The robustness and optimization of the power communication system is one of the necessary conditions for the realization of the smart grid, and the optical fiber transmission network as the cornerstone of the power communication system has achieved rapid development. In order to meet the special needs of power system communication, special power cables came into being. After nearly 30 years of development, power special cables have become increasingly mature and promising.
　　1. The characteristics of various power special optical cables
　　 Electric power special optical cables are erected through the unique line tower resources of the power system, and are attached to the power lines and photoelectric composite optical cables added to the power towers, making full use of the overhead power line corridors. The power special optical cable is less likely to be damaged by external forces and has high reliability. Although its own cost is relatively high, the construction cost is relatively low. Special optical cables rely on the power system's own line resources, avoid conflicts and entanglements with the outside world in terms of frequency resources, routing coordination, electromagnetic compatibility, etc., and have great initiative and flexibility.
Electric power special optical cables are divided into optical fiber composite overhead ground wire OPGW, optical fiber composite overhead phase wire OPPC, all-metal self-supporting optical fiber cable MASS, all-dielectric self-supporting optical fiber cable ADSS, ground wire bundled optical fiber cable ADL and ground wire winding optical cable according to the method of laying and defense. GWWOP and other several.
　　2, OPGW and ADSS comparison
　　 Here we analyze and compare OPGW optical cables and ADSS optical cables in terms of characteristics, applicable characteristics, common faults and solutions.
　　A. Differences in characteristics
The outstanding feature of the overhead ground wire composite optical cable OPGW is that the communication optical cable and the overhead ground wire on the high-voltage transmission line are integrated into a whole, and the optical cable technology and the transmission line technology are merged to become a multi-functional overhead ground wire, which is both a lightning protection wire and an overhead ground wire. It is an overhead optical cable and also a shielded wire. While completing the construction of high-voltage transmission lines, it has also completed the construction of communication lines, which is very suitable for new transmission lines. There are three main types of common OPGW structures, namely aluminum tube type, aluminum frame type and (stainless) steel tube type.
The all-dielectric self-supporting optical cable ADSS uses high-strength aramid yarn with high elastic modulus as the tensile element in the manufacture. At the same time, the geometrical size of the optical cable is small, and the weight of the cable is only one-third of the ordinary optical cable. It can be directly hanged. At the proper position of the power tower, the additional load added to the tower is very small, and the maximum span can reach 1500m. Its outer sheath is treated with neutral ionization impregnation, so that the optical cable has a strong resistance to electric corrosion, and can ensure the life of the optical cable in a strong electric field; the optical cable adopts non-metallic materials, has good insulation performance, and can avoid lightning strikes and power lines. In the event of a failure, it will not affect the normal operation of the optical cable; the use of existing power poles can be used for construction without power failure, and it can be erected on the same pole as the power line, which can reduce the project cost. Various ADSS optical cable structures can be summarized into two main types: central tube type and layer stranded type.
　　 B. Applicable features
　　OPGW optical cables are mainly used on lines with voltage levels of 500kV, 220kV, and 110kV. Affected by factors such as line power outages and safety, they are mostly used on newly built lines. The applicable features of OPGW are [4]: ​​(1) Lines with high voltage exceeding 110kV have a large range (generally above 250M); (2) Easy to maintain, easy to solve the problem of line crossing, and its mechanical characteristics can meet the requirements of large lines Spanning; (3) The outer layer of OPGW is metal armor, which has no effect on high-voltage electrical corrosion and degradation; (4) OPGW must be powered off during construction, and the power loss is relatively large, so OPGW should be used in new high-voltage lines above 110kV; (5) In OPGW's performance indicators, the greater the short-circuit current, the more it is necessary to use good conductors as armor, which will reduce the tensile strength accordingly. In the case of a certain tensile strength, the short-circuit current capacity must be increased. The metal cross-sectional area leads to an increase in cable diameter and cable weight, which poses a safety issue to the strength of the line tower.
　　ADSS optical cables are widely used on 220kV, 110kV, and 35kV voltage level transmission lines, especially on existing lines. It can meet the requirements of large span and large sag for power transmission lines. The standard ADSS design can reach 144 cores. Its characteristics are [4]: ​​(1) The theoretical value of the optical fiber tension in ADSS is zero; (2) ADSS optical cable is a fully insulated structure, which can be live-operated during installation and line maintenance, which can greatly reduce power outage losses; (3) ADSS The expansion rate can be kept constant within a wide range of temperature differences, and it has stable optical properties at extreme temperatures; (4) The electrical corrosion resistant ADSS optical cable can reduce the electrical corrosion of the optical cable caused by the high-voltage induced electric field; (5) ADSS The optical cable has a small diameter and light weight, which can reduce the impact of ice and wind on the optical cable, and its impact on the strength of the tower is also small; (6) ADSS adopts new materials and a smooth shape design to make it have superior aerodynamic characteristics.
　　 C. Common faults and solutions
　　 OPGW is affected by short-circuit faults. When the short-circuit current of the line faults impacts the OPGW optical cable, the stainless steel unit has an instantaneous high temperature. The short-circuit current capacity of the optical cable must be increased to reduce the impact of the short-circuit fault on the optical cable. According to Q=I2t, the heat resistance of OPGW can also be improved by limiting the size and duration of the actual short-circuit current.
　　 In addition to short-circuit faults, lightning strikes are another factor that causes the instantaneous high temperature of OPGW cables. Compared with a short-circuit fault, the instantaneous current intensity of a lightning strike is greater, but the duration is very short, so the heat capacity of the temperature rise caused by the lightning strike is smaller than the heat capacity generated by the short circuit, but the short-circuit current acts on the entire metal section of the OPGW optical cable, and the lightning current only Confined to a small section of one or several metal monofilaments, the concentration of energy causes the high temperature on this small section of metal wire to melt it partially or completely. This is the main reason why OPGW cable breaks due to lightning strikes.
　　 The main fault in the application of OPGW cable is strand breakage caused by lightning strikes. The current solutions are as follows:
　　 1) Develop lightning-resistant outer strand materials. The high-lightning-resistant OPGW developed in Brazil in 2000 uses a high-grade galvanized steel wire and an aluminum tube to protect the optical fiber. The high-grade galvanized steel requires more energy to melt under lightning strikes.
　　 2) The outer strands should be made of aluminum-clad steel wire as much as possible, and the thickness of the aluminum-clad steel wire should be thickened.
　　3) Try to increase the designed air gap between the outer strands and the inner strands to avoid internal heat transfer.
　　4) With the same material, use a larger outer strand diameter.　　 After the material and structure of the OPGW cable are determined, its lightning resistance characteristics are also determined.
　　 Since the ADSS optical cable runs near high-voltage wires and there is a strong electric field around it, it is very likely that electrical corrosion will cause damage to the optical cable.
　　5) Track-resistant jackets are preferred for circuits with different voltage levels. Track-resistant materials must be used for circuits with 110kV and above.
　　6) For circuits of 110kV and above, you can consider using anti-corona coils to effectively reduce the electric field on the surface of the hardware and the optical cable and reduce the leakage current.
　　7) For 220kV and above lines and powerful pole towers, the creepage corrosion of the outer skin of the optical cable by the shock-proof hammer is much safer than the shock-proof whip.
　　 8) Control the spatial potential of the cable suspension point, 110kV does not exceed 15kV, 220kV does not exceed 20kV.　　
　　 Distributed optical fiber temperature sensor can be used to monitor electrical corrosion faults.
　　3, power special optical cables with similar characteristics
　　Different power special optical cables have their own characteristics, which can meet different requirements and be used in different occasions. The following is a comparison of special optical cables with similar characteristics in practical application characteristics.
　　3.1 Optical fiber composite overhead ground wire OPGW and optical fiber composite overhead phase wire OPPC
　　In the power grid, some lines may not have overhead ground wires, but the phase wires are indispensable. In order to meet the requirements of optical fiber networking, similar to OPGW technology, adding optical fibers in a suitable method in the traditional phase line structure becomes an optical fiber composite phase line (OPPC).
　　 At present, OPGW and ADSS are widely used in the backbone network of 110kV to 500kV lines in our country for communication. For some lines that are difficult to choose OPGW and ADSS optical cables, OPPC is the supplementary product of OPGW and ADSS optical cables.
　　3.2 All dielectric self-supporting optical cable ADSS and metal self-supporting optical cable MASS
　　Considering that the MASS optical cable is erected on the same pole as the ADSS optical cable and the existing tower, in order to reduce the additional load on the tower, the MASS optical cable is required to have a small structure and light weight. Therefore, the MASS optical cable structure adopts the central tube type, that is, a layer of galvanized steel wire or aluminum-clad steel wire is stranded on the outside of the stainless steel optical fiber unit. Generally, the galvanized steel wire is mainly used for cost considerations. Because the MASS optical cable is a metal structure, the problem of electric corrosion can be easily solved through good grounding treatment and selection of weak electric field installation points.
　　3.3 Non-metallic bundled aerial optical cable (AD-Lash) and non-metallic wound optical cable GWWOP
　　 They use automatic binding machines and winding machines to bind and wind optical cables on the ground or phase wires. Their common advantages are: optical cables are light in weight, low in cost, and quick to install. It can be installed on the ground wire or 10kV/35kV phase wire without power failure; the common shortcoming is: because they are all made of organic synthetic materials as the outer sheath, they cannot withstand the high temperature generated by the phase wire or the ground wire when the circuit is short-circuited. The aging of the outer sheath material requires special machinery during construction. There are many problems in construction workability and safety, and it is vulnerable to external damage, such as bird damage, gunshots, etc., so it is not available in the power system. Wide range of applications. However, internationally, this type of technology has not been eliminated or abandoned, and is still being used within a considerable range.
　　 4. Conclusion
　　 Power special optical cables have outstanding advantages such as high reliability, long life, easy installation, low overall cost, and good safety. They are being used more and more in power system communication, technology is also constantly improving, and materials are also being updated day by day. At the same time, people's demand for special optical cables is also becoming diversified and high standards. How to improve the characteristics of power special optical cables from structural design and material selection is of profound significance. The development of power special optical cables will usher in a better tomorrow.