Application comparison of OPGW and ADSS optical cables in transmission lines
Principle of optical fiber communication technology
Optical fiber communication utilizes the principle of total reflection in which optical signals propagate in optical fibers. The optical fiber has two layers of materials: the inner layer is the optically denser medium, and the outer layer is the optically sparser medium. When light propagates in the optical fiber, total reflection will occur at the interface of the two layers of materials, and the information carried will be transmitted to the opposite end through multiple reflections.
Application of Optical Fiber Communication Technology in Transmission Lines
Comparison of the advantages and disadvantages of ADSS and OPGW optical cables in terms of structure
ADSS is the acronym for All Dielectric Self-Supporting. All-dielectric, that is, all-dielectric materials used in optical cables. Self-supporting means that the reinforcing member of the optical cable itself can bear its own weight and external load.
At present, high-strength rubber materials are usually used to withstand the horizontal stress between the towers. Because they are self-supporting, their mechanical strength is very important; the use of all-dielectric materials is because the optical cable is in a high-voltage and strong electric environment, and the tip of the metal fittings is prone to discharge. , It must be able to withstand the influence of strong electricity; because it is used overhead on the power tower, there must be special pre-twisted hardware and matching pendants to fix the optical cable on the tower.
That is, ADSS optical cable has three key technologies: optical cable mechanical design, determination of suspension points and selection and installation of supporting hardware.
OPGW optical cable, Optical Fiber Composite Overhead Ground Wire (also called optical fiber composite overhead ground wire). The optical fiber is placed in the ground wire of the overhead high-voltage transmission line, designed and installed at the same time as the overhead ground wire of the transmission line, and the erection is completed at one time to form the optical fiber communication network on the transmission line. , commonly known as OPGW cable.
Comparison of the advantages and disadvantages of ADSS and OPGW in construction
Due to the different materials and erection positions of the two optical cables, the construction techniques are quite different:
ADSS optical cable has the characteristics of light weight, good insulation performance and convenient construction, but the mechanical strength is relatively low.
OPGW optical cable and steel strand are of similar materials, and the construction process is similar to that of steel strand, but attention should be paid to the protection of the optical cable during construction.
ADSS optical cable technology appeared earlier, and was widely used in the early stage of optical cable construction. Because of its insulating properties and erected under the conductor, it can be constructed with live electricity, and the technology is very mature, and it is currently widely used in power systems.
The unique characteristics of ADSS optical cable in structure, performance, installation, maintenance and other aspects make it a popular cable type for power users. ADSS optical cable is also widely used in the reconstruction of old lines because it can be constructed with live electricity. Due to its high insulation performance, it can be constructed without power failure when crossing live low-voltage lines, avoiding many power failure procedures. When crossing the road, due to its light weight, it can be applied to isolated stalls, which can be constructed quickly and avoid long-term traffic jams. When the crossing is particularly difficult, the ADSS optical cable can also enter the ground like a cable and drill through the crossing object, but corresponding protective measures should be taken. ADSS optical cable has obvious advantages in construction.
The construction of OPGW optical cable is more complicated, and it is generally used in new lines. The construction process is similar to that of steel strands, but attention should be paid to the protection of optical cables during construction.
OPGW optical cables are mostly connected with pre-twisted fittings and towers. The joints are generally selected on tensile towers with high mechanical strength, and have sufficient length to facilitate the connection of optical cable connection personnel on the ground. When there is construction and renovation, the remaining cables can also be laid out. If the old line is installed with OPGW optical cable, it will take a long time to lose power, which will reduce the reliability of the system. For the newly erected optical cable, the strength of the tower must be re-checked and reinforced if necessary.
Comparison of the advantages and disadvantages of ADSS and OPGW optical cables in electrical aspects
Due to the different erection positions, the electrical requirements are also different.
ADSS fiber optic cables are erected with slack stress. When the weather is windy, they will be close to the conductors and require their own insulation properties. The OPGW optical cable is erected above the wire, and a sufficient safety distance should be ensured from the wire.
During long-term operation of ADSS optical cable, electrical corrosion will destroy its insulating outer layer, and these effects will increase in heavily polluted areas, and cable breakage events often occur. This requires the selection of hanging points during installation. Keep away from live objects as much as possible.
Generally, electrical corrosion mainly occurs at the position where the end of the metal fitting is in contact with the optical cable. In addition, due to capacitive coupling, an induced current will be generated on the outer sheath, and arcing will easily damage the cable under the action of water droplets and dust. In addition, when choosing the installation location on the double-circuit line, the influence of the change of the field strength when the first-circuit line is powered off should be considered.
Therefore, it is necessary to calculate the electric field strength of the transmission line according to the field strength distribution diagram of the wire suspended structure on the tower. Combine the tower structure, tensile strength, construction rationality, the sag of the optical cable and the distance between the optical cable and the power line, road, railway and building to comprehensively determine the suspension point of the optical cable, and try to use the AT outer sheath.
Because the OPGW optical cable assumes the role of the ground wire, it must withstand the lightning discharge current, and the temperature rise caused by it has a great influence on the OPGW optical cable, so grounding measures should be taken to limit it. In recent years, OPGW optical cables have broken strands from time to time, which requires us to strictly control the quality of products, and the quality of monofilament connections should be strengthened.
The OPGW optical cable should also maintain an effective safety distance from the conductor in the file. Because the optical fiber is installed inside the steel strand, the OPGW optical cable has the characteristics of anti-electromagnetic interference and light weight. It can be installed on the top of the transmission line tower without considering the optimal hanging position and electromagnetic corrosion. Therefore, OPGW optical cable has the remarkable characteristics of high reliability, superior mechanical properties, and low cost. This technique is especially suitable and economical for new installations or replacement of existing ground wires.
Comparison of advantages and disadvantages of ADSS and OPGW optical cables in operation
Compared with the operation of the two kinds of optical cables, the communication functions of the ADSS optical cable and the OPGW optical cable are the same. The OPGW cable also plays the role of lightning protection.
ADSS optical cables are mostly erected on poles and towers on transmission lines. Generally, poles and towers should be reinforced. Since they are greatly affected by galvanic corrosion, the selection of the hanging point should be as far away as possible from live objects. Considering the comprehensive effect of its mechanical properties, shock resistance and electrical corrosion, it is not easy to be used in coastal long-distance transmission lines.
The erection of ADSS optical cable lines in coastal areas meets the requirements of communication, but with the development of operation, many problems have arisen:
a. The strength of the tower after adding ADSS optical cable is not reinforced, resulting in a lot of deformation of the main material of the tower. Since the ADSS optical cable bracket is erected on the tower, the force of the tower increases, so the force calculation of the tower must be re-calculated before installation.
b. The humid air in coastal areas is mixed with a lot of salt, and the erection height of ADSS optical cable is generally low, resulting in the accumulation of water droplets with salt on the ADSS optical cable for a long time, resulting in serious high-salt electrical corrosion phenomenon.
c. The coastal wind is strong, causing many ADSS optical cable disconnection accidents. At the same time of disconnection, due to the huge impact force, the ADSS optical cable wraps the wire and causes the wire to short-circuit, or the tower falls down. ADSS fiber optic cable breakage accidents occur from time to time. Removing the ADSS cable and replacing the OPGW cable is the ultimate solution to the problem.
d. Another fatal disadvantage of ADSS optical cable is that it is easy to be burned in the event of a fire, and it is not recommended to use it in fire-prone areas.
e. Low operating life. Generally, about 10 years, the mechanical strength of ADSS optical cable generally decreases, and the number of breakage failures increases sharply.
The probability of failure of OPGW optical cable in operation is low, mainly in the following aspects:
a. Deformation of the main material of the tower. The strength of the tower installed with the OPGW optical cable is not reinforced, causing many deformations of the main material of the tower. Since the diameter of the OPGW optical cable is generally larger than the diameter of the ordinary steel strand, the original overhead ground wire is replaced by the OPGW optical cable. The force increases, so the force calculation of the tower must be re-calculated before replacement.
b. Broken strands of the optical cable. The main reason for the broken strands is that the welding quality of the broken strands and the single wire connection does not meet the requirements. OPGW optical cable disconnection has a great impact on the system. For example, if the strands of 220kV and above lines are disconnected, the loss caused by the power outage is huge.
c. The phenomenon of anti-vibration hammer shifting. At present, some lines have adopted the pre-twisted anti-vibration hammer to prevent the occurrence of the phenomenon of anti-vibration hammer shifting. However, this technology has not passed the test of time, may bring new operational problems, and has not been widely used.
d. OPGW optical cable has a long operating life and stable operation. Because it is fixed in the hard steel strand, it is less affected by the external environment, can run for a long time, and can be decommissioned with the aging of the line. Although the probability of failure of OPGW optical cable is relatively small, once a failure occurs, it will cause line tripping and even tower collapse.
The comparative analysis of ADSS and OPGW optical cables in different aspects is convenient for us to choose correctly when selecting materials.
Transmission lines have higher and higher requirements for the reliability of power communication. When designing and selecting, power grid companies should select different types of optical cables according to the different structures, performances, topography, and specific environments of optical cables to meet the requirements of operation and management. Get the best value for money.