Electricity: conductors and insulators – Overhead – Ground clamps and cable clips
Reexamination Certificate
2000-09-28
2001-06-05
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Overhead
Ground clamps and cable clips
C174S042000, C174S1170FF, C174S127000, C174S12900B
Reexamination Certificate
active
06242693
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an overhead cable (including an overhead power transmission line and an overhead ground wire) which prevents wind noise and corona noise and, at the same time, reduces the wind pressure.
2. Description of the Related Art
When wind blows against a laid overhead power transmission line, for example, a Karman vortex is generated on the downwind side of the overhead power transmission line and wind noise is caused. To prevent this wind noise, it is effective to provide a projection at the outer periphery of the overhead power transmission line to disturb the Karman vortex.
For this reason, conventionally, for example as shown in Japanese Examined Patent Publication (Kokoku) No. 53-14146, a spiral rod made of metal, formed by an aluminum wire etc., was wound around the outermost layer of the overhead power transmission line to provide the projection and this projection was used to disturb the Karman vortex and thereby prevent the wind noise.
When winding a spiral rod made of metal around the outermost layer of the overhead power transmission line, however, there arises a problem that corona noise is apt to be generated during rain.
The cause of this is that the electric field becomes stronger at the surface of the projection, so when rain is deposited there to form drops of water which subsequently drop down, a strong discharge occurs.
To prevent the corona discharge described above, it is known to form the spiral rod by a semiconductor material and an insulating material (refer to Japanese Unexamined Patent Publication (Kokai) No. 3-277114). When such a spiral rod is used, since the insulating material does not have any effect on the electric field distribution, the rod is effective for suppressing corona noise at the time of rain.
However, the work of winding the spiral rod around the outermost layer of the overhead power transmission line was very cumbersome.
Therefore, an overhead power transmission line formed by stranding an outwardly projecting strand at the outermost layer of the overhead power transmission line has been proposed (Japanese Examined Patent Publication (Kokoku) No. 6-42328).
When preliminarily winding the outwardly projecting metal strand around the outermost layer of the overhead power transmission line in this way, there is the advantage that it becomes unnecessary to wind a spiral rod later.
When stranding an outwardly projecting metal strand at the outermost layer of the overhead power transmission line, however, the weight of the overhead power transmission line is increased, and therefore there is a problem that the strength of the cable supporting structures such as the steel towers and insulators has to be increased. Further, there is a problem that it is necessary to newly prepare the gripping portions of spacers, dampers, and other parts for gripping the overhead power transmission line to match with the outwardly projecting metal strand.
SUMMARY OF THE INVENTION
The present invention was made in consideration with the above problems and has its object to provide an overhead cable which reduces the weight of an overhead cable formed by stranding an outwardly projecting strand at the outermost layer of the strands, enables conventional gripping portions of parts to be used as they are, and effectively prevents wind noise and corona noise.
To achieve the above object, the present invention provides an overhead cable formed by stranding at the outermost layer of an overhead cable comprised of a plurality of strands at least one outwardly projecting strand, wherein at least the outwardly projecting portion of the outwardly projecting strand is composed of an organic material.
Preferably a projection height H of the outwardly projecting strand from the outer circumferential surface of the ordinary strands positioned on the outermost circumference is within a range of from 1.5 mm≦H≦7.0 mm.
Preferably a reinforcing core is provided in the internal portion of the outwardly projecting strand.
Preferably the surface of the outwardly projecting strand is subjected to hydrophilic processing.
Preferably small uneven portions are provided on the surface of the outwardly projecting strand.
It is also possible to form the outwardly projecting strand by integrally forming a semiconductor body formed at a lower portion and an insulator formed at an upper portion.
It is also possible to strand two outwardly projecting strands adjacent to each other and form a groove between these outwardly projecting strands.
It is also possible to fit a holding strand in this groove.
Preferably the outwardly projecting strand is provided with an anti-unraveling means for preventing unraveling due to breakage.
Preferably the anti-unraveling means is for example comprised of side projections formed on the two sides of the outwardly projecting strand, which side projections are fit in the grooves of the ordinary strands positioned on the two sides of the outwardly projecting strand.
It is also possible to make the anti-unraveling means bottom projections formed at the two sides of the bottom of the outwardly projecting strand, which bottom projections are pressed inward at the bottoms of the ordinary strands positioned at the two sides of the outwardly projecting strand.
It is also possible to make the members constituting the bottom projections semiconductor members separate from the member constituting the outwardly projecting strand and join them to the outwardly projecting strand.
In the overhead cable according to the present invention, by forming the outwardly projecting strand by an organic material, the weight of the overhead cable can be reduced. For this reason, it becomes unnecessary to increase the strength of the steel towers and other supporting structures and the cost of construction of the steel towers etc. can be reduced.
Also, by setting the projection height H of the outwardly projecting strand equal to or larger than 1.5 mm, the wind noise characteristic can be conspicuously improved. Further, by making H less than or equal to 7.0 mm, the outwardly projecting strand made of the organic material can be easily crushed, so the gripping portions of parts such as spacers and dampers which have been conventionally used can be used as they are.
Further, in the present invention, by providing a reinforcing core in the internal portion of the outwardly projecting strand, the strength of the outwardly projecting strand can be improved, so breakage of the outwardly projecting strand can be effectively prevented. Further, when a metal is used as the reinforcing core, the linear expansion rate of the outwardly projecting strand can be made close to the linear expansion rate of the ordinary metal strands constituting the cable, so even when there are severe temperature changes, it is possible to maintain a state with the outwardly projecting strand reliably stranded in the cable.
Further, by providing an anti-unraveling means for preventing unraveling due to breakage of the outwardly projecting strand, the outwardly projecting strand will not unravel even if breaking, so short-circuits and other accidents caused due to the unraveling of a broken strand can be reliably prevented.
Further, when the surface of the outwardly projecting strand is subjected to hydrophilic processing, the water drops will not become spherical, therefore the corona noise can be effectively prevented.
Furthermore, by providing small uneven portions on the surface of the outwardly projecting strand, the position of the vortex generated on the downwind side of the cable can be moved to the rear of the cable, so the difference of the pressure between the upwind side and downwind side becomes small, and therefore the wind pressure can be reduced.
REFERENCES:
patent: D. 186072 (1959-09-01), Scofield
patent: 3033916 (1962-05-01), Scofield
patent: 3388208 (1968-06-01), Lieberman et al.
patent: 3641251 (1972-02-01), Liao
patent: 3813772 (1974-06-01), Adams
patent: 3991550 (1976-11-01), Cohen
patent: 3992566 (1976-11-01)
Abe Ken
Munakata Takeo
Shinohara Takashi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Reichard Dean A.
The Furukawa Electric Co. Ltd
Walkenhorst W. David
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