Overhead cables are overhead conductors with insulation and out sheath .They are new transmission lines between overhead conductors and underground cables .They are single core,inside conductor can be Aluminum ,Aluminum Alloy ,also with steel core or AAC core as support .Overhead cables are widely used in domestic and international transmission in countryside power transfer .They are featured with high reliability of power supply, power supply security, erection and maintenance convenience and economy .
Because Overhead cables are laid out in countryside where are exposed in the hard weather condition such as the strong wind ,rain fall ,and high temperature of sunlight .It must have the advantage of Weatherability.So existing overhead cable insulation material is made of polymer insulation and a certain amount of carbon black blend. Because the polymer insulating material can reject 94% of visible and infrared energy, it can not penetrate the interior of the polymer, but there is still a small amount (6% of the total energy) of ultra-violet light (commonly known as VA Light) can penetrate the interior of the insulation, cracking the polymer under long-term action, the surface of the insulation becomes rough or even cracked, and finally the insulation is destroyed. If more than 2% carbon black is incorporated into the insulation, it is entirely possible to prevent the intrusion of VA light, but this is detrimental to the electrical insulation properties of the cable and will cause a sharp increase in the value of B. In order to solve this contradiction, the current cable insulation is the best weatherability crosslinking insulation formula after different formulations and tests. The formula has been successfully put into trial production by some domestic manufacturers. The cross-linked two overhead cables Has also been formally put into operation .
Also another factor is that Insulation level.
Overhead cable use, due to the ground voltage is not entirely added to the insulation of the cable , the majority of its ground by the air medium to bear, which overhead cable insulation performance is higher, and significantly better than the average Ordinary oil paper and cross-linked cables. Because the oil-in-lead cable and the shield of the cross-linked cable are normally grounded, the voltage through which the cable passes is entirely on the primary insulation, while the overhead cable is shared between the primary insulation and the air medium. Therefore, all the relevant national standards stipulate that the overhead thickness of overhead cables should be thinner than that of ordinary cables. Generally, the insulation thickness of aerial cables in countries such as Europe, the United States and Japan is 10 to 20% less than that of ordinary cables. At the same time overhead cables in the long-term voltage, the insulation quality will not significantly decreased, unlike buried cable laying in the long run will produce water trees, water trees reach saturation, the cable breakdown voltage will be reduced by a 1/3 a 1/2 , While aerial cables generally do not produce water trees. Therefore, on the whole, the insulation performance of overhead cables is high.
All these above features make they work well to transfer power in the hard weather conditions .ZMS cable makes sure our overhead cable can work more than 70 years with proper way ,with no quality issue .