Abstract:
An optical sensor configuration contains an optical current sensor and/or an optical voltage sensor. The sensor configuration further contains a first and a second hollow member, preferably ring shaped profiles, which are together disposed to form a hollow section. The sensor configuration further includes an optical fiber of the current sensor disposed in an annular groove, the groove being disposed at the boundary surface between the first hollow member and the second hollow member, and/or an optical fiber of the voltage sensor is disposed in a recess of the second hollow member. The first hollow member has an annular recess into which the second hollow member is disposed whereas the first hollow member is an L-shaped or U-shaped ring with two legs and the recess is formed between the two legs.

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention is pertaining to an optical sensor arrangement comprising an optical current sensor and/or an optical voltage sensor, the sensor arrangement comprises a first and a second hollow member, preferably ring shaped profiles, which are arranged to form together a hollow section, the sensor arrangement further comprises an optical fibre of the current sensor arranged in an annular groove, said groove being arranged at the boundary surface between first hollow member and second hollow member, and/or an optical fibre of the voltage sensor arranged in a recess of the second hollow member; as well as to the use of such a sensor arrangement in gas insulated switchgear and a method for assembly and/or retrofitting an electrical switchgear. 
   In electrical switchgear, it is necessary to measure the current flowing through the switchgear and voltage between two potentials at the switchgear, e.g. the high voltage potential of a current-carrying conductor and ground. In gas insulated switchgear (GIS) the electrical conductors are arranged inside a gas filled enclosure which makes it difficult to arrange current and voltage sensors at the conductors. Because compactness of the switchgear and a space and cost saving design is always a design goal of such switchgear, the utilized sensor arrangements have to be compact, robust and easy accessible. There are different sensor types known for this task from prior art, e.g. current and voltage transformer or optical current and voltage sensor. 
   CH 694 193 A5 shows a module comprising a well-known current transformer. The module is flanged to the openings of an electrical switchgear. Because the current transformer requires a certain space, the modules have a great overall length, which increases the overall size of the switchgear. DE 43 14 821 A1 discloses a current transformer, which is integrated in the enclosure of the gas insulated switchgear. But such an arrangement increases the overall length of the switchgear. 
   Known optical sensor arrangements are often arranged remote from the switchgear. To this end, e.g. an electrical connection is made from the sensor arrangement to a high voltage busbar of the switchgear. From DE 196 34 251 A1 an optical voltage sensor is known which is arranged in a cap flanged onto a flange of an opening of a gas insulated switchgear enclosure. Although such an arrangement is compact an extra opening in the switchgear enclosure and extra electrical connections from the electrical conductors to the sensor arrangement are required. Moreover, such an arrangement does not provide for a current transformer. 
   U.S. Pat. No. 5,136,236 shows an optical sensor arrangement comprising an optical current sensor and/or an optical voltage sensor, the sensor arrangement comprises a first ( 11 ) and a second ( 5 ) hollow member, preferably ring shaped profiles, which are arranged to form together a hollow section, the sensor arrangement further comprises an optical fibre ( 12 ) of the current sensor arranged in an annular groove, said groove being arranged at the boundary surface between first and second hollow member, and/or an optical fibre ( 7   a ) of the voltage sensor arranged in a recess ( 9 ) of the second hollow member ( 5 ). 
   SUMMARY OF THE INVENTION 
   It is one object of the invention to provide an optical current and voltage sensor arrangement for an electrical switchgear, which is more compact and which is easy to integrate in the electrical switchgear and easy accessible. 
   This object is solved by the invention by providing an annular recess on the first hollow member into which the second hollow member is arranged whereas the first hollow member is a L- or U-shaped ring with two legs between which the recess is formed. 
   Such an arrangement is especially easy and compact because current and voltage sensor are provided in one unit and because the second hollow member is arranged in a recess of the first hollow member. The arrangement can easily be preassembled and can easily be integrated into an electrical switchgear. 
   It is especially advantageous to form first hollow member from electrically conductive material, preferably of metal. This ensures that the metallic enclosure of the switchgear is not interrupted by the sensor arrangement when assembled together. Hence, the enclosure acts like an electromagnetic shield, which reduces or eliminates the EMC radiation. This is especially useful when the substation is equipped with sensitive digital control and instrumentation equipment. But this is also important for the safety of the staff since the metallic enclosure is always kept on the same potential, preferably ground potential. If the second hollow member is formed of electrically insulating material it is ensured that the groove is at least partly covered by an insulating material. With such an arrangement the current measurement is not influenced by induced current in the conducting first member since no current loops can develop around the groove with the optical fibre 
   The groove extends advantageously circumferentially around the opening of the hollow section through which the current-carrying conductor is led through. 
   The optical fibre of the current sensor can easily be led to the groove through a bore in the first hollow member connecting the outer surface of the first hollow member with the groove. This ensures an easy assembly of the sensor arrangement. 
   The recess of the second hollow member is advantageously a radially extending dead end bore, which can easily be manufactured, into which at least one Pockels cell is arranged. The electric field around the conductor, which acts also in the second member, influences the Pockels cell thus enabling the measurement of the voltage by means of the effect. 
   To ensure gas tightness of the enclosure a seal is provided between the first and second hollow member. 
   The optical sensor arrangement is especially advantageously arranged between two flanges of adjacent enclosure parts of the switchgear. This allows a very simple assembly of the switchgear. 
   The design of the optical sensor arrangement allows that the sensor arrangement is preassembled and integrated as unit into the switchgear, which constitutes a very effective method to assemble or retrofit an switchgear. 
   The invention is described in the following with respect to  FIGS. 1 to 3  showing in a schematic and not limiting way an inventive optical sensor arrangement and an application of the sensor arrangement in a gas insulated switchgear (GIS) device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a typical three pole gas switchgear device, 
       FIG. 2  shows different sectional views of an inventive optical sensor arrangement as integrated in a gas insulated switchgear device and 
       FIG. 3  shows a top view of such an inventive optical sensor arrangement. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A gas insulated switchgear (GIS) device  1  typically includes two, e.g. for each phase, disconnector switches  3 , earthing switches  4 ,  7  and circuit breaker  5 , as shown in  20   FIG. 1 , although it may as well comprise other, further and/or different devices, as is well-known. Such switchgear devices  1  are well-known from prior art and hence are not explained further. The enclosure  11  of the GIS device  1  is filled with gas, e.g. SF 6  gas, and includes also mechanical parts of the switches, e.g. the contacts, drive mechanism, etc., of the different switches of the switchgear  1  and also the electrical conductor  10 , which is led through the switchgear  1 . Into the enclosure  11  is integrated also an inventive optical sensor arrangement  6  for measuring the electrical current and voltage, as described in detail in the following. 
   The optical sensor arrangement  6  is best shown in  FIGS. 2 and 3  and is described in the following with reference to  FIGS. 2 and 3 . The optical sensor arrangement  6  is arranged between two flanges  12 ,  12 ′ of two adjacent parts  11 ,  11 ′ of the switchgear enclosure. The enclosure parts  11 ,  11 ′ are connected in well-known manner by connecting means, e.g. like screws or bolts arranged in holes of the flanges  12 ,  12 ′ and holes  27  of the optical sensor arrangement  6 . Therefore, the optical sensor arrangement  6  forms a part of the switchgear enclosure. Consequently, the electrical conductor  10 , which is arranged inside the enclosure  11 , is also led through the optical sensor arrangement  6 . 
   The optical sensor arrangement  6  comprises a first hollow member having an recess, here an electrically conductive L-shaped ring  13 , preferably made from the same material as the enclosure  11 , into which a second hollow member, here an electrically insulating ring  14 , e.g. made of resin, is arranged. The cross-sectional profile of the annual recess in a transverse plane may have any shape, e.g. a rectangle but preferably a circle. L-shaped ring means that the ring  13  is having a cross-sectional profile in a longitudinal plane that is L-shaped. The two members are arranged next to each other to form a hollow section. In the embodiment shown, the second ring  14  is arranged in the recess formed by the two legs  13 ′,  13 ″ of the L-shaped ring  13 . But the two hollow members  13 ,  14  may of course be shaped differently. The second member  14  could for example be arranged between the legs of a Y- or U-shaped first member  13 , and formed from different materials. The first member  13  could be formed of any electrically conductive material, e.g. from metals or electrically conductive synthetic material, like conductive plastic or resin, but also of an electrically insulating material. The second member  14  could be formed of any suitable electrically insulating material, e.g. from synthetic material, like plastic or resin. 
   The annual recess of the first member  13  is arranged such that the electrically insulating member  14  is arranged on the inside of the optical sensor arrangement  6 , i.e. in assembled state at the inside of the switchgear  11 . Hence, the outer surface  22  of the optical sensor arrangement  6  is formed by the L-shaped ring  13 . The second ring  14  in the embodiment shown is fixed in the recess by a number of plates  20 , which are screwed to the L-shaped ring  13  with screws  21  thus cramping and holding the non-conductive ring  14  in position. The second member could of course be fixed to the first member by any suitable connection, e.g. positive or non-positive fit, fastened with screws or bolts, bonding, etc. In assemble state seals  19  are arranged between the L-shaped ring  13  and the flange  12 ′ of the enclosure  11 ′, between the electrically insulating ring  14  and the flange  12  of the enclosure  11  and between the L-shaped ring  13  and the electrically insulating ring  14  to ensure that the gas filled interior of the GIS device  1  is sealed off against the exterior and to avoid that gas leaks out from the  11 . 
   The optical sensor arrangement  6  comprises an optical current sensor and an optical voltage sensor, although it might have as well just a current or voltage sensor. 
   The optical current sensor is based on the well-known Faraday effect, which uses the fact that a polarized light signal is slowed down or accelerated in the influence of a magnetic field created as current flows through an electrical conductor  10 . Since this effect is well-known and often utilized in optical current sensors, it is not explained in detail. An annual groove  16  is arranged at the boundary surface  28  between first and second hollow member  13 ,  14 , in this embodiment on an inner face of one of the legs  13 ′,  13 ″ of the L-shaped ring  13 . Said groove  16  forms a closed loop in the ring  13 , as best seen in  FIG. 3 . But it is of course possible to arrange the groove  16  anywhere at the boundary surface between first and second hollow member  13 ,  14 , e.g. on the first  13  or second ring  14  or the groove  16  could be formed partially in first  13  and second hollow member  14 . The groove  16  is preferably concentric with the electric conductor  10 . The cross-sectional profile of the annular groove  16  in a transverse plane may have any shape, e.g. a rectangle but preferably a circle. A bore  15  connects the groove  16  with the outer surface  22  of L-shaped ring  13 . The groove  16  and the first  13  or second ring  14  are arranged and dimensioned such that the groove  16  is at least partly covered by the first  13  or second ring  14  in assembled state. An optical fibre  23  is led through the bore  15  and is arranged into the groove  16  of the L-shaped ring  13  thus ferentially encircling also the electrical conductor  10  led through the GIS device  1  and the optical sensor arrangement  6  in at least one circumferential loop. The bore  15  is preferably arranged essentially tangentially, in order to reduce the stress on the optical fibre  23  during and after the assembly. Hence, the magnetic field created by the current flowing through the electric conductor  10  influences the polarization of light traveling through the optical fibre  23  on a path around the electric conductor  10 . At the end of the optical fibre  23  the light can be mirrored back thus forcing the light to travel all the way back thus doubling the Faraday effect. But it would of course also be possible that the optical fibre  23  is led out from the groove  16  and the sensor arrangement  6  via the bore  15 . The degree of the phase shift of two polarized light signals is evaluated and is related to the current flowing through the conductor  10 . 
   The optical voltage sensor utilizes the well-known Pockels effect, which uses the fact that monochromatic light changes its circular polarization to an elliptical polarization as the light passes through an electro-optic crystal  25  (Pockels cell) arranged in the electric field of the electrical conductor  10 . Since this effect is well-known and often utilized in optical voltage sensors, it is not explained in detail. To this end, a recess, e.g. a dead end bore  18 , is provided in the second ring  14  into which at least one Pockels cell  25  is arranged. An optical fibre  24  is led to the dead end bore  18  and to the Pockels cell(s)  25  through a bore  17  in the L-shaped ring  13  aligned with the dead end bore  18 . The bore  17  and the dead end bore  18  are preferably arranged radially. The electric field passes also through the electrically insulating ring  14  thereby influencing the polarization of the light signal passing through the Pockels cell(s)  25  arranged in the bore  18 . The ellipticity of the light, which is evaluated, is then a measurement of the electrical field and consequently also of the voltage between the two potentials, e.g. the voltage potential of the conductor  10  and ground. 
   But it has to be noted that also other suitable optical current and voltage sensors might be utilized in the inventive sensor arrangement. 
   On the outer surface  22  of the optical sensor arrangement  6  an enclosure  26  might be mounted containing the opto-electronics needed to supply the optical current and/or voltage sensor with suitable light signals and to evaluate the light exiting the sensor arrangement. Also an interface to a digital data processor unit might be provided at the enclosure  26 . 
   The outer surface  22  of the sensor arrangement  6  is formed by a surface of the conductive L-shaped ring  13  so that the metallic, electrical conductive, grounded enclosure  11  is not interrupted by the sensor arrangement  6 , which is important for EMC reasons since EMC radiation is often bounded by certain limits. Basically the same could be achieved using ground straps or shields to electrically connect the two enclosure parts  11 ,  11 ′ in case the L-shaped ring  13  is formed of electrically insulating material. In this way, a very effective protection against electromagnetic radiation is achieved with the continuous conductive enclosure  11 ,  22 , which acts like an electromagnetic shield. This is also especially useful when the substation is equipped with sensitive digital control and instrumentation equipment. But this is also important for the safety of the staff since the metallic enclosure  11  is always kept on the same potential, preferably ground potential. 
   By arranging the groove  16  into which the optical current fibre  23  is arranged at the boundary surface between first and second hollow member  13 ,  14 , whereat at least on is formed of electrically insulating material, any current loops around the optical current fibre  23  due to the current induced in the enclosure  11  by the magnetic field around the electrical conductor  10  are avoided. Thus, the induced current can not influence the current measurement. 
   The enclosure  11  of the GIS device  1  is typically built of a number of single modules connected to each other, as shown in  FIG. 1 . To this end, flanges  12  are provided on the end faces of each module for joining the single modules. Suitable sealing means are to be provided between the flanges  12  to ensure the gas tightness of the enclosure  11 . The optical sensor arrangement  6  could be arranged between the flanges  12  of any two adjacent modules, also in a flanged elbow, of the electrical switchgear device  1  as described in detail above. 
   The design of the optical sensor arrangement  6  makes it possible that the arrangement is completely preassembled before it is integrated into the switchgear device  1 . This allows a very efficient assembly or retrofitting of the switchgear because the single sensor arrangement  6  is easy handlable as single unit. The sensor arrangement  6  only needs to be arranged between two flanges  12 ,  12 ′ of adjacent enclosure parts  11 ,  11 ′. To this end, the cross section of the first  13  and/or second hollow member  14  in a transverse plane is advantageously the same as a transverse cross section of the enclosure  11 , preferably circular as shown in the drawings, but they could of course have any possible other cross section. All necessary supplies and connections are either integrated into the sensor arrangement  6  or can easily be connected to it, e.g. by providing respective interfaces to a digital data processing unit.