GB2463506A

GB2463506A - Electrical clamp with two contacts or with bladed contact

Info

Publication number: GB2463506A
Application number: GB0816961A
Authority: GB
Inventors: Michael Robert Mundy
Original assignee: PBSI Ltd
Current assignee: PBSI Ltd
Priority date: 2008-09-16
Filing date: 2008-09-16
Publication date: 2010-03-17
Anticipated expiration: 2028-09-16
Also published as: GB2463506B; GB0816961D0

Abstract

A clamp for earthing an electrical conductor has comprising a body with a recess for receiving an object to be clamped. It may have first and second contact formations 34, 40 which are electrically connected to the body and, in use, make contact with the object to be clamped, thereby establishing electrical connections between the clamp and the object. The two contacts may be on opposite sides of the object to be clamped, or on the same side (134, 140, Fig 4). The use of apair of contacts reduces the current flowing at a single point. Alternatively, a single contact formation may comprise a blade configured to abrade a coating of the object to be clamped. The clamp may be used to clamp to a tower or pylon, to earth a transmission line.

Description

A CLAMP

Technical Field

The present invention relates to a clamp, and in particular to a clamp for earthing an electrical conductor such as a cable used in an electricity transmission network.

Backgjound to the Invention It is common for electricity to be transmitted between power stations, electricity sub-stations and premises by means of high-voltage conductors carried by towers or pylons.

Typically these conductors carry electricity at voltages of around 132/275/400kV. Regular maintenance of the conductors and the towers is necessary to ensure the effective operation of this transmission network. Typically, maintenance is carried out by linesmen (technicians) who must climb the tower to effect necessary repairs or maintenance. It will be appreciated that to ensure the safety of the linesmen the tower and the conductors carried must be isolated from the electricity supply during a maintenance operation.

However, additional safety measures are also taken to reduce the risk to a linesman in the event that the conductors being worked on inadvertently becomes live or voltage or current is induced into the isolated conductor by live parallel circuits.

One common safety measure is to connect all of the isolated conductors carried by a tower to earth prior to commencing work, so that in the event that electrical pressure increases in any of the conductors the electricity will safely be conducted to earth, rather than passing through the body of the technician. This earthing of the conductors is typically achieved by clamping each of the conductors with a conductive clamp (known as the line-end clamp), with the line-end clamp being electrically connected to a second conductive clamp (known as an earth-end clamp) by means of a cable, the earth-end clamp being clamped to the tower so as to establish an electrical connection between the conductors and the tower.

The tower itself is electrically connected to earth, thus by making an electrical connection between the conductors and the tower the conductors are electrically connected to earth.

Known earth-end clamps suffer from a number of disadvantages. Typically towers or pylons to which these earth-end clamps are attached have one or more coatings of paint or other non-conductive material, and thus it is difficult to make a good electrical connection between the earth-end clamp and the tower or pylon. Some known earth-end clamps include contact formations designed to penetrate the coating of a tower to make a good electrical contact. However, these contact formations are typically pointed and lead to a very small contact area between the tower and the earth-end clamp. In the event that a fault develops with one or more of the conductors carried by the tower that causes a current to flow along the earthing system, the high current passing through the single small contact area can cause arcing if there is any gap between the contact formation and the tower, and this arcing during the breakdown of the gap can damage the earth-end clamp, leading to degradation and eventual total loss of the electrical connection between the earth-end clamp and the tower. This is clearly undesirable, as it endangers linesmen working on the tower or on the conductors carried by the tower.

Summary of Invention

According to a first aspect of the invention, there is provided a clamp for earthing an electrical conductor, the clamp comprising a body which in use defines an aperture for receiving an object to be clamped and first and second contact formations which are electrically connected to the body and which, in use of the clamp, are able to make contact with the object to be clamped, thereby establishing electrical connections between the clamp and the object.

By providing first and second contact formations which, in use, contact the object to be clamped, an improved electrical connection can be made between the clamp and the object to be clamped. Moreover, by providing electrical contact between the clamp and the object to be clamped at more than one point, the current flowing through any one of the points is reduced in comparison to the current which flows through a single point in prior art clamps, and thus the risk of arcing, which can degrade the contact formation and thus the electrical connection between the clamp and the object to be clamped, is reduced.

Additionally, the provision of first and second contact formations on the clamp improves the mechanical connection between the clamp and an object to which it is attached, thus increasing the security of the clamp on the object and reducing the risk that the clamp will become disconnected from the object.

The first and second contact formations may be disposed on opposed sides of the aperture such that in use of the clamp the first and second contact formations are able to make contact with opposed sides of the object.

The first contact formation may be provided with a blade for abrading a coating of the object to be clamped. By abrading the coating in this way an improved electrical connection can be established between the clamp and the object to be clamped.

The contact formations may be substantially conical.

The first contact formation may be provided on a moveable retaining member.

The moveable retaining member may comprise a threaded body which is received in a threaded bore of the body of the clamp.

The body may be substantially Y-shaped and may comprise first and second arms defining the aperture.

The second contact formation may be provided on one of the arms defining the aperture.

The second contact formation may be provided with a blade for abrading a coating of the object to be clamped.

The clamp may be niade of aluminium. Aluminium is preferred because of its good electrical conductivity and low weight.

The body of the clamp may be of a unitary construction.

According to a second aspect of the invention there is provided a clamp for earthing an electrical conductor, the clamp comprising a body defining an aperture for receiving an object to be clamped and a first contact formation which is electrically connected to the body and which, in use of the clamp, is able to contact the object, wherein the first contact formation comprises a blade which is configured to abrade a coating of the object.

In use of the clamp of the second aspect the blade of the first contact formation abrades a coating of the object to be clamped, thus allowing a good electrical contact to be established between the clamp and the object to be clamped.

The clamp may further comprise a second contact formation which is electrically connected to the body.

The clamp of the second aspect may further comprise any of the features of the clamp of the first aspect.

Brief Description of the Drawings

Embodiments of the invention will now be described, strictly by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a view showing one side of a clamp according to the present invention; Figure 2 is a view showing one end of the clamp of Figure 1; Figure 3 is a view from above the clamp shown in Figures 1 and 2; and Figure 4 is a view showing one side of an alternative embodiment of a clamp.

Description of the Embodiments

Referring first to Figure 1, an earth-end clamp is shown generally at 10. The clamp 10 comprises a unitary body 12 which in this example is cast from aluminium, but which may be of another electrically conductive metal, or of a conductive metal alloy. Aluminium is preferred, however, as it has good electrical conductivity whilst also being relatively lightweight, which reduces the burden on a linesman who must climb a tower carrying one or more earth-end clamps 10.

The body 12 is generally Y-shaped, having at a first end an upper arm 14 and a lower arm 16 which define an aperture 18 for receiving an object to be clamped, such as part of a tower or pylon. Towards a second end of the body 12 there is provided a cable receiving formation, which in this example is a pair of cable clamp members 20, 22 for receiving a cable to connect the earth-end clamp 10 to a line-end clamp.

The cable clamp member 22 is shown in more detail in Figure 2, and comprises an electrically conductive body which is attached to the body 12 of the earth-end clamp 10 by means of threaded bolts 24 which are received in correspondingly threaded formations (shown at 26 in Figure 3) provided in the body 12. The threaded formations 26 may be, for example, threaded nuts received in apertures in the body 12. The cable clamp member 20 is attached to the body 12 in a similar manner.

The cable clamp member 22 and the body 12 define an aperture 28 whose size can be altered by turning the threaded bolts 24. Thus, a ferrule of a cable (not shown) which is used to connect the earth-end clamp 10 to a line-end clamp can be received in the aperture 28 and secured by tightening the threaded bolts 24.

Returning to Figure 1, a moveable retaining member 30 is provided towards the first end of the body 12. In this embodiment, the retaining member 30 comprises a threaded body 31 of a conductive material such as stainless steel which passes through a correspondingly-threaded bore in the upper arm 14, A handle 32 is provided at an upper end of the moveable retaining member 30 to facilitate rotation of the retaining member 30, whilst a first electrically conductive contact formation 34 is provided at a lower end of the retaining member 30. The first contact formation 34 is a generally conical formation of a conductive material such as hardened steel with a protective finish whose point is directed towards an inner surface of the lower arm 16. The first contact formation 34 is provided with a generally central notch 36 which divides the first contact formation 34 into two parts, each of which has a blade-like edge 38.

A second electrically conductive contact formation 40 is provided on an inner surface of the lower arm 16 of the body 12. The second contact formation 40 is a generally conical formation of a conductive material such as hardened steel with a protective finish whose point is directed away from the inner surface of the lower arm 16. Thus, the first and second contact formations 34, 40 are disposed on the body 12 on opposed sides of the aperture 18, with their points being directed in opposed directions. The second contact formation 40 may be provided with a generally central notch 42 which divides the second contact formation 40 into two parts, each of which has a blade-like edge 44.

In use of the earth end clamp 10 an object to be clamped, such as part of a tower or pylon supporting electrical conductors, is received in the aperture 18 of the clamp 10 between the upper and lower arms 14, 16. The handle 32 of the moveable retaining member 30 is turned, causing the first contact formation 34 to move towards the inner surface of the lower arm 16. The first contact formation 34 begins to come into contact with a first side of the object to be clamped, and as the handle 32 is turned, the blade-like edges 38 of the first contact formation 34 abrade any coating, such as paint, that may be provided on the object to be clamped. It will be understood that the rotating action of the moveable retaining member 30 enhances the abrasive action of the blade-like edges 38 of the first contact formation 34.

As the moveable retaining member 30 moves towards the inner surface of the lower arm 16, the second contact formation 40 begins to come into contact with a second side of the object to be clamped, which second side is opposed to the first side of the object to be clamped. As the handle 38 is turned, the blade-like edges 44 of the second contact formation 40 pierces any coating on the second side of the object to be clamped.

The abrasive action of the blade-like edges 38, 44 of the first and second contact formations 34, 40 removes the coating from the first and second sides of the object to be clamped, ensuring that a good electrical connection can be established between the object to be clamped and the first and second contact formations 34, 40. As the first and second contact formations 34, 40 are electrically connected to the body 12 of the clamp 10, directly in the case of the second contact formation 40 and through the moveable retaining member 30 in the case of the first contact formation 34, a good electrical connection can be established between the object to be clamped and the earth-end clamp 10. The use of two contact formations 34, 40 to make electrical connections with the object to be clamped provides two paths for current flowing through the clamp 10, thus reducing the amount of current flowing through each contact formation 34, 40 in comparison to known clamps which use a single contact formation. This reduces the risk of arcing caused by high current, which can degrade the electrical connection between the contact formation and the object to be clamped.

Additionally, the contact between the first and second contact formations 30, 40 on the clamp 10 with the object to be clamped improves the mechanical connection between the clamp 10 and the object, thus increasing the security of the clamp 10 on the object and reducing the risk that the clamp 10 will become disconnected from the object.

An alternative embodiment of a clamp is shown generally at 100 in Figure 4. The construction and function of this embodiment are substantially the same as those of the embodiment shown in Figures 1 to 3, with the exception that the first contact formation, designated 134 in Figure 4, is disposed on the lower ann 116 of the body 112 of the clamp 110, and is electrically connected thereto. In use of this embodiment, the first and second contact formations 134, 140 make electrical contact with two points on the same side of object to be clamped, thereby reducing the risk of arcing by providing multiple current paths, as described above.

It is to be appreciated that the clamps 10, 100 described above with reference to Figures 1 to 4 are merely examples of a clamps according to the present invention, and that various modifications can be made to the clamps 10, 100.

For example, additional contact formations may be provided to reduce further the risk of arcing by providing additional current paths. In the exemplary embodiments described above the cable receiving formation takes the form of moveable clamp members 20, 22 which can receive and secure a ferrule or bare terminated cable. However, it will be appreciated that other forms of cable receiving formation are possible. For example, where the cable to be received is provided with a threaded ferrule, the cable receiving formation on the body 12 of the clamp 10 may be provided as a bore with a complementary thread for receiving the threaded ferrule.

Similarly, the clamp 10 described above has a moveable retaining member in the form of a threaded body 31 which passes through a correspondingly-threaded bore in the upper arm 14 of the body 12. However, alternative moveable retaining members may be provided. For example, the body 30 may be biased towards a position in which the aperture 18 is closed by means of a tension spring or the like, or the arms 14, 16 of the body may be biased towards a condition in which the aperture is closed. However, the use of a threaded body 31 is preferred, as the rotation of the moveable retaining member 31 in securing the clamp to the object to be clamped causes any coating of the object to be clamped to be abraded, thus ensuring a good electrical connection between the clamp 10 and the object to be clamped.

Claims

CLAIMS1. A clamp for earthing an electrical conductor, the clamp comprising a body which in use defines an aperture for receiving an object to be clamped and first and second contact formations which are electrically connected to the body and which, in use of the clamp, are able to make contact with the object to be clamped, thereby establishing electrical connections between the clamp and the object.
2. A clamp according to claim I wherein the first and second contact formations are disposed on opposed sides of the aperture such that in use of the clamp the first and second contact formations are able to make contact with opposed sides of the object.
3. A clamp according to claim I or claim 2 wherein the first contact formation is provided with a blade for abrading a coating of the object to be clamped.
4. A clamp according to any one of the preceding claims wherein the first and second contact formations are substantially conical.
5. A clamp according to claim 3 or claim 4 wherein the first contact formation is provided on a moveable retaining member.
6. A clamp according to claim 5 wherein the moveable retaining member comprises a threaded body which is received in a threaded bore of the body of the clamp.
7. A clamp according to any one of the preceding claims wherein the body is substantially Y-shaped and comprises first and second arms defining the aperture.
8. A clamp according to claim 7 wherein the second contact formation is provided on one of the arms defining the aperture.
9. A clamp according to claim 8 wherein the second contact formation is provided with a blade for abrading a coating of the object to be clamped.
10. A clamp according to any one of the preceding claims wherein the clamp is made of aluminium.
11. A clamp according to any one of the preceding claims wherein the body is of a unitary construction.
12, A clamp for earthing an electrical conductor, the clamp comprising a body defining an aperture for receiving an object to be clamped and a first contact formation which is electrically connected to the body and which, in use of the clamp, is able to contact the object, wherein the first contact formation comprises a blade which is configured to abrade a coating of the object.
13. A clamp according to claim 12 further comprising a second contact formation which is electrically connected to the body.
14. A clamp according to claim 13 wherein the first and second contact formations are disposed on opposed sides of the aperture such that in use of the clamp the first and second contact formations are able to make contact with opposed sides of the object.
15. A clamp according to claim 12 or claim 13 further comprising the features of any one of claims 4 to 11.
16. A clamp substantially as hereinbefore described with reference to the accompanying drawings.