Coupling devices for operations on live elements to attain equipotential conditions

There is disclosed a coupling device for operations on live elements to attain equipotential conditions. The device comprises two conductive jaws connected to a preferably nonconductive handle. The jaws are adapted to be switched between a closed configuration, in which they are in mutual contact and surround an area adapted to receive a live element, and an open configuration in which the contact portions of the two jaws are spaced apart from each other. The two jaws have respective entry tapering portions adjacent to the contact portions and mutually converging to cause the contact portions to move apart from each other when the live element is pressed against the entry tapering portions, thereby causing the jaws to switch from the closed configuration to the open configuration against the action of an elastic member. The two jaws have respective exit tapering portions adjacent to the contact portions and mutually converging to cause the contact portions to move apart from each other when the live element is pressed against the exit tapering portions, thereby causing the jaws to switch from the closed configuration to the open configuration against the action of an elastic member.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. § 119 from Italian Patent Application No. 102018000008711, filed on Sep. 19, 2018, in the Italian Patent and Trademark Office (“IPTO”), the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention finds application in the field of maintenance on the overhead live lines (“Live-line working” and particularly “Potential working”), for example operating at ultra-high, high or medium voltage. In particular, the invention relates to a device, such as a clamp, to achieve and ensure equipotential conditions when working on these lines.

BACKGROUND ART

When an operator works in contact with a live-line, safety measures must be taken against strokes. As a rule, working should be carried out under equipotential conditions. In other words, the operator and the power line are placed in mutual electric contact to be at the same potential, whereas the operator is adequately insulated from the ground or from other objects at potentials other than that of the line. This will prevent direct passage of current through the operator's body. For example, the operator may work on a live line from an aerial insulating platform or be kept proximate to the live line by a helicopter.

In order to achieve and maintain equipotential conditions, a safety cable must be kept connected at one end to a live-live element as a bare conductive cable, and at the other end to objects in contact with the operator, such as gloves or other conductive garments, as well as with the operator-supporting structure, such as the insulating platform or the helicopter.

In order to ensure connection of the safety cable to the live element of the power line, coupling tools are commonly used, such as clamps or snap hooks, similar to those used on scaffolds for safety against the risk of fall. Such coupling tools have two jaws, which are held together in a closed configuration by a spring. In the closed configuration, the jaws surround the live-line element and hold it in a space therebetween.

In order to insert the live element into the two jaws and remove it therefrom, at least one jaw is pivoted relative to the other, against the action of a spring, to an open configuration in which a passage is created for insertion and/or removal of the live element into/from the space between the jaws.

PROBLEM OF THE PRIOR ART

Prior art coupling devices require a manual action by the operator to pivot the jaws to open the passage for the live element. For example, in clamp-like devices, two handles connected to the jaws must be pressed together, and act as levers like in common pliers or scissors. In snap-hook devices, particularly during removal of the live element, a jaw must be pressed directly toward the area between the jaws.

Similar operations are complicated by the work conditions of operators. Furthermore, operators may be exposed to the risk of contacting the electric potential before equipotential conditions are established.

Another example of known equipotential clamp is described in document CN 102904080. Such clamp is provided with a screwed handle and two jaws hinged to each other. A triangular slider is placed behind the jaws and it can be pushed against them while screwing the handle, thereby forcing the jaws to close and clamp upon a live element without allowing lateral sliding. While unscrewing the handle, a spring moves the jaws back in the open position. It shall be noted that while the device is in use, clamped on a live element, it is impossible to open the jaws for removing the live element without unscrewing the handle or damaging the device. Thus, excessive pull of the device risks to damage the live element.

JP 3318306 describes a peg for retaining and holding in position an insulating sheet upon a bare live element. For insertion and removal of the peg, such a push or pull force will be enough, that conductor and the sheet slide along the inner surfaces of the jaws, thereby opening them against the action of a spring.

Such clamp is suitable only for use up to medium voltage, because insulating sheets are not allowed by regulations in high or ultra-high voltage. Therefore, the measures required for obtaining equipotential and safe conditions for such voltages are not provided, such as an equipotential conductor and no sharp edges. Moreover, the clamp doesn't have a handle adapted to be grabbed, but it is placed in position by a further clamp. Finally, also this peg does not allow for lateral movement of the live elements on which it is clamped, since it is conceived for holding a sheet in a fixed position upon the live element.

SUMMARY OF THE INVENTION

The object of the present invention is to obviate the aforementioned prior art drawbacks, and particularly to ensure simpler and safer opening and closing of the jaws of the coupling device, while always ensuring disconnection in case of emergency, even with no direct action by the operator.

This and other objects are fulfilled by a coupling device for operating on live elements, preferably at high or ultra-high voltage, such as conductive cables or other objects associated with a power line, as defined in any of the accompanying claims. In particular, according to the invention, in the closed configuration the jaws are in mutual contact at respective contact portions to receive a live element, in an inner area between the jaws. The jaws have exit tapering portions which are adjacent to the contact portions and mutually convergent.

The exit tapering portions are shaped to cause the contact portions to move apart from each other, thereby opening the jaws, when a live element in the inner area between the jaws is pulled against the exit tapering portions with a pull-out force that exceeds a first threshold value.

The exit tapering portions may be mutually inclined, for example, with an exit angle of less than 120°, at surfaces tangent to the live element.

Advantageously, once the live element has been clamped, it can be removed from the inner area between the jaws by simply pulling a handle connected to the jaws or, in certain embodiments, directly the safety cable, to thereby overcome the resistance of the elastic member that keeps the jaws closed, without having to press the handles together against the action of the elastic member, or press one of the jaws into the inner area between the jaws. Furthermore, the length of the handle allows the operator to be at an adequate distance from the live parts when he/she moves the clamp toward the live element, or when the coupling device is moved away, during separation from such live parts, while equipotentiality is lost.

Nevertheless, preferably, when the pull-out force is lower than the threshold value, the elastic member keeps the jaws closed in spite of eventual pressures between the live element and the exit tapering portions, caused, for instance, by the weight of the coupling device and the safety cable connected thereto, which are supported by the live line element while the operator is working. For this reason, exit angles of more than 45° are preferred.

In the preferred embodiment the jaws further have entry tapering portions, which lie outside the inner area between the jaws and are formed to cause the contact portions to move apart from each other when a live element is pressed against the entry tapering portions to enter into the inner area between the jaws. Thus, the live element may be advantageously inserted into the inner area between the jaws by simply pressing the jaws against the live element, via the handle, with the live element being arranged between the entry tapering portions. For this reason, entry angles of less than 60° are preferred, which are identified at surfaces tangent to the live element.

DETAILED DESCRIPTION

Referring to the accompanying figures, a coupling device for operations on live elements, preferably at high or ultra-high voltage, to attain equipotential conditions is designated by numeral 1. The live elements, which will be recognized by live-line working operators, are exemplified without limitation as conductors, conductive cables and other objects associated with a power line. Nevertheless, reference will be generally made herein to live elements under any voltage with which equipotential conditions are to be attained, which are referenced200in the figures and are illustrated as a bare conductive cable in the preferred embodiment.

The coupling device1comprises a handle2, preferably made of an electrically nonconductive material, and two electrically conductive jaws3,4, mechanically connected to the handle2.

An electrically conductive safety cable100may be connected to one or both of the jaws3,4in a manner known in the art. The safety cable100is adapted to establish an equipotential connection between the jaws3,4and an electrically conductive mass. For this purpose, the coupling device1optionally comprises a connector5for electrical connection of the safety cable100with the jaws3,4, as shown for example inFIG. 2. The safety cable100can be supplied individually or separately from the coupling device1.

The handle2mainly extends in a longitudinal direction X-X. The handle2comprises a handling portion21which is designed to be held by an operator's hand, and is preferably longitudinally spaced apart from the jaws3,4. In the illustrated embodiments, the handle2further comprises a longitudinally extending rod22and more in detail the handling portion21of the handle2is placed at of an end portion of the rod22distal from the jaws3,4.

It shall be noted that the two jaws3,4are not necessarily directly connected to handle2but, for example, in the preferred embodiments a first jaw3is indirectly connected to the handle2via a second jaw4, which is in turn directly connected to the handle2.

In fact, the coupling device1ofFIG. 2comprises a hinge6and the jaws3,4are pivotally connected by means of the hinge6. More in detail, each jaw3,4comprises a respective rigid stem31,41connected to the hinge6. The stems31,41may have rectilinear portions and/or bent or curved portions, as described in greater detail below. Moreover, the stems31,41have a preferably rounded cross section, for example a circular cross section. The cross section is meant to be transverse to the main development direction of the stem31,41involved.

Preferably, the second jaw4, and in detail its stem41, is fixed to the handle2, e.g. to the rod22. In detail, the stem41of the second jaw4has a straight portion44which mainly extends in the longitudinal direction X-X. The second jaw4is fixed to the handle2at the straight portion44, which may be, for example, longitudinally aligned with the rod22, as shown inFIG. 2, or offset from the rod22, as shown inFIG. 1. However, in other embodiments, both jaws3,4may be non-fixedly connected to the handle2, for example being free to pivot relative to the handle2.

Both jaws have respective contact portions32,42spaced apart from the hinge6and respective main portions33,43which extend between the hinge6and the respective contact portions32,42. The main portion43of the second jaw4is substantially defined by the straight portion44, whereas the main portion33of the first jaw3is substantially defined by a curved portion between the hinge6, a maximum distance portion34having a maximum distance from the second jaw4, and the contact portion32of the first jaw3. This curved portion is formed in the stem31of the first jaw3. However, in other embodiments the main portions33,43of both jaws3,4may be curved.

The two jaws3,4are adapted to switch, and particularly to pivot relative to each other, between a closed configuration and an open configuration. In the closed configuration the contact portions32,42of the two jaws3and4are in mutual contact. Furthermore, the main portions33,43define an internal area therebetween for receiving a live element200of a power line. Therefore, in the closed configuration, this area is surrounded by the two jaws3,4.

InFIGS. 1 and 2, the jaws3,4are shown in the closed configuration. Furthermore, the live element200is shown inFIG. 1at a time that precedes its entry into the internal area between the jaws3,4, and inFIG. 2at a time that precedes its removal from the internal area.

In the open configuration, the contact portions32,42of the two jaws3,4are spaced apart, whereby the live element200may be inserted into and removed from the internal area between the jaws3,4by passing between their respective contact portions32,42.

It shall be noted that, unlike the case of snap hooks, the distance between the second jaw4and the maximum distance portion34of the first jaw3is greater in the open configuration than in the closed configuration.

In the embodiment ofFIG. 2, the first jaw3has a lever portion39which is movable toward the handle2to pivot the two jaws3,4from the closed configuration to the open configuration. In particular, the hinge6is placed between the lever portion39and the main portion33of the first jaw3. Nevertheless, the lever portion39is totally optional, as the coupling device1of the invention may be moved to the open configuration even without using such lever portions39, as explained hereinbelow.

For example, in the embodiment ofFIG. 1, the first jaw3is connected to the hinge6at one end of the jaw3proximal to the handle2, more in detail an end portion of the stem31proximal to the handle2. Here, the first jaw3has no lever portions39connected to the main portion33which extend beyond the hinge6.

The coupling device1comprises an elastic member7configured to counteract the passage of the jaws3,4from the closed configuration to the open configuration. The elastic member7may be, for example, a helical spring71arranged in the internal area between the two jaws3,4, as shown inFIG. 1. In this case, each jaw3,4comprises at least one attachment member72for the elastic member7, located at the respective main portion33,43of the jaw3,4. Optionally, at least one jaw3,4comprises a plurality of spaced-apart attachment members72for the elastic member7, such that the elastic member7may be selectively connected to different attachment members72, to thereby adjust the force exerted by the elastic member7.

Conversely, in the embodiment ofFIG. 2, the elastic member7is a torsion spring73, schematically illustrated, located between the lever portion39of the first jaw3and the handle2or the second jaw4. In this case, the elastic member7is configured to counteract the movement of the lever portion39toward the handle2.

In one aspect of the invention, the main portions33,43of the two jaws3,4have respective adjacent exit tapering portions35,45, which are connected to the contact portions32,42. In particular, the exit tapering portions35,45converge toward the contact portions32,42. In more detail, the exit tapering portions35,45and the contact portions32,42of each jaw3,4define together a unique straight or curved profile facing toward the opposite jaw3,4.

It shall be noted that, as the exit tapering portions35,45are parts of the main portions33,43, they delimit part of the internal area surrounded by the two jaws3,4. In other words, the exit tapering portions35,45are arranged between the respective contact portions32,42and the hinge6.

The exit tapering portions35,45are shaped to cause the contact portions32,42to move apart from each other when, starting from the closed configuration, a live element200within the internal area between the jaws3,4is pressed against the exit tapering portions35,45in a pull-out direction D1toward the contact portions32,42with a pull-out force exceeding a first threshold value. This will cause the jaws3,4to switch from the closed configuration to the open configuration, against the action of the elastic member7.

In other words, the exit tapering portions35,45define together a funnel-shaped guide that narrows toward the contact portions32,42. This guide is closed by the contact portions32,42in the closed configuration and is open between the contact portions32,42in the open configuration.

More in detail, the exit tapering portions35,45of the two jaws3,4have respective tangency surfaces35a,45afor the live element200. These tangency surfaces35a,45aare in such arrangement that, in the closed configuration, the live element200in the internal area surrounded by the jaws3,4may simultaneously contact both tangency surfaces35a,45a, as shown inFIG. 2.

The tangency surfaces35a,45aof the exit tapering portions35,45are inclined to each other, in the closed configuration, with an exit angle α. It shall be noted that the vertex of the exit angle α is located substantially at the contact portions32,42. The exit angle α is smaller than 120° to allow the contact portions32,42to move apart from each other during removal of the live element200. As the exit angle α decreases, removal of the live element200is facilitated by simply pulling the handle2or of the safety cable100.

In fact, the handle2and preferably also the safety cable100can be thus pulled to press the live element200in the internal area between the jaws3,4against the exit tapering portions35,45in the pull-out direction D1.

In order to further facilitate removal of the live element200from the internal area between the jaws3,4by simply pulling the handle2, the exit tapering portions35,45are in such arrangement that the hinge6is located within the exit angle α, at least in its ideal extension along straight lines tangent to the tangency surfaces35a,45a. Therefore, the pull-out direction D1is oriented away from the hinge6.

In the preferred embodiments, the elastic member7is configured to maintain the jaws3,4in the closed configuration when a live element200within the internal area surrounded by the jaws3,4is pressed against the exit tapering portions35a,45ain the pull-out direction D1toward the contact portions32,42with a pull-out force that is lower than the first threshold value. This will avoid the risk that the jaws3,4may be inadvertently opened when the operator is not pulling the jaws3,4. For this purpose, the exit angle α is preferably greater than 45°. This is because, as the exit angle α increases, the first threshold value also increases, which means that a greater pull-out force is required to bring the jaws3,4to the open configuration.

In order to facilitate the movement of the live element200in the internal area between the jaws3,4and its placement between the exit tapering portions35,45, the inner edges of the jaws3,4facing the internal area between the jaws3,4preferably have no sharp edges along the extent of the main portion33,43from the hinge6to the respective exit tapering portion35,45. This also helps to avoid the generation of intense electrical fields caused by the tip discharge effect, as described in greater detail below. Moreover, the lack of sharp edges promotes lateral sliding of the device1along the live element200.

In particular, the main portion33of the first jaw4has an inner edge33athat faces the second jaw4, and this edge has a curved profile between the hinge6, a maximum distance portion34having the maximum distance from the second jaw4, and the exit tapering portion35of the first jaw3. This inner edge33ais identified in the curved portion of the stem31of the first jaw3. Depending on the presence or lack of a tapering plate37, described below, the curved profile of the inner edge33aof the first jaw3may continue without interruptions even further than the exit tapering portion35, at least up to the contact portion32, along the stem31.

Furthermore, the main portion43of the second jaw4has an inner edge43athat faces the first jaw3. The inner edge43aof the second jaw4extends substantially straight in the longitudinal direction X-X from the hinge6to the exit tapering portion45of the second jaw4. This inner edge43ais defined in the straight portion44of the stem41of the second jaw4. Also in this case, the straight profile of the inner edge43aof the second jaw4may optionally continue without interruptions even further than the exit tapering portion45, for example up to the contact portion42, along the stem41, based also on the presence tapering plates47.

According to a preferred aspect of the invention, the two jaws3,4further comprise respective entry tapering portions36,46. The entry tapering portions36,46are adjacent and connected to contact portions32,42, and converge toward the contact portions32,42. However, unlike the exit tapering portions35,45, the entry tapering portions36,46are connected to the main portions33,43through the contact portions32,42. In other words, the entry tapering portions36,46extend from the contact portions32,42away from the main portions33,43, as well as from the hinge6.

However, for each jaw3,4, the entry tapering portions36,46continue the straight or curved profile of the exit tapering portions35,45and of the contact portions32,42. In other words, the exit tapering portions35,45, the contact portions32,42and the entry tapering portions36,46define together the unique profile already described with reference to the exit tapering portions35,45and the contact portions32,42only, which profile in turn optionally continues without interruptions the profile of the inner border33a,43aof the respective jaw3,4, based on the presence or lack of tapering plates37,47.

The entry tapering portions36,46are shaped to cause the contact portions32,42to move apart from each other from the closed configuration, when a live element200is pressed against the entry tapering portions36,46in an insertion direction D2toward the contact portions32,42, upon attainment of an insertion force that is equal to or smaller than a second threshold value. This will cause the jaws3,4to switch from the closed configuration to the open configuration, against the action of the elastic member7. Clearly the insertion force shall be intended as a non-zero force, which means that there must actually be a positive pressure between the live element200and the entry tapering portions36,46. It shall be noted that, when insertion begins, the live element200is out of the internal area enclosed between the jaws3,4.

In other words, the entry tapering portions36,46define together a funnel-shaped guide that narrows toward the contact portions32,42and toward the internal area between the two jaws3,4. This guide is closed by the contact portions32,42in the closed configuration and is open between the contact portions32,42in the open configuration.

It shall be noted that, in at least one jaw3,4, the entry tapering portion36,46is inclined to the exit tapering portion35,45. In particular, the jaws3,4are substantially tangent to each other at the contact portions32,42, preferably without crossing.

The insertion direction D2is substantially opposite to the pull-out direction D1, and particularly is oriented toward the hinge6.

The exit tapering portions36,46of the two jaws3,4have respective tangency surfaces36a,46afor a live element200. These tangency surfaces36a,46aare in such arrangement that, in the closed configuration, the live element200located out of the internal area surrounded by the jaws3,4may simultaneously contact the tangency surfaces36a,46a, as shown, for example, inFIG. 1. The tangency surfaces36a,46aof the entry tapering portions36,46are inclined to each other, in the closed configuration, with an acute insertion angle β, preferably of less than 45°, e.g. substantially of 30°.

The insertion angle β is preferably selected to be smaller than the exit angle α, such that the second threshold for the insertion force, will be less than the first threshold for the pull-out force. This is useful because, while it is preferable that low extraction forces, such as the weight of the coupling device1itself, will not be sufficient to move the jaws3,4to the open configuration, there is no reason to set high thresholds for the insertion force.

It shall be noted that the live element200may be inserted into the internal area between the jaws3,4by simply pressing the jaws3,4, via the handle2, against the live element200, when the latter is placed between the entry tapering portions36,46. This operation is further facilitated if at least one of the jaws3,4is fixed to the handle2, as discussed above with reference to the second jaw4, to thereby prevent undesired movements of the jaws3,4relative to the live element200.

In certain embodiments, as shown for example inFIG. 2, at least one jaw3,4, preferably both, comprise a tapering plate37,47fixed along the stem31,41of the jaw3,4. Each tapering plate37,47has a smooth surface facing the opposite jaw3,4, so as to define the unique straight or curved profile described with reference to the contact portions32,42, exit tapering portions35,45and entry tapering portions36,46. In fact, the contact portion32,42, the exit tapering portion35,45and the entry tapering portion36,46(if any) of the jaw3,4are formed in the respective tapering plate37,47at the smooth surface. This will help the live element200to slide between the contact portions32,42, while preserving the stem31,41of the jaw3,4from abrasion and, at the same time, while avoiding damage to the live element or any other object,200.

The two jaws3,4, namely the stems31,41of the two jaws3,4, have respective end portions38,48distal from the handle2. It shall be noted that the distal end portions38,48are connected to their respective contact portions32,42through the entry tapering portions36,46.

Furthermore, at least one jaw3,4, preferably both, has a curved profile, for example a spiral, between the respective distal end portion38,48and the respective entry tapering portion36,46. In particular, the curved profile has an outer surface facing away from the contact portions32,42, which has no tips. More in detail, the end portions38,48will preferably close to contact against the main portions33and43. Advantageously, the absence of tips directed toward or away from the internal area between the jaws3,4prevents the formation of high electric fields caused by corona discharge, as well as the emission of sound waves (noise) and shortwave ultraviolet radiation (UV-C).

A skilled person may obviously envisage a number of changes to the above disclosed variants, without departure from the scope of the appended claims. In particular, various characteristics as shown in the embodiments ofFIGS. 1 and 2can be freely used in the other embodiment, including the longitudinally aligned or offset connection between the handle2and the second jaw4, the provision of the tapering plates37,47, the provision of the connector5distinct from the hinge6for connection of the safety cable100, the provision of the lever portion39and the type of elastic member7, if any.