WO2013064788A1

WO2013064788A1 - Method and device for measuring a voltage

Info

Publication number: WO2013064788A1
Application number: PCT/FR2012/052546
Authority: WO
Inventors: Lionel Duvillaret; Gwenaël GABORIT; Frédéric LECOCHE
Original assignee: Kapteos
Priority date: 2011-11-03
Filing date: 2012-11-05
Publication date: 2013-05-10
Also published as: FR2982370A1; FR2982370B1

Abstract

The invention relates to a device (1) for measuring a voltage comprising first and second conducting terminals (2, 4) between which the voltage is measured; an isolator (6) separating the first and second terminals; an optical sensor (16) measuring the electric field at a location between the first and second terminals, the optical sensor comprising an isotropic electrooptical crystal (30) between the first and second terminals; and a detector (18) determining the voltage on the basis of the electric field measured.

Description

METHOD AND DEVICE FOR MEASURING VOLTAGE

Field of the invention

The present invention relates to a device and a method for measuring a voltage.

Presentation of the prior art

Some applications require the measurement of a high voltage, continuous or alternative, for example greater than a thousand volts. This is, for example, the measurement of the voltage of a power transmission network that can be greater than 100000 volts. It can also be the measurement of the voltage of a power supply line of a train which can vary from more than 1000 volts to more than 10000 volts.

There are high voltage measuring devices that include conventional inductive or capacitive measuring transformers, and provide a measuring device with a voltage several orders of magnitude lower than the high voltage. However, such measuring devices have a number of disadvantages: large size, limited bandwidth, insufficient measurement accuracy.

There are, in addition, optical devices for measuring voltage. These measuring devices can use optical sensors adapted to measure an electric field, especially Pockels cells. The value of the high voltage is determined from the measurement of the electric field.

US 6,252,388 discloses a voltage measuring device, adapted for measuring a high voltage, comprising a Pockels cell and in which a shield is provided to protect the Pockels cell against external disturbances so as to obtain a measurement. precise.

A disadvantage of the voltage measuring device disclosed in US 6,252,388 is that it is temperature sensitive. Therefore, it is necessary to provide a system for correcting the variations of the measured signals due to the temperature.

There is therefore a need for an optical device for measuring a voltage, continuous or alternating, in particular a high voltage, whose operation is independent of the temperature.

summary

Thus, an embodiment of the present invention provides a voltage measuring device comprising first and second conductive terminals between which the voltage is measured; an insulator separating the first and second terminals; an optical sensor measuring the electric field at a location between the first and second terminals, the optical sensor comprising an isotropic electro-optical crystal between the first and second terminals; and a detector determining the voltage from the measured electric field.

According to an exemplary embodiment of the invention, the crystal comprises a face less than 2 centimeters from the first terminal.

According to an exemplary embodiment of the invention, the crystal is in contact with the first terminal.

According to an exemplary embodiment of the invention, the device comprises an enclosure containing a source of a light beam, the light beam passing through the crystal; and a light beam analysis system having passed through the crystal.

According to an exemplary embodiment of the invention, the terminals are perpendicular to a direction and the crystal comprises at least one face of the type <100>, <010> or <001> perpendicular to said direction, the light beam reaching the crystal on said face, the beam being inclined with respect to said direction by an angle of less than 10 degrees.

According to an exemplary embodiment of the invention, the terminals are perpendicular to a direction and the crystal comprises at least one face of the type <110>, <011> or <101> parallel to said direction, the light beam reaching the crystal on said face, the beam being inclined at an angle less than 10 degrees with respect to an additional direction perpendicular to said face.

According to an exemplary embodiment of the invention, the enclosure is metallic and is fixed to the first terminal, on the side of the first terminal opposite the insulator, the first terminal comprising an opening for the passage of the light beam.

According to an exemplary embodiment of the invention, the device comprises at least one optical fiber connecting the enclosure to the first terminal for transporting the light beam.

According to an exemplary embodiment of the invention, the device does not include an optical fiber between the first and second terminals.

According to an exemplary embodiment of the invention, the device comprises a layer surrounding the crystal, the layer having a relative permittivity equal to the relative permittivity of the crystal to 10%.

According to an exemplary embodiment of the invention, the device comprises a dielectric portion connecting the first terminal to the second terminal and comprising an outer wall surrounding the crystal. An embodiment of the present invention provides a fault detection device, comprising a measuring device as previously described, and an additional optical sensor measuring the electric field at an additional location between the first and second terminals outside the the dielectric portion.

Brief description of the drawings

These and other objects, features, and advantages will be set forth in detail in the following description of particular embodiments in a non-limitative manner with reference to the accompanying figures in which:

Figure 1 is a schematic sectional view of an exemplary embodiment of a voltage measuring device according to the present invention;

Figures 2 to 4 are partial and schematic sections of variants of the voltage measuring device of Figure 2;

FIG. 5 is a variant of the analysis system of the voltage measuring device of FIG. 2;

Figure 6 is a partial schematic sectional view of another embodiment of a voltage measuring device according to the present invention;

Figure 7 is a schematic section of an exemplary embodiment of an abnormality detection device according to the invention;

Figure 8 is a schematic sectional view of another embodiment of a voltage measuring device according to the present invention;

Figure 9 is a partial and schematic sectional view of a variant of the voltage measuring device according to the present invention;

FIG. 10 illustrates the evolution of the state of polarization of the wave reflected by the measuring device of FIG. 9; Figure 11 is a partial and schematic sectional view of a variant of the voltage measuring device according to the present invention; and

FIG. 12 illustrates the evolution of the state of polarization of the wave reflected by the measuring device of FIG. 11.

detailed description

For the sake of clarity, the same elements have been designated by the same references in the various figures and, moreover, as is customary in the representation of the integrated circuits, the various figures are not drawn to scale. In the rest of the description, the adjectives "upper" or "lower" are defined in relation to an axis D which, for example, is vertical. However, it is clear that the D axis could be oriented in any way. In addition, reference is made hereinafter to the description of the optical waves with rectilinear polarization, circular polarization and elliptical polarization. In order not to burden the present description, we speak, as is often done in practice, of rectilinear, circular or elliptical waves, and it is understood that each time is optical waves whose polarization is respectively rectilinear , circular or elliptical. In the rest of the description, unless otherwise indicated, the terms "substantially", "about", "approximately" and "of the order of" mean "to within 10%".

FIG. 1 represents, partially and schematically, an exemplary embodiment of a voltage measuring device 1 according to the invention.

The measuring device 1 comprises two conductive terminals 2 and 4, for example metallic, separated by an insulator 6. The insulator 6 has the shape of a hollow tube of axis D on the outer surface of which are distributed fins 8. The internal volume of the insulator 6 can be filled with a solid, a liquid or a gas having a high dielectric strength, for example sulfur hexafluoride. It can also be filled with a composite medium. The terminals 2, 4 are separated by a distance H measured along the axis D. The insulator 6 is made of an insulating material, for example ceramic. The insulator 6 is connected to the terminals 2, 4 by sealed connections 9. For example, the internal diameter dl of the insulator 6 can vary from 1 to 30 centimeters and the length H can vary from 10 centimeters to 6 meters.

In the following description, the terminal 2 is called the upper terminal and the terminal 4 is called the lower terminal. The upper terminal 2 can be connected to a high voltage power line, not shown. The lower terminal 4 may be attached to a metal support, not shown, connected to ground, earth or a reference potential as a neutral. The dimensions of the insulator 6, and in particular the shape of the fins 8, are determined to prevent the formation of an electric arc between the two terminals 2, 4 and to limit the partial discharges between one of these terminals 2, 4 and the isolator 6. The device 1 can be used for the measurement of the potential difference between the high-voltage line and earth, ground or a reference potential as a neutral. For example, the measuring device 1 may be provided at an insulator of a train pantograph or be provided at an electrical transformer station or at a network control point. electric.

The measuring device 1 comprises a tube 10 of axis D fixed at its ends to the terminals 2, 4. The tube 10 is delimited by an internal cylinder 12 of axis D and of diameter d2 and an outer cylinder 14 of axis D and of diameter d3. The difference between the diameters d3 and d2 corresponds to the thickness e1 of the tube 10. By way of example, the diameter d2 can vary from 0.5 to 5 centimeters and the thickness ei can vary from 1 to 10 millimeters, from preferably from 1 to 5 millimeters. The tube 10 may not be hollow, in this case the inner diameter is 0. Alternatively, the thickness ei of the inner tube 10 may not be uniform. Preferably, the relative permittivity of the material constituting the inner tube 10 is greater than or equal to 100, preferably greater than or equal to 1000. It may be a ceramic. The tube 10 may comprise several concentric layers of dielectric materials which may have identical or different relative permittivities, but which, advantageously, make it possible to isolate the electric field lines contained inside the inner tube 10 from external disturbances. As an alternative, the terminals 2 and 4 may extend inside the inner tube 10 so as to increase the value of the electric field present inside the inner tube 10.

The insulator 6 can be separated from the inner tube 10, a solid, a liquid, a gas or a composite medium then being present between the insulator 6 and the inner tube 10. Alternatively, the insulator 6 and the tube internal 10 can be confused.

Alternatively, the inner tube 10 may be a weakly conductive tube. It may nevertheless be advantageous to use a tube made of a dielectric material so as to avoid any electrical losses by Joule effect.

The measuring device 1 comprises an electric field optical sensor 16 connected to a processing module 18 by electrical cables 20. The processing device 18 is adapted, from the signals supplied by the optical sensor 16, to determine the value of the voltage between the upper and lower terminals 2, 4.

In the first embodiment of the invention, the optical sensor 16 is disposed at the lower terminal 4. The optical sensor 16 comprises a crystal 30 disposed in the inner tube 10, between the terminals 2 and 4. At least one The crystal face 30 is less than 2 centimeters, preferably less than 1 centimeter, from the lower terminal 4. The crystal 30 may be in contact with the lower terminal 4 or separated from the lower terminal 4 by a transparent support. The thickness e2 of the crystal 30, measured along the axis D, may vary from 0.2 to 5 millimeters, preferably from 0.2 to 2 millimeters.

Crystal 30 is an isotropic electro-optical crystal. An isotropic electro-optical crystal is a crystal whose optical properties are isotropic in the absence of an electric field and whose optical properties are anisotropic in the presence of an electric field. Preferably, the crystal 30 is bare, that is to say without electrode deposited on these faces. The crystal 30 may be zinc tellurium (ZnTe), cadmium telluride (CdTe), cadmium tellurium and zinc (Cd- _x Zn _x Te) (with x ranging from 0.01 to 0.15). , bismuth oxide and silicon (BSO), gallium arsenide (AsGa) or indium phosphide (InP).

The crystal 30 is surrounded by a layer 32 whose outside diameter is equal to the inside diameter d2 of the tube 10. The thickness, measured along the axis D, of the layer 32 may be substantially equal to the thickness e2 of the crystal 30. Alternatively, the thickness of the layer 32 may be greater than the thickness e2 of the crystal 30, the layer 32 then covering the crystal 30. The layer 32, with possibly the crystal 30, delimits an upper face 33 perpendicular to the axis D. The relative permittivity of the layer 32 is substantially equal to the relative permittivity of the crystal 30. By way of example, the crystal 30 and the layer 32 have a relative permittivity that can vary from 4 to 60, preferably 7 to 15. The material forming the ring 32 may be a resin or glue comprising a charge for adjusting the relative permittivity of the layer 32.

The crystal 30 preferably has, in a plane perpendicular to the axis D, a square or rectangular section having a side whose length can vary from 0.5 to 4 millimeters, preferably from 1 to 3 millimeters.

Alternatively, the layer 32 is not present. The crystal 30 then has the shape of a cylinder of axis D. The sensor 16 comprises a system 34 for transmitting a light beam 35 to the crystal 30 and a system 36 for analyzing the light beam 37 coming from the crystal 30. The electrical and / or optical components of the systems 34 and 36 are arranged in a metal enclosure 38 fixed to the lower terminal 4 and disposed on the side of the lower terminal 4 opposite to the inner tube 10. The metal enclosure 38 and the lower terminal 4 form a Faraday cage, protecting the components contained in the enclosure 38 against external electromagnetic interference.

The lower terminal 4 comprises at least one opening 39 allowing the passage of the light beams 35, 37. The opening 39 is covered, at least in part, by the crystal 30. The dimensions of the opening 39 are determined in such a way that not to disturb the protection provided by the Faraday cage formed by the metal enclosure 38 and the lower terminal 4. The opening 39 is, for example, a circular opening of axis D having a diameter of less than 5 millimeters, preferably less than at 2 millimeters. The opening 39 may be filled with a transparent material. However, the crystal 30 can play the role of a sealed wall closing the opening 39. The face of the crystal 30 in contact with the lower terminal 4 receives the incident beam 35 and is designated by the reference 40. The face of the crystal 30 opposite to the face 40 is designated by the reference 42. The axis D is perpendicular to the faces 40, 42. In the first embodiment of the measuring device shown in Figure 1, the incident beam 35 enters the crystal 30 by the face 40 passes through the thickness e2 of the crystal 30, is reflected on the face 42, crosses again the thickness e2 and leaves the crystal 30 by the face 40. The propagation direction of the incident beam 35 is slightly inclined with respect to the axis D. Preferably, the angle between the incident beam 35 and the axis D is less than 10 degrees, preferably less than 5 degrees. However, it may be advantageous if the angle between the incident beam 35 and the axis D is not exactly equal to zero, to avoid certain undesirable reflection phenomena, especially in the case of the use of a laser. In addition, since the reflected beam 37 is symmetrically inclined to the incident beam 35 with respect to the axis D, the beams 35 and 37 are separated in a simple manner.

In the first embodiment of the measuring device according to the invention, the measuring device 1 does not comprise an optical fiber. In particular, there is no optical fiber between terminals 2, 4.

The operating principle of the optical sensor 16 is as follows. The electric field present at the crystal 30 varies certain optical properties of the crystal 30. The light beam passing through the crystal 30 is therefore modified. The modification of the light beam is detected by the sensor 16 which provides a signal representative of the intensity of the measured electric field, from which the value of the voltage between the terminals 2 and 4 can be determined.

When a potential difference is present between the upper terminal 2 and the lower terminal 4, an electric field appears between the terminals 2, 4 and is, in the absence of an obstacle, parallel to the axis D. In addition, in the inner tube 10, the electric field tends to have a substantially constant intensity of the terminal 2 to the terminal 4. In fact, the inner tube 10 reduces the formation of electric field overcurrent peaks near the terminals 2, 4. As a result, the intensity of the electric field near the lower terminal 4 is substantially identical to the intensity of the electric field halfway between the terminals 2, 4. The value of the electric field measured using the crystal 30 located at proximity of the lower terminal 4 is therefore well representative of the average amplitude of the electric field between the terminals 2, 4.

The fact that only the crystal 30 is disposed between the terminals 2, 4, in the absence of other optical or electronic components of the sensor 16, reduces the disturbances of the lines of the electric field in the tube 10. In addition, as the crystal 30 is embedded in the layer 32 which has the same relative permittivity and that the face 33 is perpendicular to the axis D, the lines of the electric field are advantageously not disturbed in the vicinity of the crystal 30 and remain substantially parallel to the axis D .

Advantageously, since there are no optical fibers in the tube 10, the bulk of the crystal 30 in a plane perpendicular to the axis D can be reduced, and in particular be smaller than 4 millimeters. The outer diameter d3 of the tube 10 can therefore also be reduced. The amount of dielectric material needed for making the tube 10 can be reduced.

Advantageously, the tube 10 is not hollow but filled with the dielectric material. This further improves the uniformity of the electric field between terminals 2 and 4.

FIG. 2 represents, in more detail, an exemplary embodiment of the sensor 16 of FIG. 1, particularly suitable for measuring a variable voltage, for example an alternating voltage. The face 42 of the crystal 30 opposite to the lower terminal 4 may be covered with a reflective layer 44 to improve the reflection of the incident light beam 35. In addition, an antireflection treatment may be applied to the face 40 to improve the transmission of the beam bright incident 35.

The system 34 for emitting light beam 35 may be a polarized light source 46, coherent or not, comprising for example a light emitting diode and a polarizer or a laser diode.

The analysis system 36 receives the light beam 37 returned by the reflecting surface 42, and having thus crossed the crystal 30 twice. The system 36 comprises a rectilinear polarizer 48 receiving the beam 37. At the exit of the polarizer 48 is arranged a photodetector 50 which provides a signal proportional to the intensity of the incident wave on the polarizer 48 in the polarization direction of this polarizer 48. It is noted that, usually in the field of anisotropic optics, a polarizer is called an element capable of fixing the polarization of the light which passes through it in the direction of a polarizer. device using this light, and called "analyzer" the same device when it is placed on the side of the detector of a system, and is used to analyze the polarization of the light it receives. In the present description, the term "polarizer" will always be used, whether it is placed in a position where it fixes the polarization or in a position where it analyzes the polarization of the light that it receives, since it This is the same hardware device.

As described in particular in the publication entitled "Electro-optic sensors for electric field measurements." II. "Choice of the crystals and complete optimization of their orientation" to the names of Lionel Duvillaret, Stéphane Rialland and Jean-Louis Coutaz, for an electro crystal -optical to which is applied an electric field Ë and crossed by a light beam, we can determine n + and n- own refractive indices of the crystal equal to the half-axes of the ellipse corresponding to the intersection of the ellipsoid indices of the electro-optical crystal in the presence of the electric field and the plane of polarization of the incident light beam. It is possible to determine the modification undergone by the light beam passing through the crystal from these own refractive indices n + and n-.

In the present embodiment, the detection of the electric field is carried out by detecting the polarization state modulation of the light wave passing through the crystal in the presence of the electric field Ë.

It is measured, from the light beam emitted 37, a signal representative of the phase difference Δφ induced between the two states of rectilinear polarization allowed to occur. propagate in the crystal 30. The phase difference Δφ is given by the following relation (1):

where L is the distance traveled by the light beam in the crystal 30 (i.e. twice the thickness e2), λ is the wavelength of the light beam 37. The expressions of the indices n ₊ and n_ depend on the electric field present at the crystal 30 and are given by the following relations (2) and (3):

n_ = n_ (E = 0) - ^ (Δίζ · E) ² + (AK _h · E) ² (3) where n ₊ (Ë = 0) and n_ (Ë = 0) are the refractive indices of the crystal In the absence of electric fields and ΔΚ _& and AK _h are the main sensitivity vectors of crystal 30.

It follows that the phase shift Δφ corresponds to the sum of the phase shift Δφ ^ due to the electric field Ë and the phase shift Δφ ₀ in the absence of a field, the phase shifts Δφ ^ and Δφ ₀ being given by the relations (4) and ( 5) following:

4πι ^ (Δκ _¾ ^■ Ë) ² + (AK _b ^■ Ë) ²

Ap _è = (4)

_A 2π (η ₊ (Ε = 0) - n_ (Ë = 0)) L

Δφ ₀ = ± (5)

Since the crystal 30 is an isotropic electro-optical crystal, the proper refractive indices n ₊ (Ë = 0) and n_ (Ë = 0) when the electric field is zero are equal. The phase shift Δφ ₀ is therefore zero, whatever the environment of the sensor, and in particular whatever the temperature or the surrounding pressure at the level of the sensor 30.

The polarization of the incident light beam 35 is a rectilinear or approximately rectilinear polarization or a circular or approximately circular polarization. In this case, the orientation of the linear polarization is at 45 °, or approximately 45 °, with respect to the directions associated with the own refractive indices n + and n-. Preferably, the polarization of the incident light beam 35 is a circular or approximately circular polarization since there is then no particular adjustment of the orientation of the polarization to be carried out.

In the measuring device according to the present invention, the orientation of the electric field in the crystal 30 is known. Indeed, the electric field Ë is oriented parallel to the axis D. In the present embodiment of the measuring device 1 according to the invention, the crystal 30 is oriented so that the parallel faces 40, 42 of the crystal 30 correspond to <100> or <010> or <001> faces of the crystal 30, or approximately to <100> or <010> or <001> faces of the crystal 30. In addition, the direction of propagation of the incident beam The angle between the incident beam 35 and the axis D is less than 10 degrees, preferably less than 5 degrees.

In this configuration, the vector AK _b is zero and the vector AK _a is parallel to the axis D. The amplitude AK _a of the vector AK _a is given by the following relation (6):

_AK = ₄₁ r n ³ (6) where n is the refractive index of the crystal 30 in the absence of electric field and r / _[] _ is an element of the tensor ^¬ electro optical crystal 30. The expression of the phase shift Δφ is therefore particularly simple and is given by the following relation (7):

47ûLEr ₄₁ n ³

Δφ = - ^ - (7) λ

The polarizer 48 converts the polarization state modulation of the light beam 37 having passed through the crystal 30 into an amplitude modulation of the light beam. The polarization axis of the polarizer 48 is approximately 45 degrees aligned with the directions associated with the own refractive indices n ₊ and n_.

The photodetector 50 makes it possible to convert the amplitude modulation of the light beam coming from the polarizer 48 into a electric current i _] _ whose expression is given by the following relation (8):

i! I = ₀ d + s) (8) where I _Q is the average current supplied by the photodetector 50 and s is the useful signal that has approximately the expression given by equation (9) below:

s = A * E (t) = B * V (t) (9) where A and B are constants and V (t) is the voltage between terminals 2 and 4, expressed here as a function of time t. The constants A and B and the current _Q can be determined by calibration.

Alternatively, the detection of the electric field can be carried out by amplitude modulation or phase modulation of the light beam. Examples of amplitude modulation or phase modulation are described in the publication "Electro-optic sensors for electric field measurements." Theoretical comparison among different technical modulation "in the names of Lionel Duvillaret, Stéphane Rialland and Jean-Louis Coutaz.

The measuring device 1 according to the first embodiment of the invention has a particularly simple structure since it requires, for the analysis of the light beam received only a polarizer 48 and a photodetector 50. In particular, the sensor 16 does not include no quarter-wave or half-wave blade.

FIG. 3 shows a variant of the sensor 16 in which the systems 34 and 36 contained in the metal enclosure 38 are arranged at a distance from the lower terminal 4. The light beams 35, 37 are transmitted by optical fibers 62, 64 between the metal enclosure 38 and the lower terminal 4. It may be polarization-maintaining fibers whose ends 66 and 67 are connected to collimators. The polarizer 48 is disposed between the crystal 30 and the optical fiber 64 which may consist, for example, of a plastic fiber at very low cost. The optical fiber 62 is a fiber for delivering at its end 67 a rectilinear or approximately rectilinear polarization beam or circular or approximately circular polarization. By way of example, a circular or approximately circular polarization beam may be obtained by means of a polarization-maintaining fiber followed by a quarter-wave birefringent element. The optical fibers 62, 64 do not penetrate the volume between terminals 2 and 4.

An advantage of the measuring device of FIG. 3 is that the electronic and optoelectronic components of the systems 34 and 36 of the sensor 16 can be deported from the rest of the device, in particular from the assembly comprising the terminals 2, 4 and the insulator 6. This can further facilitate the maintenance operations of the measuring device. The systems 34 and 36 can be integrated in the processing module 18.

FIG. 4 represents another variant of the sensor 16 in which the incident light beam 35 passes through the crystal 30 in a direction substantially perpendicular to the axis D, that is to say in a direction substantially perpendicular to the orientation of the field At this point, deflection prisms 70, 72 are arranged on either side of the crystal 30. In addition, a polarizer 77 is disposed between the crystal 30 and the prism 72. The prism 70 is in contact with a side face 74 of the crystal 30 and the polarizer 77 is in contact with the prism 72 on the one hand and with the side face 76 of the crystal 30, parallel to the face 74. The faces 74 and 76 are parallel to the axis D and correspond to faces <110>, <011> or <101> of the crystal 30 or approximately to faces <110>, <011> or <101> of the crystal 30. The polarizer 48 previously described is not present.

In this configuration, the vector AK _a is perpendicular to the faces 40 and 42 and the vector AK _b is perpendicular to the faces 74 and 76. The amplitude AK _a of the vector AK _a is given by the preceding relation (6). The expression of phase shift Δφ is therefore particularly simple and is given by the relation (7) above.

With respect to the variant shown in FIG. 4 in which the light beam passing through the crystal 30 is perpendicular to the electric field Ë, the measuring device shown in FIG. 1, in which the light beam passing through the crystal 30 is substantially parallel to the electric field Ë, has the advantage of being more compact in a direction perpendicular to the axis D. In addition, the sensitivity of the measuring device shown in Figure 1 in which the light beam passing through the crystal 30 is substantially parallel to the electric field Ë is substantially twice the variation shown in FIG. 4 for the same crystal thickness traversed by the light beam due to the round-trip of the light beam in the crystal 30.

FIG. 5 represents a variant of the analysis system 75 in which the analysis system 75 comprises a non-polarizing separator plate 80 receiving the reflected beam 37 and which separates the beam 37 into two beams 82, 84. The beam 82 crosses a polarizer 86 and is detected by a photodetector 88. The beam 84 passes through a polarizer 90 and is detected by a photodetector 92.

The axes of the polarizers 86, 90 are crossed and oriented so as to maximize the optical power modulation, induced by the electric field, and measured by the analysis system 75. The photodetectors 88, 92 have the same characteristics and provide a current identical when subjected to the same light beam.

The photodetector 88 delivers the current i _] _ according to the preceding relation (8) while the photodetector 92 delivers a current 2 according to the following relation (12):

i ₂ = i0 ds) (10) The processing device 18 can perform the subtraction of the currents it and 2 to obtain a useful signal whose amplitude is equal to twice the amplitude of the signal s. In addition, the subtraction currents it and 2 makes it possible to overcome a part of the noise present on the current ÏQ.

Alternatively, the splitter plate 80 may be replaced by a polarization splitter, for example a Wollaston prism which transforms the emitted beam 37 into two linearly polarized beams orthogonal to each other. In this case, the polarizers 86 and 90 are not present.

According to another variant, the separator blade 80 can be replaced by an optical device, non-polarizing, three-beam separation. The optical device may comprise a diffraction grating. The optical separation device provides beams 82 and 84 described above and a third beam that is provided to a photodetector without the interposition of a polarizer. The third beam makes it possible to have an optical power reference and to improve the accuracy of the measurement by performing a normalization.

FIG. 6 represents another exemplary embodiment of measurement device 95 in which crystal 30 is disposed between terminals 2 and 4, away from terminals 2 and 4. Crystal 30 is, for example, located halfway between terminals 2 and 4. The light beam can be led from the transmission system 34 to the crystal 30 by a polarization-maintaining optical fiber 100 and then transmitted from the crystal 30 to the analysis system 36 by another fiber 102, a polarizer 103 being placed between the crystal 30 and the fiber 102. The fiber 102 may be for example a plastic fiber at very low cost.

Fig. 7 shows an exemplary embodiment of an abnormality detection device 110 according to the present invention. The anomaly detection device 110 comprises an optical sensor 16 as described above in relation to FIG. 1. It further comprises an additional optical sensor 16 ', identical to the optical sensor 16, except that the crystal 30' of the sensor 16 'is not arranged in the tube internal 10 but between the tube 10 and the insulator 6. The crystal 30 'rests on the lower terminal 4 or is close to the lower terminal 4. A layer 32' surrounds the crystal 30 'and has a relative permittivity similar to that crystal 30 '. Therefore, the electric field present at the crystal 30 'can vary under certain conditions, for example during a fault or a malfunction of the insulator 6. An example is the presence of frost or salt mist covering the insulator 6. Another example is the presence of a dust deposit due to atmospheric pollution covering the insulator 6.

The processing device 18 'receiving the signals provided by the sensors 16 and 16' can compare the two received signals. A variation of this difference can then mean that there is a malfunction of the insulator 6 linked, for example, to the pollution of the fins 8.

FIG. 8 is a partial and schematic representation of another exemplary embodiment of a voltage measuring device 120 according to the invention. The device 120 comprises a current carrying element 122, for example a cable or a set of disjointed cables, disposed in a chamber 124. The enclosure 124 may be a cylindrical enclosure and the conductive element 122 may be arranged substantially according to the invention. The axis of the enclosure 124. The conductive element 122 is separated from the enclosure 124 by an insulator which corresponds to the internal volume of the enclosure 122 filled with a solid, a liquid, a gas or a composite medium having a high dielectric strength, for example sulfur hexafluoride. In addition, insulating supports, not shown, can be distributed in the enclosure along the transport element 122 to maintain the transport element 122. By way of example, the internal diameter of the enclosure 122 can to be of the order of 1 meter.

The measuring device 120 is particularly suitable for equipping a high-voltage disconnector or a high-voltage circuit breaker. The measuring device 120 comprises an electric field optical sensor 16 connected to a processing module 18, the sensor 16 and the module 18 possibly having the structures described above. The crystal 30 of the optical sensor 16 is disposed in the enclosure 124. At least one face of the crystal 30 is less than 2 centimeters, preferably less than 1 centimeter, from the inner wall of the enclosure 124. The crystal 30 may be in contact with the inner wall of the enclosure 124 or separated from the inner wall of the enclosure 124 by a transparent support. The crystal 30 may be surrounded by the layer 32 and the opening 39 is made in the enclosure 124. In the measuring device 120, the electric field Ë is oriented radially with respect to the axis of the enclosure 124. From therefore, the orientation of the electric field in the crystal 30 is substantially identical to that of the measuring device 1 described above, the axis D, described above, being oriented according to a diameter of the enclosure 124 for the device 120.

FIG. 9 represents an alternative embodiment of the sensor 16 adapted for measuring a continuous voltage or varying slowly as a function of time. Although this variant is described in relation to the measuring device 120 of FIG. 8, it can also be implemented with the examples of measuring devices described in FIGS. 1 to 7.

In this variant, the polarized wave source 46 is a rectilinear wave source and the direction of the axis of the polarizer 48 is oriented approximately at 45 ° with respect to the direction of polarization of the rectilinear wave provided by the source. 46.

In addition, the sensor 16 comprises a polarization modulator 130. The polarization modulator 130 is placed between the polarized light source 46 and the opening 39 and is traversed by the incident beam 35 and the reflected beam 37. Preferably, the incident beam 35 having passed through the polarization modulator 130 directly reaches the crystal 30 without passing through any other device capable of modifying its polarization and the reflected beam 37 reaches the polarization modulator 130 after being reflected by the crystal 30 without having passed through any other device capable of modifying its polarization.

The polarization modulator 130 is adapted to vary the direction of polarization of the rectilinear wave emitted by the source 46 periodically. By way of example, the polarization modulator 130 is adapted to rotate the polarization direction of the rectilinear wave emitted by the source 46 at a constant angular velocity ω. By way of example, the angular velocity ω can vary from about 1000 rpm to about 100000 rpm.

The polarization modulator 130 may be a half-wave, or approximately half-wave, rotating plate whose rotational speed is ω / 2. The rotation of the half wave plate 130 is, for example, performed by an electric motor, not shown. When the polarization modulator 130 is a rotating half-wave plate, the sensor 16 further comprises a quarter-wave plate 132 or approximately quarter wave, which is traversed by the reflected beam 37 and which is disposed between the half-wave plate 130 and polarizer 48. Preferably, one of the slow or fast axes of the quarter-wave plate 132 is aligned with the direction of polarization of the rectilinear wave provided by the source 46.

FIG. 10 represents the evolution of the polarization state of the reflected beam 37 after passing through the half-wave plate 130 and before crossing the quarter-wave plate 132 when the electric field at the crystal is not zero . The state of polarization of the reflected beam 37 is then an elliptical polarization whose major axis is aligned with the direction of polarization of the rectilinear wave provided by the source 46 and whose minor axis evolves periodically, at a 4ω pulse between the null value (in which case the polarization is in fact rectilinear) and a maximum value. In FIG. 10, the states of rectilinear and elliptical polarization are represented. extremes 134, 136 and an intermediate elliptical polarization state 138. The maximum value of the small axis of the elliptical polarization is proportional to the square of the electric field applied to the crystal 30.

The quarter-wave plate 132 transforms the elliptical polarization of the reflected beam 37 into a rectilinear polarization whose polarization direction oscillates periodically at a pulse 2ω and whose oscillation amplitude varies linearly with the electric field applied to the crystal 30.

The polarizer 48 converts the polarization state modulation of the light beam 37 having passed through the quarter wave plate 132 into an amplitude modulation of the light beam.

The photodetector 50 makes it possible to convert the amplitude modulation of the light beam coming from the polarizer 48 into an electric current 13 whose expression is given by the following relation (11):

i ₃ = i ₂ * (i + _U ) (11) where 12 is the average current supplied by the photodetector 50 and u is the useful signal which has approximately the expression given by the following relation (12):

u = C * E (t) * sin (cp ₀ -2cot) = F * V (t) * sin (cp ₀ -2cut) (12) where cpg, C and F are constants and V (t) is the voltage between the central element 122 and the enclosure 124, which is assumed to be constant or slowly varying as a function of time. The constants cpg, C and F and stream 2 can be determined by calibration. The voltage V being substantially constant or changing slowly as a function of time, a filtering operation, simple to implement, at the frequency 2ω can then be performed to obtain the F * V term.

Alternatively, one of the slow or fast axes of the quarter-wave plate 132 may be inclined at approximately 45 ° to the polarization direction of the rectilinear wave. provided by the source 46. In this case, a relation similar to the relation (12) described above is reached.

FIG. 11 shows a variant of the polarization modulator 130, in which the polarization modulator 130 comprises an electro-optical phase modulator 140, controlled by a voltage source 142, and a quarter-wave plate 144, or approximately quarter 'wave. The modulator 140 is located between the source 46 and the quarter wave plate 144 and the quarter wave plate 144 is located between the modulator 140 and the crystal 30. The XL and XR axes, slow and fast, of the phase modulator 140 form an angle of approximately 45 ° with respect to the direction of polarization R of the rectilinear wave provided by the source 46. The control voltage of the phase modulator 140 is a periodic voltage, for example in the form of sawtooth, whose frequency is ω / 2π. Preferably, one of the slow or fast axes of the quarter wave plate 144 is aligned with the polarization direction R of the rectilinear wave provided by the source 46.

In the case where the modulator 130 has the structure shown in FIG. 11, the measuring device 120 does not include the quarter-wave plate 132.

FIG. 12 represents the evolution of the polarization state of the reflected beam 37 after passing through the modulator 130 shown in FIG. 11 and before passing through the rectilinear polarizer 48 when the electric field at the crystal is not zero. In the forward direction, the incident beam 35 passes successively through the phase modulator 140 and then the plate 144. After reflection, the reflected beam 37 passes successively through the plate 144 and then the phase modulator 140. The polarization state of the reflected beam 37 is then a rectilinear polarization whose direction oscillates, periodically at a pulsation ω, between two extreme directions 146 and 148 passing through a median direction 150 which is approximately aligned with the direction of polarization of the rectilinear wave provided by the source 46 . The polarizer 48 converts the polarization state modulation of the light beam 37 having passed through the phase modulator 140 into an amplitude modulation of the light beam.

The useful signal u of the expression (11) described above has approximately the expression given by the following relation (13):

u = C * G (t) * sin (cp ₁ -cut) = H * V (t)) * sin (9 ₁ -Qt) (13) where cp] _, G and H are constants. The constants φ] _, G and H and the current 2 can be determined by calibration.

The voltage V being substantially constant or changing slowly as a function of time, a filtering operation, simple to implement, at the frequency ω can then be performed to obtain the term H * V.

The voltage measuring device according to the invention has several advantages. The measuring device according to the invention can be lightweight, allowing transport, installation and maintenance at low cost. In addition, the voltage measuring device according to the invention is compatible with existing isolator structures, allowing a simple implementation.

Various embodiments with various variants have been described above. It is noted that one skilled in the art can combine various elements of these various embodiments and variants without being creative. In particular, the use of optical fibers for transporting the signals between the crystal 30 and the transmission systems 34 and analysis 36 may be provided with the variants and embodiments described in connection with FIGS. 4, 5, 7 and 9.

Claims

A device (1; 95; 120) for measuring a voltage comprising:

first and second conductive terminals (2, 4; 122, 124) between which the voltage is measured;

an insulator (6) separating the first and second terminals;

an optical sensor (16) measuring the electric field at a location between the first and second terminals, the optical sensor comprising an isotropic electro-optical crystal (30) between the first and second terminals; and

a detector (18) determining the voltage from the measured electric field.

2. Measuring device according to claim 1, wherein the crystal (30) comprises a face (40) less than 2 centimeters from the first terminal (4).

3. Measuring device according to claim 2, wherein the crystal (30) is in contact with the first terminal (4; 124).

4. Measuring device according to any one of claims 1 to 3, comprising an enclosure (38) containing:

a source (46) of a light beam (35), the light beam passing through the crystal (30); and

an analysis system (36) of the light beam having passed through the crystal.

The measuring device according to claim 4, wherein the source (46) provides a linearly polarized wave, the device further comprising a polarization state modulator (130) located between the source (46) and the crystal (30) adapted to periodically vary the polarization state of the light beam provided by the source.

The measuring device according to claim 5, wherein the polarization state modulator (130) comprises a half-wave or approximately half-wave plate rotated at a constant speed.

The measuring device according to claim 5, wherein the polarization state modulator (130) comprises an electro-optical phase modulator (140) and a quarter wave plate (144).

8. Measuring device according to any one of claims 4 to 7, wherein the terminals (2, 4) are perpendicular to a direction (D) and wherein the crystal (30) comprises at least one face (40) of the type <100>, <010> or <001> perpendicular to said direction, the light beam (35) reaching the crystal on said face, the beam being inclined with respect to said direction (D) by an angle of less than 10 degrees .

9. Measuring device according to any one of claims 4 to 7, wherein the terminals (2, 4) are perpendicular to a direction (D) and wherein the crystal (30) comprises at least one face (74) of the type <110>, <011> or <101> parallel to said direction, the light beam (35) reaching the crystal on said face, the beam being inclined at an angle less than 10 degrees with respect to an additional direction perpendicular to said face.

10. Measuring device according to any one of claims 4 to 9, wherein the enclosure (38) is metallic and is fixed to the first terminal (4; 124), on the side of the first terminal opposite the insulator. (6), the first terminal comprising an opening (39) for the passage of the light beam.

11. Measuring device according to any one of claims 4 to 9, comprising at least one optical fiber (62, 64) connecting the enclosure (38) to the first terminal (4) for transporting the light beam (35). .

12. Measuring device according to any one of claims 1 to 11, comprising no optical fiber between the first and second terminals (2, 4).

13. Measuring device according to any one of claims 1 to 12, comprising a layer (32) surrounding the crystal (30), the layer having a relative permittivity equal to the relative permittivity of the crystal to 10%.

14. Measuring device according to any one of claims 1 to 13, comprising a dielectric portion (10) connecting the first terminal (4) to the second terminal (2) and comprising an outer wall (14) surrounding the crystal (30). ).

15. Measuring device according to any one of claims 1 to 13, wherein the first terminal (124) is cylindrical, the second terminal (122) being disposed in the first terminal.

A fault detection device, comprising a measuring device (1) according to claim 14, and an additional optical sensor (16 ') measuring the electric field at an additional location between the first and second terminals (2, 4) to the outside of the dielectric portion (10).