Types and structural forms of power optical cables

1.OPGW optical fiber composite overhead ground wire (also called optical fiber composite overhead ground wire). Optical fiber is placed in the ground wire of overhead high voltage transmission line, and an optical fiber communication network is formed on the transmission line. This structure has the dual functions of ground wire and communication, and is generally called OPGW optical cable. 2.OPPC (Opticalphase Conductor for short) is a new type of special optical cable in power communication system, which combines optical fiber units into wires in the traditional phase line structure. It makes full use of the line resources of the power system, especially the distribution system, and avoids conflicts with the outside world in terms of frequency resources, routing coordination, electromagnetic compatibility, etc., so that it has dual functions of transmitting electric energy and communication. 3.ADS is the abbreviation of all dielectric self-supporting. All-dielectric optical cable is made of all-dielectric materials. Self-supporting means that the reinforcing member of the optical cable itself can bear its own weight and external load. This name points out the use environment and key technology of this kind of optical cable: because it is self-supporting, mechanical strength is very important; All-dielectric materials are used because the optical cable is in a high voltage and high voltage environment and must be able to withstand the influence of high voltage; Because it is used overhead on the power tower, there must be supporting pendants to fix the optical cable on the tower. That is, ADS optical cable has three key technologies: mechanical design of optical cable, determination of suspension point, selection and installation of supporting hardware. 4.OPLC fiber composite low-voltage cable or power fiber. A cable that combines optical fiber in the structural layer of power cable to make it have both power transmission and optical fiber communication functions is called optical fiber composite power cable. Like OPGW, optical fiber composite power cable integrates two functions, thus reducing the total cost of engineering construction investment and operation and maintenance, which has obvious technical and economic significance.

1 ground wire wound optical cable GWWOP and bundled optical cable ADL

(1) ground wire wound optical cable GW WOP (ground wire wound optical cable) is a kind of optical cable directly wound on overhead ground wire, which is spirally wound around the ground wire along the transmission line with the ground wire as the central axis to form an optical transmission medium attached to the transmission line bracket.

(2) All-insulated cable (ADL) is a kind of cable that is connected to the ground wire or phase wire through one or two weatherproof tapes, covered aramid wires or metal wires. Compared with GWWOP optical cable, it reduces the attenuation or stress increase caused by bending and winding of optical cable.

These two kinds of optical cables are collectively referred to as —OPAC (optical cable) and are generally used for lines below 35kV. The electric power department developed and used this kind of optical fiber communication network as early as the early 1980s, which is an economical and fast way to establish an optical fiber communication network in the electric power system. They are not self-supporting optical cables, but attached to the original line or phase line, as shown in figure 1. Therefore, the optical cable has the advantages of light weight, flexibility and small outer diameter, and generally adopts the all-dielectric central tube optical cable structure. As shown in Figure 2, the nonmetallic reinforcement layer usually adopts flexible materials such as aramid yarn, glass fiber yarn and glass fiber tape.

These two types of cables need special equipment when they are installed. After installation, the optical cable is in direct contact with the power line, which needs to withstand the high temperature generated by the phase line or the ground line when the line is short-circuited, and there is the problem of aging of the outer sheath material. Therefore, although the research and application is earlier than ADS optical cable, it has not been widely used in China. In line design, it is also necessary to check the strength of power lines and towers with ice and wind load.

2 All-dielectric self-supporting optical cable ADS and metal self-supporting optical cable-quality

(1) All-dielectric self-supporting optical cable (ADS) is a kind of special optical cable which is erected on the same pole as the power line by using the existing high-voltage transmission tower. It has the advantages of low engineering cost, convenient construction, high safety and easy maintenance.

ADS optical cable is self-supporting overhead laying, which should have a large tensile strength to ensure that it can withstand the influence of external environment during normal operation. The main load-bearing component of ADS optical cable is aramid yarn, which can be divided into two types according to the structure: central tube type and layer-stranded type, in which the layer-stranded type is divided into single-sheath structure and double-sheath structure, as shown in Figure 3 below.

In the mechanical design of ADS optical cable, besides having a certain tensile strength, it is also necessary to consider the safe distance from the ground when installing ADS optical cable under a certain span and the safe distance from the ground when fully loaded, so as not to affect the normal operation of the pavement. On the other hand, there is a certain high-voltage electric field around the high-voltage power line, which is easy to corrode and damage the ADS optical cable. Therefore, when laying ADS optical cable, it is necessary not only to choose suitable suspension points, but also to have certain electrical corrosion resistance. According to the standard requirements of DL/T 788-200 1 all-dielectric self-supporting optical cable, the outer sheath is divided into Class A (potential less than 12kV) and Class B (potential greater than 12kV), in which the working potential of Class B sheath (usually referred to as electric resistance and heat tracing sheath material) is generally recommended not to exceed 25kV according to practical application.

(2) Metal overhead self-supporting optical cable-stainless steel tube optical fiber unit structure. Considering that Volkswagen optical cable and ADS optical cable are erected on the same pole, in order to reduce the extra load on the tower, Volkswagen optical cable is required to be small in structure and light in weight. Therefore, the structure of mass optical cable adopts central tube, that is, a layer of galvanized steel wire or aluminum-clad steel wire is wound outside the stainless steel optical fiber unit. Generally, considering the cost, galvanized steel wire is mainly used, as shown in Figure 3.

Volkswagen cable is similar to ADS cable in mechanical design, and it also needs to check span-tension-sag. However, when installing and laying, it is necessary to choose a suitable suspension point, on the one hand, to keep a safe distance from the power line; On the other hand, because the large-capacity optical cable is a metal structure, the problem of electrical corrosion can be easily solved through good grounding treatment and selection of weak electric field installation points. Due to the all-metal structure of Volkswagen optical cable, it can also be used as an effective rat-proof optical cable in some areas where rats are rampant.

3 OPGW and OPPC optical fiber composite overhead ground wire

(1) OPGW (optical fiber composite overhead ground wire)-It has the lightning protection function of traditional ground wire, provides lightning shielding protection for transmission wires, and transmits information through optical fiber composite in ground wire. There are three common OPGW structures, namely aluminum tube type, aluminum skeleton type and stainless steel tube type, as shown in Figure 4.

One of the key technologies of OPGW is the temperature rise caused by short-circuit current and the maximum service temperature of OPGW. Fig. 4 In the first two kinds of OPGW, when short-circuit current strikes, the aluminum tube and aluminum skeleton will generate relatively high temperature, which will spread to the inside, affect the optical fiber transmission and even break the fiber, while the stainless steel tube type has been obviously improved. If the structure contains aluminum, after the temperature exceeds 200℃, aluminum will produce irreversible plastic deformation at first. At the same time, when the structure is damaged, the increased sag of OPGW can not only keep a safe distance from the conductor, but also may collide with the conductor. If it is an all-steel structure, it can work at 300℃ for a short time.

The application of OPGW in the new line has a high cost performance. In design, when the short-circuit current of OPGW is large, more aluminum cross-sectional area is needed, and the tensile strength decreases accordingly. However, under the condition of a certain tensile strength, the only way to improve the short-circuit current capacity is to increase the cross-sectional area of metal, which leads to the increase of cable diameter and cable weight, thus causing safety problems to the strength of transmission towers. However, when designing OPGW, its electrical properties (such as DC resistance) and mechanical properties (such as span-tension-sag characteristics) should be close to other grounding wires.

(2) OPPC (Optical Fiber Composite Phase Conductor)-Optical fiber units are combined in the phase line, which has dual functions of phase line and communication, making up for the situation that there is no overhead ground wire for communication in the newly-built power grid line, mainly including central tube type and layer stranded type, as shown in Figure 5.

Although OPPC is similar in structure to OPGW, it is quite different in design. Firstly, considering the influence of long-term operating temperature on optical fiber transmission performance and optical fiber life, OPPC has the function of phase line and carries power transmission for a long time; Secondly, the mechanical and electrical properties of OPPC should be consistent with those of adjacent wires, such as DC resistance or impedance similar to those of adjacent wires, so as to ensure the three-phase balance of remote voltage change; Thirdly, OPPC is installed in high-voltage system, and its installed hardware and accessories (such as tension clamp, suspension clamp and terminal junction box) need insulation. The clamp can use the corresponding insulation tension string or insulation hanging string, and the photoelectric insulation/separation and connection need special technology, which requires high construction requirements.

4 photoelectric hybrid cable GD for access network

GD (Photoelectric Hybrid Cable for Access Network), commonly known as integrated optical cable, integrates optical fiber, metal wire pair and feeder, and can transmit optical signals, electrical signals and electric energy at the same time. Its typical structure is shown in Figure 6.

With the rapid development of access network technology and market, optical fiber communication has entered a new round of rapid growth stage. Mobile communication, digital TV (intermediate conversion), broadband access, FTTx, rural village-to-village communication projects and so on continue to extend communication optical cables and equipment to users. Remote base stations, communication rooms, user access points and other equipment have been widely used, but the power supply of equipment has become a very difficult problem for communication operators. To solve this problem, china communications standards association issued YD/T 2 159-20 10, which provided a theoretical basis for the design and application of this product.

Although we can supply power and transmit information to remote equipment through GD optical cable, there is line loss in the feeder, which increases with the extension of transmission distance, and there is also the problem of voltage drop. Therefore, high voltage DC remote power supply is undoubtedly the best solution for long-distance communication. The principle of the high-voltage DC telecontrol power supply system is to isolate and boost the 48 V DC of the switching power supply in the machine room to about 200~400 V DC high voltage through the local equipment of the telecontrol power supply, and transmit the DC high voltage to the telecontrol equipment through the feeder in GD optical cable. During transmission, the power supply is suspended from the air to the ground, and the voltage is inverted by the remote equipment and converted into the voltage required by the remote equipment (such as DC48 V or AC220V), so as to finally realize the normal communication of the remote equipment, as shown in Figure 7.

In the structural design of GD optical cable, the cross-sectional area of feeder is mainly selected. The cross-sectional area of the feeder is related to the transmission distance, the power of the electrical equipment, the transmission voltage level and the receiving voltage range of the remote power supply equipment. After the cable design, it is necessary to further check the cable loss. In general, the cable loss power should not exceed 10% of the output power of the remote local equipment.

5 Optical Fiber Composite Low Voltage Cable-OPLC

OPLC (Optical Fiber Composite Low Voltage Cable)-The protected optical fiber unit is placed in the power cable, which can be used in the power system with rated voltage of 0.6/ 1kV and below, and at the same time solve the problem of optical fiber information communication. The concept of power and fiber to the home (PFTTH) advocated by OPLC, that is, with the help of passive optical network (PON) technology, the concept of "multi-network convergence" such as telecommunication network, power transmission network, TV network and Internet is completely in line with the wave of "triple play" proposed by domestic telecom operators at present, so we can build a telecom public service platform through OPLC to accelerate and save the construction of domestic fiber to the home.

In the design of OPLC, the main consideration is the choice of optical unit structure. Stranded optical cable can contain more optical fibers, which is more suitable for the branch and handover application of optical cable in distribution network. Butterfly optical cable can be cold connected with quick connector during construction, which is quick and convenient to construct and more suitable for home use. According to the networking characteristics and the number of cores actually used, we choose three structures as optical units of OPLC, namely, central tube optical cable, stranded optical cable and butterfly optical cable, and the optical units are made of nonmetallic all-dielectric materials, as shown in Figure 8.

According to the different laying forms, the stranded optical unit and the central beam tube optical unit can be divided into dry type and ointment filling type. Dry light unit can meet the needs of vertical laying of a large number of core wires, especially in the vertical wiring of high-rise buildings, which can solve the problem of dripping ointment during vertical laying and provide convenience for the application of OPLC in different occasions. Considering that the close-fitting optical fiber structure is sensitive to temperature, it is generally not recommended to use it in OPLC. As shown in Figure 9, OPLC structure can be divided into two categories: household use and distribution network use.