Electrical cable link apparatus and electrical cable system comprising the apparatus

This application is a national phase application based on PCT/EP2014/065518, filed Jul. 18, 2014, the content of which is incorporated herein by reference.

The present inventions relate to electrical cable link apparatus and systems and particularly to the link boxes employed to implement earthing link and cross-bonding link.

Link boxes are network components installed near HV (or MV or LV) cable joints and terminations and used to connect their screen conductors together through “cross-bonding” techniques. In particular, in a three-phase high voltage network line, the screens of each cable are cyclically connected such that the totally induced sheaths or screen current adds up to zero (e.g. vector currents) over the entire lengths of the line in order to minimize losses due to the axial induction currents in the metallic screen of each cable.

A typical link box comprises a metal box with a removable top cover and is provided by three lateral openings for screen cables entry, and an external earth connection. During installation, screen cables ends are firstly stripped of from the insulating sheath, inserted inside the lateral openings of the box, then fastened by means of screw terminals to the metal conductors implementing a specific connection scheme.

Document WO-01/73796 describes a three-phase high voltage cable arrangement having a cross-bonded cable screens and cross bonded water sensing wires. There are additional losses caused by the axial induction currents in the metallic screen of a cable. Such additional losses in the cable sheath, screen and other metallic system components can be reduced by grounding of the screens or metal sheaths at one end to avoid providing a closed loop for the induction currents, or by a so-called “cross-bonding” of the cable sheaths or screens to largely compensate the induction voltages such that the screen/sheath current and consequent losses are minimized in spite of the entire arrangement being grounded at both ends.

In underground network, electrical cable link apparatus are the only points accessible by operators for detecting physical/electric parameters on the network by employing electronic sensing devices. Sometimes, these points are positioned in impervious environments (e.g. deserts areas) where power sockets for supplying electric power to these devices are not available.

The Applicant observes that the use of an electrical cable link apparatus to obtain diagnostics information by employing electronic sensing devices finds problems due to the need of providing suitable electric power supply to such sensing devices.

The Applicant has found that the electrical power to be supplied to the electronic sensing device installed in an electrical cable link apparatus can be obtained by inductive coupling with the current flowing in the screen conductors connected to the electrical link apparatus. In this way, it is also possible to have electric power supply even if the network line is disconnected from a load because screen current is always present, despite in this configuration no current circulates in the cable.

According to a first aspect, the present invention relates to an electrical cable link apparatus comprising:

a first electrical conductor structured to conduct a first electrical current from a first screen portion of a first external electrical cable; an electrical linking module connected to the first electrical conductor and structured to implement a cross-bonding/earthing link; a first inductor device inductively coupled to the first electrical conductor and able to generate a supply voltage.

Particularly, the first inductor device includes a conductive coil. In accordance with an embodiment, the first inductor device is a toroidal inductor and includes a magnetic core surrounding the first electrical conductor and around which the conductive coil is wound.

Particularly, the apparatus comprises a voltage source connected to the first inductor device to receive a first induced electrical current and provide a corresponding supply voltage, the voltage source comprising a voltage regulator including an AC/DC converter.

In an embodiment, the electrical cable link apparatus comprises a sensor module arranged to receive the supply voltage; the sensor module being configured to detect physical/electric parameters from the electrical linking module. Preferably, the sensor module comprises at least one of the following sensor devices: current sensor, partial discharge sensor, voltage sensor and temperature sensor. Particularly, said partial discharge sensor is one of the following devices: high frequency current transformer HFCT, capacitive coupler, electromagnetic antenna.

Advantageously, the electrical cable link apparatus further comprises an electronic managing module arranged to receive the supply voltage and structured to exchange data/commands with the sensor module.

In accordance with an embodiment, the electrical cable link apparatus further comprises: at least one electrical conductor structured to conduct an electrical current from a screen portion of a second external electrical cable; at least one second inductor device inductively coupled to the at least one electrical conductor to provide an induced electrical current from the electrical current and connected to the first inductor device. Advantageously, the first inductor device and the at least one second inductor device are connected in accordance with one of the following electrical configurations: series configuration, parallel configuration.

In an embodiment, the electrical cable link apparatus further comprises: a second electrical conductor structured to conduct a second electrical current from a second screen portion of the first external electrical cable; a coaxial cable comprising the first electrical conductor and the second electrical conductor ( 14 ); wherein the first inductor device is arranged to be inductively coupled with the first and the second electrical conductors.

Advantageously, the electrical cable link apparatus further comprises: a housing having a plurality of walls and a removable cover and structured to accommodate the electrical linking module, the first inductor device and the voltage source. Preferably, the electrical cable link apparatus further comprises at least one electrical cable connector mounted on a wall of the housing to connect the first electrical conductor with an external screen cable connectable to the first screen portion of the first external electrical cable.

According to a second aspect, the present invention relates to an electrical cable system comprising:

a first screen cable connectable to a first cable screen portion and structured to conduct a first electrical current; a second screen cable connectable to a second cable screen portion structured to conduct a second electrical current; and an electrical cable link apparatus, comprising:

a first electrical conductor connected to the first screen cable; a second electrical conductor connected to the second screen cable; a first inductor device inductively coupled to at least the first electrical conductor to provide and able to generate a supply voltage; an electrical linking module connected to the first and second electrical conductors and structured to implement a cross-bonding/earthing link.

Particularly, said electrical cable system further comprises a sensor module electrical arranged to receive the supply voltage; the sensor module being configured to detect physical/electric parameters from the electrical linking module.

Further characteristics and advantages will be more apparent from the following description of a preferred embodiment and of its alternatives given as a way of an example with reference to the enclosed drawings in which:

FIG. 1 shows schematically a first embodiment of an electrical cable system comprising an AC electrical power transmission line, a screen conductor line and an electrical cable link apparatus configured to perform a cross-bonding link;

FIG. 2 shows schematically a second embodiment of the electrical cable system comprising an electrical cable link apparatus configured to perform an earthing link;

FIGS. 3 and 4 show a lateral section view and a top view of an electrical cable link apparatus employable in the embodiment of FIG. 1 .

In the following description, same alphanumeric references are used for analogous exemplary elements when they are depicted in different drawings. FIG. 1 shows schematically a first embodiment of an electrical cable system 1000 comprising an AC (Alternate Current) electrical power transmission line 1 , a screen conductor line 2 and an electrical cable link apparatus 3 .

In accordance with the first embodiment, the electrical power transmission line 1 shows a three-phase configuration and comprises a first electrical cable L 1 , a second electrical cable L 2 and a third electrical cable L 3 which can be, as an example, of the high voltage type, each corresponding to a different phase of the system 1000 . Particularly, each cable L 1 -L 3 of the electrical power transmission line 1 includes a central conductor element 4 surrounded by an insulation body (not shown) and a metallic screen 5 . The screen 5 can have a cross section of 35-50 mm 2 and has a conductivity of about 0.017.

The screen is generally made of copper but can also comprise a conductive sheath. Each electrical cable L 1 -L 3 of the electrical power transmission line 1 can also include further conductors or insulating layers. The first embodiment illustrated in FIG. 1 refers to an electrical power transmission line 1 for which a so-called “cross-bonding” of cable screens is performed.

In accordance with the example of FIG. 1 , the electrical transmission line 1 is provided with a cable joint assembly comprising a first cable joint J 1 , a second cable joint J 2 and a third cable joint J 3 . Particularly, each cable joint J 1 -J 3 is structured to join the conductor elements 4 of the respective cable L 1 -L 3 . As shown in FIG. 1 , in the first joint J 1 the screen 5 is separated in a first screen portion L 11 and a second screen portion L 12 of the first cable L 1 . In the second cable joint J 2 the screen 5 is separated into a first screen portion L 21 and a second screen portion L 22 of the second cable L 2 . In the third cable joint J 2 the screen 5 is separated into a first screen portion L 31 and a second screen portion L 32 of the third cable L 3 . Alternatively, instead of joints J 1 -J 2 the cables L 1 -L 3 are connected to respective electrical terminations.

In accordance with the described example, the screen conductor line 2 comprises a first screen cable SC 1 , a second screen cable SC 2 and a third screen cable SC 3 . The first screen cable SC 1 is, as an example, a coaxial cable including: a first tubular conductor 6 , connected by a wiring conductor 8 to first screen portion L 11 of the first cable L, and a first inner conductor 7 , connected to the second screen portion L 12 of the first cable L 1 . The second screen cable SC 2 and the third screen cable SC 3 are connected to the second cable L 2 and the third cable L 3 , respectively, in a manner analogous to the one above described for the first screen cable SC 1 . As an example, the first screen cable SC 1 comprises an insulator body (not shown) isolating the first inner conductor 7 from the tubular conductor 6 and outer isolating sheath.

In accordance with the illustrated example, the electrical cable link apparatus 3 is a cross-bonding linking box configured to compensate induction voltages such that the screen currents and consequent losses are minimized. In accordance with the schematization of FIG. 1 , the electrical cable link apparatus 3 comprises: an internal conductor line 9 , an electrical linking module 10 an inductor device 11 inductively coupled to the internal conductor line 9 to provide an electrical power, such as a supply voltage. Particularly, the electrical cable link apparatus 3 is also provided with a voltage source 24 connected to the inductor device 11 and a sensor module 19 connected to the voltage source 24 . Particularly, the electrical cable link apparatus 3 can be provided with a housing 30 .

The internal conductor line 9 comprises a first internal cable C 1 including a second tubular conductor 13 which is a portion of, or is connected to, the first tubular conductor 6 of the first screen cable SC 1 . The first internal cable C 1 also comprises a second inner conductor 14 which is a portion of, or is connected to the first inner conductor 7 of the first screen cable SC 1 . The internal conductor line 9 also comprises a second internal cable C 2 , analogous to the first internal cable C 1 but which is connected to the second screen cable SC 2 , and a third internal cable C 3 , analogous to the first internal cable C 1 but which is connected to the third screen cable SC 3 . The first internal cable C 1 , the second internal cable C 2 and a third internal cable C 3 are preferably connected to the first screen cable SC 1 , the second screen cable SC 2 and the third screen cable SC 3 by respective pass-through ports or coaxial cable connectors 15 . The internal cables C 1 -C 3 allow the currents of the screens 5 of the cables L 1 -L 3 reaching the electrical link module 10 . Preferably, each of the internal cables C 1 -C 3 shows a coaxial structure.

In accordance with the embodiment of FIG. 1 , the electrical linking module 10 is configured to implement the cross-bonding link by mutually crossing the conductors of the internal cables C 1 -C 3 coming from the phases of the cable system 1000 . In accordance with the example schematized in FIG. 1 , the electrical linking module 10 comprises a first cross-connecting element 16 (e.g. a rail), a second cross-connecting element 17 and a third cross connecting element 18 .

The first cross-connecting element 16 connects the second tubular conductor 13 of the first internal cable C 1 with the second inner conductor 14 of the second tubular conductor C 2 . The second cross-connecting element 17 connects the second tubular conductor 13 of the second internal cable C 2 with the second inner conductor 14 of the third tubular conductor C 3 . The third cross-connecting element 18 connects the second tubular conductor 13 of the third internal cable C 3 with the second inner conductor 14 of the first tubular conductor C 1 . The above described cross-bonding link allows to substantially reduce the losses of currents associated with screen currents of the electrical cables L 1 , L 2 e L 3 .

Advantageously, the inductor device 11 is inductively coupled with one or more of the conductors of internal cables C 1 -C 3 to generate from the current flowing into said internal cables C 1 -C 3 (received from the screen portions L 11 , L 12 , L 21 , L 22 , L 31 , L 32 of the external electrical cable L 1 , L 2 , L 3 ) at least one output current to be provided to the voltage source 24 .

Particularly, the inductor device 11 comprises at least one first inductor T 1 , such as a conductive coil (i.e. a solenoid), inductively coupled, as an example, with the first internal cable C 1 . In a preferred embodiment, the first inductor T 1 is a toroidal inductor comprising a circular ring-shaped magnetic core around which a conductive coil is wound. The circular ring-shaped magnetic core can be of high magnetic permeability material such as an example, iron powder or ferrite.

In greater detail, the first toroidal inductor Ti is arranged so as to surround at least one conductor among the second tubular conductor 13 and/or the second inner conductor 14 of the first internal cable C 1 . Particularly, the first toroidal inductor Ti is arranged to act as a secondary circuit of a current transformer wherein the second tubular conductor 13 and/or the second inner conductor 14 acts as a primary circuit: this allows, advantageously, to generate a voltage in the secondary circuit (i.e. the first toroidal inductor T 1 ) related to the current flowing in the primary circuit (i.e. second tubular conductor 13 and/or the second inner conductor 14 ).

As a matter of fact, it has been found that the current typically circulating in the cable screens and in the corresponding internal cables C 1 -C 3 is in the range of 4÷20 A, and this current value enables to extract from each toroidal inductor a power of about 1÷5 W, sufficient to guarantee the operation of a sensor device connected thereto, such as the partial discharge wireless monitoring device described in EP 2 297 589.

The first toroidal inductor T 1 can be designed with a specific primary to secondary transformer ratio according to the amount of expected current flowing into the second tubular conductor 13 and/or the second inner conductor 14 and the expected load associated with the electronic sensing apparatus 12 . As an example, considering that the screen currents are in the order of tens of Ampere, the first toroidal inductor T 1 can have a coiled wire having a number of coils included in the range 100-1000; the first internal cable C 1 is considered to have 1 or 2 coils.

Preferably, the first toroidal inductor T 1 surrounds both the second tubular conductor 13 and the second inner conductor 14 of the first internal cable C 1 having coaxial structure; this arrangement is particularly advantageous since, due to the cross-bonding link performed, the two currents in the first internal cable C 1 partly add up so inducting a greater current in the secondary circuit formed by the first toroidal inductor T 1 .

In accordance with an example, the inductor device 11 is provided with a second inductor T 2 inductively coupled to the second internal cable C 2 and/or a third inductor T 3 inductively coupled to the third internal cable C 3 . The second inductor T 2 and the third inductor T 3 can be analogous to the first inductor T 1 and can be coupled to the second internal cable C 2 and the third internal cable C 3 , respectively, in a manner analogous to the one above described with reference to the first internal cable C 1 . The second inductor T 2 and the third inductor T 3 allow to generate from the currents flowing into the corresponding internal cables C 2 -C 3 respective output currents. Particularly, the second inductor T 2 and the third inductor T 3 can be toroidal inductors.

The first T 1 , the second T 2 and the third inductors T 3 can be electrically interconnected in series or in parallel so to increase the obtained voltage or current, in accordance with specific needs. FIG. 1 refers to an example in which the coiled wire of the first inductor T 1 , the second inductor T 2 and the third inductor T 3 are connected in series by a first connecting wire 21 . In accordance with the illustrated example, the coiled wire of the first inductor T 3 is connected by a second connecting wire 22 to a first powering terminal 23 of the voltage source 24 to supply an electrical AC current I and a related voltage.

The voltage source 24 can include an AC/DC converter and a DC/DC voltage regulator, preferably provided with overvoltage protections, connected to the powering terminal 23 and configured to receive the electrical voltage associated with the AC electrical current I and supply a DC and stable powering voltage Vcc to a second powering terminal 25 of the sensor module 19 . As an example, the voltage source 24 provides an electrical voltage of 12 V to the sensor module 19 .

The sensor module 19 is structured to sense electrical or other type of physical parameters detectable into the electrical cable link apparatus 3 . Particularly, the sensor module 19 can include one or more of the following sensors: current sensor, partial discharge sensor, voltage sensor and temperature sensor. These sensors can be associated with the three second tubular conductors 13 in the electrical linking module 10 .

Preferably, the electrical cable link apparatus 3 can be also provided with a logging (i.e. a data storing component) and monitoring module 26 which can exchange data or control signals with the of the sensor module 19 . The logging and monitoring module 26 is powered by the DC/DC voltage regulator 24 and can include a microcontroller or a field-programmable gate array (FPGA).

As an example, the voltage source 24 and the logging and monitoring module 26 can be included into a single case to form a powering and managing module 20 . The powering and managing module 20 and the sensor module 19 are schematically shown in FIG. 1 as assembled in an electronic sensing apparatus 12 . It is observed that the logging and monitoring module 26 can be internal or external to the housing 30 .

FIG. 2 refers to a second embodiment of the electrical cable system 1000 which is configured to perform an earthing link. Particularly, the screens 5 of the first cable L 1 , the second cable L 2 and the third cable L 3 are connected, by a first screen conductor W 1 , a second screen conductor W 2 and a third screen conductor W 3 , respectively, to the pass-through ports 15 of the electrical cable link apparatus 3 . The screen conductors W 1 -W 3 are particularly made with electrical cables having a non-coaxial structure. In the electrical cable link apparatus 3 of FIG. 2 , the second inner conductors 14 , which are portions of, or are connected to, the screen conductors W 1 -W 3 , are inductively coupled with the inductor device 11 . The inductor device 11 can be made in a manner analogous to the one described with reference to FIG. 1 .

The electrical linking module 10 of FIG. 2 is configured to implement an earthing link and comprises a first connecting element 27 , a second connecting element 28 and a third connecting element 29 (e.g. made by conductive rails) which connect a corresponding second inner conductor 14 to a ground terminal GND. The electronic sensing apparatus 12 and its powering method can be analogous to the ones described with reference to FIG. 1 .

A particular embodiment of the electrical linking module 10 of FIG. 1 , implementing a cross-bonding link, will be now described with reference to FIG. 3 and FIG. 4 . The housing 30 of the electrical linking module 10 is a box made, as an example, of metal and is provided with a removable top cover 31 , a base 49 and four lateral walls 32 . The removable top cover 31 can be fixed to the walls 32 by one or more nut-and-bolt assemblies 33 .

One of the lateral walls 32 is provided with the coaxial cable connectors 15 structured to connect the screen cables SC 1 -SC 3 with the internal cable C 1 -C 3 . As an example, one of the coaxial cable connectors 15 is structured to connect the first tubular conductor 6 and the first inner conductor 7 ( FIG. 1 ) of the first screen cable SC 1 to the second tubular conductor 13 and second inner conductor 14 of the first internal cable C 1 , respectively. FIGS. 3 and 4 also show an outer sheet 34 of the screen cables SC 1 -SC 3 and a further outer sheet 35 of the internal cables C 1 -C 3 . Moreover, hot shrinkable tubes 36 filled in with a resin compound 37 can be provided to fix each screen cable SC 1 -SC 3 to the corresponding coaxial cable connectors 15 .

Preferably, the coaxial cable connectors 15 are chosen so as to withstand the maximum link box voltage and current rating, and guarantee a good mechanical stability and reliability, an easy and fast mating (connection) procedure and a fast installation on the cable ends. More preferably, the coaxial cable connectors 15 show an high protection degree with regard to water and dust. As an example, the coaxial cable connectors 15 can show a structure similar to common coaxial cable connectors (e.g. Bayonet Neill Concelman, BNC; N-Type; F-type; etc.) but with adequate dimensions. In order to guarantee a perfect sealing, a resin casting can be applied upon the connectors.

In accordance with the shown example, each toroidal inductor T 1 -T 3 surrounds a segment of the internal cables C 1 -C 3 and an inside portion of the respective coaxial cable connectors 15 . Moreover, the electrical linking module 10 comprises three first interconnecting terminals 38 which connects each one of the second tubular conductors 13 to a first end of the respective cross-connecting element 16 - 18 . The electrical linking module 10 also includes three second interconnecting terminals 39 which connect each one of the second inner conductors 14 to a second end of the respective cross-connecting element 16 - 18 . FIG. 3 also shows an insulating sheath 48 coating the inner conductors 14 .

Moreover, each second interconnecting terminal 39 is connected, by a respective connection wire 40 , to a corresponding transient voltage suppressor device 41 configured to put the second interconnecting terminal 39 in contact with a ground terminal if the electrical voltage on the respective second interconnecting terminal 39 overcomes a threshold value. This situation can occur because of faults (due, for example, to lightning) causing overvoltage in the cable screens 5 .

The first interconnecting terminals 38 and the second interconnecting terminals 39 are supported by a base structure 45 which is sunk in a pouring hardened resin compound 46 filling a region extending from an internal wall 47 and the lateral wall 32 wherein the coaxial cable connectors 15 are arranged. The pouring resin compound allows to insulate and seal housing 30 from water.

According to the example shown in FIGS. 3 and 4 , the powering and managing module 20 is housed in a respective case 42 external to the housing 30 . FIGS. 3 and 4 also illustrates, a pass-through port 44 allowing connection of the powering and managing module 20 with the first inductor Ti via the second connecting wire 22 and with the three sensor modules 19 , each placed on a respective cross-connecting element 16 - 18 , by means of further connecting wires 43 .

As an example, the case 42 is a plastic enclosure separated from the housing 30 and fixable to the top cover 31 ; the plastic enclosure avoids shielding of a radio communication equipment which can be housed in the powering and managing module 20 . Alternatively, the case 42 can be pre-formed in the top cover 31 itself, so to create a protruding volume.

Different kind of sensors can be connected to the internal screen conductors to monitor specific diagnostic quantities but in accordance with an example, each sensor module 19 of FIGS. 3 and 4 is a partial discharge (PD) sensor, since the screen conductors coming from the joints or terminals carries also the potential partial discharge current. Partial discharge sensors can be implemented either as high frequency current transformers (HFCT), capacitive couplers, or electromagnetic (antenna) sensors.

Another parameter which can be detected from the electrical cable link apparatus 3 is the screen current flowing in the screens 5 . This current can be sensed by means of a small current transformers or Hall effect sensor included into the sensor module 19 . Also screen voltage can be monitored as well as temperature if required.

With reference to the installation of the electrical cable link apparatus 3 , the hot shrinkable tubes 36 is applied to the screen cables SC 1 -SC 3 which are inserted into the corresponding coaxial cable connectors 15 . Subsequently, the hot shrinkable tubes 36 are made to shrink so as to fix each screen cables SC 1 -SC 3 to the corresponding coaxial cable connector 15 . The electrical and electronic components placed inside the electrical cable link apparatus 3 are preferably pre-installed as described above and so no further steps are required during installation to perform their electrical connections.

The described electrical cable link apparatus 3 allows extracting electrical energy, and so feeding the electronic sensing apparatus 12 , from the electrical current flowing in the screen cables SC 1 -SC 3 (or the screen conductors W 1 -W 3 ) which reach the apparatus 3 itself to implement a particular electrical link. Thus, a separated powering system configured to supply electrical energy to sense and monitor electrical devices placed into the electrical cable link apparatus 3 is not necessary and electrical energy consumption is reduced. This allows exploiting the electrical cable link apparatus 3 for diagnostic purposes in a very efficient manner.

Moreover, the example of the electrical cable link apparatus 3 described with reference to FIGS. 3 and 4 is particularly advantageous since it requires very easy installation procedure and offers high protection degree with regard to water and dust.