GB2324417A - Arrangement of overhead multi-circuit power transmission lines - Google Patents

Abstract

An overhead electric power transmission system comprises at least two circuits each incorporating two or three conductors (56 to 60) extending between remote locations and periodically supported on a series of spaced upright supports (50). The corresponding conductors (52,58 54,60 56,62) of each circuit are at the same electrical potential, and are supported closely adjacent one another on each support (50). Conductors at significantly different potential being spaced apart sufficiently to ensure electrical integrity therebetween. Adjacent corresponding conductors (52,58 54,60 56,62) are maintained at close spacing by spacer means (64) at periodic locations along the lengths of the conductors between said supports (50).

Description

POWER TRANSMISSION SYSTEM Overhead transmission systems are designed to carry electrical power safely from one geographic location to another for the benefit of customers.

Conventionally such systems incorporate lines supported above the ground on lattice steel towers, wooden poles or the like, with the individual conductors or wires being sufficiently separated from one another to ensure safe electrical clearance therebetween, and from personnel or objects likely to pass below the conductors.

Many such transmission lines comprise bare conductors each of which is electrically insulated from the supporting towers by conventional insulators but which rely upon air insulation both to the ground (which is electrically connected to some part of the system) and to the other conductors of the circuit which at any one time are charged to significantly different electrical potentials.

Thus there is a necessity for the individual conductors of a circuit to have a preferred minimum clearance therebetween for safety purposes and sufficient to provide access thereto by personnel for maintenance purposes.

An electrical circuit may comprise two conductors (single phase) or three conductors (three phase), low system voltages for such systems commonly falling within the range of 11 to 25 kV.

Although some overhead lines incorporate conductors which are covered with an insulating material to allow brief or temporary infringement of the safe electrical clearances that would be needed for bare conductors, the provision of such insulating covers is not intended to provide long term primary insulation between conductors at significantly different potentials. It is therefore still necessary for the individual conductors to be spaced from one another sufficiently for complete electrical integrity.

It is sometimes desirable for overhead transmission systems to carry multiple conductors at the same electrical potential either to offer multiple circuits interposed by switching means or multiple current paths not involving switching means between spaced geographic locations.

It is established practice in such situations to provide the multiple circuits on a single route of support towers or the like. However, the conductors of the two circuits are customarily sufficiently spaced from one another to allow maintenance work to proceed on the conductors of one circuit without interference by the conductors of the other circuit, while the conductors of each circuit must be sufficiently spaced from each other and from the conductors of the other circuit to avoid potential contact therebetween.

Thus it will be appreciated that the overall space required to contain the conductors of multiple circuits at any given point along the length of the route, and in particular at the supporting tower or the like, is substantial.

This is of particular relevance in routes that are arranged as rings so that customers can be supplied via alternative routes in the event of faults - access to the faults must be at a premium to provide an effective, efficient system.

Figure 1 of the drawings illustrates schematically a conventional single three-phase circuit arrangement in which horizontally spaced conductors 2,4,6 are carried on a pole support 8, the conductors each being spaced apart by a distance d to provide safe electrical clearance therebetween, and to enable access thereto for maintenance purposes. The width of the single circuit is therefore 2d.

Figure 2 of the drawings illustrates schematically a conventional single three-phase circuit arrangement in which vertically-spaced conductors 10,12,14 are carried on a pole support 16, the conductors each being spaced apart by a distance d1 to provide safe electrical clearance therebetween, and to enable access thereto for maintenance purposes. The depth of the single circuit is therefore 2dl.

Figure 3 of the drawings illustrates schematically a conventional double three-phase circuit arrangement on a pole support 18 in which the vertically-spaced conductors 20,22,24 of the first circuit are spaced apart by a distance d2, the vertically spaced conductors 26,28,30 of the second circuit are spaced apart by the same distance d2, and the equivalent conductors of the two circuits are horizontally spaced apart by a distance d3. The overall depth of the double circuit is therefore 2d2 and the width is d3.

Figure 4 of the drawings illustrates schematically an alternative conventional double three-phase circuit arrangement on a pole support 32 in which the three conductors 34,36,38 of one circuit are located in a substantially triangular configuration to one side of the support 32 with the conductors at different potentials spaced apart by a distance d4, and in which the three conductors 40,42,44 of the other circuit are similarly located to the other side of the pole support 32. The two circuits are spaced apart by a distance ds sufficient to provide electrical safety and adequate room for maintenance. The overall width and depth of such an arrangement is substantial, and requires a relatively complex pole support 32.

It would be desirable to be able to provide a multiple circuit overhead electric power transmission system of a more compact configuration than heretofore but which still incorporates the necessary electrical integrity and in which the individual circuits can still be operated independently of one another.

According to one aspect of the present invention there is provided an overhead electric power transmission system comprising at least two circuits each incorporating two or three conductors extending between remote locations and periodically supported on a series of spaced upright supports, the corresponding conductors of each circuit being at substantially the same electrical potential, characterised in that the corresponding conductors of each circuit are supported closely adjacent one another on each support, conductors at significantly different potential being spaced apart sufficiently to ensure electrical integrity therebetween, adjacent corresponding conductors being maintained at close spacing by spacer means reacting therebetween at periodic locations along the lengths of the conductors between said supports.

According to a further aspect of the present invention there is provided a method of transmitting electric power comprising the steps of providing at least two circuits each incorporating two or three conductors, extending said conductors between remote locations with the conductors being periodically supported on a series of spaced upright supports, the corresponding conductors of each circuit being at substantially the same electrical potential, the conductors at significantly different potentials being supported on the supports sufficiently spaced apart to ensure electrical safety therebetween, characterised by supporting the corresponding conductors of each circuit closely adjacent one another on each support, and providing spacer means between adjacent corresponding conductors at periodic locations along the length of the conductors between the supports to maintain the close spacing between said corresponding conductors.

It will be appreciated that the close spacing of the conductors of similar potential at the supports considerably reduces the complexity and size of the supports, while the presence of the spacer means along the lengths of the conductors enables the conductors to provide mutual mechanical support to one another without undue electrical stress.

The arrangement of the invention offers many of the traditional advantages of the multiple route ring circuits but with lower route length, the potential for upgrading existing routes, higher structural efficiency and lower environmental impact and risk than heretofore.

Figure 5 of the drawings illustrates schematically a threephase circuit arrangement according to the invention, while Figure 6 of the drawings shows part of the length of a power transmission system according to the invention, and Figure 7 of the drawings shows a switching arrangement incorporated in a twin circuit system according to the invention.

Referring to Fig. 5, there is shown a support pole 50 on the cross-arm of which are supported the three covered conductors 52,54,56 of a first, three-phase circuit, and the three covered conductors 58,60,62 of a second three-phase circuit. The pairs of conductors 52 and 58, 54 and 60, and 56 and 62 are at similar potentials to one another (normally within 10%), and are supported on the pole 50 at closely spaced locations, all the conductors being electrically insulated from the pole 50. The pairs of conductors at significantly different potentials are of course spaced apart sufficiently for electrical integrity.

Fig. 6 shows the conductors extending between spaced apart poles 50, the conductors of each pair of conductors being maintained in close spaced relationship by spacers 64 reacting therebetween. These interconductor spacers are located at periodic positions along the lengths of the conductors. As well as maintaining interconductor spacing, these spacers 64 provide an arrangement that is more resistant to the elements than heretofore, the mutual support provided by the conductors reducing, for example, the propensity to the build-up of snow and ice on the individual conductors as can happen with a single, independent wire.

Such an arrangement effectively provides two electrically independent circuits for supplying electricity to the same geographic location - ie. different groups of customers can be supplied from the two different circuits.

Switching means S may be incorporated in the circuits as shown in Figure 7 to enable the two circuits to be sub-divided or combined to meet operational requirements, where A,B and C are separate groups of customers and D indicates the source of electrical supply. In such an arrangement, where the two parallel lines Z represent a single phase or three phase narrow ring circuit according to the invention, supplies can be maintained to some customers when one inter switch circuit is faulted.

The system of the invention may be arranged to incorporate more than 2 circuits, while each circuit may be single-phase or three-phase, providing all conductors of the same or similar potential are located closely adjacent one another.

Claims (4)

1. An overhead electric power transmission system comprising at least two circuits each incorporating two or three conductors extending between remote locations and periodically supported on a series of spaced upright supports, the corresponding conductors of each circuit being at substantially the same electrical potential, characterised in that the corresponding conductors of each circuit are supported closely adjacent one another on each support, conductors at significantly different potential being spaced apart sufficiently to ensure electrical integrity therebetween, adjacent corresponding conductors being maintained at close spacing by spacer means reacting therebetween at periodic locations along the lengths of the conductors between said supports.

2. A method of transmitting electric power comprising the steps of providing at least two circuits each incorporating two or three conductors, extending said conductors between remote locations with the conductors being periodically supported on a series of spaced upright supports, the corresponding conductors of each circuit being at substantially the same electrical potential, the conductors at significantly different potentials being supported on the supports sufficiently spaced apart to ensure electrical safety therebetween, characterised by supporting the corresponding conductors of each circuit closely adjacent one another on each support, and providing spacer means between adjacent corresponding conductors at periodic locations along the length of the conductors between the supports to maintain the close spacing between said corresponding conductors.

3. An overhead electric power transmission system substantially as described with reference to and as illustrated by Figs. 5 to 7 of the accompanying drawings.

4. A method of transmitting electric power substantially as described with reference to Figs. 5 to 7 of the accompanying drawings.