each other. Circuit arrangement according to one of the preceding claims, characterized in that the first coupler ( 9 ) is a three dB coupler with Θ ₁ = π / 4, where Θ _{1 represents} a first coupling angle. Circuit arrangement according to one of the preceding claims, characterized in that the second coupler ( 10 ) is a three dB coupler with Θ ₂ = π / 4, where Θ _{2 represents} a second coupling angle. Circuit arrangement according to any preceding claim, characterized in that the output signal at the output gate ( 18 ) of the polarizer ( 3 ) the input signal for the first three dB coupler ( 9 ) corresponds to the first coupling angle Θ ₁ = π / 4. Circuit arrangement according to one of the preceding claims, characterized in that the second input gate ( 21 ) of the first coupler ( 9 ) a first anechoic conclusion ( 13 ) and to the first exit gate ( 20 ) of the first coupler ( 9 ) the optical fiber measuring coil ( 5 ), which are associated with a second Jones matrix J = J (α) and a first z-component transfer function T _z = T _z (α) in dependence on the first rotation angle α of the plane of polarization of the undeflected light wave and the number of turns N. are. Circuit arrangement according to one of the preceding claims, characterized in that the second output port ( 22 ) of the first coupler ( 9 ) around the second electrical conductor ( 15 ) wound optical fiber compensation coil ( 12 ), the second winding number N ₀ , a third Jones matrix J ₀ = J ₀ (α ₀ ) and a second z-component transfer function T _z0 = T _z0 (α ₀ ) in dependence on the second rotation angle α ₀ are assigned to the polarization plane of the deflected light wave. Circuit arrangement according to one of the preceding claims, characterized in that the optical waveguide measuring coil ( 5 ) as well as the optical waveguide compensation coil ( 12 ) on the input side to the second three dB coupler ( 10 ) are connected to the second coupling angle Θ ₂ = π / 4, the second off Gangstor ( 26 ) a reflection-free second degree ( 14 ) to its optical fiber compensation coil ( 12 ), input side, opposite second input port ( 24 ) owns. Circuit arrangement according to one of the preceding claims, characterized in that the optical waveguide measuring coil ( 5 ) and the optical fiber compensation coil ( 12 ) optionally have the following parameters: - equal length L, - same main refractive indices n _x , n _y , - same Verdetkonstante V, - same birefringence δ and - have different numbers of turns N, N ₀ . Circuit arrangement according to one of the preceding claims, characterized in that, for the entire z-component transfer function T _zges , taking into consideration the z-component transfer function T _{z of} the measuring part ( 11 ) and taking into account the z-component transfer function T _{z0 of} the compensation part ( 16 ) the equation T CGUs = ½ cosΘ 1 T z cos 2 - ½ sinΘ 1 T z0 sinΘ 2 (V) applies. Circuit arrangement according to one of the preceding claims, characterized in that the evaluation device ( 8th ) has a control loop including an integrator. Circuit arrangement according to Claim 15, characterized that the control loop has a stability behavior based on the "harmonics Balance "with transients. Circuit arrangement according to Claim 15 or 16, characterized in that the integrator ( 8th ) essentially from a first operational amplifier ( 28 ), one between the inverting input ( 33 ) and the output ( 31 ) parallel-connected capacitor ( 29 ) and one at the exit ( 31 ) on closed, series-connected resistance ( 30 ), the resistance ( 30 ) with the compensation coil ( 12 ) associated second electrical conductor ( 15 ), which is connected to ground, and at the output ( 31 ) of the first operational amplifier ( 28 ) the measuring voltage u _{Mess is} tapped. Circuit arrangement according to claim 17, characterized in that the second electrical conductor ( 15 ) the output ( 34 ) of a second operational amplifier ( 32 ), whereby a "floating" optical fiber compensation coil ( 12 ) and wherein the inputs of the second operational amplifier ( 32 ) whose inverting input ( 35 ) connected to the output of the resistor ( 30 ) and its noninverting input ( 36 ), on which the mass is applied, are. Circuit arrangement according to claim 17 or 18, characterized in that with the integrator ( 8th ) from the resistance value R, from the capacitor value C and from the course of the photocurrent i _ph (t) the measured value i _{R of} the current i ₀ according to the equation i 0 = 1 / RC ∫ i ph (t) dt + c (VI) can be determined. Circuit arrangement according to one of the preceding claims, characterized in that the integrator receiving the photocurrent i _ph (t) ( 8th ) is designed such that the permanent control deviation, ie the difference of the rotation angle α (t) -α ₀ (t) in dependence on the settling time t with t to infinity, goes to zero and the integrator ( 8th ) supplies the measured value i _{R on the} output side. Circuit arrangement according to claim 1 to 20, characterized in that according to the equation

an optical transformer is present, wherein the Faraday effect for rotating the polarization planes of the in the optical fiber measuring coil ( 5 ) and the optical fiber compensation coil ( 12 ) separated current light waves around the respective rotation angle α, α ₀ - the associated Faraday angles - is present, wherein the forming angles of rotation α, α ₀ proportional to the current measurement i _F in the measuring part ( 11 ) or the measured value i _R in the compensation part ( 16 ) corresponding to the proportionalities α ~ i and α ₀ ~ i ₀ .