Optically-based electric current metering system and use thereof

Abstract

The invention relates to an optically-based electric current metering system and to the use thereof.

Description

[0001]Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -1- Optically based current measuring system and its use The invention relates to an optically based current measuring system and its use. Background of the invention In many areas of energy technology it is necessary or desirable to measure current. Measuring high voltages always presents a challenge in order to avoid endangering users. To achieve this, a high level of insulation is necessary. Typically, insulating oils are used to achieve high insulation capacity, which provide good galvanic isolation. However, oils cannot be used everywhere without further ado, as they can pose a danger to the environment.Unlike electrical sensors, optical sensors generally require less effort for galvanic isolation because the materials used already have intrinsic insulating properties. This means that, where necessary, the amount of insulating oil can be kept to a minimum. Conventional inductive converters cannot be used, particularly for measuring currents in high-voltage direct current networks. However, optical sensors can be used here. Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -2- One possibility for providing such sensors is sensors that utilize the Faraday effect.For example, German patent application DE 43 34 469 A1 discloses a polarimetric, fiber-optic current transformer consisting of a sensor head located at high-voltage potential in the immediate vicinity of the current conductor and an evaluation unit positioned in the station (or control room), with optical waves from a laser being coupled into the sensor head. Furthermore, German patent application DE 19517128 A1 discloses an arrangement for measuring an alternating magnetic field that utilizes the magneto-optical Faraday effect. The Faraday effect is a magneto-optical effect that describes the rotation of the polarization plane of a linearly polarized electromagnetic wave in a medium when a magnetic field parallel to the wave's propagation direction prevails in the medium. Most dielectric materials exhibit the Faraday effect when exposed to a strong magnetic field.The rotation of the polarization plane is greater, the stronger the magnetic flux density. The angle of rotation β by which the polarization plane rotates is calculated as follows: β = V ⋅ d ⋅ B, where d is the length of the light path through the substance, B is the magnetic flux density, and V is the Verdet constant. The Verdet constant V depends on the medium and the wavelength. A positive Verdet constant leads to a mathematically negative rotation if the magnetic field is parallel to the direction of propagation, while an antiparallel magnetic field leads to a mathematically positive rotation. If a wave passes through the medium in forward and backward directions, it rotates twice by the same angle, unlike left- or right-rotating waves. Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -3- Substances with optical activity, for which passing through the medium in the opposite direction would reverse the rotation. Magnetometers and current sensors are manufactured based on this effect, using fiber optic cables. Two methods exist for measuring electrical currents using the Faraday effect. Firstly, the Faraday effect leads to the rotation of a linearly polarized light wave, whereby the electrical current in the small-signal range is proportional to the angle of rotation. The evaluation can thus be carried out using polarizers. Secondly, the Faraday effect leads to a phase shift between two oppositely circularly polarized light waves. The phase shift can be evaluated interferometrically or polarimetrically. Due to the reciprocal design of the interferometers, the interferometric determination of the phase shift is complex and cost-intensive.The well-known polarimetric evaluation of the phase shift requires the placement of a λ / 4 plate in the optical beam path to constantly shift both waves by 90° relative to each other. However, the use of crystals and prisms destabilizes the sensor over the operating temperature range between -40°C and 85°C. Solutions are also presented that use so-called polarization splitters. These solutions are also intrinsically temperature-dependent in the splitter and must be temperature-compensated. Optical current sensors must be compensated for the temperature fluctuations of the magneto-optical coupling. Likewise, the optical and electrical components of the sensor must be compensated for the temperature fluctuations. Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measurement system and its use Application number: Subsequent application to DE 102023205899.5 -4- The long-term stability of the sensor is particularly critical in direct current measurement technology. Long-term destabilization of the sensor occurs due to thermal destabilization of the electro-optical receiver, the optical source, reduced / increased magneto-optical coupling (Faraday effect), temperature influences, vibrations along the measuring fiber optic cable, or temperature-dependent linear birefringence along the measuring fiber optic cable. The sensors used in these applications are also expensive and highly complex. Due to their high complexity, the technology can be used by network operators, but not for independent commissioning or maintenance in the event of complications. European Patent EP 2870485 B1, for example, is known from the prior art. This patent describes a polarimetric optical current sensor with inherent and extrinsic temperature compensation.With extrinsic temperature compensation, a delay element in front of the measuring coil is suitably distorted so that the temperature affects the delay of the element and compensates for it with the Faraday effect. Furthermore, it should be noted that with polarimetric optical current sensors based on a full-glass body, coupling and decoupling optical radiation into and out of the sensitive element is particularly difficult, since even slight mechanical vibrations of the glass body can trigger the protective device. Determining the deviation and producing it is extremely complex to this extent and requires sophisticated and cost-intensive technology. Interferometric variants also require increased modulation effort, making them generally even more expensive than polarimetric variants.Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -5- Further costs can arise from the fact that special connection technologies, complicated evaluation technology and complicated temperature compensation technologies are required to increase the measurement accuracy. Furthermore, the European patent EP 2966459 B1 is known from the prior art, in which a similar method for alternating current measurement technology is presented. This method and device cannot be used for direct current technology. Against this background, the object of the invention is to provide a current measuring system that is cost-effective and more temperature-stable than previous solutions. This object is achieved by an optically based current measuring system according to claim 1 and.the use of such an optically based current measuring system according to claims 11 and 12. Further advantageous embodiments are the subject matter of the dependent claims. The invention is explained in more detail below with reference to the figures. These show: Fig. 1 a first schematic representation of aspects according to embodiments of the invention, and Fig. 2 a second schematic representation of aspects according to embodiments of the invention. Detailed description of the invention The invention is described in more detail below with reference to the figures. It should be noted that different aspects are described, which can each be used individually or in combination. This means that any aspect can be used with different embodiments of the invention, unless explicitly shown as a pure alternative.Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -6- Furthermore, for the sake of simplicity, reference will generally only be made to one entity below. Unless explicitly stated, the invention may, however, also comprise several of the entities concerned. In this respect, the use of the words “a”, “an” and “an” is to be understood only as an indication that at least one entity is used in a simple embodiment. Where methods are described below, the individual steps of a method can be arranged and / or combined in any desired order, unless the context explicitly indicates otherwise. Furthermore, the methods can be combined with one another unless expressly stated otherwise.Numerical values ​​are generally not to be understood as exact values, but also include a tolerance of + / - 1% up to + / - 10%. Reference to standards or specifications is to be understood as reference to standards or specifications that apply / applied at the time of the application and / or – if priority is claimed – at the time of the priority application. However, this does not imply a general exclusion of applicability to subsequent or replacing standards or specifications. Embodiments of the invention are explained below with reference to the figures. An exemplary optically based current measuring system according to the invention is shown in Figure 1. The optically based current measuring system according to the invention has a quasi-monochromatic light source 1, a polarizer 2, a first non-polarizing beam splitter 4.1 and a second non-polarizing beam splitter 4.2.Furthermore, the optically based current measuring system according to the invention has a linear, highly birefringent element 8 and an element for generating a circular polarization 9, wherein the element for generating a circular polarization 9 Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -7- is arranged adjacent to a current conductor L to be measured. In addition, the optically based current measuring system according to the invention has a measuring element with a Faraday effect 10 (at least in sections adjacent to a current conductor L to be measured) and a reflector 11. In operation, light from the light source 1 is first guided through the polarizer 2 to the first non-polarizing beam splitter 4.1, wherein the (proportionately) non-polarizing beam splitter 4.1 reflected light is guided through the linearly highly birefringent element 8 and the subsequent element for generating circular polarization 9, wherein the reflector 11 is arranged after the element for generating circular polarization 9, so that incoming light is again guided through the element for generating circular polarization 9 and the linearly highly birefringent element 8 back to the first non-polarizing beam splitter 4.1. During operation, however, the light transmitted through the first non-polarizing beam splitter 4.1 is also (proportionately) guided to a second beam splitter 4.2. The optically based current measuring system according to the invention further comprises a first delay element 5.1 and a second delay element 5.2, wherein the first delay element 5.1 and the second delay element 5.2 are of the same type or different.The optically based current measuring system according to the invention further comprises a first polarizing beam splitter 7.1 with at least one first optical output O1 and one second optical output O2 and a second polarizing beam splitter 7.2 with at least one first optical output O3 and one second optical output O4, as well as an opto-electronic conversion unit (not shown in Figure 1), wherein the first delay element 5.1 is arranged in the transmitting branch of the second beam splitter 4.2, and the second delay element 5.2 is arranged in the reflecting branch of the second beam splitter 4.2, wherein the first polarizing beam splitter 7.1 is arranged downstream of the first delay element 5.1, and the second polarizing beam splitter 7.2 is arranged downstream of the second delay element 5.1.Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -8- The first delay element 5.1 is arranged at a different angle than the second delay element 5.2 with respect to a similarly incident polarized light, wherein the first polarizing beam splitter 7.1 is arranged at a different angle than the second polarizing beam splitter 7.2 with respect to a similarly incident polarizing light. During operation, the opto-electronic conversion unit evaluates light from the optical outputs of the first polarizing beam splitter 7.1 and the second polarizing beam splitter 7.2 in order to obtain a temperature-dependent signal in order to be able to reduce temperature-related errors in measuring the Faraday effect due to current flow in the current conductor to be measured.Parts of the current sensor can be provided integrated on a single micro-optical assembly OSA. This micro-optical assembly OSA can, for example, be provided with optical connectors (for single-mode fibers) in order to connect, for example, a light source 1 or one (or more) opto-electronic conversion unit(s) to the optical outputs O1... O4. In one embodiment of the invention, the linearly highly birefringent element 8 comprises a HiBi fiber. According to a further embodiment of the invention, the element for generating circular polarization 9 comprises a delay element, in particular a λ / 4 plate. In a further embodiment of the invention, the delay element is also arranged in spatial proximity to the linearly highly birefringent element 8, so that the delay element and the linearly highly birefringent element 8 have essentially the same temperatures.Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -9- In yet another embodiment of the invention, the measuring element with Faraday effect has a glass fiber, in particular a glass fiber coil around the current conductor to be measured. According to yet another embodiment of the invention, the first delay element 5.1 and the second delay element 5.2 each have a λ / 4 plate. In another embodiment of the invention, the order of the first delay element 5.1 and the order of the second delay element 5.2 are the same. However, it can also be provided in alternative embodiments of the invention that the order of the first delay element 5.1 and the order of the second delay element 5.2 are different.According to a further embodiment of the invention, the optoelectronic conversion unit comprises a photodiode. In yet another embodiment of the invention, the first non-polarizing beam splitter 4.1 and the second non-polarizing beam splitter 4.2, as well as the first delay element 5.1 and the second delay element 5.2, are arranged in a micro-optical assembly OSA. Additional elements can easily be provided in the current sensor as well as in the micro-optical assembly OSA. For example, lenses 3, in particular gradient index lenses, can be part of the current sensor as well as in particular of the micro-optical assembly OSA. Likewise, the current sensor and in particular the micro-optical assembly OSA can further comprise the polarizer 2. Although the use of the optically based current measuring system for measuring direct currents is described above, the current measuring system is not limited to this.Rather, the optically based current measuring system according to the invention can also be used alternatively or additionally for measuring alternating currents. Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -10- The invention describes an optically based current measuring system which enables the temperature-compensated measurement of electrical currents based on the Faraday effect. The invention is explained in more detail below with reference to Figure 1 and exemplary components. A quasi-monochromatic light source 1, e.g. a (super) LED or a laser, couples radiation (e.g. infrared, visible light, etc.) into a glass fiber.The radiation is linearly polarized in a defined direction by a polarizer 2. The polarizer 2 can be arranged inside or outside a micro-optical assembly (OSA), or can be connected to the micro-optical assembly (OSA) as a fiber polarizer 2. The alignment of the fiber polarizer or polarizer 2 with respect to the fiber axes and connectors must be ensured. The radiation is converted from the fiber optic cable into collimated radiation via a lens 3, for example a gradient index lens, and split by a first non-polarizing beam splitter 4.1. The reflected portion, or optionally the transmitted portion, is coupled via another (preferably similar) lens 3 into a linearly highly birefringent (HiBi) fiber 8. The slow fiber axis of the birefringent fiber 8 (HiBi fiber) is rotated by 45° or -45° relative to the polarizer 2.The radiation coupled into the birefringent fiber 8 excites two partial optical signals which can be regarded as independent linear polarizations if the coherence length of the radiation source 1 is smaller than the difference in the optical path length between the HiBi fiber principal axes 8. Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -11- A delay element 9 is connected to the end of the HiBi fiber 8 as a unit for transforming linear polarizations into two orthogonal, circular polarization states. The slow principal axis of the unit is related to the polarizer 2 at either 0° or 90°. Both circularly polarized signals receive a phase shift ∆^ within the downstream measuring coil 10. ^= 2^^^ each on the outward path and the return path, so that after reflection at a reflector 11 and a return path the phase shift is cumulative ^ ^= ∆4^^^. The phase shift is coupled by the delay element 9 into the principal axes of the HiBi fiber (8), which are reversed compared to the forward path, and mapped onto two linearly polarized signals. The exchange of the principal axes leads to a compensation of the linear birefringence of the HiBi fiber 8 and thus to the correlation of the partial signals, which are fed to the micro-optical assembly OSA as a superimposed polarization signal. The modified, polarized signal is coupled into the evaluation path via the first non-polarizing beam splitter 4.1. A second non-polarizing beam splitter 4.2 splits the signal again, creating two optical signal channels, which have a different operating point (1st operating point and 2nd operating point) and both have a sin dependence of the Faraday effect.Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -12- In particular, two different operating points with different temperature characteristics of the optical signal arise. Operating point 1 / 4, 5.1 and 7.2 The phase shift due to the Faraday effect leads to an elliptical opening of the linear polarization. If no measuring current flows through the conductor L, the output signal is linearly polarized and aligned with polarizer (1). The λ / 4 plate 5.1 is adjusted so that the slow or fast principal axis is 0° or 90° to the principal axis of the birefringent fiber 8. This places the λ / 4 plate 5.1 at a +45° or -45° angle to the input polarizer 2, resulting in a static offset of ^ = 90° between the subfields of the superimposed optical signals. A polarizing beam splitter 7.2 is aligned with the angle of the λ / 4 plate 5.1 (0° or 90° to its main axes) and allows the measurement of the signal components ^. ^,^ and ^ ^,^ in push-pull operation. For the signals of the optical receiver behind 7.2, ie at the optical outputs O3 and O4, the following applies: The sum and difference calculation provides a value depending on the laser intensity ^ ^ independent signal ^ ^ . Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -13- In addition, ^ ^ depending on the temperature dependence of the Faraday effect ^ ^ , as well as the temperature dependence ^ ^ of the λ / 4 plate 5.1. Here ^ describes a linearized representation of the temperature-dependent deviation of the retardation plate from the ideal $ % delay, where " ^^#^ describes the temperature-dependent delay value of the λ / 4 plate. This means that within the scope of the invention, operating point 1 reacts sensitively to temperature changes and polarization changes of the Faraday effect. These two effects overlap at operating point 1. Within the scope of the invention, a λ / 4 plate 5.1 can be used which intentionally has a high temperature dependence due to a multiple order (multiple order or low order). In particular, a λ / 4 plate 5.1 can also be integrated into a micro-optical assembly OSA, so that the heating of the λ / 4 plate follows a changed ambient temperature within a short time. The micro-optical assembly OSA is preferably arranged in the current sensor according to the invention such that the ambient temperature has a similar relationship to the temperature of the measuring coil 10.Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -14- Operating point 2 / 4, 5.2, 6, 7.1 The optical wave with its phase shift Δ^ due to the Faraday effect is transferred to the second optical channel via the beam splitter 4.2. A λ / 4 plate 5.2 is inserted into the beam path so that it is aligned parallel or orthogonally with the input polarizer 2. Element 5.2 is thus positioned at +45° or -45° to the principal axes of the birefringent fiber 8. The phase shift Δ^ = 4^^^ in the principal axes of the birefringent fiber, due to the measuring current ^ in the conductor L, leads to a modulation of the polarization state into an elliptical polarization state. The λ / 4 plate 5.2 modulates the polarization state of the optical signal into a linear polarization state with a rotation angle λ.^ = 2^^^ = ∆^ / 2. To adjust the operating point, polarizers or polarizing beam splitters 7.2 are used, whose orientation is +45° or -45° to the input polarizer 2 and generate two channels in push-pull operation, which form the operating point 2. The operating point 2 is inherently insensitive to the Faraday effect (cos^^ ^ ^), so that delay elements of 0th, 1st, or multiple order can be used for element 5.2. The following applies to the electrical signals of the optical receiver at 7.1, ie at the optical outputs O1 and O2: Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -15- ^ ^, − ^ ^ * = * ^,* = sin^2& ^ ^ ^ ^ ^ cos ^ ^ ^,* + ^ ^,* This can ^ *approximately independent of the temperature-dependent delay value ^ ^ of the element (5.2) ^ * ≈ sin^2& ^ ^, where for ^ ^ applies This means that within the scope of the invention, a temperature-independent channel can be provided by the current measuring system and, in particular, the micro-optical assembly OSA. In this temperature-independent channel, the element 5.2 is aligned parallel or orthogonal to the input polarizer 2, thus making the temperature dependence of the element 5.2 negligible. Thus, the detection of the phase shift can be achieved by measuring a transformed rotation angle of the linear polarization. In addition, a compensating element (also integrated into the micro-optical assembly OSA) can be provided, which can be achieved by an additional rotation &- = −2& ^The Faraday effect is compensated. Temperature compensation: Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -16- The signals from operating points 1 and 2 are evaluated in the receiver at the outputs of beam splitters 7.1 and 7.2. The signals from operating points 1 and 2 can be normalized with each other as described above by summing and subtracting in order to achieve independence from fluctuations in the power of light source 1. The difference between the two operating points can then be determined. The following temperature dependencies are effective: ^ Operating point 1: Effect of temperature on o Temperature dependence of the Faraday effect 10 through Verdet constant sin^^^ o Temperature dependence of the delay element 9 in the form cos^^ .^ o Temperature dependence of the delay element 5.1 in sin^^ ^ ^ ^ Operating point 2: Effect of temperature on o Temperature dependence of the Faraday effect 10 through Verdet constant sin^^^ o Temperature dependence of the delay element 9 in the form cos^^ . ^ o Temperature dependence of the delay element 5.2 in cos^^ ^ ^ The temperature-dependent signal is calculated by subtracting generated, where the proportions cos^^ / ^ of the delay elements 0 can be neglected if cos^^ / ^ ≈ 1 for ^ / ≪ 1. Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Follow-up application to DE 102023205899.5 -17- The values ​​obtained from operating points 1 and 2 can be used to correct the Verdet constant in the receiver. The dominant influence of the temperature dependence is the dependence due to the quarter-wave plate 5.1. In order to detect the temperature dependence of the Faraday effect, it is assumed that the temperature effect on the λ / 4 plate occurs simultaneously and at the same level as the temperature effect on the measuring coil 10, which can be achieved, for example, by a compact design. If the temperature effect on the measuring coil 10 and the λ / 4 plate is essentially the same, the difference between the operating points depends exclusively on the λ / 4 plate and can be used as a temperature signal.The invention provides a novel optically based current sensor based on the more cost-effective polarimetric measurement technology. To still achieve high measurement accuracy—up to the limits of the native temperature dependence of the Faraday effect—the novel current sensor can utilize two redundant operating points with different temperature characteristics of the channels. While both channels can be used to measure a current, a temperature-dependent difference results between the channels, which can be used to correct the measured current. Reference number: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measurement system and its use Application number: Subsequent application to DE 102023205899.5 -18- The optical structure of the sensor is designed to enable mass production in a micro-optical assembly (OSA) (also known as an optical sub-assembly). Micro-optical assemblies (OSA) describe optical assemblies made up of micro-optics. After alignment (either mechanically or manually) of the elements of a micro-optical assembly (OSA) – if necessary – the aligned elements can be fixed, for example, by gluing. The advantage of micro-optical assemblies (OSA) is that they have low insertion loss and are almost equivalent to a fiber-optical solution. The principle presented can be applied to both DC and AC measurement technology.

Claims

Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: subsequent application to DE 102023205899.5 -19- Claims 1. Optically based current measuring system, comprising ^ a quasi-monochromatic light source (1), ^ a polarizer (2), ^ a first non-polarizing beam splitter (4.1) and ^ a second non-polarizing beam splitter (4.2), ^ a linear highly birefringent element (8). ^ an element for generating a circular polarization (9), wherein the element for generating a circular polarization (9) is arranged adjacent to a current conductor (L) to be measured, ^ a measuring element with Faraday effect (10), ^ a reflector (11), ^ wherein light from the light source (1) is first guided through the polarizer (2) to the first non-polarizing beam splitter (4.1), wherein the light from the non-polarizing beam splitter (4.1) reflected light is guided through the linearly highly birefringent element (8) and the subsequent element for generating a circular polarization (9), ^ wherein the reflector (11) is arranged after the element for generating a circular polarization (9), so that incoming light is again guided through the element for generating a circular polarization (9) and the linearly highly birefringent element (8) back to the first non-polarizing beam splitter (4.1), ^ wherein the light transmitted through the first non-polarizing beam splitter (4.1) is guided to a second beam splitter (4.2), ^ the system further comprising ^ a first delay element (5.1) and a second delay element (5.2), wherein the first delay element (5.1) and the second delay element (5.2) are of the same type or different, ^ a first polarizing beam splitter (7.1) with at least one first optical output (O1) and one second optical output (O2) and ^ a second polarizing beam splitter (7.2) with at least one first optical output (O3) and one second optical output (O4). Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -20- ^ an opto-electronic conversion unit, ^ wherein the first delay element (5.1) is arranged in the transmitting branch of the second beam splitter (4.2), and ^ the second delay element (5.2) is arranged in the reflecting branch of the second beam splitter (4.2), ^ wherein the first polarizing beam splitter (7.1) is arranged downstream of the first delay element (5.1), and ^ the second polarizing beam splitter (7.2) is arranged downstream of the second delay element (5.1), ^ wherein the first delay element (5.1) is arranged at a different angle than the second delay element (5.2) with respect to a similarly incident polarized Light, ^ where the first polarizing beam splitter (7.1) is arranged at a different angle than the second polarizing beam splitter (7.2) with respect to a similarly incident polarizing light, ^ wherein the optoelectronic conversion unit evaluates light from the optical outputs of the first polarizing beam splitter (7.1) and the second polarizing beam splitter (7.2) to obtain a temperature-dependent signal in order to be able to reduce temperature-related error components in the measurement of the Faraday effect due to current flow in the current conductor to be measured.

2. Optically based current measuring system according to claim 1, characterized in that the linearly highly birefringent element (8) comprises a HiBi fiber.

3. Optically based current measuring system according to claim 1 or 2, characterized in that the element for generating a circular polarization (9) comprises a delay element, in particular a λ / 4 plate. 4.The optically based current measuring system according to claim 3, characterized in that the delay element is arranged in spatial proximity to the linearly highly birefringent element (8), so that the delay element and the linearly highly birefringent element (8) have essentially the same temperatures.

5. The optically based current measuring system according to one of the preceding claims, characterized in that the measuring element with the Faraday effect comprises a glass fiber, in particular a glass fiber coil, around the current conductor to be measured. Our reference: TUD 47599 P DEWO Applicant: Technical University of Dortmund, Germany Title: Optically based current measuring system and its use Application number: Subsequent application to DE 102023205899.5 -21- 6. Optically based current measuring system according to one of the preceding claims, characterized in that the first delay element (5.1) and the second delay element (5.2) each have a λ / 4 plate.

7. Optically based current measuring system according to claim 5, characterized in that the order of the first delay element (5.1) and the order of the second delay element (5.2) are the same or different.

8. Optically based current measuring system according to one of the preceding claims, characterized in that the optoelectronic conversion unit has a photodiode.

9. Optically based current measuring system according to one of the preceding claims, characterized in that the first non-polarizing beam splitter (4.1) and the second non-polarizing beam splitter (4.2), as well as the first delay element (5.1) and the second delay element (5.2) are arranged in a micro-optical assembly (OSA).

10. An optically based current measuring system according to claim 9, characterized in that the micro-optical assembly (OSA) further comprises the polarizer (2).

11. Use of an optically based current measuring system according to one of the preceding claims for measuring direct currents.

12. Use of an optically based current measuring system according to one of the preceding claims 1 to 10 for measuring alternating currents.

Images