Field of application

The present invention relates to a current measuring device for electric lines, according to the preamble of the independent claim.

The device referred to may advantageously be used for providing measurement values of the current passing through medium or high voltage electric cables of energy transport lines, in particular in the proximity of switches, transformers or also in transformation rooms or other mains equipment.

More in particular, the device object of the present invention may advantageously be used for providing current measurement values to devices for controlling the electric energy distribution network.

Prior art

As is known, in the field of distribution of medium and high voltage electric energy, the need of acquiring punctual voltage and current information is increasingly felt for allowing an optimal management of the line and in particular for allowing an increasingly efficient detection of faulty sections by remotely controlled systems.

To this end, devices are already widespread, which are arranged along the lines for measuring voltage and current and providing measurement values adapted for allowing the detection of different types of faults (for example short circuits of a phase to ground, short circuits between phases, discharges to ground, etc.).

More in detail, current measuring devices on the line are known, obtained with a Rogowski coil. The latter, as is known, comprises a toroidal solenoid winding arranged around the cable of a line and subject to be run through by an induced current proportional to the variation of the current passing through the line cable.

A drawback of such device lies in the fact that the induced current that flows through the winding in turn generates a magnetic field, the flow whereof is linked to the ring defined by the development of the same winding, causing errors in the current measurement. In order to obviate such drawback, Rogowski coils are known which comprise two solenoid windings, which develop along rings parallel to one another, are connected in series and are crossed by the induced current in opposite directions, so as to generate two equal and opposite magnetic fields, which generate flows linked to the ring of each winding having a null resultant.

To this end, US patent 5,414,400 describes a measuring device obtained with a Rogowski coil, which comprises two toroidal copper windings connected in series and obtained on a single printed circuit provided with a central hole. More in detail, the two windings are carried out by radial deposits provided on both faces of the printed circuit electrically connected to one another by metallized holes obtained between the two faces of the printed circuit. In particular, the two windings have radial deposits alternating and peripherally staggered for allowing the turns of the two windings not to overlap on one another.

A drawback of this device lies in the production difficulty related to the arrangement thereof due to the make of both windings on a same printed circuit.

A further drawback of this device consists in providing current measurements not sufficiently accurate for the presence of noises due to the magnetic fields that are not perfectly compensated, generated by the induced current that crosses the two windings. In order to obviate this last-mentioned drawback, current measuring devices have been made available on the market provided with windings having equal shape and dimensions. To this end, for example, patent EP 1264188 is known which describes a measuring device obtained with a Rogowski coil comprising two windings having the same dimensions, connected in series and each made on a respective printed circuit.

Each winding consists of radial deposits provided on both faces of the respective printed circuit and of electrical connections arranged for connecting the ends of deposits on the two faces and obtained through metallized through holes obtained going from one face of the printed circuit to the other.

The main drawback of the device described in patent EP 1264188 lies in the fact that it is subject to measurement errors due to noises generated by external magnetic fields that enter the space provided between the two windings.

A measuring device is further known from US patent 6,624,624 comprising a first and a second ring winding connected in series to one another, and respectively made on a first and on a second printed circuit, which are positioned parallel to one another and are assembled together with a layer of insulating material sandwiched therebetween.

Also this last-mentioned device of the known type is subject to measurement errors due to noises generated by external magnetic fields, since the arrangement of the insulating material between the two printed circuits does not prevent the insertion of said external magnetic fields in the gap between the first and the second solenoid.

US patent 2007/01 14992 describes a further measuring device of the known type, which comprises a first, a second and a third ring solenoid made of a conductive material and connected in series to one another. In particular, the turns of the first solenoid are arranged nested within the turns of the second solenoid, which are in turn arranged nested within the turns of the third solenoid.

The main drawback of the known device described in US 2007/01 14992 lies in its high construction complexity linked to the arrangement of the turns of the three solenoids nested the ones within the others, implying a high production difficulty of the device with consequent high production costs.

Disclosure of the invention

The main object of the present invention therefore is to overcome the drawbacks shown by the known solutions mentioned above by providing a current measuring device for electric lines capable of providing highly accurate measurements.

A further object of the present invention is to provide a current measuring device for electric lines which is not affected by the noises due to external magnetic fields.

A further object of the present invention is to provide a current measuring device for electric lines which is constructively simple and inexpensive to make and totally reliable operatively.

Brief description of the drawings

The technical features of the invention, according to the above objects, are clearly found in the contents of the claims below and the advantages of the same will appear more clearly from the following detailed description, made with reference to the annexed drawings, which show a purely exemplifying and non-limiting embodiment thereof, wherein:

- figure 1 shows a plan view of current measuring device object of the present invention;

- figure 2 shows a schematic exploded view of current measuring device object of the present invention;

- figure 3 shows a schematic section view of the current measuring device shown in figure 1 , according to line III - III of the same figure 1 ;

- figure 4 shows a perspective view of a detail of the current measuring device object of the present invention relating to some turns of the two solenoids;

- figure 5 shows a wiring diagram of the connections between the turns of the two solenoids of the current measuring device object of the present invention.

Detailed description

With reference to the annexed drawings, reference numeral 1 globally denotes the current measuring device for electric lines of the present invention.

According to the embodiment shown in the annexed figures, the current measuring device 1 is operatively associable to an electric cable 2 of a line for transporting electric energy, for example medium or high voltage three-phase current, for measuring an indicative value of the line current that flows within the same electric cable 2.

Said current measuring device 1 comprises a supporting structure 3 provided with at least one central through opening 4', 4" into which the electric cable 2 can be inserted, one first solenoid 5 (indicated with a continuous line in the annexed figures) and one second solenoid 6 (indicated with a dashed line in the annexed figures) arranged on the supporting structure 3, which develop as a ring around the through opening 4', 4" and are connected in series to one another.

The first and the second solenoid 5, 6 are subject to be run through by an induced current generated by magnetic induction following the variation of the line current that flows through the electric cable 2. The induced current that flows in the solenoids 5, 6 is proportional to the line current.

Advantageously, the induced current runs through the first solenoid 5 advancing according to the ring development thereof around the electric cable 2 in a first (clockwise) direction, whereas it runs through the second solenoid 6 advancing according to the ring development thereof in a second (counter clockwise) direction contrariwise the first one.

According to the idea at the basis of the present invention, the first solenoid 5 is obtained with first turns 7 wound around a first core 1 1 of the supporting structure 3 developing as a ring around the through opening 4', 4", and with second turns 8 wound around a second core 12 of the supporting structure 3 developing as a ring around the through opening 4' , 4" parallel to the development in the form of a ring of the first core 1 1. The second solenoid 6 is obtained with third turns 9 wound around the first core 1 1 and interposed between the first turns 7 of the first solenoid 5, and with fourth turns 10 wound around the second core 12 and interposed between the second turns 8 of the first solenoid 5. The term "interposed" means that one or more third consecutive turns 9 of the second solenoid 6 may be positioned between two first turns 7 of the first solenoid 5, and one or more fourth consecutive turns 10 of the second solenoid 6 may be positioned between two second turns 8 of the first solenoid 5, that is, one or more first consecutive turns 7 of the first solenoid 5 may be positioned between two third turns 9 of the second solenoid 6, and one or more second consecutive turns 8 of the first solenoid 5 may be positioned between two fourth turns 10 of the second solenoid 6.

Advantageously, according to the particular embodiment shown in the annexed figures, the first turns 7 of the first solenoid 5 are positioned so that they alternate with the third turns 9 of the second solenoid 6 in the ring development of the first core 1 1 around the electric cable 2, and the second turns 8 of the first solenoid 5 are positioned so that they alternate with the fourth turns 10 of the second solenoid 6 in the ring development of the second core 12 around the electric cable 2.

According to the embodiment shown in the annexed figures, the supporting structure 3 comprises a first plane support 13 of insulating material, wherein the first core 1 1 (around which the first turns 7 of the first solenoid 5 and the third turns 9 of the second solenoid 6 are wound) is defined, and a second plane support 14 of insulating material and parallel to the first one 13, wherein the second core 12 (around which the second turns 8 of the first solenoid 5 and the fourth turns 10 of the second solenoid 6) is defined.

More in detail, the first and the second plane support 13, 14, preferably made of vetronite, are respectively provided with a first through opening 4' and with a second through opening 4" aligned with each other, around which the first core 1 1 and the second core 12 of the supporting structure are respectively wound as a ring.

Advantageously, the first turns 7 of the first solenoid 5 and the third turns 9 of the second solenoid 6 are carried out on a first printed circuit 1 5 comprising said first plane support 13, and the second turns 8 of the first solenoid 5 and the fourth turns 10 of the second solenoid 6 are carried out on a second printed circuit 16 comprising the second plane support 14.

More in detail, according to the embodiment shown in the annexed figures, the two printed circuits 15, 16 are arranged parallel to one another and are respectively provided with a first 17 and with a second 18 inner face facing each other, and with a first 19 and with a second 20 outer face facing opposite directions.

According to the embodiment shown in the annexed figures, turns 7, 8, 9, 10 of solenoids 5, 6 are carried out by tracks 21 , 22, 23, 24 provided on both faces 17, 19 and 18, 20 of the corresponding printed circuit 15, 16, and by metallized holes 25, 26 obtained between tracks 21, 22, 23, 24 of the two faces. Preferably, tracks 21 , 22, 23, 24 forming turns 7, 8, 9, 10 of solenoids 5, 6 substantially develop radially relative to the central circular opening 4', 4" of the corresponding printed circuit 15, 16, each one defining with the ends thereof an outer contour 27 and an inner contour 28 of the two solenoids 5, 6 substantially with a circular shape.

More in detail, the first turns 7 and the third turns 9, made on the first printed circuit 15, are carried out each one by a corresponding first track 21 and by a corresponding second track 22 respectively provided on the first outer face 19 and on the first inner face 17 of the first printed circuit 15, and by a corresponding first metallized hole 25 connecting the two tracks 21 , 22 of said first faces 19, 17; likewise, the second turns 8 and the fourth turns 10, made on the second printed circuit 16 are carried out each by a corresponding third track 23 and by a corresponding fourth track 24 respectively provided on the second inner face 18 and on the second outer face 20 of the second printed circuit 16, and by a corresponding second metallized hole 26 connecting the two tracks 23, 24 of the second faces 18, 20.

Preferably, the first turns 7 and the third turns 9, made on the first printed circuit 15, and the second turns 8 and the fourth turns 10, made on the second printed circuit 16, are obtained in a per se conventional manner through techniques for manufacturing printed circuits, which for example envisage the laying of metal layers, in particular copper, on an insulating substrate, the making of the through holes on the substrate, the metallization thereof through galvanic deposition, and the removal of the copper layers outside the tracks.

More in detail, the first and the second tracks 21, 22 respectively provided on the first outer face 19 and on the first inner face 17 of the first printed circuit 15 are obtained by the laying respectively of a first and of a second metal layer on the corresponding first face 19,

17, and the subsequent removal of the metal laying outside the tracks 21 , 22 preferably by a photo etching process.

Likewise, the third and the fourth tracks 23, 24 respectively provided on the second inner face 18 and on the second outer face 20 of the second printed circuit 16 are obtained by the laying respectively of a third and of a fourth metal layer on the corresponding second face

18, 20, and the subsequent removal of the metal laying outside tracks 23, 24 preferably by a photo etching process.

Moreover, the first metallized holes 25, which connect the first and the second tracks 21 , 22 of the first printed circuit 15, and the second metallized holes 26, which connect the third and the fourth tracks 23, 24 of the second printed circuit 16, are respectively obtained by first and second through borings made between the two faces of the corresponding printed circuit 15, 16, and a subsequent deposition of copper inside the borings thus made (preferably by a galvanic deposition process).

Preferably, the first and the second metallized holes 25, 26 are positioned along the inner contour 28 of solenoids 5, 6 and arranged at the same distance from the centre of the current measuring device 1. In this way, advantageously, the inner contours 28 of the two solenoids 5, 6 are coincident with each other. With reference to the embodiment shown in figure 4, the first track 21 and the second track 22 of each first turn 7 and of each third turn 9 have projections on the plane of the first printed circuit 15 that are slightly inclined relative to each other (forming a first angle preferably comprised between 0.1 ° and 0.5°), which meet at the first metallized hole 25 that electrically connects the first 21 and the second 22 track.

Likewise, the third track 23 and the fourth track 24 of each second turn 8 and of each fourth turn 10 have projections on the plane of the second printed circuit 16 that are slightly inclined relative to each other (forming a second angle preferably comprised between 0.1 ° and 0.5°), which meet at the second metallized hole 26 that electrically connects the third 23 and the fourth 24 track.

Advantageously, the first solenoid 5 comprises first electrical connections 29 suited to electrically connect the first turns 7 thereof wound around the first core 1 1 of the supporting structure 3 to the second turns 8 thereof wound around the second core 12 of the supporting structure 3; likewise, the second solenoid 6 comprises second electrical connections 30 suited to electrically connect the third turns 9 thereof wound around the first core 1 1 to the fourth turns 10 thereof wound around the second core 12.

According to the embodiment shown in the annexed figures, the first and the second electrical connections 29, 30 are arranged between the two printed circuits 15, 16 for connecting turns 7, 9 made on the first printed circuit 15 and respectively belonging to the first and to the second solenoid 5 and 6, respectively to turns 8, 10 made on the second printed circuit 16 and belonging to the same respectively first and second solenoid 5 and 6. Preferably, the first electrical connections 29 of the first solenoid 5 comprise third and fourth metallized holes 29' and 29" arranged for respectively connecting the outer faces 19, 20 of the two printed circuits 15, 16 and the inner faces 17, 18 of the two printed circuits 15, 16. More in detail, each third metallized hole 29' of the first electrical connections 29 electrically connects the first track 21 (provided on the first outer face 19 of the first printed circuit 15) of the corresponding first turn 7 of the first solenoid 5 to the fourth track 24 (provided on the second outer face 20 of the second printed circuit 16) of the corresponding second turn 8 of the first solenoid 5. Moreover, each fourth metallized hole 29" of the first electrical connections 29 electrically connects the second track 22 (provided on the first inner face 17 of the first printed circuit 15) of the corresponding first turn 7 of the first solenoid 5 to the third track 23 (provided on the second inner face 18 of the second printed circuit 16) of the corresponding second turn 8 of the first solenoid 5.

Similar to the first electrical connections 29, the second electrical connections 30 of the second solenoid 6 comprise fifth and sixth metallized holes 30' and 30" arranged for respectively connecting the outer faces 19, 20 of the two printed circuits 15, 16 and the inner faces 17, 18 of the two printed circuits 15, 16.

More in detail, each fifth metallized hole 30' of the second electrical connections 30 electrically connects the first track 21 (provided on the first outer face 19 of the first printed circuit 15) of the corresponding third turn 9 of the second solenoid 6 to the fourth track 24 (provided on the second outer face 20 of the second printed circuit 16) of the corresponding fourth turn 10 of the second solenoid 6. Moreover, each sixth metallized hole 30" of the second electrical connections 30 electrically connects the second track 22 (provided on the first inner face 17 of the first printed circuit 15) of the corresponding third turn 9 of the second solenoid 6 to the third track 23 (provided on the second inner face 18 of the second printed circuit 16) of the corresponding fourth turn 10 of the second solenoid 6.

According to the embodiment shown in the annexed figures, the first and the second electrical connections 29, 30 are positioned along the outer contour 27 respectively of the first and of the second solenoid 5, 6, with the first electrical connections 29 arranged at a distance from the centre of device 1 different from that of the second electrical connections 30 for preventing contact between first and second electrical connections 29, 30. In this way, the outer contours 27 of the two solenoids 5, 6 are slightly spaced from each other. Figure 5 shows a wiring diagram of the connections between the turns of the two solenoids, wherein the first and the second turns 7, 8 of the first solenoid 5 are indicated with continuous segments and the third and the fourth turns 9, 10 of the second solenoid 6 are indicated with dashed segments. More in detail, the first turns 7 of the first solenoid 5 and the third turns 9 of the second solenoid 6 carried out on the first printed circuit 15, are positioned on a top horizontal line, which represents the first printed circuit 15, and the second turns 8 of the first solenoid 5 and the fourth turns 10 of the second solenoid 6 carried out on the second printed circuit 16, are positioned on a bottom horizontal line, which represents the second printed circuit 16.

With reference to the embodiment shown in said figure 5, each first turn 7 of the first solenoid 5, carried out on the first printed circuit 15, is connected to the next second turn 8 of the first solenoid 5, carried out on the second printed circuit 16, by the corresponding fourth metallized hole 29" of the first electrical connections 29. More in detail, the latter electrically connects the second track 22 of the first turn 7 to the third track 23 of the second turn 8 carried out on the second inner face 18 of the second printed circuit 16.

Moreover, the second turn 8 of the first solenoid 5 is in turn connected to the next first turn 7 of the first solenoid 5 carried out on the first printed circuit 15 through the corresponding third metallized hole 29' of the first electrical connections 29. More in detail, the latter electrically connects the fourth track 24 of the second turn 8 to the first track 21 of the next first turn 7 carried out on the first outer face 19 of the first printed circuit 15.

Always with reference to the embodiment shown in figure 5, each third turn 9 of the second solenoid 6, carried out on the first printed circuit 15, is connected to the next fourth turn 1 0 of the second solenoid 6, carried out on the second printed circuit 16, by the corresponding sixth metallized hole 30" of the second electrical connections 30. More in detail, the latter electrically connects the second track 22 of the third turn 9 to the third track 23 of the fourth turn 10 carried out on the second inner face 18 of the second printed circuit 16.

Moreover, the fourth turn 10 of the second solenoid 6 is in turn connected to the next third turn 9 of the second solenoid 6 carried out on the first printed circuit 15 through the corresponding fifth metallized hole 30' of the second electrical connections 30. More in detail, the latter electrically connects the fourth track 24 of the fourth turn 10 to the first track 21 of the next third turn 9 carried out on the first outer face 19 of the first printed circuit 15.

Advantageously, the first and the second printed circuit 15, 16, which respectively comprise the first and the second plane support 13, 14 of the supporting structure 3, are assembled together with a first layer of insulating material 32, preferably made of prepeg, sandwiched therebetween.

Such first layer of insulating material 32 is crossed by the first and by the second electrical connections 29, 30 which respectively connect the first and the second turns 7, 8 of the first solenoid 5 and the third and the fourth turns 9, 10 of the second solenoid 6, to one another. Advantageously, the current measuring device 1 comprises a first metallic screen 33 arranged for coating the first outer face 19 of the first printed circuit 15, and a second metallic screen 34 arranged for coating the second outer face 20 of the second printed circuit 16.

According to a particular embodiment, the first and the second metallic screen 33, 34 are respectively made with a first and a second metallic foil, preferably of copper, respectively arranged on the first outer face 19 of the first printed circuit 15 and on the second outer face 20 of the second printed circuit 16. Advantageously, the two metallic screens 33, 34 are connected to each other by peripheral metallic coatings 35 laid on the side of the printed circuits 15, 16, preferably by a metallization process, so as to obtain a total coverage of the current measuring device 1. The first and the second metallic screen 33, 34 allow obtaining a strong attenuation of the capacitive coupling caused by the presence of electrical fields with a strong intensity, which would affect the operation of the electrical and electronic components of the current measuring device 1. In particular, the metallic screens 33, 34 allow reaching particularly high levels of accuracy in current measurement also in the presence of particularly high noise.

Advantageously, a second and a third layer of insulating material 36, 37 are provided, respectively interposed between the first printed circuit 15 and the first metallic screen 33, and between the second printed circuit 16 and the second metallic screen 34. The second and the third layer of insulating material 36, 37 have the function of preventing contact respectively between the first metallic screen 33 and the first tracks 21 provided on the first outer face 19 of the first printed circuit 15, and between the second metallic screen 34 and the fourth tracks 24 provided on the second outer face 20 of the second printed circuit 16. Preferably, a further laying of metal (not shown), preferably gold, is provided on the metallic screens 33, 34 of the current measuring device 1 for preventing the surface oxidation of the metallic screens 33, 34 themselves.

The invention thus described thus achieves the intended purposes.

In particular, the fact that the first and the second solenoid 5, 6 respectively comprise first and third turns 7, 9 carried out on the first printed circuit 15 and respectively second and fourth turns 8, 10 carried out on the second printed circuit 16, eliminates the presence of any gap between the two solenoids 5, 6, making the subject current measuring device 1 insensitive to noises caused by external magnetic fields and thus capable of providing measurement values with a high accuracy.