Patent Description:
Underground cables, when compared to equivalent overhead lines, are more expensive because they have to be bigger to reduce the electrical resistance and the heat produced, they need special insulation and/or cable cooling, generally provided by forced air ventilation or water cooling. Furthermore, the transitions between overhead lines and underground cables require termination points. This results in higher costs.

However, underground cables help in ensuring uninterrupted power supply that is hitherto less common in overhead systems due to, e.g., heavy winds and gales, failure of supporting structures, etc.. Underground cables can transmit power across densely populated areas where land is costly or environmentally or aesthetically sensitive. Therefore, in certain areas, the benefits of underground cables outweigh disadvantages of undergrounding.

Among the cable underground installation methods, tunnel installation, whose depth is typically about <NUM>-<NUM> meters, is generally used in urban locations where direct bury installation would cause unacceptable disruption. This has the advantage that other underground services such as water and sewerage are unaffected, and there is a larger freedom of selecting the cable path, which, for example, can cross rivers or railways.

The positioning of a single span of a power cable, in particular high voltage cable, into tunnels presents difficulties. The cable is supplied on drums which typically do not fit into the tunnel, so that the cable has to be fed into the tunnel lengthways. Generally, a single cable span is shorter than the tunnel where it is to be deployed, thus a plurality of joints is requested with increase of cost, installation time, and safety issues. Furthermore, joints are weak points of a cable installation where faults may occur. Additionally, since, as explained, high voltage cables for undergrounding are heavy (for example, a <NUM> kV cable weighs about <NUM>/m), deploying a single cable for a length greater than <NUM> presents problems in terms of managing of the supplier drum and pulling force exerted on the cable.

<CIT> relates to cable installation in tunnels. The cable is supplied on a drum and motorised rollers are used to lead the cable to the top of the tunnel. Inside the tunnel, the cable is supported from a support beam by beam rollers which support a cable hanger. The beam rollers can roll along the support beam, carrying the cable with them. As the cable is advanced, beam rollers are provided at the tunnel opening. The cable is fully unrolled and supported along its entire length by the support beam. Once a <NUM> length is positioned at the desired position, it is moved to clips on the side wall. The lengths of cable are joined after they have been moved to the clips.

<CIT> relates to cable installation in tunnels. Known cable installation methods include so-called hand pulling, nose pulling and bond pulling. Bond pulling is most suitable for long runs of heavy cables. The cable is advanced along the tunnel in a temporary position suspended from the tunnel roof. As the cable is advanced along the tunnel, rollers are fitted over an I-beam with cable hangers that support the cable. The rollers are spaced by Kevlar bars so that the regular spacing of the rollers is maintained when they are pulled along the I-beam from the entry point of the cable. <CIT> describes a method for pulling a power cable with a mobile cable puller comprising: a guide rail, a plurality of moving vehicles, a connection unit, a driving unit, a hanger and a cable pulling control unit. <CIT> describes a suspension device used to carry a linear material over a cradle receiver and release the linear material onto the receiver, comprising a suspension means, a release means and an activation means. A laying apparatus comprises such suspension devices and a rail means prepared above a cradle receiver on which the suspension devices are to be movably held. <CIT> describes an underground cable laying method comprising the steps of: installing a rail and a winch in an underground power outlet; installing a traction roller on the rail; moving the cable to the starting position of the installation section; supporting the cable to the suspension belt of the first pull roller; installing a pulling eye at the tip of the cable to connect the traction line of the winch to the pulling eye at the tip of the cable, or connecting the traction line of the winch to the first traction roller; actuating the winch to advance the cable; when the cable advances a certain length, supplying a new traction roller to the rail at the starting position of the installation section, and supporting the cable on the suspension belt of the new traction roller. <CIT> describes a mobile support for use in pipe installation, wherein the support may also be used with a cable, wire or line, which includes a chassis, a clamp to hold pipe, and a friction reducing apparatus connected to the chassis. The friction reducing apparatus may be wheels or a sliding skid. The rollers may engage a track or the inside walls of a duct. A locking mechanism may hold the support in place relative to the track and provide structural support. <CIT> describes an apparatus for installing cables or pipes in tunnels comprising a motorized vehicle. A cable/pipe positioning arm is at one end of the vehicle, which is controllable to move a cable/pipe from a temporary installation position to a final installation position. A cable/pipe sagging arm is at the other end of the vehicle, which is controllable to apply a desired amount of sagging to a length of cable/pipe between adjacent final installation positions. The apparatus can be driven along the cable/pipe performing the positioning and sagging in a single sequence.

The Applicant aims at providing a method and an equipment for the installation of a power cable in a tunnel where a long cable span, particularly longer than <NUM>, can be deployed without the need of joints.

This aim is achieved by a method for the installation of a single power cable span in a tunnel where the cable is clamped successively by a plurality of trolleys both sliding along a rail installed in the tunnel during the installation and acting as fixed supports for the cable once the installation is completed, wherein during the installation the cable single span is moved along the tunnel from end to end thereof by pulling said trolleys through a pulling rope fixed thereto. No pulling forces are directly applied on the cable head and there is no need of intermediate pulling aids along the tunnel. The cable is installed in the final position attached to the trolleys fixed in the tunnel, with no need of cable handling inside the tunnel. Therefore, the overall process is quick and easy equipment is needed. Similarly, the cable substitution, for example in case of failure, is also quick and simple.

Accordingly, the present disclosure relates to a method for the installation of a single power cable span in a tunnel having an entrance and an exit, the method comprising the steps of:.

According to an embodiment, at least a number of trolleys are locked on the rail inside the tunnel. All of the trolleys inside the tunnel can be stationarily locked on the rail.

According to an embodiment, the present method further comprises a step of dragging the cable head portion to the endpoint by an auxiliary pulling rope when the cable head portion reaches a predetermined position outside the tunnel and is disconnected from the trolley.

According to an embodiment, when the cable head portion reached a predetermined end point outside of the tunnel, a predetermined sag is imparted to the single cable span inside the tunnel by:.

According to an alternative embodiment, a predetermined sag is imparted to the cable span while it advances along the tunnel. This process comprises providing a sagging apparatus provided near the tunnel entrance and operating it to push down a cable portion substantially equidistant from two trolleys, thus providing the predetermined sag.

According to another aspect, the present disclosure relates to an equipment for the installation of a single power cable span in a tunnel, comprising:.

wherein the device for the releasable connection of the trolley to the rope and the device for the releasable connection of the trolley to the single cable span comprise clamps with respective halves.

In an embodiment, the present equipment comprises an auxiliary pulling device and an exit auxiliary pulling rope driven by the auxiliary pulling device connectable to the head portion of the single cable span.

In the present description and claims, as high voltage (HV) cable it is meant a cable rated for a voltage above <NUM> kV.

Using the method and the equipment of the present disclosure it is possible to install a long single cable span of a power cable without the need of joints connecting subsequent cable spans. Therefore, the installation is easier and cheaper, and the installed cable is more reliable.

Further characteristics and advantages will be more apparent from the following description of some embodiments given as a way of an example with reference to the enclosed drawings in which:.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

The present disclosure, in at least one of the aforementioned aspects, can be implemented according to one or more of the following embodiments, optionally combined together.

For the purpose of the present description and of the appended claims, the words "a" or "an" should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. This is done merely for convenience and to give a general sense of the disclosure.

With reference to the attached Figures, the aim of the method and the equipment according to the present disclosure is the positioning of a single span of HV cable <NUM> from a starting point <NUM> (<FIG>) to an end point <NUM> (<FIG>), wherein part of the cable path is in a tunnel <NUM> and the remaining parts are outside of the tunnel. In the case depicted, the tunnel <NUM> is under the ground level and the starting point <NUM> and the end point <NUM> are at the ground level. The cable path comprises an entrance shaft <NUM> (<FIG>) and an exit shaft <NUM> (<FIG>), respectively in communication with a tunnel entrance <NUM> and a tunnel exit <NUM>.

The method of installation of the single cable span <NUM> in the tunnel <NUM> comprises the step of positioning the head portion <NUM> (<FIG>) of the cable <NUM> near the tunnel entrance <NUM>. This step can comprise one or more of the sub-steps as described below.

As shown in <FIG>, the single cable span <NUM> can be delivered at the starting point <NUM> rolled in a basket or turntable <NUM>, for example carried by a vehicle <NUM>, such as a wheeled vehicle or even a boat depending on the position of the starting point <NUM>. The single cable span <NUM> can be initially unloaded from the basket <NUM> using, for example, a pick-up arm (not shown in the figures) picking up the cable head portion <NUM> and moving it in a transition structure <NUM> guiding and holding the cable <NUM> from the basket <NUM> to the entrance shaft <NUM>. During the movement of the cable <NUM> along the transition structure <NUM>, the cable <NUM> is progressively unloaded from the basket <NUM>.

In an embodiment shown in <FIG>, the transition structure <NUM> can comprise one or more trenches <NUM> optionally housing rollers, chutes, pushers <NUM>, for moving, guiding and/or easing the advance of the cable towards the entrance shaft <NUM>. The transition structure <NUM> can also comprise a joint chamber <NUM> for the connection of the cable span to a cable of the network, once deployed.

In an embodiment, as shown in <FIG>, a plurality of first supports <NUM>, for example made of steel, are installed in the entrance shaft <NUM>. The first supports <NUM> can have rollers for guiding the cable.

The step of positioning the head portion of the cable <NUM> near the tunnel entrance <NUM> can further comprise the sub-step of installing an auxiliary pulling device, such as an auxiliary entrance winch <NUM>, at the bottom of the entrance shaft <NUM> to pull the cable head portion <NUM> near the tunnel entrance <NUM> through an entrance auxiliary rope <NUM>. The above-mentioned pushers <NUM> and the auxiliary entrance winch <NUM> can be driven in a synchronized manner.

The method further comprises a step of laying the single cable span <NUM> in the tunnel <NUM>. To this purpose, an installation equipment is provided in the tunnel <NUM> and near the tunnel entrance <NUM> and exit <NUM>, for example in the entrance shaft <NUM> and in the exit shaft <NUM>, as will be described in detail below.

As from <FIG>, at least one rail <NUM> is installed in the tunnel <NUM>, longitudinally extending along the same, from the tunnel entrance <NUM> to the tunnel exit <NUM>. In an embodiment, one rail <NUM> is fixed at the tunnel wall for each single cable span <NUM> to be deployed in the tunnel <NUM>. In case of a plurality of cables to be installed, a corresponding plurality of rails <NUM>, substantially parallel one another, can be installed (as from <FIG>), before or after the deployment of a cable span on a rail. In case of a tunnel <NUM> having circular or semi-circular cross section, for example, the rails <NUM> are installed to the tunnel wall circumferentially along the cylindrical tunnel wall, parallelly to the longitudinal axis thereof.

In an embodiment, in order to install the rail <NUM> in the tunnel <NUM>, a plurality of rail support structures <NUM> for supporting the rails <NUM> are fixed along the tunnel to the tunnel walls. The rail support structures <NUM> are, for example, made of steel and can be spaced along the tunnel length of the same distance, for example no more than <NUM> meters. In an embodiment, the rail support structures <NUM> are arc-shaped to fit the circular or semi-circular tunnel wall, as shown for example in <FIG>. The rails <NUM> and the rail support structures <NUM> are fixedly installed in the tunnel <NUM> because they are used both for laying the single cable span <NUM> and for supporting the same in the tunnel <NUM> once the installation is completed, as will be described in more detail in the following.

In an embodiment, a pulling device <NUM>, for example comprising a pulling winch, is installed near the tunnel exit <NUM>, for example at the exit shaft <NUM>, as from <FIG>. A rope buffer, for example comprising an idle roller <NUM>, is provided near the tunnel entrance <NUM>, for example at the entrance shaft <NUM>, as from <FIG>. A pulling rope <NUM> is stored in the rope buffer, for example is wound in the idle roller <NUM>, and, by extending longitudinally along the tunnel <NUM>, is connected to the pulling winch <NUM> such that the pulling winch <NUM> can pull the rope <NUM> stored in the idle roller <NUM>. In an embodiment, the pulling rope <NUM> is positioned to extend parallel to and near the rail <NUM>.

As from <FIG>, a first trolley <NUM> is connected to the rail <NUM>, being slidable thereon, for example at the tunnel entrance <NUM>. In order to minimize the friction with the rail <NUM>, the trolley <NUM> can comprise bearings <NUM> with low friction coefficient. In an embodiment, the rail <NUM> is I-shaped and the bearings <NUM> engage the I-shaped rail <NUM> on both sides of the I-shaped rail. Then, the trolley <NUM> is connected to the rope <NUM> and to the single cable span <NUM>, in particular to the cable head portion <NUM>, for example in the mentioned order. To this purpose, the trolley <NUM> comprises a device <NUM>, namely a first clamp, for the releasable connection of the rope <NUM> to the trolley <NUM> and a device <NUM>, namely a second clamp, for the releasable connection of the single cable span <NUM> to the trolley <NUM> with. The first and second devices <NUM>, <NUM> are designed such that, once connected to the cable <NUM> and to the rope <NUM>, the trolley <NUM> can slide along the rail <NUM> thanks to the pulling force exerted by the pulling rope <NUM> and can integrally carry the cable <NUM> with no pulling stress exerted thereon. The first clamp of the device <NUM> comprises two first halves <NUM> for releasably clamping the rope <NUM> and the second clamp of the device <NUM> comprises two second halves <NUM> for releasably clamping the cable <NUM>.

Then, the trolley <NUM> is moved along the rail <NUM> by pulling the pulling rope <NUM>, driven by the pulling device <NUM>, and slides along the rail <NUM> for a predetermined first longitudinal distance L shorter than the rail <NUM> overall length, as shown in the <FIG> and <FIG>. During this operation, the single cable span <NUM> is longitudinally carried along the rail <NUM> for substantially the same first longitudinal distance L. For example, the above-mentioned predetermined first longitudinal distance L is no longer than <NUM> meters. A minimum distance can be of <NUM> meter or less, but the skilled person can appreciate that the shorter the distance L is, the higher the number of trolleys to be used for the cable deployment is, and this implies an increase of the cost and time of installation.

Then, further trolleys <NUM>, having the same features of the first trolley <NUM>, are connected, one after the other, to the rail <NUM> at the tunnel entrance <NUM>, as shown in <FIG>. Then, each further trolley <NUM> is connected to the rope <NUM> and to the single cable span <NUM>, as described for the first trolley. Each further trolley <NUM> is connected to a cable portion at a longitudinal distance from the preceding trolley <NUM> (the first trolley <NUM> in the case of <FIG>). Then, each further trolley <NUM> is made to slide along the rail <NUM> as already described for the first trolley <NUM>, for a predetermined additional longitudinal distance, for example equal to the first longitudinal length L. During this operation, the single cable span <NUM> longitudinally moves further along the rail <NUM> for the same distance.

Once the first trolley <NUM> reaches the rail end near the tunnel exit <NUM>, the cable head portion <NUM> is detached from the first trolley <NUM>.

The single cable span <NUM> is further moved such that the cable head portion <NUM> is carried to and outside the exit shaft <NUM>, particularly it reaches the overhead end point <NUM>, as from <FIG>. During this moving, the cable span <NUM> is detached from a suitable number of trolleys <NUM>, while at the tunnel entrance <NUM> the cable span <NUM> is joint to an equally suitable number of further trolleys <NUM>.

In an embodiment, an auxiliary pulling device, such as an auxiliary exit winch <NUM>, is positioned at the overhead endpoint <NUM> (<FIG>). The auxiliary pulling device drives an exit auxiliary pulling rope (not shown in the Figures) connected to the cable head portion <NUM> to pull the single cable span <NUM> towards the endpoint <NUM>. The pulling force exerted by the exit auxiliary pulling rope on the cable head portion <NUM> (and, accordingly, on the single cable span <NUM>) is partly relieved by the tractive force of the pulling rope <NUM> still operatively connected to most of the single cable span length.

An exit transition structure <NUM> guiding and holding the single cable span <NUM> and the exit auxiliary pulling rope from the tunnel exit <NUM> through the exit shaft <NUM> is provided. A second trench <NUM> can house a part of the exit transition structure <NUM>. The second trench <NUM> can connect the end point <NUM> to the exit shaft <NUM>.

In an embodiment, a plurality of second supports <NUM>, for example made of steel, are installed in the exit shaft <NUM>. Analogously to the first supports <NUM>, the second supports <NUM> can have rollers for guiding the cable head portion <NUM> and the auxiliary pulling rope.

At the end point <NUM>, cable head portion <NUM> of the single cable span <NUM> can be connected to one or more power cables of the electric network by a second joint chamber (not illustrated).

As mentioned above, in order to raise the head portion <NUM> of the single cable span <NUM> outside the tunnel <NUM>, the pulling rope <NUM> and a predetermined number of trolleys <NUM> are disconnected from the single cable span <NUM>, and the disconnected trolleys <NUM> are removed from the rail <NUM> (<FIG>). Then, as shown in the <FIG>, both the pulling rope <NUM> (which keeps on pulling the further trolleys <NUM> and, accordingly, the single cable span <NUM> connected thereto) and the exit auxiliary pulling rope (connected to the cable head portion <NUM>) driven by the auxiliary exit winch <NUM> are pulled, for example in a synchronized manner, until the cable head portion <NUM> reaches a predetermined position outside the tunnel, for example until it reaches the endpoint <NUM>. Depending on the length of the single cable span <NUM> to be extracted from the tunnel <NUM>, beside the first trolley <NUM>, further trolleys <NUM> can be sequentially disconnected from the pulling rope <NUM> and from the single cable span <NUM> and removed from the rail <NUM>.

In an embodiment, at least a number or all of the trolleys <NUM> inside the tunnel <NUM>, once the cable head portion <NUM> reached the endpoint <NUM>, can be stationarily locked to the rail <NUM>, thus providing a permanent support for the deployed cable span <NUM>. The choice about the number of trolleys <NUM> to be left into the tunnel <NUM> can be determined by installation considerations like the cable weight.

According to an embodiment, when the cable head portion reached a predetermined end point outside of the tunnel, the pulling rope is left joined to the trolleys inside the tunnel.

In an embodiment, the method further comprises a step of imparting the single cable span <NUM> with a sagging, as depicted in the <FIG> and <NUM>. Said step comprises the sub-steps of locking to the rail <NUM> the trolley <NUM> nearest to the tunnel exit <NUM> when the cable head portion <NUM> has reached a predetermined end point <NUM> outside the tunnel <NUM>. The locked trolley <NUM> is disconnected from the rope <NUM> while maintaining the connection with the single cable span <NUM>, as shown in <FIG>. The pulling rope <NUM> is then pulled by the pulling device <NUM> (as from <FIG>) such that it pulls all the trolleys <NUM> still slidable on the rail <NUM> (not locked thereto) and still connected both to the cable <NUM> and to the rope <NUM>. This pulling could require the addition of at least one further trolley <NUM> at the tunnel entrance <NUM> and its connection to the single cable span <NUM> and the pulling rope <NUM>. The pulling lasts until the cable portions between all of the trolleys <NUM> inside the tunnel <NUM> reach a predetermined sag, as shown in <FIG>.

In an embodiment, the step of imparting the cable with a predetermined sag further comprises the additional sub-step of applying a vertical load to the above-mentioned cable portions, for example in the middle of the same (central arrow in <FIG>). In an embodiment, this sub-step is simultaneous to the driving of the pulling rope <NUM> such that it pulls to slide on the rail <NUM> the trolley <NUM> nearest to the locked trolley <NUM>. Then, the trolley <NUM> nearest to the locked trolley <NUM> is in turn locked to the rail <NUM>. The procedure is repeated for all of the trolleys <NUM> inside the tunnel <NUM>.

According to an alternative embodiment, a predetermined sag is imparted to the cable span <NUM> while advancing along the tunnel <NUM>. A sagging apparatus <NUM> (<FIG>) is provided inside the tunnel <NUM> at a distance from the connection point of the trolley <NUM> to the rail <NUM> at the tunnel entrance <NUM>, said distance being at least substantially equal to half of the length L. The sagging apparatus <NUM> comprises a pushing arm <NUM> which, in stand-by condition, is positioned vertically above the cable span <NUM>. When the centre of a cable portion comprised between two trolleys (which are advancing on the rail <NUM> as pulled by the pulling rope <NUM>) arrives substantially under the pushing arm <NUM>, the latter is lowered operated to push the cable down thus obtaining the predetermined sag. The sagging operation is over when the cable span <NUM> inside the tunnel <NUM> is sagged as sought.

As the sagged cable span <NUM> is moved along the rail <NUM> by a pulling force exerted on the trolleys <NUM> bearing it, the sag is maintained during the deployment.

At the end of any of the optional sagging procedures, at least a number or all of the trolleys <NUM> inside the tunnel <NUM> once the cable head portion <NUM> reached the endpoint <NUM> can be stationarily locked to the rail <NUM>, as already explained above.

When the cable head portion reached a predetermined end point outside of the tunnel, the installation method of the present disclosure is taken as finished. Subsequently, the single cable span so installed can be connected to the power network by, for example, the first and second joint chambers mentioned above.

Claim 1:
Method for installing a single power cable span (<NUM>) in a tunnel (<NUM>) having an entrance (<NUM>) and an exit (<NUM>), the method comprising the steps of:
- positioning the head portion (<NUM>) of the single cable span (<NUM>) near the tunnel entrance (<NUM>);
- laying the single cable span (<NUM>) in the tunnel (<NUM>) past the tunnel exit (<NUM>),
wherein the step of laying the single cable span (<NUM>) in the tunnel (<NUM>) comprises repeating the following sub-steps until the cable head portion (<NUM>) reaches an endpoint (<NUM>) outside the tunnel (<NUM>):
- at the tunnel entrance (<NUM>) connecting a trolley (<NUM>) in a slidable manner on a rail (<NUM>) longitudinally extending along the tunnel (<NUM>) between the tunnel entrance (<NUM>) and the tunnel exit (<NUM>);
- joining the trolley (<NUM>) to a pulling rope (<NUM>) and to the single cable span (<NUM>);
- moving the trolley (<NUM>) along the rail (<NUM>) by pulling the pulling rope (<NUM>);
- after a predetermined length (L) connecting another trolley (<NUM>) to the rail (<NUM>) at the tunnel entrance (<NUM>) and joining said other trolley (<NUM>) to the pulling rope (<NUM>) and to the single cable span (<NUM>);
- at the tunnel exit (<NUM>) disconnecting the trolley (<NUM>) from the pulling rope (<NUM>) and from the single cable span (<NUM>) and removing it from the rail (<NUM>);
- when the cable head portion (<NUM>) reached the endpoint (<NUM>), locking at least the trolley (<NUM>) nearest to the tunnel exit (<NUM>) on the rail (<NUM>) inside the tunnel (<NUM>).