|What is an underground optical cable?|
|Underground cables are used for power transmission and distribution, while overhead structures become impractical. Such locations may be congested areas where the cost of right of way is too high or where local laws prohibit overhead lines for safety reasons, or intersections in wide waters around factories and substations or where overhead crossing is not allowed for various reasons. The type of cable used depends on the voltage and service requirements. Recent improvements in design and manufacturing have led to the development of cables for high voltage applications. This makes it possible to use underground cables for short or medium distance power transmission.|
Underground cable construction
|The type of cable used at a particular location depends on mechanical factors and the voltage required for operation. According to the voltage, these cables are divided into low-voltage cables with working voltage up to 1kv, high-voltage cables with working voltage up to 11KV, ultra-high voltage cables with working voltage up to 33KV, ultra-high voltage cables with working voltage up to 66KV and ultra-high voltage power cables with working voltage over 132KV.|
|In addition to the above factors, the current rating of the cable also depends on many other factors, such as the cable laying method used, the spacing between cables, the number of cores and the thermal conductivity of the soil. Cable manufacturers use a variety of factors to take care of each of them. Approximate indication of current carrying capacity under Indian conditions based on maximum conductor temperature of 80 ° C for 11KV and above cables. The ground ambient temperature of 30 ° C is suitable for most parts of India.|
Disadvantages of underground optical cable
v Underground is more expensive. In highly urbanized areas, the cost of underground transmission may be 10-14 times of the cost.
v The location of the underground cable is not always obvious, which may cause the excavator to accidentally damage the cable or get electric shock.
v Underground cables are more likely to be damaged by ground movement.
Advantages of underground optical cable
v It is less damaged by severe weather conditions (mainly lightning, wind and ice).
v Underground cables can only be installed to 30 m, 400 KV with a narrow enclosure of about 1-10 m, while overhead lines need a enclosure of about 20-200 m wide to maintain safety, maintenance and repair permanently.
v Underground cables will not cause harm to low flying aircraft or wildlife.
v The underground cable is the key part of the overhead high-voltage power line and in some cases provides an economical and reasonable solution for the entire length. The impact of underground cables on the environment can be minimized by using appropriate technologies in appropriate places.
Causes of underground cable failure
v The most common failure point is the cable sealing box, which is mainly due to the poor workmanship of the cable joint when sealing the end.
v Another most common reason is that the lead sheath of the cable is mechanically pierced, such as by crowbars, especially in industrial facilities where excavation and construction operations are carried out in areas with multiple underground cables.
v The cable may also be damaged due to vibration fatigue or overheating.
What is aerial optical cable?
Overhead optical cable is a kind of optical cable usually used for external installation of electric pole. Due to its installation environment, the design of overhead optical cable must consider protecting it from natural damage and man-made damage or theft. The laying method of overhead cable is not difficult to implement, because it can be installed by using the existing overhead poles and lines, thus saving more construction costs and shortening the construction period. Overhead cables are mainly used at or below the level of sub trunk lines, usually in flat terrain or low fluctuation areas. They are easily affected by natural disasters such as typhoon, ice and flood, as well as external forces and their own mechanical strength. Therefore, the failure rate of overhead optical cable is higher than that of pipeline or directly buried optical cable.
Type of overhead optical cable
|According to the installation mode, the overhead optical cable can be generally divided into catenary and self-supporting. Catenary Wire Aerial Cable is a conventional outdoor loose tube cable, which can be spirally bound to a sling or another cable (common in CATV). Self supporting aerial cable or all dielectric self-supporting (ADSS) cable (common style, such as Figure-8 aerial cable), which is bonded to insulating steel or all dielectric conductor rope to provide support. ADSS cables are usually made of heavier sheaths and stronger metal or aramid strength members. Nowadays, self-supporting aerial optical cable is used more and more widely.|
GYTC8S: GYTC8S is a typical self-supporting outdoor optical cable. It is suitable for aerial application, and its good moisture resistance and compression resistance are suitable for pipelines and buried methods. The metal reinforcement is composed of stranded wires as the supporting part and polyethylene sheath to form an 8-shaped structure. Corrugated steel tape armouring and polyethylene outer sheath provide pressure resistance and gunshot resistance. As the central strength, the steel wire reinforcement improves the tensile strength. In addition, it is surrounded by loose tube and water blocking system.
|GYXTC8S: GYXTC8S is also suitable for long-distance communication in the air environment. This 8-shaped overhead cable is usually used for 4-core to 12 core types. Waterproof tape provides waterproof performance. Corrugated steel tape and polyethylene outer sheath provide pressure resistance and gun shot resistance. As a self-supporting member, the 8-shaped steel wire provides excellent strain performance and convenient installation.|
|As a familiar self-supporting overhead cable, the 8-shaped self-supporting overhead cable is designed for convenient and economical one-step installation, and is widely used for long-distance and building network communication. According to the structure and materials of optical cables, there are 8-shaped self-supporting overhead optical cables such as GYTC8S, GYXTC8Y and GYXTC8S on the market.|
GYXTC8Y 8-shaped light self-supporting cable features:
|Excellent mechanical performance and environmental protection performance. The cable is small in diameter, light in weight, self supporting and easy to install. Low dispersion and attenuation. Medium density polyethylene sheath: low friction installation, excellent protection against environmental hazards. Stainless steel or galvanized steel self support. The load supporting element is made of galvanized wire, which can provide high tensile strength. High strength loose tube resistant to hydrolysis. 8-shaped light self supporting cable.|
|GYXTC8Y: GYXTC8Y is a light self supporting cable with a cross section of figure 8, which is suitable for long-distance communication in the air environment. The tensile strength of the stranded wire is high, meeting the self support requirements. It can also be used for pipeline and buried methods. The metal reinforcement is similar to GYTC8S. The steel wire and loose tube are filled with waterproof compound to ensure compact and longitudinal water blocking.|
Features of GYTC8S self-supporting outdoor optical cable:
Excellent mechanical performance and environmental protection performance. The cable is small in diameter, self supporting and easy to install. Low dispersion and attenuation. Corrugated steel tape armouring and polyethylene outer sheath provide extrusion and shot resistance. The cross section is shown in Figure 8. As a self-supporting member, the stranded wire provides excellent strain performance and convenient installation. Steel wire reinforcement provides good tensile strength to ensure tensile strength. The water blocking system improves the waterproof ability.
Comparison between overhead system and underground system
v Compared with the overhead system, the maintenance cost of the underground system is very low.
v The service of the underground system will not be interrupted due to thunderstorms, lightning and objects falling on the wires.
v No interference to communication lines in the underground system.
v Due to insulation difficulties, the underground system cannot operate above 66 KV, but the overhead system can be designed for operation up to 400 KV or higher.
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