Comparison of practical application of electric special cable

- May 09, 2018-

The robustness and optimization of the power communication system is one of the prerequisites for realizing the smart grid, and the optical fiber transmission network, which is the cornerstone of the power communication system, has achieved rapid development. In order to meet the special needs of the power system communication, special power cable has emerged. After nearly 30 years of development, the special optical cable for power has not only matured but also has promising prospects.

1, the characteristics of various types of power special optical cable

Power special optical cable is set up through the power line system's unique line tower resource. It is attached to the power line and the optoelectronic composite optical cable attached to the power pole tower, making full use of the overhead power line corridor. Power special optical cables are less likely to be damaged by external forces and have high reliability. Although their own cost is relatively high, the cost of construction is low. The special optical cable relies on its own line resources to avoid contradictions and disputes with the outside world in terms of frequency resources, route coordination, and electromagnetic compatibility, and has great initiative and flexibility.

Electrical special optical cables are divided into optical fiber composite overhead ground wires OPGW, optical fiber composite overhead overhead wires OPPC, all-metal self-supporting optical cables MASS, all-media self-supporting optical cables ADSS, ground bundled optical cables ADL and ground-wound optical cables. GWWOP and other kinds.

2. Comparison between OPGW and ADSS

Here we analyze and compare OPGW fiber optic cable and ADSS fiber optic cable in terms of characteristics, applicable characteristics, common faults, and solutions.

A. Features difference

The prominent feature of the OPGW composite cable is to integrate the overhead cable on the communication cable and the high-voltage power transmission line, integrate the optical cable technology with the transmission line technology, and become a multi-functional overhead ground wire, which is not only a lightning protection line, but also It is an overhead cable, and it is also a shielded cable. While completing the construction of high-voltage transmission lines, it also completed the construction of communication lines, which is very suitable for new transmission lines. There are three major types of common OPGW structures, namely, aluminum pipes, aluminum frames, and (stainless) steel pipes.

Full-medium self-supporting optical cable ADSS uses high-strength aramid yarn with high elastic modulus as a tensile element in its manufacture. At the same time, the cable has a small geometric size, and the cable weight is only one-third of the ordinary optical cable, and can be directly mounted. In the proper position of the power tower, the additional load on the tower is very small, with a maximum range of up to 1500m. Its outer sheath is impregnated with neutral ionization, so that the optical cable has a strong anti-electric corrosion ability, can guarantee the life of the optical cable in a strong electric field; the optical cable uses non-metallic materials, good insulation properties, can avoid lightning strikes, power line out In the event of a failure, it will not affect the normal operation of the optical fiber cable. With the existing power pole tower, it can be constructed without power failure and be erected on the same pole as the power line, which can reduce the construction cost. A variety of ADSS cable structures can be summarized as the most important central tube type and layered type.

B. Applicable features

The OPGW cable is mainly used on 500kV, 220kV, and 110kV voltage grade lines, and is affected by factors such as line blackouts and security, and is mostly applied on new lines. The applicable features of the OPGW are [4]: (1) Lines with high voltage exceeding 110kV have a large range (usually above 250M); (2) Easy to maintain, easy to solve for line crossing problems, and its mechanical characteristics can satisfy large lines (3) The outer layer of OPGW is metal armored, which has no impact on high-voltage corrosion and degradation; (4) OPGW must be powered off during construction, and the loss of power outage is large. Therefore, OPGW should be used in new high-voltage lines over 110kV; (5) In OPGW's performance index, the larger the short-circuit current, the more it is necessary to use good conductors for armoring, and accordingly, the tensile strength is reduced. In the case of a certain tensile strength, the short-circuit current capacity must be increased, only increasing. The cross-sectional area of the metal leads to an increase in cable diameter and cable weight, which raises a safety issue for the strength of the line tower.

The ADSS fiber optic cable is widely used on 220kV, 110kV, and 35kV voltage grade transmission lines, and is especially used on established lines. It can meet the large span and large sag of power transmission lines. The standard ADSS design can reach 144 cores. Its characteristics are [4]: (1) The theoretical value of the fiber tension in ADSS is zero; (2) The ADSS fiber optic cable is fully insulated and can be charged during installation and line maintenance, which can greatly reduce power outage losses; (3) ADSS The expansion and contraction rate can be kept constant in a wide range of temperature difference, and it has stable optical characteristics under the limit temperature; (4) Electro-resistance ADSS fiber optic cable can reduce the electric corrosion of the optical cable by high-voltage induced electric field; (5) ADSS The small diameter and light weight of the cable can reduce the influence of ice and wind on the cable, and its effect on the strength of the tower is also very small. (6) ADSS uses a new type of material and a smooth shape design, making it have superior aerodynamic characteristics.

C. Common faults and solutions

The OPGW is affected by a short-circuit fault. When the short-circuit current of the line fault strikes the OPGW cable, the stainless steel unit is transiently hot, and 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 the 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 contributes to the transient high temperature of the OPGW cable. Compared with the short-circuit fault, the lightning current intensity is greater, but the duration is very short, so the thermal capacity of the lightning rise caused by the temperature rise 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 cable, and the lightning current is only Confined to a small segment of one or more metallic monofilaments, the concentration of energy causes the high temperature on this small segment of wire to be sufficient to partially or completely melt it. This is the main reason why lightning strikes cause OPGW cable to break stocks.

The main fault in the OPGW cable application is the broken stock caused by lightning strikes. The current solutions are:

1) Develop lightning-resistant outer strand materials. In 2000, the high-resistance OPGW developed in Brazil consisted of an advanced galvanized steel wire and an aluminum tube that protects the fiber. Advanced galvanized steel requires more energy to melt under lightning strikes.

2) Use aluminum-clad steel wire as far as possible for the outer strands, and increase the thickness of the aluminum-clad aluminum-clad steel wire.

3) Try to increase the design air gap between the outer strand and the inner strand to avoid heat transmission.

4) With the same material, a larger outer strand diameter is used.

After the material and structure of the OPGW cable are determined, its lightning resistance characteristics are also determined.

Since the ADSS cable runs near the high-voltage wire and there is a strong electric field around it, there is a high possibility of damage to the cable caused by the electric corrosion phenomenon.

5) It is preferred to use the trace-resistant jacket in the circuits with different voltage levels, and it is necessary to use the trace-resistant material for the 110kV and above lines.

6) For 110kV and above lines, anti-corona coils can be considered to effectively reduce the electric field on the surfaces of the gold and optical cables and reduce the leakage current.

7) For the 220kV and above lines and the strong poles and towers of the hanging point, the impact corrosion resistance of the shockproof hammer on the outer skin of the cable is much more secure than that of the shockproof whip.

8) The space potential of the control cable suspension point is 110kV not exceeding 15kV and 220kV not exceeding 20kV.

Distributed fiber optic temperature sensors can be used to monitor electrocorrosion failures.

3, characteristics of similar special power cable

Different power special optical cables have their own characteristics, meet different requirements for use, and apply to different occasions. The following is a comparison of the characteristics of practical optical cables with similar characteristics.

3.1 Optical fiber composite overhead ground wire OPGW and optical fiber composite overhead line OPPC

In the power grid, some lines may not have overhead ground lines, but the phase line is essential. In order to meet the requirements of optical fiber networking, similar to the OPGW technology, the optical fiber composite phase line (OPPC) becomes an appropriate method to join the optical fiber in the conventional phase line structure.

In China, OPGW and ADSS are widely used in the backbone network of 110kV to 500kV lines. For some lines where OPGW and ADSS optical cables are difficult to use, OPPC is a complementary product for OPGW and ADSS optical cables.

3.2 all-media self-supporting optical cable ADSS and metal self-supporting optical fiber cable MASS

Consider that the MASS fiber optic cable and the existing pole tower should be erected on the same pole as the ADSS fiber optic cable. To reduce the additional load on the mast tower, the MASS cable structure is required to be small and lightweight. Therefore, the MASS cable structure adopts a central tube type, that is, a layer of galvanized steel wire or aluminum-clad steel wire is twisted on the outside of the stainless steel fiber unit, usually considering the cost, and is mainly galvanized steel wire. Because the MASS fiber optic cable is a metal structure, the problem of electric corrosion can be easily solved by a good grounding treatment and by selecting a weak electric field installation point.

3.3 Metal-free bundled aerial cable (AD-Lash) and metal-wound cable GWWOP

They bundle and wind optical cables on ground or phase wires with automatic binders and winders. Their common advantages are: light weight, low cost, and rapid installation. In the ground or 10kV/35kV phase line can be installed without interruption; the common shortcoming is: as they are all made of organic synthetic materials for outer sheath, so can not bear the high temperature generated by the phase line or ground line when the line is short-circuited. For the problem of aging of outer sheath material, special machinery is needed for construction, and there are many problems in construction workability and safety, and it is vulnerable to external damages such as bird damage and gun shooting, and therefore cannot be obtained in the power system. Wide range of applications. However, at the international level, such technologies have not been eliminated or abandoned and are still applied within a reasonable range.

4 Conclusion

Power special optical fiber cables have outstanding advantages such as high reliability, long service life, easy installation, low overall cost, and good safety. They are used more and more in power system communications, and technologies are constantly improving. Materials are also being updated. At the same time, people's demand for special optical cables also tends to be diversified and high standards. How to improve the characteristics of electric special optical cables from the aspects of structural design and material selection is of profound significance. The development of electric special optical cables will usher in a better tomorrow.