GB2087167A - Device for the temporary earthing of electrical plants - Google Patents

Abstract

An earthing device for temporarily connecting the phase conductors 9a, 9b and 9c of an electric plant, for example a cubicle-enclosed switchgear, to an earthed conductor 16j, comprises an electrically insulating frame consisting of several insulator elements 14, which together with contact members 15a, 15b and 15c connected by conductors 16a, 16b and 1 6c, respectively, to the phase conductors 9a, 9b and 9c, respectively, and a contact member 15j connected to the earthed conductor 16j, are clamped together into one unit, which is mounted in the electric plant. Temporary earthing is performed by means of a bar 20, which is inserted into the earthing device, for example, through a hole in a wall of a cubicle in which the electric plant is housed. <IMAGE>

Description

SPECIFICATION Device for the temporary earthing of electrical plants This invention relates to a device of the kind employed for the temporary earthing of phase conductors in an electric plant, which device com- prises a number of fixed contact members corresponding to the number of phase conductors, each contact member being connected to a respective phase conductor, and an earthing bar arranged to be inserted into the contact members for temporary earthing of the phase conductors. The device is intended mainly for use in low voltage plants, by which is meant plants for a system voltage of at the most 1000 V.

For the protection of personnel during maintenance work on electric plants it is prescribed, among other things, that the different phase conductors of the plant must be temporarily earthed and shortcircuited at the location of the work. In the case of cubicle-enclosed high voltage switchgear it is previously known to perform such temporary earthing with the aid of an earthing bar which is inserted through a hole in the enclosure of the switchgear. By means of this earthing bar, contact members which are arranged on the different phase conductors are interconnected and connected via the bar to a protective earthing contact (see German Gebrauchsmuster No. 72 15 614). In this known device, the contact members are U-shaped and provided with magnetic cores for contact pressure amplification.

For reasons of space, among other things, this design cannot be used in low voltage plants, and in such applications a design has been used in which a contact bar is mounted separately on each phase conductor, said contact bars each having a respective hole therein for reception of the earthing bar, these holes possibly being provided with contact sleeves. In this way it has been possible to reduce the space requirement, but the design involves inconvenient and expensive adjusting and fitting operations to make the earthing bar pass through all the contact bars.

The present invention aims to provide a device of the kind referred to, preferably intended for low voltage plants, which is not impaired by the abovementioned drawbacks.

According to the invention, a device of the kind referred to is characterised in that said contact members are fixed relative to each other in an electrically insulating body, which has a hole extending between the contact members for inserting the earthing bar, said body with contact members forming a separate constructional unit fixedly mounted in the plant.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a schematic front view of part of a she.et-metal enclosed, low voltage switchgear, this view showing the upper portions of two cubicles from which the front doors have been removed, Figure 2 is a side view, on an enlarged scale, of a first embodiment of an earthing device which is included in the switchgear of Figure 1, Figures 3a and 3b are a front view and a partially sectioned side view, respectively, of an insulator element which is included in the earthing device of Figure 2, Figure 4 is a partially sectioned side view of a first embodiment of a contact sleeve for the earthing device of Figure 2, Figure 5 is a view similar to Figure 4 of a second embodiment of a contact sleeve for the earthing device of Figure 2, Figures 6a and 6b are a side view and a front view, respectively, of a second embodiment of an earthing device for the switchgear of Figure 1, Figure 7 is a side view of an alternative embodiment of an earthing bar for an earthing device according to the invention, Figure 8 is a side view of a third embodiment of an earthing device forthe switchgear of Figure 1, Figure 9 is a front view of the earthing device of Figure 8, Figure 10 is a central section through one of the contact plates included in the earthing device of Figures 8 and 9, Figure 1 7 is a front view of an apparatus group provided with an earthing device according to the invention, and Figure 12 is a sectional view taken on the line A-A of Figure 11.

Figure 1 shows the upper parts of two cubicles 1, 2, secured together side-by-side, the cubicle 1 being an apparatus cubicle and the cubicle 2 a cable cubicle. Through the upper part of the cubicle 1 extend horizontal busbars 3, to which vertical busbars 4 are connected. To the vertical busbar system there are connected, in turn, an apparatus group 5 for high rated current (up to about 800 A) and an apparatus group 6 for lower rated current (up to 63 A). The apparatus group 5 may, for example, comprise a load switch 7 with series-connected knife fuses 8. The terminal bars on the load side of the group 5 are connected to connection bars 9a, 9b, 9c, which extend into the cable cubicle 2 for connection of outgoing cables to the load object.The connection bars 9a, 9b, 9c are fixedly connected to an earthing device 10, which will be described in greater detail hereinafter with reference to Figures 2-5. The apparatus group 6 may, for example, comprise a central thread fuse with or without a group switch and is provided with connection contacts of plug-in design.

The cable connection to the load object of the group 6 is effected via a row of terminal blocks which is arranged in immediate association with fixed plug-in contacts and on the load side of the apparatus group. The row of terminal blocks comprises blocks 11 for the phase conductors and a number of blocks 12 for signal and operating conductors. At one end of the row of blocks there is arranged an earthing device 13, which will be described in greater detail hereinafter with reference to Figures 8-10.

The embodiment of the earthing device 10 shown in Figure 2 comprises a number of compression mouided insulator elements 14, one of which is shown in Figures 3a and 3b, which, together with contact sleeves 15a, 15b, 1 5e and 15jwith respective connection conductors 16a, 16b, and 16j, are arranged in a stack which is held together by means of four screws 17, which extend through the stack between a rear end plate 18 and a front end plate 19.

The earthing device 10 is attached directly to the connection bar 9b, to which the contact sleeves 1 sub of the earthing device is fixed. The two connection bars 9a and 9c are each connected to the contact sleeves 15a and 1 sic in the earthing device via the connection conductors 16a and 16c, respectively.

The contact sleeve 15j is disposed between the contact sleeve 15a and the front end plate 19 and is connected via the connection conductor 16jto an earthed protective conductor (not shown). All the contact sleeves are arranged coaxially and may be interconnected by way of an earthing bar 20 which, when a temporary earthing has to be effected, is inserted through a central hole in the end plate 19 to the position shown in Figure 2. In this way, all the phase conductors are short-circuited and earthed.

Figures 4 and 5 show two different embodiments of contact sleeves for the earthing device shown in Figure 2. The contact sleeve 15' shown in Figure 4 is externally screw-threaded and provided with a collar 21 and a nut 22 for securing the contact sleeve to a connection conductor 16.

The contact sleeve 15" shown in Figure 5, on the other hand, is directly pressed on to the connection conductor 16. Both contact sleeves are provided internally with contact plaes 23 with upwardlyfolded flaps for reducing the transition resistance, for example of the design disclosed in German published Patent Application No.1 286 170. The connection conductors 16 are built up of several parallel copper strips, each having a thickness of, for example, 1 mm, thus giving the conductors a certain flexibility. The contact sleeves, which furthermore have a certain freedom of movement between the insulators 14, are thus given the possibility of becoming aligned in relation to the earthing device bar 20 when this is inserted into the earthing device.

Figures 6a and 6b are a side view and front view, respectively, of an earthing device intended for apparatus groups with lower rated current, where the connection between the phase conductors and the earthing device takes place by means of cables which are secured to terminal bars 24a, 24b, 24c on the earthing bar. For the protective earth connection, a bar 24j is used in the example shown. The end plates 25,26 of the earthing device are constructed as attachment brackets for securing the device on a mounting surface disposed perpendicular to the front of the switchgear cubicle. In other respects, this earthing device is constructed in substantially the same way as the one shown in Figure 2.

With an earthing device in accordance with the invention, either the earthing bar may be smooth and the fixed contact sleeves 15 provided internally with contact plates 23 according to the embodiments shown in Figures 2-5, or the earthing bar may be provided with contact plates, whereas the contact sleeves have smooth contact surfaces. Figure 7 shows an earthing bar 20' of the latter design provided with resilient contact plates 23' which surround the bar at the locations which, when the bar is inserted into the earthing device, confront the contact sleeves 1 Sa-1 Sc and 15j. The contact plates 23' consist of relatively thin plates of, for example, beryllium bronze provided with punched, outwardlyfolded contact flaps. The plates are fixed in slots, extending around the bar, by means of O-rings, or the like.As in the case of the earthing device shown in Figure 2, the fixed contact sleeves 15a,15b,15c are intended to be connected to the phase conductors of the apparatus group in question, and the contact sleeves 1 Sj is intended to be connected to an: earthed positive conductor. If the earthing bar is provided in this way with contact plates (instead of the fixed contact sleeves), the total cost of earthing a switchgear may be considerably reduced since the earthing bar may be common to several groups whereas an earthing device must be provided for each group.

Figures 8 and 9 are a side view and a frohtview, respectively, of one embodiment of the earthing device 13 of Figure 2, intended for small apparatus groups with a rated current of up to 63 A. The earthing device is built up of a number of compression moulded insulator elements 27 which, between themselves, fix contact plates 28 being held together by two through-going screws 29. A rear end plate 30 of the device has an attachment which is mountable on a supporting bar of standard design, so that the earthing device may be mounted together with ordinary terminal blocks in a row, as is clear from Figure 1. The insulator elements 27 and the contact plates 28 have a through-hole 31 for an earthing bar 20.The plates 28 are provided with connection members 32 for connection conductors 33a, 33b, 33c, 33j, through which the earthing device is connected to the phase conductor and protective earthing conductor, respectively, of the associated group. Adjacent the hole 31, inwardly-directed contact tongues 34 are punched in the plates. As will be clear from Figure 10, the contact tongues have a U-shaped deflection in the middle, the tongues thus being flexible in the radial direction so that good contact is made with the earthing bar without rendering the insertion or withdrawal of the bar difficult.

Figures 11 and 12 show an apparatus group 35 mounted in a switchgear cubicle, comprising a load switch and an earthing device 10 of the design shown in Figure 2. The door 36 of the apparatus group is provided with an aperture 37, through which an earthing bar 20 provided with a detachable handle 38 may be inserted into the earthing device.

Thus, temporary earthing may be performed behind a closed door. The apparatus is provided with a lid 39 arranged on the inside of the door, this lid being connected via a link mechanism 40 to an operating handle 41 of the load switch. By means of this interlocking, the earth bar cannot be inserted until the switch is opened.

The invention is not limited to the embodiments shown, but several modifications are feasible. For example, the insulating body of the earthing device need not consist of a plurality of congruent insulating elements arranged in a stack, which are held together by bolts extending axially through the stack, but the body may also consist of two halves which are held together, which halves are provided at their confronting surfaces with recesses for the contact members and the earthing bar. Further, the fixed contact members of the earthing device need not necessarily consist of special contact sleeves or contact plates, but may in principle also consist of, or example, simple busbars with through-holes for the earthing bar.

Claims (10)

1. Adeviceforthetemporaryearthing of phase conductors in an electric plant, which device comprises a number of fixed contact members corresponding to the number of phase conductors, each contact member being connected to a respective phase conductor, and an earthing bar arranged to be inserted into the contact members for temporary earthing of the phase conductors, characterised in that the contact members are fixed relative to each other in an electrically insulating body, which has a hole extending between the contact members for inserting the earthing bar, said body with contact members forming a separate constructional unit fixedly mounted in the plant.

2. A device according to claim 1, comprising a protective earthing contact, which is mounted together with the phase contact members in said body in such a way that, during its insertion, the earthing bar makes contact with the protective earthing contact before making contact with the phase contact members.

3. A device according to claim 1 or 2, in which the earthing bar at its contact points is provided with resilient contact plates which surround the bar.

4. A device according to claim 1 or 2, in which the fixed contact members comprise sleeves in which resilient contact plates are arranged.

5. A device according to claim 1 or 2, in which the fixed contact members consist of plates with holes for the earthing bar, inwardly-directed resilient contact tongues being punched in the part of the plates located nearest the hole.

6. A device according to any of the preceding claims, in which the contact members are connected to their respective phase conductors via flexible connection conductors.

7. A device according to any of the preceding claims, in which the insulating body comprises a stack of mutually congruent insulator elements, which are compressed by bolts which extend axially through the stack, the contact members being fixed between insulator elements positioned adjacent each other.

8. A device according to any of claims 1 to 6, in which the insulating body consists of two halves, held together by screws, which at their confronting surfaces have recesses for the contact members and the earthing bar.

9. A device according to any of the preceding claims, mounted in a switchgear cubicle, in which the contact members are arranged in alignment with an aperture, provided in a wall of the switchgear cubicle, for the earthing bar, the aperture being provided with a lid which is interlocked to a switch for the group conductor in which the earthing device is arranged, so that the earthing bar cannot be inserted until the switch is opened.

10. A device for the temporary earthing of phase conductors in an electric plant, constructed and arranged substantially as hereinbefore described with reference to, and as illustrated in, Figures 2 to 4, Figures 2,3 and 5, Figures 6a and 6b, or Figures 8 to 10, of the accompanying drawings.