AU2004206987A1

AU2004206987A1 - Switchgear portable earthing device

Info

Publication number: AU2004206987A1
Application number: AU2004206987A
Authority: AU
Inventors: Adolf Lamprecht
Original assignee: Thew & Mccann Pty Ltd
Current assignee: Thew & Mccann Pty Ltd
Priority date: 2003-09-03
Filing date: 2004-09-02
Publication date: 2005-03-17
Anticipated expiration: 2024-09-02
Also published as: AU2004206987B2

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "SWITCHGEAR PORTABLE EARTHING DEVICE" The following statement is a full description of this invention, including the best method of performing it known to us:

TITLE

"SWITCHGEAR PORTABLE EARTHING DEVICE" FIELD OF THE INVENTION THIS INVENTION relates to switchgear portable earthing devices. In particular, the invention relates, but is not limited to, a portable mechanism which enables the connection of an electric cable between a piece of electrical apparatus in a metal-enclosed switchboard and the earthing system, for the purpose of carrying out work on the electrical apparatus of which the switchboard may be part. (In some countries, electrical "earth" is also referred to as electrical "ground".) BACKGROUND ART It is normal practice to use a device or equipment to make an electrical connection between a normally-live part of a high voltage electric power line or apparatus to electrical earth, before allowing any worker to approach the line or apparatus, unless specific live working procedures are employed for safe working while the line or apparatus is in service. This connection is made after the normally-live part has been disconnected from the electrical network and tested to prove that it is no longer live.

It is a usual requirement that any device or portable assembly of cables used for connecting live parts to electrical earth is able to withstand the high electromechanical forces and thermal stresses which occur if the electrical supply is connected by mistake onto the electric line or apparatus with the earthing connections in place. These forces and stresses are sustained until the electrical supply is automatically disconnected by control systems in the electrical network, or until conducting part of the current circuit fails and interrupts the current flow.

Modern in indoor electrical switchboards normally have devices installed to perform the function of connecting normally-live parts to electrical earth. These devices are designed as part of the switchboard.

SUMMARY OF THE PRESENT INVENTION In older switchboards, such devices may not be provided, and in this case, portable cable assemblies are connected between normally-live parts and electrical earth.

It is an object of the present invention to provide a switchgear portable earthing device to connect a portable cable assembly to such a switchboard.

The invention preferably includes a portable cable assembly attached to the switchgear portable earthing device. The configuration in which the cables are connected may vary, and this configuration is not material to the proper functioning of the invention. The portable cable assembly is an important part of every equipment using the invention, but is not an integral part of the invention.

A device to perform this function must make a connection to a normally-live part which may be in an orifice enclosed inside the switchboard.

Contact with this normally-live part is commonly made from below the orifice. A contact piece connected to the portable cable assembly is raised vertically into the orifice and placed in electrical contact with the orifice contact. The cable which is part of the portable cable assembly hangs from the clamp down the orifice, and is connected to the remaining cables in the portable cable assembly and thereby to electrical earth.

If electrical supply is incorrectly restored to the line or apparatus, high electromechanical forces arise from the high current flow to electrical earth in the portable cable system. These forces act to pull the contact piece off the contact, or to destroy the mechanism which holds the clamp against the apparatus live part. .Other devices of this art have been tested and are unable to resist these downward force of the connecting cable conducting the current to electrical earth. The electric current arc which is drawn when the contact piece separates from the live part in the switchboard may cause damage to or destruction of the switchboard.

The invention is designed to fix the contact piece onto the live part inside the orifice, and to withstand the electromechanical forces applied by the portable cable assembly to keep the contact piece and the portable cable assembly in place until electrical supply is switched off by automatic systems.

Typically, three units of the invention are connected to a portable cable assembly with one or more cable leads of the portable cable assembly being fixed to a suitable clamp or cable lug for fixing to earth points, the whole comprising one complete set of equipment to be applied to a three-phase switchboard. However, any number of units of the invention may be connected by an appropriate configuration of portable cables to earth clamps or other earth connections in an assembly.

In one form, though it need not be the only or indeed the broadest form, the invention resides in a switchgear portable earthing device comprising: a contact piece head, which is arranged to carry an electrical contact piece and a cable connection thereto, and which preferably allows exit of a connecting cable which is connected to a portable cable assembly; a contact piece, which may be in the form of a switchgear contact piece normally manufactured as a part by the switchboard manufacturer, or may be a part made with the mechanism itself; an insulating pole, placed between a locking mechanism and the contact piece head, whereby the contact piece head is inserted into the orifice and which may be rotated by hand to raise the contact piece head into the orifice; a rotating mechanism, which may be screwed along a threaded rod and thereby raise the insulating pole and contact head into the orifice, or by reversing may lower the insulating pole from the orifice of the switchboard, or which by unlocking from the threaded rod may slide freely along the threaded rod; a threaded adjusting rod or other structure, whereby the mechanism may be screwed upwards into the orifice of the switchboard such that the mechanism is rigidly fixed between the normally live contact part and a floor or supporting surface in the manner of a strut; and a foot or other assembly fitted to the device or a combination of the devices in a set, for bearing firmly on a floor or supporting surface, preferably in the bottom of the electrical switchboard panel.

Preferably, a locking mechanism is provided in the rotating mechanism and is unlockable to allow the rotating mechanism to slide freely along the threaded rod.

BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, preferred embodiments will now be described with reference to the accompanying drawings, in which: FIG. 1 is a side elevational view of the earthing device connected to a portable cable assembly; FIGS. 2 and 3 are top perspective views of the device; FIG. 4 is a side elevational view of the device; FIG. 5 is a sectional side view taken on line A-A on FIG. 4; FIG. 6 is a sectional side view of the upper portion of the contact piece head on a larger scale.

M

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The earthing device in accordance with the present invention is generally indicated by numeral 100.

Referring to FIGS. 5 and 6, the primary contact 22is made (or alternatively is supplied by the switchgear manufacturer) to fit the particular orifice contact of each switchboard. The primary contact made by the applicant is a new design, such that three dimensions only are varied to make it to the correct size of each of a common configuration for contacts of all known switchboards of the types with upwards vertical entry to the orifice contacts. The primary contact 22 made by the applicant is made from annealed copper, and the securing of the contact parts is by means of a circlip 24. The design of the primary contact 22 made by the applicant is considered to be a part of this application.

The primary contact 22 is fixed to a primary contact attachment 23 with a cap screw 1 of stainless steel or other suitable material. The primary contact attachment 23 is made from annealed copper.

The primary contact 22 and the primary contact attachment 23 are located in the contact head 19, into which an end of a cable 51 of the portable cable assembly 50 is inserted through a slotted aperture 25 in the side of the head. The primary contact attachment 23 is fixed in the contact head 19 by means of a grub screw 8. The end of the portable cable 51 is stripped of electrical insulation and secured in the primary contact assembly 23 by a hexagonal compression operation commonly used for the purpose.

The contact head 19 carrying the contact assembly is supported on the end of the insulating pole 21 which is a heavy-duty insulating tube made of fibreglass or other suitable material of appropriate electrical insulating and mechanical properties.

A top pad 30 is fixed to the insulating pole 21 with a pin 7 of stainless steel or other suitable material. The top pad 20 is secured to the base of the contact head 19 with a screw ring 18 of aluminium or other suitable material which is captive on the insulating pole 21 when assembled and screws into a threaded part on the bottom of the head 19.

Referring to FIGS. 4 and 5, the rotating mechanism 26 is fixed to the bottom end of the insulating pole 21 with four or other suitable number of grub screws 5 of suitable material and commonly-available type. The insulating pole 21 is fixed into a joining boss 15 of aluminium or other suitable material.

The threaded rod 13 slides freely through a central hole in the joining boss The threaded rod 13 is prevented from contacting the inside surface of the insulating pole 21 by the threaded rod guide 11 which is fixed to the end of the threaded rod 13 by a countersunk screw 2 of suitable material. The threaded rod guide 11 is made of a non-conducting material of suitable properties to ensure low sliding friction on the inner surface of the insulating pole 21.

The threaded rod 13 may be enclosed in two split nut halves (17) parts forming a complete split nut around the threaded rod 13. The split nut halves 17 may be separated by two springs 3 which may be compressed to allow the split nut halves 17 to bear onto the threaded rod 13, thereby allowing the stating mechanism 16 to advance by rotation along the threaded rod 13.

The split nut halves 7 may be encased in the split nut cage 14. A tapered tab on the top of each split nut half 5 may protrude through the outer surface of the split nut cage 14, such that mechanical force inwards on both tabs together will force the two split nut halves 7 to move together against the restraining compressive force exerted by the springs 13. By coming together, the split nut thread meshes with the thread on the threaded rod 13.

The split nut cage 14 is fixed to the joining boss 15 with two grub screws 10 and two locking dowels 4. The locking dowels 4 are disposed around the circumference of the joining boss 15 diametrically opposite each other, and the grub screws 10 are likewise diametrically opposed on an axis at right angles to that of the locking dowels 4.

The locking dowels 4 act to secure the locking collarl6which may slide along the outside surface of the split nut cage 14 and over the end of the joining boss 15. The locking collar 16 is made of brass or other suitable material with a low coefficient of sliding friction when in contact with the material of the tabs of the split nut halves 7. The locking collar 16 has a guard ring formed in the body to prevent an operator's hand being pinched when the locking collar 16 slides over the joining boss The locking collar 16 has two bayonet slots 16a which mate with the locking dowels 4 protruding from the joining boss. When the locking collar 16 slides over the end of the joining boss 15, it may mate with the pins 4 at the end of its travel, at which point the locking collar 16 may be rotated to lock onto the dowels 4, preventing the locking collar 16 from sliding back along the joining boss 15. The configuration of the slots 16a is arranged to provide a resistance to rotation of the locking collar 16 in an unlocking direction when secured over the locking dowels 4.

At the bottom of the travel of the locking collar 16, the split nut halves 7 are held apart by the separating springs 3, and the rotating mechanism 26 may thereby be freely moved along the threaded rod 13 to the position at which it is desired to lock it to the threaded rod.

As the locking collar 16 is moved from the bottom of its travel over the surface of the split nut cage 14, its inner surface moves along the taper of the protruding tabs of the split nut halves 7, pushing the split nut halves 7 into contact with the threaded rod 13. When the locking collar 16 reaches the pins 4 and is rotated to lock it in place, the split nut halves 7 are fixed around the threaded rod 13. The rotating mechanism 26 is then able to apply axial force to the threaded rod 13 by rotating the locking mechanism by hand. An alternative form of rotating mechanism may use a lever to move the two split nut halves 7 together around the threaded rod 13, after which the rotating mechanism 26 may screw along the threaded rod 13 in the same way. A further alternative rotating mechanism has been designed by the applicant which does not have the locking feature in the rotating mechanism. The alternative form of the rotating mechanism may provide a fixed thread part around the threaded rod 13. The threaded rod may be threaded with a multiple-helix ("multiple-start") thread, for faster screwing of the mechanism along the threaded rod 13. However, this alternative mechanism does not have the feature to be unlocked from the threaded rod 13 and to have free movement along the threaded rod 13 when so unlocked. It must be screwed by hand rotation to the desired position along the rod 13.

The base plate 12 may be of a form which is fitted for a single device or for a multiple number of devices in an arrangement. The base plate 12 may be fixed to the bottom end of the threaded rod 13 with a nut 6 or other suitable fixing to prevent rotation or other movement of the threaded rod 13 in relation to the base plate 12. The base plate 12 may have a serrated pattern or other means formed into the underside to allow secure grip when forced against a concrete or metal surface in the bottom of the switchgear panel.

A hose 9, at the lower end of the threaded rod 13 may be in the form of a cylindrical piece of rubber or other resilient or elastic material to act as a protective device. The hose 9 may prevent the locking mechanism, when freed from the threaded rod 13, falling under the weight of the contact head and cables onto the base plate 12, and causing injury thereby to an operator.

OPERATION

The operator will take the complete assembly of the earthing devices 100 and their attached portable cable assembly 50 to the vicinity of the switchgear at which the earth assembly is to be placed. After completing necessary tests, the operator gains access through normal procedures to the orifices of the switchgear into which the earthing devices 100 will be placed.

The operator applies the earth clamp or connection 52 in an approved manner to the designated earth point.

The operator places the first device 100 below the orifice into which it is to be inserted, ensuring the locking mechanism is free and at the bottom of its travel.

The operator places his/her foot on the base plate 12. The operator then lifts the insulating pole 21 and inserts the contact head 19 into the orifice.

When the contact assembly 22 in the contact head 19 contacts the contact inside the orifice, the operator lifts the locking collar 16, slides it vertically upwards and over locking dowels 4, and rotates it to lock the locking collar 16 in the upper position.

The operator then rotates the insulating pole 21 to screw the contact assembly 22 tightly into the orifice over the contact, holding the screw ring 18 to ensure the cable does not twist around the pole. Contact with the orifice contact is normally evident to the opertaor by feel.

When tight, the device 100 is ready for service.

Additional devices 100 are then installed (normally three), to complete the earthing operation.

The telescopic action of the insulating pole 21 and threaded rod 13 enables the contact assembly 22 to be held in mechanical contact, as well as electrical contact, with the contact of the switchgear. This mechanical contact opposes any electromechanical forces which may be generated if the normally live part is reconnected to the electrical network while the device 100 is in place.

The locking capability of the rotating mechanism 26 allows easy extension/retraction of the device 100 for installation/removal.

The device 100 provides a high level of safety for the operator should the normally-live part of the switchgear be reconnected to the electrical network.

Various other changes and modifications may be made to the embodiments described and illustrated without departing from the present invention.

Claims

1. A switchgear portable earthing device comprising: a contact piece head, arranged to carry an electrical contact piece and a cable connection thereto, and which optionally allows exit of a connecting cable which is connected to a portable cable assembly; a contact piece, being a switchgear contact piece manufactured as part by the switchboard manufacturer, or being a part made with the device itself; an insulating pole, placed between a locking mechanism and the contact piece head, whereby the contact piece head is inserted into an orifice and being rotated by hand to raise the contact piece head into the orifice; a rotating mechanism, being screwed along a threaded rod to raise the insulating pole and contact head into the orifice, or by reversing to lower the insulating pole from the orifice of the switchboard, or which by unlocking from the threaded rod being slidable freely along the threaded rod; a threaded rod or other structure, whereby the insulating pole is screwed upwards into the orifice of the switchboard such that the device is rigidly fixed between a normally live contact part in the switchboard and a floor or supporting surface in the manner of a strut; and a foot or other assembly fitted to the device or a combination of the devices in a set, for bearing firmly on a floor or supporting surface, optional in the bottom of the electrical switchboard panel.

2. A device as claimed in Claim 1 wherein: a locking mechanism is provided in the rotating mechanism and is unlockable to allow the rotating mechanism to slide freely along the threaded rod.

3. A switchgear portable earthing device including: an insulating pole, having a contact piece head at one end, the contact piece being arranged to carry an electrical contact piece with a connecting cable connecting to a portable cable assembly; a threaded adjusting rod, slidably received in the other end of the insulating pole, and having a foot or like structure to bear on a floor or supporting surface; and a rotating mechanism operable to be screwed along the threaded adjusting rod to raise, or lower, the contact head piece into, or out of, engagement with electrical switchgear to be earthed, orwhich is operable to be unlocked from the threaded adjusting rod to slide freely therealong.

4. A device as claimed in Claim 3, wherein: the contact piece head is arranged to carry an electrical contact piece, the contact piece being in the form of a switchgear contact piece incorporated in, or mountable on, the contact piece head.

5. A device as claimed in Claim 3 or Claim 4 wherein: the insulating rod is rotatable relative to the threaded adjusting rod to raise or lower the contact piece head into, or out of, engagement with the electrical switchgear to be earthed.

6. A device as claimed in Claim 3 or Claim 4 wherein: the rotating mechanism includes a locking mechanism which is unlockable to allow the rotating mechanism to slide freely along the threaded adjusting rod.

7. A device as claimed in Claim 6 wherein: the locking mechanism includes a pair of split nuts releasably engageable with threads on the threaded adjusting rod and a locking collar or lever to selectively engage or release the split nuts with the threads.

8. A switchgear portable earthing device substantially as hereinbefore described with reference to the accompanying drawings.

9. A method of erecting a normally-live switchgear part substantially as hereinbefore described with reference to the accompanying drawings. DATED this second day of September 2004. THEW &McCANN PTY LTD By its Patent Attorneys FISHER ADAMS KELLY