EP0389029A1

EP0389029A1 - Gripping device and holder for handling a tubular fuse

Info

Publication number: EP0389029A1
Application number: EP90200557A
Authority: EP
Inventors: Aloysius Gerardus Majella Hemmer
Original assignee: Holec Systemen en Componenten BV
Current assignee: Danfoss Power Solutions II BV
Priority date: 1989-03-22
Filing date: 1990-03-08
Publication date: 1990-09-26
Anticipated expiration: 2010-03-08
Also published as: EP0389029B1; IE67789B1; DE69020763D1; IE901046L; DK0389029T3; ES2073504T3; NZ233017A; AU618457B2; DE69020763T2; NL8900711A; AU5205890A; ATE125063T1; GR3017530T3

Abstract

Gripping device (1) for longitudinally fitting and removing a tubular fuse (32) for electrical medium- and high-voltage installations. The gripping device (1) having a sleeve-type cavity (4) for receiving a terminal electrode (25) of the tubular fuse (32). An annular element (26) having an ellipsoidal projection and bent into a V-shape around its short axis being fitted in the cavity (4) for providing a friction coupling to the terminal electrode (25). For displacing the annular element (26) in axial direction of the cavity (4) by hand, a sleeve (29) is slideably latched over the cavity (4) and provided with an edge (30) abutting the annular element (26). For making electrical contact to the terminal electrode (25) of the tubular fuse (32) contact elements (20) are arranged in the cavity (4). A conductor (6) extends from the cavity (4) for detachably connecting the terminal electrode (25) to a contact (39) of a holder (34) for receiving the tubular fuse (32).

Description

The invention relates to a gripping device for handling a tubular fuse having terminal electrodes situated at the ends.
As is known, specially constructed blow-out fuses are used in practice to protect electrical medium-voltage and high-voltage installations against short-circuit currents and overload currents. Said blow-out fuses are constructed of a closed hollow tube of electrically insulating material, generally porcelain, in which one or more electrically conducting fusible wires or fusible strips are accommodated, if necessary, surrounded by quenching agent for extinguishing a discharge arc if the blow-out fuse comes into operation. Situated at the ends of said tubular fuses are cylindrical terminal electrodes which are connected to the fusible wires or fusible strips, respectively. In addition to these closed tubular fuses, there are also in practice so-called open tubular fuses in which the hollow tube is open at the ends.
To receive tubular fuses in an electrical installation, fork-type contacts are generally used in practice for connecting the terminal electrodes. Said forked contacts should have, inter alia, a sufficiently high clamping force to achieve a reliable electrical connection with a desirable low contact resistance. This means, however, that a relatively high force has to be exerted in the direction transverse to the tube when fitting the tubular fuse in order to open the forked contacts. The tubular fuse is then brought forcibly to its final position under the influence of the spring action of the forked contacts.
Said forked contacts have the disadvantage that, when fitting and removing the tubular fuse, forces are exerted thereon in the radial direction. It is precisely this radial force action to which the tubular fuse is relatively sensitive from the point of view of breakage, crack formation and the like in the tube and in the connection of the fusible wires or fusible strips to the terminal electrodes. The fact that this manner of fitting is nevertheless used quite a lot in practice is due to the ability of the porcelain tube to be used as a handle for handling the tubular fuse during the operation.
A mechanically more beneficial fitting is that in which so-called tulip contacts are used for making contact to the terminal electrodes of the tubular fuse. In this case, the tubular fuse is connected by exerting a force in the axial direction instead of a force in the radial direction. The tubular fuse is in fact able to absorb relatively high forces in this direction without the risk of breakage, crack formation and the like.
An additional advantage of this type of fitting is the fact that the tubular fuse can easily be introduced into a closed sleeve-type holder of electrically insulating material to provide a voltage-tight structure as a protection against splashed water, contamination and the like, to provide optimum insulation of the tubular fuse with respect to its environment and to achieve a suitable electrical field control and potential distribution. However, a problem arises in this connection with regard to handling the tubular fuse since its porcelain tube is no longer accessible as a handle.
The object of the invention is therefore, in the first instance, to provide a gripping device for handling a tubular fuse with terminal electrodes situated at the ends for fitting and removing it in the axial direction.
For this purpose, the invention provides a gripping device comprising a shaft having a cylindrical cavity and provided with a mouth for receiving a terminal electrode of the tubular fuse, a clamping element being fitted in the cavity for exerting a frictional force on the terminal electrode concerned in order to couple the tubular fuse to the gripping device, and means acting on the clamping element for influencing the frictional force in a manner such that the coupling to a terminal electrode received in the cavity can be broken with manual force.
This achievement is based on the circumstance that relatively large mechanical forces can be exerted on the tubular fuse in the axial direction, specifically in the sense that, when a terminal electrode is received in the cavity, the clamping element can be brought into contact with the terminal electrode concerned by means of a force in the axial direction of the tubular fuse. The clamping element is dimensioned in a manner such that it exerts a frictional force on the terminal electrode concerned which is adequate for, inter alia, displacing the tubular fuse. To replace a tubular fuse easily and quickly without the necessity for separate means, it is necessary for it to be possible to break the coupling between the gripping device and the tubular fuse easily with manual force, and this is provided for according to the invention.
All this means that tubular fuses can easiLy be fitted and removed with the gripping device according to the invention even at positions with difficult access, for example in compact installation boxes. In the case of tubular fuses to which non-axial contact is made, for example, a relatively complicated cradle construction in which the tubular fuse is fitted in a cradle structure capable of being moved outwards from an installation box is used for this purpose in order to make replacement of the tubular fuse possible.
By providing an electrically suitably insulating shaft, a service engineer is always able to remain at a safe distance from voltage-carrying components of an installation box in fitting or removing a tubular fuse. It will be clear that the gripping device according to the invention provides, in addition to the relatively easy handling of a tubular fuse therewith, also a greater dimensioning freedom for designers of, for example, electrical installation boxes, because the position of the tubular fuses is less governed by the requirements of accessibility for the fitting and removal thereof. This may per se result in more compact installations occupying less space, and this is of importance, inter alia, in connection with the generally restricted housing of electrical distribution stations, transformer houses etc.
With respect to the cross contacting of tubular fuses as described above, axial contacting has a relative disadvantage in the sense that an electrode connection should always be of a detachable construction, for example in the form of a terminal cap which is connected to the rest of the electrical installation via a screw joint, litz wire or in another detachable manner.
After the tubular fuse has been fitted, the gripping device has to be removed after which the terminal cap can be mounted. In removing or "pulling" a tubular fuse, the reverse process has to be followed. In a three-phase electrical installation, three tubular fuses should always be fitted or, if necessary, removed in this manner for each installation section protected.
The invention is therefore further based on the idea that the fitting or removing of a tubular fuse can proceed more rapidly by incorporating the gripping device itself in the electrical circuit of the tubular fuse concerned. In a further embodiment of the invention this is achieved in a manner such that the cavity is formed by a sleeve-type body of electrically conducting material, an open end of which forms the mouth for receiving a terminal electrode of the tubular fuse, which sleeve-type body is designed to make electrical contact with the terminal electrode of the tubular fuse to be received therein, and an electrical conductor connected to the sleeve-type body and projecting out wards. In addition to a mechanical coupling, an electrical connection of the gripping device to the terminal electrodes of a tubular fuse is now also provided. By incorporating the gripping device directly in the electrical installation, the use of a separate terminal cap is consequently no longer necessary. In addition to saving installation time, this consequently also yields a certain material saving.
A further embodiment of the invention has the characteristic that the free end of the conductor extends laterally from the sleeve-type body in the direction of the mouth for the purpose of detachably electrically coupling the conductor. A gripping device constructed in this manner offers the advantage that the gripping device can be coupled to, or uncoupled from, the terminal electrode concerned in one movement operation. In the preferred embodiment, the free end of the conductor is constructed for the coupling thereof as a plug connection.
If a tubular fuse has functioned, the current circuit protected thereby has become dead. In many cases, however, its terminal electrode situated on the supply side is still live. In the case of medium-voltage and high-voltage installations, the other terminal electrode of the tubular fuse then usually also carries a voltage which it is dangerous to touch. For the purpose of removing the tubular fuse in the case of a tubular fuse axially connected in the usual manner with a terminal cap, the supply side should therefore first be rendered dead and then the two terminal electrodes of the tubular fuse have to be earthed in order to allow any residual charges to drain to earth. The terminal cap can then be removed, after which the tubular fuse concerned can be removed from its holder.
These operations are not necessary with the gripping device according to the invention directly incorporated in the installation because, to remove the tubular fuse, no components of the installation have to be rendered dead beforehand in order subsequently to pull the tubular fuse out of the holder concerned with separate means.
Although the shaft of the gripping device could be constructed, for example, as an elongated insulated rod, this is less efficient because depending on the requirements and safety regulations imposed, the length of the rod may, for example, be approximately 1.5 m for a voltage of 24 kV. Such length is not only unmanageable as regards space but also has a mechanical disadvantage in the sense that, as a consequence of the relatively large length of the shaft, a proportionately large moment of force can be exerted on the appropriate terminal electrode of the tubular fuse, with the risk of damage thereto.
In order to avoid these disadvantages, yet another embodiment of the gripping device according to the invention has the characteristic that the shaft comprises an elongated body of electrically insulating material whose end adjacent to the sleeve-type body is provided with a thickened section to achieve a suitable electric field control and to reduce the electric potential in the direction of the elongated body, an electrically conducting screen to be connected to earth being mounted at the free end of the elongated body.
Instead of a shaft length of 1.5 m, it is now possible for an appreciably reduced length of approximately 20 cm to be sufficient at 24 kV. A contact-safe situation is provided under all circumstances by connecting the electrically conducting screen to earth.
The contact safety can further be increased by arranging for the free end of the elongated body to be adjoined by a plate extending in the radial direction, a plate-type electrically conducting screen being mounted with a handle for handling the gripping device at the side facing away from said end. By arranging for the plate to adjoin the insertion end of a holder for the tubular fuse, a desirable electrical field distribution and a seal against splashed water, contamination and the like can be achieved for the tubular fuse in such a holder and also the intended voltage-tightness.
Although the connection of the screening plate to earth can be achieved in various manners, in another embodiment of the invention, at least one passage opening is provided in the plate for a contact pin to be connected to earth. By constructing the said contact pin, for example, so as to slide under spring force, it will be clear to the person skilled in the art that a connection of the screening plate to earth can be achieved thereby, which connection is only broken after the tubular fuse has been pulled out of the voltage-carrying contact, and this benefits the safety of the service engineer.
To indicate that the tubular fuses have functioned, a terminal electrode thereof is provided with a so-called tell-tale pin or striker pin which shoots outwards from the terminal electrode concerned if the fusible wires or the fusible strips have blown. In order to make it possible to indicate that a tubular fuse has functioned, yet another embodiment of the invention has the characteristic that the end of the sleeve-type body facing away from the mouth, and the shaft are provided with a passage opening for an actuating element on which the tell-tale pin mounted in a terminal electrode of the tubular fuse concerned is able to act.
After the tubular fuse has functioned, the movement of the tell-tale pin concerned is transmitted to the end of the shaft via the actuating element. In an embodiment of the gripping device according to the invention based thereon, use is made thereof in that there is mounted at the end of the shaft facing away from the sleeve-type body an indicating mechanism which can be activated by means of the actuating element to indicate that a tubular fuse coupled to the gripping device has functioned.
In a preferred embodiment, the indicating mechanism comprises a lever mechanism attached to the screening plate and having a first and a second position, the actuating element being a trapped pin which can be moved in the passage opening. The said lever mechanism may form part of a larger mechanical system for controlling a plurality of coupled tubular fuses, such as, for example, in an electrical three-phase installation and/or interaction with the control mechanism of one or more switches.
To achieve a reliable electrical connection of a terminal electrode received in the cavity of the gripping device, a further embodiment of the invention has the characteristic that, to make electrical contact to a particular terminal electrode of the tubular fuse, contact elements which are mutually displaced in the tangential direction are situated along the inside circumference of the sleeve-type body. Preferably, the contact elements, viewed from the mouth, are arranged in front of the clamping element. This latter is specifically of importance because the electrical connection to the terminal electrode is then always made at a section thereof on which the clamping element does not have to act. Any damage to the terminal electrode as a consequence of the frictional action of the clamping element then has no effect on the electrical connection to the terminal electrode concerned.
Because the terminal electrodes of commercially available tubular fuses have a specified diameter and length on which both the contact elements and the clamping element have therefore preferably to act separately from one another, it is possible to use compact contact elements occupying little space for making axial contact to a particular terminal electrode.
For this purpose; an embodiment of the invention has the characteristic that the contact elements are constructed from a loop-shaped strip of resilient electrically conducting material with backwardly bent ends, the sleeve-type body being provided, near the mouth, with tooth-type projections on which the contact elements act with their backwardly bent ends. As a consequence of the loop shape, each contact element acts at two points on the terminal electrode and at two points on the sleeve-type body of the gripping device. In addition to an adequate compensation for tolerance differences, the width of the loop-shaped strip can remain limited, as intended, as a result of this multiple contacting for each contact element.
In order to facilitate the making of contact between the gripping device and the respective terminal electrode of a tubular fuse, an embodiment of the invention has the characteristic that the contact elements are provided, near the backwardly bent ends, with guide strips pointing in the direction of the mouth for guiding a terminal electrode of the tubular fuse to be received in the sleeve-type body in the axial direction of the latter.
As already discussed above, it is desirable from a mechanical point of view to exert forces exclusively in the axial direction on a particular tubular fuse when coupling the gripping device thereto. An embodiment of the gripping device according to the invention which is suitable for this purpose has the characteristic that the clamping element comprises a curved annular element of resilient material, the central opening of which forms the boundary of a receiving opening for receiving a terminal electrode of the tubular fuse, which annular element is supported in the cavity so as to be displaceable at least in the radial direction in order to vary the receiving opening, the means for influencing the frictional force comprising means acting on the annular element for the displacement thereof.
Further curvature of the annular element has the result that the receiving opening bounded thereby is made smaller, and this results in an increase in the frictional force on a terminal electrode inserted into said receiving opening. Reduction of the curvature, for example, by displacing the clamping element in the radial direction results in a reduced frictional force for the purpose of uncoupling the gripping device with manual force, as desired.
A preferred embodiment of the invention has the characteristic that the annular element has an ellipsoidal projection and is curved in a V-shape around the short axis thereof, two slits situated opposite each other and extending at an angle in the axial direction being situated in the wall of the cavity, in which slits the annular element is received so as to be movably supported both in the axial and in the radial direction at its circumference in a manner such that a virtually circular receiving opening is bounded, a further sleeve being mounted over the mouth and having an edge which extends inwards from the circumference and which forms a stop for the annular element, which further sleeve is latched so as to be slideable in the axial direction over the mouth.
By starting from an element having an ellipsoidal projection, the result is achieved that by bending it around the short axis thereof a receiving opening having a virtually circular section and consequently a uniform action on the circular-cylindrical terminal electrode concerned are obtained. The slits are positioned in a manner such that the annular element undergoes a bending to the extent that the receiving opening bounded by it is smaller than the diameter of the terminal electrode. On coupling the gripping device with the tubular fuse, the annular element is displaced further into the slits as a consequence of said smaller receiving opening, as a result of which the receiving opening is enlarged and the terminal electrode can be inserted into it. The slits are positioned in a manner such that the annular element always tends to assume the position associated with the original, smaller receiving opening under the influence of its own spring force.
A very easy manner of uncoupling the gripping device is achieved as a preferred embodiment in a manner such that the stop of the further sleeve is situated near the mouth and the annular element is received in the cavity in a manner such that the curve thereof is up against the stop of the further sleeve. The further sleeve latched over the mouth thus prevents the annular element emerging to the outside from the cavity. With the aid of the further sleeve, the annular element can be displaced in the slits and the receiving opening can easily be widened with manual force to reduce the frictional force exerted.
The invention also relates to a holder for a tubular fuse, characterized by a cylindrical housing of electrically insulating material having an open end for receiving the tubular fuse in the housing, a closed end provided with a contact for receiving a terminal electrode of the tubular fuse and having a further contact projecting laterally from the housing near the open end for the purpose of making contact to the conductor of the gripping device. Preferably, the further contact is constructed for coupling the conductor of the gripping device as a plug connection.
Desired compact dimensions of both the gripping device and the holder can be obtained by manufacturing them of casting resin.
The invention is illustrated below with reference to a drawing of a preferred embodiment of the gripping device which is also suitable for incorporation in an electrical installation. In the drawing:

Figures 1a and 1b diagrammatically show respectively a longitudinal section and an elevation of a part of the gripping device according to the invention,
Figures 2a and 2b diagrammatically show respectively a longitudinal section and an elevation of the sleeve-type body for receiving a terminal electrode of a tubular fuse,
Figures 3a and 3b diagrammatically show elevations of a preferred embodiment of an electrical contact element to be received in the sleeve-type body according to Figure 2,
Figures 4a and 4b diagrammatically show the contact element according to Figures 3a and 3b in the state of making contact to, respectively, a terminal electrode of smaller and larger diameter,
Figures 5a, 5b and 5c diagrammatically show respectively the projection, a section in the unloaded state and sections in the loaded state of the ellipsoidal clamping element according to the invention,
Figure 6 diagrammatically shows a section of the further sleeve-type body for coupling to the gripping device according to Figure 1, and
Figure 7 diagrammatically shows, partially in section and elevation, a tubular fuse coupled to the gripping device and fitted in a holder according to the invention.

Figure 1a shows a longitudinal section through the preferred embodiment of the gripping device 1 according to the invention, which in addition to handling a tubular fuse, can also be used for connecting it electrically. For the sake of clarity, the clamping element and the contact elements are not shown.
The gripping device 1 essentially comprises an elongated shaft 2 of insulating material which is adjoined at one end by a thickened section 3 which is adjacent to one end of a sleeve 4 of electrically conducting material. The other end of the sleeve 4 forms the mouth 5 for receiving a terminal electrode of a tubular fuse. Connected to the sleeve 4 is furthermore a conductor 6 which projects outwards and has a pin-type end 7 projecting beyond the mouth 5. The conductor 6 is surrounded by an insulation sheath 8 adjacent to the thickened section 3.
The other end of the shaft 2 is adjoined by a flat plate 9 of insulating material extending in the radial direction and a screening plate 10, connected thereto, of electrically conducting material. The screening plate 10 is provided on either side with triangular upright walls 11 which are joined to each other by means of a spindle 12. The spindle 12 also serves as a shaft for handling the gripping device. In order to earth the screening plate in the fitted state of the gripping device, the flat plate 9 is provided with openings 13 for receiving therein a pin which is connected to earth (not shown).
A passage opening 14 extends into the shaft 2 from the sleeve 4 to the screening plate 10. After the tubular fuse has functioned, a tell-tale pin or striker pin received in a terminal electrode of the tubular fuse is able to move in said passage opening or activate an actuating element (not shown) mounted therein.
Figure 1b shows the elevation of the gripping device seen from the spindle 12 in Figure 1a. In an embodiment suitable for a medium voltage of 24 kV, the gripping device shown in Figure 1a is approximately 30 cm long and the plate 9 is approximately 12 cm wide and 15 cm high. With these dimensions, the gripping device is eminently suitable for use in compact installation boxes and the like.
Figure 2a shows a longitudinal section through the sleeve 4 of electrically conducting material. Near the mouth 5, four teeth 15 are formed in the wall of the sleeve for attaching thereto the contact elements for making electrical contact with a terminal electrode of a tubular fuse to be received in the mouth 5.
Provided in the wall of the sleeve 4 are two slits 16, 17 which are situated opposite each other and extend at an angle in the axial direction for supporting a clamping element in the sleeve 4, as will be discussed later in more detail. An opening 18 provided with a screw thread is furthermore provided in the wall of the sleeve.
Figure 2b shows an elevation of the sleeve 4 viewed from the slit 16. The opening 19 in the wall of the sleeve 4 serves to connect to the latter the conductor 6, as shown in Figure 1a. The conductor 6 can be attached to the sleeve by soldering as a result of manufacturing the sleeve from solderable material.
Figure 3a shows a plan view of a preferred embodiment of a contact element 20 for use in the gripping device according to the invention. The contact element 20 is constructed from a loop-shaped strip 21 made of resilient, electrically conducting material, for example an alloy of beryllium and copper, having backwardly bent ends 22 which, in the fitted state, act on a tooth 15 of the sleeve 4 as shown in Figures 2a and 2b. Near the ends 22, the contact element is provided with guide strips 23 which point inwards and which have an end 24 perpendicular to the plane of the drawing, all this being clearly visible from the elevation in the direction of the bent-over ends 22 shown in Figure 3b.
Figures 4a and 4b show the contact element 20 according to Figure 3 in the loaded state. The terminal electrode 25, partially shown in Figure 4a, of a tubular fuse has a smaller diameter than the terminal electrode 25′ shown in Figure 4b. In practice, such situations arise as a result of tolerance differences in the dimensions of the terminal electrodes. It can clearly be seen that four contact junctions A, B, C, D or A′, B′, C′, D′ respectively are formed between the wall of the partially shown sleeve 4 and the terminal electrode 25, 25′. A reliable electrical connection having a desirable low contact resistance to a terminal electrode can be brought about by accommodating two or more such contact elements in the sleeve 4. The contact surface of the contact element is provided for this purpose with a coating of silver.
Figures 5a, 5b and 5c show the preferred embodiment of a clamping element for use in the gripping device according to the invention. As shown in Figure 5a, the clamping element comprises an annular element 26 having an ellipsoidal projection and is bent into a in-shape around the short axis for reception in the gripping device, as shown in Figure 5b. The annular element 26 formed in this manner is introduced into the slits 16 of the sleeve 4 starting from its edge 27, see Figure 2. In this operation, the annular element 26 undergoes a bending such that it assumes a shape shown in section in Figure 5c, depending on the diameter of the terminal electrode of the tubular fuse concerned. The receiving opening bound by the annular element 26 is virtually circular as a consequence of its ellipsoidal form so that the inside edge 28 thereof acts on the terminal electrode virtually along the entire outside circumference thereof.
As can be seen from Figure 5c, the annular element 26 is prestressed in a manner such that it always tends to assume the shape shown in Figure 5b under the influence of its spring force, in which shape the receiving opening bounded thereby is relatively smaller than the diameter of the terminal electrode of a tubular fuse.
The receiving opening can be increased, against the spring force of the element, by exercising a force, in the axial direction on the annular element, from the curve thereof, with which force the frictional force exercised on the terminal electrode is decreased and the coupling to the gripping device can easily be released by hand.
To displace the annular element in the axial direction in this manner by hand, a further sleeve 29 is provided which is to be mounted over the mouth 5 of the sleeve 4 and which has an edge 30 which is turned inwards and which is situated opposite the mouth 5 in the fitted state. Provided in the wall of the further sleeve 28 is a slit-type opening 31 which corresponds to the opening 18 of the sleeve 4, see Figure 2. By accommodating a screw (not shown) in the opening 18, the further sleeve 29 is trapped so as to slide with respect to the sleeve 4.
Instead of the construction shown having a further sleeve 29 which can be displaced by hand with respect to the sleeve 4 in order to uncouple the gripping device and a terminal end, constructions are also conceivable in which, for example, the further sleeve 29 can be displaced by means of a mechanism acting thereon from the handle 12 of the gripping device. Instead of a further sleeve 29, constructions which act via the passage opening 14 of the gripping device on the clamping element are also possible for influencing the frictional force exerted thereby on a terminal electrode (not shown).
Figure 7 shows diagrammatically, partially in section and in elevation, the assembled gripping device 1 according to the invention combined with a tubular fuse 32 having terminal electrodes 25, 33 and a holder 34.
The holder 34 has a closed end 35 at which a tulip-shaped receiving contact 36 is mounted for making axial contact with the terminal electrode 33 of the tubular fuse 32. The receiving contact 36 is fed to the outside as a bus contact 38 via a conductor 37 for the purpose of further connection with an electrical installation.
The gripping device 1 acts on the terminal electrode 25 of the tubular fuse 32 and is coupled via the contact elements 20, the sleeve 4, the conductor 6 connected thereto and the pin-type end 7 thereof to a bus contact 39 which projects laterally from the holder and which is in turn again connected to a further bus contact 40 to receive the tubular fuse in an electrical installation. It will be clear to a person skilled in the art that other connections, such as rails, screw couplings etc. can also be used, instead of the bus contacts 38, 40, for receiving the holder 34 or the tubular fuse 32 in an electrical installation. Contact can also be made to the conductor 6 of the gripping device 1 in detachable manners known per se, the plug connection shown, however, being preferable.
The plate 9 situated at the end of the shaft 2 of the gripping device 1 is dimensioned in a manner such that the holder 34 is completely sealed at its openend in order to prevent the penetration of dirt and the like and also to achieve a suitable field control and contact safety. The electrical screen 10, 11 attached to the plate 9 of the shaft 2 is earthed via spring pins 41 which extend into the openings 13 of the plate 9.
Mounted between the plate 10 of the electrically conducting screen and the plate 9 is a tilting mechanism 42, the one end 43 of which interacts with an end of a pin 47 which is trapped so as to slide in the longitudinal direction in the passage opening 14 of the gripping device 1 by means of a disc 45 joined thereto and stops 46 and whose other end is situated opposite the terminal electrode 25 of the tubular fuse 32 from which a tell-tale pin or striker pin emerges outwards to indicate the tubular fuse 32 has functioned.
If the fusible wires or fusible strips in the tubular fuse 32 have blown, said tell-tale pin emerges outwards, as a result of which the pin 45 is displaced and the end 44 of the tilting mechanism is moved in the direction of the plate 9. The change in position of the end 44 can be used to indicate that the tubular fuse 32 has functioned.
Although the invention has been illustrated above with reference to a preferred embodiment, a person skilled in the art will be able to make diverse modifications and additions without departing from the scope thereof and the idea on which the invention is based.

Claims

1. Gripping device for handling a tubular fuse having terminal electrodes situated at the ends, characterized by a shaft having a cylindrical cavity and provided with a mouth for receiving a terminal electrode of the tubular fuse, a clamping element being fitted in the cavity for exerting a frictional force on the terminal electrode concerned in order to couple the tubular fuse to the gripping device, and means acting on the clamping element for influencing the frictional force in a manner such that the coupling to a terminal electrode received in the cavity can be broken with manual force.

2. Gripping device according to Claim 1, characterized in that the cavity is formed by a sleeve-type body of electrically conducting material, an open end of which forms the mouth for receiving a terminal electrode of the tubular fuse, which sleeve-type body is designed to make electrical contact with the terminal electrode of the tubular fuse to be received therein, and an electrical conductor connected to the sleeve-type body and projecting outwards.

3. Gripping device according to Claim 2, characterized in that the free end of the conductor extends laterally from the sleeve-type body in the direction of the mouth for the purpose of detachably electrically coupling the conductor.

4. Gripping device according to Claim 3, characterized in that the free end of the conductor is constructed for the coupling thereof as a plug connection.

5. Gripping device according to one or more of Claims 2 to 4 inclusively, characterized in that the shaft comprises an elongated body of electrically insulating material whose end adjacent to the sleeve-type body is provided with a thickened section to achieve a suitable electric field control and to reduce the electric potential in the direction of the elongated body, an electrically conducting screen to be connected to earth being mounted at the free end of the elongated body.

6. Gripping device according to Claim 5, characterized in that the free end of the elongated body is adjoined by a plate extending in the radial direction, a plate-type electrically conducting screen being mounted with a handle for handling the gripping device at the side facing away from said

7. Gripping device according to Claim 6, characterized in that at least one passage opening is provided in the plate for a contact pin for connecting the screen to earth.

8. Gripping device according to one or more of Claims 2 to 7 inclusi vely, characterized in that the end of the sleeve-type body facing away from the mouth, and the shaft are provided with a passage opening for an actuating element on which the tell-tale pin mounted in a terminal electrode of the tubular fuse concerned is able to act.

9. Gripping device according to Claim 8, characterized in that there is mounted at the end of the shaft facing away from the sleeve-type body an indicating mechanism which can be activated by means of the actuating element to indicate that a tubular fuse coupled to the gripping device has functioned.

10. Gripping device according to Claim 9, characterized in that the indicating mechanism is a lever mechanism attached to the screening plate and having a first and a second position, the actuating element being a trapped pin which can be moved in the passage opening.

11. Gripping device according to one or more of Claims 2 to 10 inclusively, characterized in that, to make electrical contact to a particular terminal electrode of the tubular fuse, contact elements which are mutually displaced in the tangential direction are situated along the inside circumference of the sleeve-type body.

12. Gripping device according to Claim 11, characterized in that the contact elements, viewed from the mouth, are arranged in front of the clamping element.

13. Gripping device according to Claim 11 or 12, characterized in that the contact elements are constructed from a loop-shaped strip of resilient electrically conducting material with backwardly bent ends, the sleeve-type body being provided, near the mouth, with tooth-type projections on which the contact elements act with their backwardly bent ends.

14. Gripping device according to Claim 13, characterized in that the contact elements are provided, near the backwardly bent ends, with guide strips pointing in the direction of the mouth for guiding a terminal electrode of the tubular fuse to be received in the sleeve-type body in the axial direction of the latter.

15. Gripping device according to one or more of the preceding claims, characterized in that the clamping element comprises a curved annular element of resilient material, the central opening of which forms the boundary of a receiving opening for receiving a terminal electrode of the tubular fuse, which annular element is supported in the cavity so as to be displaceable at least in the radial direction in order to vary the receiving opening, the means for influencing the frictional force comprising means acting on the annular element for the displacement thereof.

16. Gripping device according to Claim 15, characterized in that the annular element has an ellipsoidal projection and is curved in a V-shape around the short axis thereof, two slits situated opposite each other and extending at an angle in the axial direction being situated in the wall of the cavity, in which slits the annular element is provided so as to be movably supported both in the axial and in the radial direction at its circumference in a manner such that a virtually circular receiving opening is bounded, a further sleeve being mounted over the mouth and having an edge which extends inwards from the circumference and which forms a stop for the annular element, which further sleeve is latched so as to be slideable in the axial direction over the mouth.

17. Gripping device according to Claim 16, characterized in that the stop of the further sleeve is situated near the mouth and the annular element is received in the cavity in a manner such that the curve thereof is up against the stop of the further sleeve.

18. Gripping device according to one or more of the preceding claims, characterized in that the shaft is manufactured from casting resin.

19. Holder for a tubular fuse, characterized by a cylindrical housing of electrically insulating material having an open end for receiving the tubular fuse in the housing, a closed end provided with a contact for receiving a terminal electrode of the tubular fuse and having a further contact projecting laterally from the housing near the open end for the purpose of making contact to the conductor of the gripping device.

20. Holder according to Claim 19, characterized in that the further contact is constructed for detachably electrically coupling the conductor of the gripping device.

21. Holder according to Claim 20, characterized in that the further contact is constructed for coupling the conductor of the gripping device as a plug connection.

22. Holder according to Claim 21, characterized in that the holder is manufactured from casting resin.

23. Contact element as described in any of the preceding claims suitable for use in the gripping device and a holder according to one or more of the preceding claims.