Optical Ground Wire (OPGW) Cable – MELONTEL

OPGW cable, Optical Fiber Composite Overhead Ground Wire (also known as fiber composite overhead ground wire). It is an innovation to place the optical fiber in the ground wire of the overhead high-voltage transmission line to form the optical fiber communication network on the transmission line. This kind of structure with dual functions of ground wire and communication is generally called OPGW optical cable.

Your professional OPGW Cable factory and supplier in China! Melontel, one of the leading Chinese communication equipment manufacturers, is here today. This article will tell you everything about the OPGW cable. Continue reading to learn more.

Optical fiber uses the difference in the refractive index of the core and cladding materials to transmit light energy in the optical fiber, which has become a major revolution in the history of communications.

Optical fiber cables are light in weight and small in size, and have been adopted by power systems to transmit dispatching telephones, telecontrol signals, relay protection, TV images and other information between substations and central dispatching stations.

In order to improve the stability and reliability of the fiber optic cable, engineers developed a structure in which the fiber optic cable is combined with the phase conductor of the transmission line, the overhead ground wire and the power cable.
Due to the wrapping of the metal wires, the OPGW cable is more reliable, stable and firm. Compared with other methods of optical cable, the overhead ground wire and optical cable are combined into one, which not only shortens the construction period, but also saves construction costs.

If the OPGW made of aluminum clad steel wire or aluminum alloy wire is used, it is equivalent to erecting a good conductor overhead ground wire, which can obtain multiple benefits: reduce the potential supply current of the transmission line, reduce the power frequency overvoltage, and improve the power line to the communication line. interference and dangerous effects, etc.

Because the optical fiber 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 has significant features such as high reliability, superior mechanical properties, and low cost. This technique is especially suitable and economical for new installations or replacement of existing ground wires.

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There are three main categories: 1. Aluminum tube type, 2. Aluminum frame type， 3. (Stainless) Steel tube type.

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The installation design of OPGW should consider the coordination with wire stress, sag and insulation gap, and its load should not exceed the allowable range of existing towers and foundations.

The characteristic curve should be calculated according to the main technical parameters of the selected OPGW, and the layout drawing, outline drawing and installation drawing of the junction box, various hardware and accessories should be designed in combination with the actual engineering.

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1. Lines with high voltage exceeding 110kV have a large span (generally more than 250M).

2. Easy to maintain, easy to solve the problem of line crossing, and its mechanical characteristics can meet the needs of large line crossing.

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 outage loss is relatively large, so OPGW should be used in new high-voltage lines above 110kv.

5. In the performance indicators of OPGW, the larger the short-circuit current, the more armored conductors are required, and the tensile strength is correspondingly reduced. However, under the condition of a certain tensile strength, to increase the short-circuit current capacity, only increase the metal Cross-sectional area, resulting in an increase in cable diameter and cable weight, which poses a safety problem to the strength of the line tower.

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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.

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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.

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.

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.

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.

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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.

OPGW is composed of one or more optical units and one or more layers of twisted single wires. At present, the most commonly used optical cable structures are central bundle type and layer twist type.

The central bundle type is to place the optical unit in the middle of the OPGW, the layered type is to make the outer diameter of the optical unit the same as the outer diameter of the twisted wire, and the fiber optic sleeve is made of stainless steel.

Optical fiber composite overhead ground wire (OPGW) should not only meet the technical requirements of the optical fiber communication of this project (such as fiber type, fiber core number, fiber attenuation, dispersion, etc.), but also meet the necessary mechanical properties and electrical properties as a ground wire (such as high mechanical properties, vibration resistance, corrosion resistance, and a certain electrical conductivity and sufficient heat capacity, etc.).

1.It has sufficient breaking force, and the diameter should not be too large, and the weight per unit length should not be too large. When the ambient temperature is +10/+15°C, the sag of the OPGW should be basically the same as the sag of the ground wire that is shunted to it.

2.In order to ensure normal and safe operation, under the condition that the maximum design external load is determined, the safety factor of OPGW should be greater than or equal to 3.0, and the communication quality should be guaranteed.

3.It has good anti-fatigue and anti-vibration characteristics, and the allowable average running tension should be higher than or equal to 20% UTS.

4.When lightning strikes the OPGW, the communication quality cannot be affected, and the metal part cannot be broken.

5.When the fiber has enough excess length, when the bearing force reaches 70% of the ultimate tensile strength, the fiber should not bear the tensile force, and the optical signal has no obvious attenuation.

6.When the ambient temperature is +40°C, the single-phase line is short-circuited to ground in the power line. The OPGW should be able to withstand the impact of an instantaneous large short-circuit current, and the mechanical properties cannot be affected. The compound in the optical fiber metal sleeve Cannot be spoiled.

7.Maximum allowable short-circuit current. When the single-phase line of the power line is short-circuited to ground on the line, a short-term large short-circuit current will appear on the overhead ground line. This current will generate a lot of heat and cause the temperature of the OPGW and the shunt line to rise suddenly.

8.The OPGW optical cable is used as a ground wire of the transmission line. In addition to meeting the requirements of the transmission line design regulations for the ground wire, the OPGW should also meet the requirements of the tower use conditions and the specific terrain conditions of the project.

At present, the most commonly used central beam tube type and layer twisted wire have their own advantages and disadvantages, and both can meet the performance requirements. Depending on the project conditions, the focus is different.

Generally, the central bundle type is suitable for transmission lines of 110kV and below, and the layered type is suitable for transmission lines above 220kV.

The domestic common outer stranded wire is the right twist direction, and the outer single wire should not be less than 3.0mm. Considering the lightning protection performance of OPGW, the outer wire is generally made of aluminum clad steel structure.

From the point of view of convenient circuit design, the weight and outer diameter of OPGW should be kept as close as possible to the ground wire of the shunt. Under the condition that the tower conditions allow, the weight and outer diameter of OPGW can be left with a certain margin.

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In the neutral-grounded power system, when a single-phase-to-ground short-circuit fault occurs in an overhead power line, a large short-circuit current will pass through the ground wire, and the thermal effect generated by the fault current will produce a large amount of heat on the OPGW and the shunt line. heat, which can damage the fiber optic link.

In order to ensure the safety and reliability of communication, it must be ensured that the temperature rise of the OPGW shall not exceed the allowable value for the normal operation of the OPGW.

In OPGW engineering design, thermal stability calculation should be carried out according to the characteristics of short-circuit current changes. The shunt ground wire is mostly made of aluminum-clad steel strands with higher conductivity, so as to better shunt the OPGW.

The short-circuit current heat capacity calculation of OPGW should take into account the development of the power system within 5 to 10 years after the project is put into operation, and be determined according to the maximum operation mode.

The duration of the short-circuit current should be determined according to the voltage level of the system and the configuration of the system protection. The short-circuit current capacity of the system flowing through the OPGW cannot be greater than its allowable short-circuit current capacity.

At present, the main methods to solve the problem of thermal stability are as follows: OPGW is grounded on a base-by-base basis on each base tower, the ground wire of the shunt is also grounded on a base-by-base basis on each base tower, the cross-section of the ground wire that is branched is increased, and the segment selection is as follows: The ground wire model of its shunt, and the segmented selection of OPGW model, etc.

The mechanical properties of OPGW mainly include rated tensile strength (RTS), annual average operating stress, and maximum service stress.

RTS is determined by the structure of the product, and the latter two are the range of design values. Under rare wind speed or rare icing check weather conditions, the maximum tension of OPGW at the suspension point should not exceed 66% of the rated breaking force. The average operating tension of OPGW should not be greater than 20% of the rated breaking force.

The rated tensile strength of OPGW with the same section is inversely proportional to the ratio of aluminum to steel, and is also inversely proportional to its short-circuit current heat capacity. Therefore, in the case of a certain outer diameter, the short-circuit current heat capacity must be sacrificed to increase the rated tensile strength.

In the specific engineering design, it is necessary to neutralize the contradiction between the two, and strive to meet the requirements of rated tensile strength and short-circuit current heat capacity.
In order to keep the OPGW sag consistent with the shunt ground wire, the sag characteristics of the OPGW should match the shunt ground wire.

When OPGW is designed, its safety factor should not be less than 2.5, and it should be greater than the safety factor of the wire.

There are G.652 and G.655 two kinds of single-mode fibers commonly used in the transmission process of new SDH long-distance optical cables.

G.652 is mainly suitable for transmission systems with a transmission rate not greater than 10Gb/s, and G.655 is mainly suitable for transmission systems with a transmission rate not less than 10Gb/s. In engineering design, it can be selected according to the actual situation of the project.

The number of OPGW cores should be determined according to the demand for business volume. At present, 24 cores are commonly used for 110kV and below lines in China, and 36 cores/48 cores/72 cores are commonly used for 220kV and above lines. Also getting bigger.

There are G.652 and G.655 two kinds of single-mode fibers commonly used in the transmission process of new SDH long-distance optical cables.

G.652 is mainly suitable for transmission systems with a transmission rate not greater than 10Gb/s, and G.655 is mainly suitable for transmission systems with a transmission rate not less than 10Gb/s. In engineering design, it can be selected according to the actual situation of the project.

The number of OPGW cores should be determined according to the demand for business volume. At present, 24 cores are commonly used for 110kV and below lines in China, and 36 cores/48 cores/72 cores are commonly used for 220kV and above lines. Also getting bigger.

If you need customized products, please contact our team of engineers for a free consultation.

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The large span project has the characteristics of large span, relatively high tower, and difficult construction. In addition to the above factors, the following points need to be considered:

1. The anti-vibration scheme must be designed separately;

2. The mechanical strength is higher than that of ordinary lines.

In the actual design process, the regulations and specifications should be strictly followed, the appropriate structure of the optical cable should be selected, the contradiction between the rated tensile strength and the short-circuit current thermal capacity should be reconciled as much as possible in the design, and the required optical fiber should be determined according to the actual business volume demand. number and type, select a valid shunt ground wire. Finally, an OPGW suitable for this project is designed to provide a safe and stable transmission channel for the transmission of power data.