What is Aerial Bundle Cable？
Origin of Aerial Bundle Cable
The so-called Aerial Bundle Cable is relative to the cable said, is the tower will be erected by the conductor at a certain height transmission of electrical energy lines. For high-voltage transmission and distribution network overhead line insulation to ground is generally by air, before the distribution lines (10kV in addition to the following 380V) is generally also used for bare conductors, but due to the complexity of the urban power distribution environment, often short-circuit grounding and lightning strikes on the line, resulting in a reduction in the reliability of the power supply, so the general 10kV overhead lines are used for the following insulated conductors (i.e., the conductor outside the parcel of insulation layer), which is the The so-called insulated overhead line(Aerial Bundle Cable).
Overhead line has a low-voltage and high-voltage points, the general model is divided into many kinds of, such as street lamp overhead
line, JKLYJ * 10KVA * 50 * 100, which explains the voltage of the overhead line, the model, the material, the core cross-sectional area and length.
Development status of Aerial Bundle Cable
Most of the traditional high-voltage power transmission methods use either high-voltage overhead lines or high-voltage cable lines as the transmission channel, and their respective advantages and disadvantages and their scope of application are well established.
A new high-voltage power transmission method between overhead wires and underground cables – overhead cables have come into existence. France, Sweden, Finland and other countries in accordance with its dense forests, in the early sixties took the lead in the research and development of overhead cables, overhead cables have been widely used in Europe, the United States, Japan and Southeast Asia, South Korea and China’s Taiwan Province of China are also a large number of high-voltage production of overhead cables, the use of overhead cables for power supply.
In the city’s old power grid renovation in most of the use of overhead cables. Shanghai has taken the lead in the use of 1 ~ 10kV overhead cable more than 100 kilometers, Guangzhou, Beijing, Shenyang, Wuhan, Dalian and other major cities and tourist attractions are also more imported and domestic aerial cable, and thus the cable manufacturers have been on the horse, research and development of such new popular products. Among them, Harbin and Shandong and several cable factory, the early eighties from Northern Europe, Finland and other countries introduced a modern crosslinking production equipment, has become the backbone of China’s production of aerial cable manufacturers, some of its aerial cable products have been exported to the United Arab Emirates and the Philippines and other countries.
Nowadays, many manufacturers in China can produce Aerial Bundle Cable to meet the needs of different countries in the world.
Categorisation of Aerial Bundle Cable
Overhead cable is not the ordinary oil paper insulated cable or cross-linked insulated cable hanging directly on the overhead tower, but the use of similar to the production process of cross-linked cable manufacturing a special cable.
General aerial cable is single-core, according to its structure can be divided into hard aluminium wire structure, hard drawn copper wire structure, aluminium alloy wire structure, steel or aluminium alloy core support structure and self-supporting three-core grain structure (the core can be hard aluminium or hard copper wire), etc.
Hard aluminium wire structure is light weight, moderate tension, cable is easy to bend, easy to install, and low cost, can be easily installed in the existing tower use, general transformation or new construction projects are mostly used in this way.
Hard-pulled copper wire structure is heavier, but the tension is large, resistance to the role of external forces, and even when the tower breaks the cable can still continue to energise. Aluminium alloy wire structure of light weight, tensile force, mainly used for span of 100m large span tower system.
Steel or aluminium alloy core support structure is generally used for 35kV voltage system, the span is also larger, with square insulating parts to support the line (bare wire) and the three insulated phase line separation, support line can be used as a lightning line, the biggest advantage is that the arc droop is small, the arc weight is only about 2.4% of the span.
Self-supporting three-core stranded structure for the span of the medium system, the disadvantage of this cable is: three-core cable manufacturing length is shorter than the single-core, more joints, and there is an external semi-conductive shielding layer, at the end of the cable to be like ordinary cables such as the device termination head or stress cone structure.
Key features of Aerial Bundle Cable
1, High reliability of power supply
The use of overhead cables can greatly reduce all types of short-circuit faults (especially overhead bare wire common flashover faults), compared with overhead bare wire, the failure rate is 4-6 times lower.
Domestic aerial cable in Shanghai in 1988 for trial operation, test aerial cable along the Huaihai Road dense boulevard through, after the Shanghai area typhoon season and summer high temperature test, running well, its power supply failure rate than the original bare overhead conductor is greatly reduced. Overhead cable in use will not produce water tree, cable after years of operation, insulation quality without significant decline.
2, Good power supply security
The use of overhead cables to make personal electric shock casualties have been greatly reduced. Shanghai Cable Research Institute has set up a special topic, “overhead cable insulation on personal safety research and testing”. Tests and calculations show that: even with a hand touching the surface of the cable insulation charged, the induced current is less than 0.1mA (10kV) and 0.2mA (35kV), much lower than the national electrical safety regulations of 50-100mA lethal standards. Can be seen in the overhead cable energised, when the human body or other animals inadvertently touch the cable insulation surface, as long as the cable is not breakdown, will not cause harm to humans and animals.
3, Easy to set up and maintenance
Aerial cable can be erected in any kind of tower, can also be erected along the wall, under special circumstances can also be in the bushes through, directly fixed in the tree poles with the gold. Can be set up in a single circuit, can also be set up on the same pole back to the line, without requiring a wide “electrical corridor”. In the installation can be conveniently set up in the original overhead line, the use of the original cross-arms and vases, can also use a full set of matching fittings and accessories. Can also be based on the actual situation on site, please manufacturers of special or self-made some special fittings, so the construction is extremely convenient. Overhead cables do not have to carry out special inspections, and will not be due to tree flash and residents throwing debris, or crane boom mistakenly collision and the formation of short-circuit tripping accidents, thus greatly reducing the line maintenance and overhaul work.
4, The economy is reasonable
Although the use of aerial cable than the use of overhead bare wire in the price is more expensive, but cheaper than ordinary underground installation of cable.
Thus, the use of overhead cables, although the one-time investment is slightly higher, but a combination of other factors, its operating costs will be significantly lower than the overhead bare wire. Such as the use of overhead cables makes the line corridor shrink, and even more lines share a tower, reducing the cost of land acquisition, operation also do not need to cut and trim the trees under the line, saving the cost of cutting and trimming, the most important thing is to reduce the line failure and the direct or indirect losses caused by the cost.
Therefore, its comprehensive cost is obviously lower, more economical and more reasonable.
Main technical performance of Aerial Bundle Cable.
High-voltage overhead cable insulation, in addition to the high electrical performance requirements must be met, but also requires good weather resistance , in order to work safely under sunlight for a long time. Existing overhead cable insulation materials are made of polymer insulation materials and a certain amount of carbon black blended. Because the polymer insulation materials can account for 94% of the energy of visible light and infrared light to reject, so that it can not penetrate the polymer inside to, but there are still a small amount (accounting for 6% of the total energy) of ultraviolet light (commonly known as VA light) can penetrate the insulation inside, in the long-term action of the polymer cleavage, the surface of the insulation becomes rough or even cracked, and ultimately make the insulation damage. If the insulation into more than 2% of carbon black can completely prevent the invasion of VA light, but this is not good for the cable’s electrical insulation performance, will make the gtB value rises sharply.
In order to solve this contradiction, the cable insulation is after different formulas and many tests to determine the best weathering crosslinking insulation formula, the formula has been successful trial production by some domestic manufacturers, with the production of this material crosslinking two overhead cables have also been formally put into operation.
Overhead cable use, due to the ground voltage is not entirely added to the cable insulation , the majority of its ground is borne by the air medium, the insulation performance of the overhead cable is higher, and significantly better than the general ordinary oil paper and cross-linked cable.
Because the lead of the oil paper cable and cross-linked cable shielding layer is usually grounded, so the cable through the voltage is completely added to the main insulation, while the aerial cable is the main insulation and the air medium together. Therefore, the relevant standards in various countries have stipulated that the overhead cable than the grounding of ordinary cable insulation thickness to obtain some thin, generally Europe, America and Japan and other countries of the insulation thickness of the overhead cable than ordinary cables are 10-20% thin.
At the same time, overhead cables in the long-term voltage, insulation quality will not decline significantly, not like buried cable in long-term operation will produce water tree, water tree saturation, the cable breakdown voltage will fall 1 / 3 a 1/2, and the overhead cable does not generally produce water tree. Therefore, comprehensively, the insulation performance of the aerial cable is higher.
Inner and outer semi-conductive shielding
1KV low-voltage overhead cable, due to the conductor surface electric field strength is very low, do not need to use the inner semi-conductive shielding layer .
When the overhead cable close to the grounding body, 10kV overhead cable conductor surface electric field strength of 2 ~ 3kV/mm, 35kV overhead cable conductor surface electric field strength can be as high as 5kV/mm or so, it is necessary to use the inner semi-conductive layer can not be.
Because the cable in the conductor and insulation layer is not bonded, in the temperature change of the two layers will be disconnected from each other, in case of rainy weather, disconnected part of the full of water vapour, so that its electrical strength is reduced. Dry air resistance of up to 3kV/mm, while the wet air only 0.5 a 1KV/mm. so that the cable in normal operation, the conductor surface and insulation gap between the formation of a layer of corona, in addition to causing corona discharge loss, but also very easy to destroy the insulation medium. For this reason, countries around the world, more than 10kV overhead cable are used within the conductor semi-conductive shielding.
Phase single-core overhead cable does not have to use the outer semi-conductive shielding, but more than 10kV three-core textured overhead cable must be used outside the semi-conductive shielding. Because the three-core texture of the aerial cable and its external electric field is not uniform, if there is no external semi-conductive shielding layer, then in the air when wet, will produce a strong corona discharge.
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