AU5726599A - Device and method for optically detecting an electric current and a component of an electric field - Google Patents

Description

GR 98 P 3500 P - 1 Description Device and method for optically detecting an electric current and a component of an electric field 5 The invention relates to a device and a method for optically detecting an electric current and at least one component of an electric field. An optical measuring device for measuring an 10 electric current flowing in an electrical conductor by utilizing the Faraday effect is disclosed in EP 088 419 Bl. Such an optical measuring device is also denoted as a magnetooptic current transformer. The Faraday effect is understood to be the rotation of the 15 plane of polarization of linearly polarized light which is propagating in a medium in the presence of a magnetic field. The angle of this rotation is proportional in this case to the path integral over the magnetic field along the path covered by the light with 20 the Verdet's constant as constant of proportionality. Arranged in the vicinity of the electrical conductor for the purpose of measuring the current is a Faraday element which contains an optically transparent material exhibiting the Faraday effect. In the 25 exemplary embodiment of EP 088 419 Bl, this Faraday element is designed as a solid glass ring which surrounds the electrical conductor. Linearly polarized light is launched into said electrical conductor. The magnetic field produced by the electric current effects 30 a rotation of the plane of polarization of the light, propagating in the solid glass ring, by a polarization rotational angle which is evaluated by an evaluation unit as a measure of the strength of the magnetic field, and thus of the strength of the electric 35 current. After traversing the Faraday element, the light, which carries measurement information on the electric current in a polarization modulation, is split in an analyzer, which is designed as a beam-splitting GR 98 P 3500 P - la Wollaston prism, into two component light signals with planes of polarization orientated at right GR 98 P 3500 P - 2 angles to one another. At the same time, the analyzer converts the polarization modulation into an intensity modulation of the two component light signals. The measurement information is therefore coded in the 5 intensity of the two component light signals. In another embodiment, known from WO 91/01501 Al, the Faraday element is designed as an optical monomode fiber which surrounds the electrical conductor in the form of a measuring winding with N 10 turns. The light guided in the monomode phase therefore runs around the electrical conductor N times overall. With each round-trip pass, the light experiences a rotation of its state of polarization in accordance with the strength of the electric current or the 15 magnetic field. The measuring sensitivity of this fiber-optic Faraday element can therefore be set by the number of turns per unit length. Moreover, EP 0 613 015 Al discloses an optical measuring device for measuring an electric voltage by 20 utilizing the Pockels effect, which is also denoted as an electrooptic voltage transformer. The electric voltage to be measured is applied in this case to an electrooptic crystal which then modifies a light signal, which is transirradiated through it, as regards 25 its polarization properties. This modification is traced back in an evaluation unit to the original measured variable, the electric voltage. In this case, the electrooptic crystal causes a change in the polarization properties on account of an electric field 30 which forms in the crystal as a consequence of the applied electric voltage. Again, an optical combined transformer for an electric current and an electric voltage is disclosed in the company publication "Optical Combined Current & 35 Voltage H.V. Sensors", GEC-Alsthom T&D. In this case, a magnetooptic current transformer with a solid glass ring and an electrooptic voltage transformer with an GR 98 P 3500 P - 2a electrooptic crystal, which is connected to a capacitive voltage divider, are GR 98 P 3500 P - 3 integrated into the combined transformer. The electrooptic voltage transformer detects, in particular, the electric field strength which prevails within a capacitor element of the capacitive voltage 5 divider in which the electrooptic crystal is arranged. The electrooptic voltage transformer and the magnetooptic current transformer have completely independent light paths. The integration to form the combined transformer is carried out in such a way that 10 the two individual transformers, which are not interconnected optically, are merely accommodated in a common housing in the form of a high-voltage insulator. The measurement information is transmitted in the form of an intensity modulation of the light sign& 15 guided in an optical conductor in the case of said embodiments of the optical transformers. Problems can arise in this case, since the light intensity in the optical conductor reacts sensitively to external interference such as, for example, mechanical 20 vibrations or temperature fluctuations. An optical sensor based on a fiber Bragg grating is disclosed in the survey article "In-fib Bragg grating sensors" by Y.J. Rao, Meas. Sci. Technol., Vol. 8, 1997, pages 355 to 375. A fiber Bragg 25 grating can be used to detect a change in length of an optical fiber. A Bragg grating which is firstly inserted into an optical fiber is essentially a periodic local modulation of the refractive index in the core of the optical fiber. This modulation of the 30 refractive index in the core is also denoted below as "core index modulation". The locally limited core index modulation constitutes a discontinuity for an impinging light signal at which partial or else total reflection comes 35 about at specific wavelengths. Which wavelength or which wavelength component is affected thereby depends in this case on the design of the core index modulation GR 98 P 3500 P - 3a of the Bragg grating. Consequently, the design of the core index modulation tunes the Bragg grating GR 98 P 3500 P - 4 to a specific wavelength or a specific wavelength spectrum. Since a change in length of the optical fiber influences the local period of the core index 5 modulation, there is also a change in the wavelength content both of the reflected and of the passed, that is to say the transmitted, light signal. The corresponding modification as regards the wavelength content can therefore be used as a measure of the 10 change in length of the optical fiber. In addition to detecting elongation/compression, this measuring principle can also be used to detect other physical measured variables, such as temperature, pressure, sound, acceleration, high magnetic fields and also 15 force. The survey article named does not indicate an embodiment of the sensor on- the basis of the fiber Bragg grating for detecting an electric field or an electric voltage. The object of the invention is, then, to 20 specify a device and a method of the type respectively denoted in the introduction which permit simultaneous detection of electric current and a component of an electric field which is improved and/or simplified by comparison with the prior art. In particular, the aim 25 in this case is to economize on optical components. A device in accordance with the features of the independent patent claim 1 is specified for the purpose of achieving the partial objects relating to the device. 30 The device according to the invention for optically detecting an electric current and at least one component of an electric field is a device which comprises a light path with an optical series connection of 35 - at least one current-sensitive Faraday element, and - at least one element which is sensitive to the at least one component of the electric field.

GR 98 P 3500 P - 5 A method in accordance with the features of the independent patent claim 13 is specified in order to achieve the partial object relating to the method. The method according to the invention for 5 optically detecting an electric current and at least one component of an electric field is a method in which a) a transmitted light signal is generated and fed into an optical series circuit composed of at least one current-sensitive Faraday element and of 10 at least one element sensitive to the at least one component of the electric field, at least one component of the transmitted light signal is influenced in successive sequence b) by the at least one current-sensitive Faraday 15 element as regards a state of polarization, and c) by the at least one element, sensitive to the at least one component of the electric field, as regards an optical property differing from the state of polarization, 20 and d) at least one first measured variable for the at least one component of the electric field is derived from the influence exerted on the property differing from the state of polarization, and 25 e) a second measured variable for the electric current is derived from the influence exerted on the state of polarization. The invention is based in this case on the finding that the optical detecting of an electric 30 current and a component of an electric field can advantageously be combined when a single light signal traverses both at least one current-sensitive Faraday element and at least one element sensitive to the at least one component of the GR 98 P 3500 P - 6 electric field, and is influenced by the respective variable to be measured. The component of the electric field is also denoted below as "field component". The Faraday element and the element sensitive 5 to the at least one field component are present in an optical series connection, the sequence playing no role in this context. The Faraday element and the element sensitive to the field component in this case influence parameters of the transmitted light signal fed in which 10 are different and, above all, can also be detected selectively. These selectively detectable parameters can be, for example, the state of polarization and the wavelength content of the transmitted light signal. The electric current and the field component can therefore 15 also be detected separately, that is to say individually, with the aid of the combined arrangement of the Faraday element and the element sensitive to the field component in the optical series connection. Compared with an operation of the Faraday 20 element and the element sensitive to the field component in a fashion completely independently of one another, the solution according to the invention economizes on optical components such as, for example, a second light source or separate incoming and outgoing 25 optical conductors. The device according to the invention for detecting electric current and a field component can therefore be produced more cost effectively and, moreover, also has less need for space than two separate devices. 30 Consequently, it is particularly well suited for use in the supply of electric power. Because of its small overall size, the device can be integrated with particular ease into other existing operational equipment such as, for example, an outdoor circuit 35 breaker or a gas-insulated switchgear.

GR 98 P 3500 P - 7 Particular refinements and developments of the device and of the method according to the invention follow from the respectively dependent subclaims. A design variant in which the at least one 5 element sensitive to the at least one field component is designed as a Bragg element is advantageous. The coding, generally usual in the case of Bragg elements, of the measurement information in the wavelength content results in the case of this design variant in a 10 sensitivity to interference which is substantially reduced by comparison with the prior art. The relevant interference influences the intensity of a light signal used for transmitting the measurement information more strongly than the wavelength content. 15 In a further embodiment of the device, the Bragg element contains a piezoelectric body which reacts to the at least one field component with a change in shape on account of its piezoelectricity. An optical conductor is mechanically connected to the 20 piezoelectric body such that the change in shape of the piezoelectric body effects a change in length of the optical conductor. In this case, the optical conductor can be both an incoming and an outgoing optical conductor of the Faraday element. The sequence of the 25 arrangement of the Faraday element and the Bragg element does not play a decisive role. A Bragg grating with a predetermined Bragg wavelength is located inside the optical conductor precisely at the point which is varied by the change in shape of the piezoelectric body 30 as regards length. The local change in length of the optical conductor also leads to variation in the core index modulation fundamental to the Bragg grating, such that a different wavelength component from a transmitted light signal which strikes the Bragg 35 grating is reflected than in the absence of the field component. Consequently, as regards wavelength content the field component influences both the component of GR 98 P 3500 P - 7a the transmitted light signal traversing the Bragg element, which component is denoted here as transmitted light signal, and the component of the transmitted light signal reflected at the Bragg element, GR 98 P 3500 P - 8 which is denoted here as reflected light signal. The reflected light signal essentially consists of a wavelength which corresponds to the Bragg wavelength. The transmitted light signal, by contrast, has a gap in 5 its wavelength spectrum precisely at the point of the Bragg wavelength. In a further preferred embodiment, the piezoelectric body consists of monocrystals such as quartz, lithium niobate (LiNbO 3 ) or lithium tantalate 10 (LiTaO 3 ), a piezoelectric polymer such as, for example, polyvinylidene fluoride (PVDF), or else a piezoceramic. Since the piezoelectric monocrystals which can be used all exhibit anisotropic behavior, the piezoelectric body can be cut with varying orientation from the 15 relevant crystal. Likewise preferred is a design variant in which the light path which includes the optical series connection of the Faraday element and the element sensitive to the field component comprises several 20 optical conductors. In particular, these optical conductors can exhibit a different type of optical conductor. In this case, the optical conductors are preferably used in the form of a multimode fiber, a monomode fiber, a polarizing fiber, or else a 25 polarization-maintaining fiber. In one design variant, several Bragg elements with Bragg gratings of different Bragg wavelength in each case are integrated into the incoming and outgoing optical conductors of the Faraday element. The 30 individual Bragg elements react in this case to field components which are different in each case and present along the incoming or outgoing optical conductor. It follows that there is an advantage in another refinement of the device, in the case of which a 35 broadband light source is provided whose emitted light spectrum comprises at least all the Bragg wavelengths of the Bragg gratings inserted into the incoming or GR 98 P 3500 P - 9 outgoing optical conductor. An SLD (superluminescent diode), an ELED (edge-emitting light-emitting diode), an SFS (superfluorescent fiber source) or a TFL (tuneable fiber laser) are suitable broadband light 5 sources in this regard. The emitted wavelength spectrum of these light sources then preferably has a half-value width of up to 200 nm. Light sources with an even larger emission spectrum are likewise suitable. As regards a TFL, the emission spectrum is understood here 10 to be that wavelength region which the TFL covers. It is also possible for there to be present more than one light source which feed light into the light path in a fashion offset relative to one another temporarily and/or spectrally. 15 An embodiment is advantageous which undertakes a wavelength-selective evaluation of at least the component of the transmitted light signal which is influenced as regards its state of polarization by the Faraday element, and as regards its wavelength content 20 by at least one Bragg element. The measurement information concerning the field component present at the respective Bragg element, and concerning the electric current flowing through the Faraday element can be determined by wavelength-selective splitting via 25 an optical filter or a spectrometer in accordance with the respective Bragg wavelengths. Only a single Faraday element is usually provided in the light path. However, there are also embodiments of the device in which two or more Faraday 30 elements are traversed by the transmitted light signal. Advantageous embodiments of the method, which result from the corresponding subclaims, essentially exhibit the same advantages as the abovenamed, respectively corresponding refinements of the device.

GR 98 P 3500 P - 10 Particularly advantageous is a variant of the method in which in addition to the at least one first measured variable for the at least one field component and the second measured variable for the electric 5 current, there is also determined a third measured variable for an electric voltage of an electrical conductor in which the electric current flows. This third measured variable is derived in this case from the first measured variables for the field components. 10 Since field components are measured along the incoming or outgoing optical conductor, the electric voltage, defined as the line integral of the electric field characteristic between the electrical conductor and a point at ground potential, for example the location of 15 the evaluation unit, can be approximated by these measured field components. For this purpose, the line integral is replaced by a summation of the first measured variables, weighted with dimensions of the respective piezoelectric bodies, for the field 20 components. The method therefore respectively supplies a measured variable for the electric current and for the electric voltage. Preferred exemplary embodiments will now be explained in more detail with the aid of the drawing. 25 For the purpose of illustration, the drawing is not made to scale, and certain features are represented schematically. In detail: Figures 1 and 2 show devices for optically detecting an electric current via a fiber coil, 30 and field components via Bragg elements, Figure 3 shows a further device for optically detecting an electric current via a solid glass ring, and a field 35 component via a Bragg element, and Figure 4 shows a Bragg element for optically detecting a field component.

GR 98 P 3500 P - 10a Parts corresponding to one another are provided with the same reference symbols in Figures 1 to 4.

GR 98 P 3500 P - 11 Figure 1 shows a device for optically detecting an electric current I and components Ei (where 1 5 i n) of an electric field which are also denoted here as field components Ei. The serial index "i" 5 assumes values of 1 to n from the set of natural numbers. The essential sensitive constituents of the device are a current-sensitive Faraday element F in the form of a fiber coil, and several Bragg elements Bi (where 1 5 i n), which react sensitively in each case 10 to the field component Ej, which is present at the respective Bragg element Bi. The electric current I flows in an electrical conductor 50 at which an electric voltage U is present referred to ground potential. The Bragg elements Bi and the Faraday 15 element F are connected optically in series in the exemplary embodiment of figure 1. A transmitted light signal LS fed into this series connection firstly traverses the Bragg elements Bi and then the Faraday element F. The transmitted light signal LS experiences 20 a change in a wavelength content in the Bragg elements Bi, and a change in a state of polarization in the Faraday element F. The transmitted light signal LS is generated by a broadband light source 20, which is designed ass a 25 superluminescent diode (SLD), and fed via a coupler 40 into an incoming optical conductor 11 of the Faraday element F. This incoming optical conductor 11 is designed as a monomode fiber in the exemplary embodiment of figure 1. The Bragg elements Bi are 30 integrated into this incoming optical conductor 11. The Bragg elements Bi are tuned to Bragg wavelengths ki (where 1 5 i n) differing from one another by introducing respectively differing core index modulations into the incoming optical conductor 35 11. This is performed by respectively different local modulation periods. The transmitted light signal LS is then reflected at least partially in the spectral GR 98 P 3500 P - lla region of the respective wavelength ki at the associated Bragg element Bi. Owing to the reflection of the transmitted GR 98 P 3500 P - 12 light signal LS at the individual core index modulations of the respective Bragg elements Bi, a reflected light signal LR with a wavelength content which comprises the individual Bragg wavelengths ki runs 5 back in the direction of the broadband light source 20. However, the reflected light signal LR is diverted at the coupler 40 in the direction of an evaluation unit 30. Present at the end, averted from the broadband 10 light source 20, of the length of the incoming optical conductor 11 within which the Bragg elements Bi are integrated is a transmitted light signal LT which is composed of wavelength components of the transmitted light signal LS which differ from the Bragg wavelengths 15 ki. These wavelength components pass all the Bragg elements Bi without hindrance. The transmitted light signal LT therefore exhibits a wavelength spectrum provided with gaps, the gaps being located precisely at the points of the individual Bragg wavelengths X 1 . 20 If the measured variable, in the present case the field components Ei, is applied to the Bragg elements Bi, the wavelength content both of the reflected and of the transmitted light signals LR and LT is thereby influenced. In the case of the reflected 25 light signal LR, the individual Bragg wavelengths ki themselves are displaced, whereas it is said gaps in the wavelength spectrum in the case of the transmitted light signal LT. Since the transmitted light signal LT is also fed in the further course of events to the 30 evaluation unit 30, detection of the two displacements in the evaluation unit 30 permits redundant determination of first measured variables Mli for the field components Ej. For this purpose, the fundamental field component Ei is deduced from the respective 35 displacements in the evaluation unit 30. Before the transmitted light signal LT reaches the evaluation unit 30, it firstly traverses the Faraday element F. The GR 98 P 3500 P - 13 transmitted light signal LT is linearly polarized in a polarizing optical conductor 12 before entering the Faraday element F. Under the influence of the electric current I flowing in the current conductor 50, the 5 state of linear polarization is then rotated by a Faraday rotational angle in the fiber coil, surrounding the electrical conductor 50 by several turns, of the Faraday element F. The resulting Faraday rotational angle is a function of the material of the fiber coil, 10 the number of the turns and the electric current I. A current-coded transmitted light signal LT' is present at the output of the Faraday element F. In its wavelength content, this current-coded transmitted light signal LT' includes coded measurement information 15 on the field components Ei and measurement information, coded in its state of polarization, on the electric current I. The current-coded transmitted light signal LT' is fed to the evaluation unit 30 via an outgoing optical conductor 13 of the Faraday element F. The 20 outgoing optical conductor 13 is designed as a polarization-maintaining optical conductor in the device of figure 1. At the input, the evaluation unit 30 firstly contains means for wavelength-selective splitting both 25 of the reflected light signal LR and of the current coded transmitted light signal LT'. The splitting is performed in this case in frequency bands which respectively comprise only a single Bragg wavelength X 1 . The first measured variables Mli for the field 30 components Ej can be determined from these wavelength bands. Also provided is a further wavelength component which comprises none of the Bragg wavelengths ki. This wavelength band serves the purpose of determining a second measured variable M2 for the electric current I. 35 For this purpose, the evaluation unit has an arrangement, known per se, for evaluating a light signal which contains the measurement information on the electric current I in the form of a coding or GR 98 P 3500 P - 13a modulation of the state of polarization. This arrangement comprises, in particular, GR 98 P 3500 P - 14 an analyzer which converts the polarization modulation into an intensity modulation. The incoming optical conductor 11 runs along a connecting path between the current conductor 50 and 5 the broadband light source 20, which is likewise at ground potential, like the evaluation unit 30. Consequently, the electric voltage U, which is present at the current conductor 50, is obtained by line integration of the electric field along this connecting 10 path. This line integral can be approximated with the aid of the field components Ei detected via the Bragg elements Bi. The approximation is performed in this case by a summation of products from the first measured variables Mli for the field components Ei and local 15 dimensions of the respectively associated Bragg elements Bi. This evaluation is carried out in a voltage unit 31 which is connected downstream of the evaluation unit 30. In this case, the first measured variables Mli serve as input variables of the voltage 20 unit 31. As output variable, the voltage unit 31 supplies a third measured variable M3 for the electric voltage U. Consequently, the device shown in figure 1 can be used to detect and evaluate both the electric current I and the electric voltage U. The device 25 therefore constitutes a combined transformer. In an embodiment which is not shown, the broadband light source 20, together with an electronic control, as well as the evaluation unit 30 and the voltage unit 31 are combined to form a single 30 optoelectronic unit. In particular, the calculations for the third measured variable M3 are then performed in the same arithmetic unit, for example in a microprocessor, in which the first measured variables Mli and the second measured variable M2 are also 35 determined.

GR 98 P 3500 P - 14a The device shown in figure 2 is likewise used for optically detecting the electric current I and the electric voltage U. It resembles the device shown in figure 1 in many parts. A substantial difference 5 consists, GR 98 P 3500 P - 15 however, in that with the exemplary embodiment of figure 2 the Bragg elements Bi are integrated not into the incoming optical conductor 11, but into the outgoing optical conductor 13. 5 The transmitted light signal LS is therefore firstly fed into the Faraday element F and varied as regards its state of polarization by the electric current I. A current-coded transmitted light signal LS' is then present at the output of the Faraday element F. 10 Said signal traverses the Bragg elements Bi. The current-coded transmitted light signal LT' is present at the output of said elements and is fed, in turn, into the evaluation unit 30. The evaluation is performed in a similar way to the exemplary embodiment 15 of figure 1. By contrast with figure 1, the exemplary embodiment of figure 2 contains no optical branch which feeds a reflected light signal LR to the evaluation unit 30. The light components reflected at the Bragg 20 elements Bi traverse the polarizing optical conductor 12 on their way back in the direction of the broadband light source 20 for a second time, experiencing very severe attenuation such that it is no longer sensible to carry out evaluation in the evaluation unit 30. 25 A further device for optically detecting an electric current I and a field component Ei is illustrated in figure 3. The Faraday element F is designed here as a solid glass ring. After traversing the sole Bragg element B 1 , the transmitted light signal 30 LT leaves the outgoing optical conductor 11 and is linearly polarized in a solid polarizer 120, which corresponds to the polarizing fiber 12 of the exemplary embodiments of figures 1 and 2. Subsequent thereto, the linearly polarized transmitted light signal LT passes 35 the solid glass ring surrounding the electrical conductor 50 once and is influenced in this case by the electric current I as regards its state of polarization.

GR 98 P 3500 P - 16 Directly at the output of the glass ring, this polarization modulation is converted into an intensity modulation by a beam-splitting analyzer 121 in the form of a Wollaston prism. The analyzer 121 generates a 5 first and a second current-coded component light signal LT1' and LT2', which carry the measurement information on the electric current I in the form, in each case, of an intensity modulation. The first and second current-coded component 10 light signals LT1' and LT2' are guided to the evaluation unit 30 via a first or second outgoing optical conductor 131 or 132. The incoming optical conductor 11 and two outgoing optical conductors 131 and 132 are each designed in the example shown in 15 figure 3 as monomode fibers. However, this is not mandatory. In another embodiment, it is also possible to use multimode fibers. The evaluation unit 30 of figure 3 is identical to that of figure 1 except for the fact that the conversion of the polarization 20 modulation into the intensity modulation has been brought forward directly to the Faraday element F. Only a single Bragg element Bi for detecting a single field component Ei is provided in the device of figure 3. This offers advantages, in particular, 25 whenever the distance between the electrical conductor 50 and ground potential is only short. A relevant example is gas-insulated switchgear. On the other hand, the device of figure 3 can also be applied whenever only a rough approximation is desired for the electric 30 voltage U. The rough approximation is then performed only via the one first measured variable M 1 of the field component Ei. A Bragg element B 1 used in the exemplary embodiments of figures 1 to 3 and used for optically 35 detecting a field component Ei is illustrated in more detail in figure 4. The Bragg element B 1 comprises a GR 98 P 3500 P - 16a piezoelectric body P 1 . The latter has a bore through which, for example, the incoming optical GR 98 P 3500 P - 17 conductor 11 is guided. The piezoelectric body Pi and the incoming optical conductor 11 are permanently interconnected mechanically in the region of the bore. Precisely in this region, the incoming optical 5 conductor 11 has a Bragg grating Gi with the predetermined Bragg wavelength ki. The Bragg grating Gi is formed by the above-described core index modulation. In the case of other exemplary embodiments not illustrated, the incoming optical conductor 11 can, 10 however, also be wound around the piezoelectric body

P

1 , or be embedded in a slot on a surface of the piezoelectric body P 1 . In the case of these embodiments which are not shown, the Bragg grating Gi is also located in each case in the contact region of the 15 incoming optical conductor 11 with the piezoelectric body P 1 . Because of the piezoelectricity of the piezoelectric body P 1 and the permanent mechanical connection to the incoming optical conductor 11, the 20 field component El to be measured firstly causes a change in shape of the piezoelectric body P 1 and, consequently, a change in length of the incoming optical conductor 11. This change in length leads to a modification of the core index modulation in the Bragg 25 grating Gi, such that, finally, the displacements, already addressed above, in the wavelength content both of the reflected light signal LR and of the transmitted light signal LT result. These displacements are then respectively proportional to the original field 30 component El. The piezoelectric body Pi consists of quartz in the present case.

Claims (21)

1. A device for optically detecting an electric current (I) and at least one component (EI, Ei, E.) of 5 an electric field, comprising a light path with an optical series connection of - at least one current-sensitive Faraday element (F), and - at least one element (B 1 , Bi, B,) which is 10 sensitive to the at least one component (Ei, Ei, En) of the electric field.

2. The device as claimed in claim 1, characterized in that the light path includes several optical conductors (11, 12, 13, 131, 132), in particular of 15 different types of optical conductor.

3. The device as claimed in claim 2, characterized in that the individual optical conductors (11, 12, 13, 131, 132) are designed as multimode fibers, monomode fibers, polarizing fibers or as polarization 20 maintaining fibers.

4. The device as claimed in claim 2 or 3, characterized in that the at least one element sensitive to the at least one component (Ei, Ei, E,) of the electric field is integrated into an incoming 25 optical conductor (11) or into an outgoing optical conductor (13) of the Faraday element (F).

5. The device as claimed in one of the preceding claims, characterized in that the element sensitive to the at least one component (E 1 , Ei, En) of the electric 30 field is designed as a Bragg element (B1, Bi, B.) .

6. The device as claimed in claims 4 and 5, characterized in that the Bragg element GR 98 P 3500 P - 19 (B 1 , Bi, Bn) comprises a field-sensitive piezoelectric body (Pi) which is connected mechanically to the incoming or outgoing optical conductor (11, 13), and a Bragg grating (G 1 ), which is respectively inserted into 5 the incoming and outgoing optical conductors (11, 13) and has a predetermined Bragg wavelength (Xi).

7. The device as claimed in claim 6, characterized in that the piezoelectric body (Pi) consists of a piezoelectric material, in particular of a monocrystal 10 such as quartz, LiNbO 3 , LiTaO 3 , a polymer or a piezoceramic.

8. The device as claimed in one of the preceding claims, characterized in that the Faraday element (F) surrounds an electrical conductor (50) in which the 15 electric current (I) flows, and is designed, in particular, as a fiber coil or as a solid glass ring.

9. The device as claimed in one of the preceding claims, characterized in that means for linear polarization (12, 120) of a transmitted light signal 20 (LS) are connected upstream of the Faraday element (F).

10. The device as claimed in claim 9, characterized in that means for converting (121) an influence, caused in the Faraday element (F) by the electric current (I) and exerted on a state of polarization, into an 25 intensity modulation are connected downstream of the Faraday element (F).

11. The device as claimed in one of the preceding claims, characterized in that a broadband light source (20) is provided for feeding a transmitted light signal 30 (LS) into the light path.

12. The device as claimed in one of the preceding claims, characterized in that an GR 98 P 3500 P - 20 evaluation unit (30) is provided, into which the light path opens and which, in particular, includes wavelength-selective means, preferably an optical filter or a spectrometer. 5

13. A method for optically detecting an electric current (I) and at least one component (Ei, Ei, En) of an electric field, in the case of which a) a transmitted light signal (LS) is generated and fed into an optical series circuit composed of at 10 least one current-sensitive Faraday element (F) and of at least one element (Bi, Bi, Bn) sensitive to the at least one component (Ei, Ei, En) of the electric field, at least one component of the transmitted light signal 15 (LS) is influenced in successive sequence b) by the at least one current-sensitive Faraday element (F) as regards a state of polarization, and c) by the at least one element (B1, Bi, B.), sensitive 20 to the at least one component (Ei, Ei, En) of the electric field, as regards an optical property differing from the state of polarization, and d) at least one first measured variable (Mli, Mli, 25 Mln) for the at least one component (El, Ei, En) of the electric field is derived from the influence exerted on the property differing from the state of polarization, and e) a second measured variable (M2) for the electric 30 current (I) is derived from the influence exerted on the state of polarization.

14. The method as claimed in claim 13, characterized in that the transmitted light signal (LS) is influenced as regards wavelength content by the at 35 least one element (B 1 , Bi, B,) sensitive to the at least one component (Ei, Ei, En) of the electric field. GR 98 P 3500 P - 21

15. The method as claimed in claim 14, characterized in that the transmitted light signal (LS) is influenced as regards wavelength content by a Bragg element (B 1 , Bi, B,). 5

16. The method as claimed in claim 15, characterized in that a piezoelectric body (Pi) of the Bragg element (B 1 , Bi, B,) is varied as regards its shape by the at least one component (Ei, E 1 , E,) of the electric field, and an incoming or outgoing optical 10 conductor (11, 13), respectively mechanically connected to the piezoelectric body (Pi), of the Faraday element (F) is varied as regards its length, as a result of which the transmitted light signal (LS) is influenced as regards wavelength content in a Bragg grating (G 1 ), 15 inserted respectively into the incoming and outgoing optical conductors (11, 13), of predetermined Bragg wavelength (Xi).

17. The method as claimed in one of the preceding claims, characterized in that the transmitted light 20 signal (LS) is linearly polarized before entry into the Faraday element (F).

18. The method as claimed in one of the preceding claims, characterized in that the influence caused in the Faraday element (F) by the electric current (I) and 25 exerted on the state of polarization is converted into an intensity modulation.

19. The method as claimed in one of the preceding claims, characterized in that a broadband transmitted light signal (LS) is provided. 30

20. The method as claimed in claims 14 to 19, characterized in that at least the component of the transmitted light signal (LS) influenced as regards its state of polarization and wavelength content is evaluated in a wavelength-selective fashion. GR 98 P 3500 P - 22

21. The method as claimed in one of the preceding claims, characterized in that a third measured variable (M3) for an electric voltage (U) of an electrical conductor (50) in which the electric current (I) flows 5 is derived from the at least one first measured variable (Mi 1 , Mli, Mln) for the at least one component (Ei, Ej, En) of the electric field.