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EP-4383491-B1 - SECTIONING, GROUNDING, AND SHIELDING BOX WITHOUT GROUNDING OF THE SCREENING OF THE CABLES OF A HIGH VOLTAGE THREE-PHASE ELECTRICAL CIRCUIT IN ALTERNATED CURRENT

EP4383491B1EP 4383491 B1EP4383491 B1EP 4383491B1EP-4383491-B1

Inventors

  • Gabbani, Simona

Dates

Publication Date
20260506
Application Date
20231206

Claims (9)

  1. A sectioning box (1) suitable for sectioning a cable shielding (2, 3, 4) of a three-phase high voltage electric circuit in alternating current, where the shielding of each cable (2, 3, 4) is electrically connected, upstream and downstream of its sectioning point, to a first conductor (8a, 9a, 10a) and respectively to a second conductor (8b, 9b, 10b) arranged inside each other in a bonding cable (8, 9, 10), wherein it has modular modules (11, 12, 13, 14), electrically connected by means of male/female electrical interconnection systems, comprising at least one head module (11) and one tail module (12), where the head module (11) comprises a front head flange (15) and a rear head flange (16) separated in the direction of an axis (L) of the head module (11) by a gap (17) having a dielectric filling material (21) in solid or gel form, where for each bonding cable (8, 9, 10) said head module (11) includes a pair of electrical connectors comprising a first electrical connector (22, 23, 24) of the external conductor (8a, 9a, 10a) of the bonding cable (8, 9, 10) incorporated in the dielectric filling material (21) and a second electrical connector (25, 26, 27) of the internal conductor (8b, 9b, 10b) of the bonding cable (8, 9, 10) incorporated in the dielectric filling material (21), and where said tail module (12) comprises a flange (28) provided with electrical connectors (29, 30, 31, 32, 33, 34) short-circuited for grounding the conductors (8a, 9a, 10a, 8b, 9b, 10b) of the bonding cables (8, 9, 10), wherein for each bonding cable (8, 9, 10) said head module (11) has an access through hole (18, 19, 20) of the bonding cable (8, 9, 10) to said gap (17), said access hole (18, 19, 20) being through the front head flange (15) of the head module (11), wherein the first electrical connector (22, 23, 24) and the second electrical connector (25, 26, 27) have respective terminals (22a, 25a, 23a, 26a, 24a, 27a) which extend in respective through holes (38, 39, 40, 41, 42, 43) of said rear head flange (16) of the head module (11), wherein the terminals (29a, 30a, 31a, 32a, 33a, 34a) of the electrical connectors (29, 30, 31, 32, 33, 34) provided in the flange (28) of the tail module (12) are of the opposite type to the terminals (22a, 25a, 23a, 26a, 24a, 27a) of the first and second electrical connectors (22, 23, 24, 25, 26, 27) provided in the rear end flange (16) of the head module (11), wherein said first electrical connector (22, 23, 24) comprises a structural conductor element of mechanical connection (22b, 23b, 24b) between said front head flange (15) and said rear head flange (16) of the head module (11), and wherein said first electrical connector (22, 23, 24) comprises a first bush (22c, 23c, 24c) coaxial to said through hole (18, 19, 20) of said front head flange (15) and a transverse arm (22d, 23d, 24d) connecting said first bush (22c, 23c, 24c) and said structural conductor element (22b, 23b, 24b).
  2. The sectioning box (1) according to claim 1, characterised in that said structural conductor element (22b, 23b, 24b) extends in direction of the axis (L) of the head module (11) and has an end fixed to the front head flange (15) and an opposite end fixed to the rear head flange (16) of the head module (11).
  3. The sectioning box (1) according to any preceding claim, characterised in that the arrangement of the pairs of electrical connectors of the head module (11) is symmetrical with respect to said axis (L) of the head module (11).
  4. The sectioning box (1) according to any preceding claim, characterised in that said front head flange (15) and said rear head flange (16) of the head module (11) are in the form of parallel discs connected orthogonally by said structural conductor element (22b, 23b, 24b) of each pair of electrical connectors of the head module (11).
  5. The sectioning box (1) according to the preceding claim, characterised in that said second electrical connector (25, 26, 27) comprises a second bush (25b, 26b, 27b) coaxial to said first bush (22c, 23c, 24c).
  6. The sectioning box (1) according to any one of the preceding claims, characterised in that said modular modules (11, 12, 13, 14) comprise at least one intermediate module (13) interposed between said head module (11) and said tail module (12) and having partial discharge sensors (36) along the conductors (8a, 9a, 10a, 8b, 9b, 10b) of the bonding cables (8, 9, 10).
  7. The sectioning box (1) according to any one of the preceding claims, characterised in that said modular modules (11, 12, 13, 14) comprise at least one intermediate module (13) interposed between said head module (11) and said tail module (12) and having shield current sensors (36) along the conductors (8a, 9a, 10a, 8b, 9b, 10b) of the bonding cables (8, 9, 10).
  8. The sectioning box (1) according to any one of the preceding claims, characterised in that said modular modules (11, 12, 13, 14) comprise at least one intermediate module (13) interposed between said head module (11) and said tail module (12) and having recuperators of electricity (36) from the conductors (8a, 9a, 10a, 8b, 9b, 10b) of the bonding cables (8, 9, 10).
  9. The sectioning box (1) according to any one of the preceding claims, characterised in that said modular modules (11, 12, 13, 14) comprise at least one intermediate module (14) interposed between said head module (11) and said tail module (12) and having surge voltage limiters (37) from the conductors (8a, 9a, 10a, 8b, 9b, 10b) of the bonding cables (8, 9, 10).

Description

The present invention relates to a sectioning box of the cable shielding of a three-phase high voltage (HV) alternating current (AC) electric circuit . As is well known, the shield of each phase cable is electrically connected, upstream and downstream of its sectioning point, to a first conductor and a second conductor arranged inside each other in a bonding cable entering the sectioning box. In three-phase high-voltage (HV) alternating current (AC) circuits, the shields in the cables for conveying fault currents can be connected together in various configurations in order to minimise induced circulating currents. In the case of cross-bonding or middle point bonding circuits, the shields are accessible along the cable route, in the vicinity of the joints, in the aforementioned sectioning boxes. Sectioning boxes can typically be of direct earthing, cross-bonding and ungrounded screen continuity. These configurations are usually achieved either with the same boxes, but with different internal configurations, or with boxes of different construction. The different construction may be dictated by economic considerations, as the direct earthing box may be more compact than the others since it does not have to house arresters (and thus not subject to potential explosions) and does not have to provide earth insulation. Inside the boxes, the insulation of the bonding cable, which, as mentioned above, is the cable connected directly to the shield of the HV cable near the j oint, is removed, exposing the conductor. This conductor can reach significant voltage levels and in the event of a fault even hundreds of kV. For this reason, boxes of the known type, which are typically insulated from cable conductors in the air, have important dimensions to ensure that there are no discharges in the air between conductors at different potentials. Inside the box, if it is not a direct earthing box, there are so-called Surge Voltage Limiters (or SVL). Surge voltage limiters are non-linear resistive elements whose function is to keep the voltages induced in the shields below a certain value which, if exceeded, could lead to perforation of the insulating sheath. When the voltage level characteristic of the specific limiter is exceeded, this passive element, normally an insulator, becomes conductive by connecting the screen to earth potential, preventing discharge and thus perforation of the bonding cable insulation. Every time the limiter becomes conductive, permanent conductive carbon channels are created in it, which reduce the level of insulation provided by the insulator. These channels represent a kind of ageing of the limiter which, over time, could lead to the limiter exploding in the presence of overvoltage. For this reason, the sectioning boxes are dimensioned and tested to withstand the explosion of one or more limiters. These components, the limiters, should be tested periodically. The testing of these elements can require long, and therefore normally costly, out-of-service times. Finally, another characteristic that these boxes must have is airtightness. Sectioning boxes are typically located below street level and are therefore subject to more or less frequent immersion. It is an absolute priority to ensure the airtightness of the box, as the ingress of water could cause a short circuit between the conductors of the bonding cables stripped of their insulation. In addition, any water that might seep into the box could back up between the wires of the bonding cables, reaching the AT coupling and causing further problems and malfunctions. For the above reasons, sectioning boxes are normally particularly large (to ensure separation between conductors without insulation), metallic and with numerous locking bolts to prevent water ingress and to resist possible explosions of the limiters. These characteristics make them particularly heavy and require at least two operators to position and install them. Although the boxes may be initially configured at the factory, after installation, tests must be carried out on the cables before commissioning. Such tests require temporarily changing the configuration of the boxe's internal connections and then resetting them. During these operations, the connections may not be restored correctly, causing malfunctions in the AT circuit. In cable shields, residual induced currents normally circulate, which could not be completely eliminated by transposition. In the event of perforation of the cable's insulating sheath, the screen may find itself electrically connected directly to earth. Such an alteration of the original earthing pattern of the screens encourages the circulation of more or less high levels of unwanted induced currents. Monitoring these currents is an indirect measure of the condition of the cable's insulating sheath. These currents have the same frequency as the phase current. Currents generated by partial discharges also circulate in the shields themselves. Partial discharges