The composite overhead ground cable (OPGW for short) is unique to the power system and has a new technology of dual functions of power line ground and fiber communication. As an emerging information transmission channel, OPGW has developed rapidly in China in recent years. It has the characteristics of large communication capacity, anti-interference, safety and reliability, and does not occupy line corridors. At the same time, it will be the communication cable and high-voltage transmission line ground. Cleverly combined into a whole, its good mechanical properties and electrical conductivity not only meet the lightning protection requirements of ordinary ground wire, but also have good shielding effect of good conductors, which can greatly reduce the electromagnetic hazard of the transmission line to the adjacent weak electric line. At present, OPGW does not have a unified production serial number, which integrates various requirements of electromechanical characteristics, thermal stability and communication fiber, and each parameter is mutually restricted. OPGW manufacturer due to differences in the manufacturing process and manufacturing equipment, the parameters of which each partial product weight, so even if the parameter OPGW satisfy various manufacturers are required, the overall characteristics of the product meets the requirements of the project line must also be designed by The personnel perform the verification check.

The OPGW optical cable knows from the above that it has the dual functions of grounding and fiber-optic communication, so the circuit design is the same as the general grounding design. The following is only a brief introduction.

1 OPGW structure and classification

1.1 OPGW structure

OPGW fiber optic cable is a composite ground wire that puts the optical fiber in the overhead ground wire and combines lightning protection and communication functions. Therefore, it is called optical fiber composite overhead ground wires (OPGW or OPGW optical cable, OPGW optical cable). A dual function line with traditional overhead ground and fiber optic communication capabilities. The basic structure of the OPGW consists of a fiber-optic core (light unit) and a stranded metal wire (aluminum-clad steel wire ACS or aluminum alloy wire AA). Among them, the optical fiber provides a transmission channel, the steel component mainly provides mechanical strength, and the aluminum component mainly carries short-circuit current.The outer layer of OPGW is aluminum-clad steel or aluminum alloy wire, which requires a single-strand diameter of not less than 3.0mm to reduce lightning strikes. The outermost twist of the OPGW is right-handed .

In addition, the OPGW is divided into a layered type, a central beam tube type, a single tube, a double tube, etc. according to the structure of the light unit , as shown in the following figure.

Figure 1 OPGW structure of aluminum tube + layer twisted plastic tube

Figure 2 OPGW structure of the central aluminum tube

Figure 3 OPGW structure of layered stainless steel tube

1.2 OPGW classification

Generally, there are two types of loose sleeves.

Loose sleeve: The loose sleeve type is to insert the optical fiber into the loose tube filled with grease to form a certain excess length. The excess length is generally controlled at about 0.7% of the total length of the optical cable. The optical fiber has its own length to satisfy the initial elongation of the entire ground line and The deformation generated during the operation to ensure that the fiber in the cable is not stressed, but the structure is loose.

Tight sleeve: The tight sleeve type is based on the requirement that the fiber can be subjected to the force. In order to meet the requirements of the fiber force, the external force corresponding to the fiber is applied with about 1% elongation in the production, that is, the prestressing force is applied to the fiber. ". Through the screened fiber, the tensile strength is higher than the tensile strength of the outer strand and can be destroyed after the outer strand is twisted .

Due to the above design differences, when the metal cross-section and the destructive force are the same, the design safety factor of the loose-sleeve structure is 70% to 75% of the tight-fitting structure. Due to the structural characteristics, the loose-type type is low in price, and is suitable for lines with less external load conditions and less severe terrain changes. The tight-set type is more expensive, suitable for harsh external load conditions, large terrain changes and ground force stress. Complex lines.Therefore, when designing the cable type, it is not easy to compare the two different structures of the OPGW cable. The structure should be selected according to its specific strengths and weaknesses, combined with specific conditions and cost performance.

For the transmission line of the non-heavy ice area, the OPGW of the loose-sleeve stainless steel tube layer twisted structure should be adopted. The structure type of the OPGW of the heavy-duty area transmission line should be determined by technical and economic comparison in combination with the line icing condition. In the loose and tight type can meet the requirements of the line, to choose the loose type is appropriate. It is advisable to use a tight sleeve type for the heavy ice zone.

The same layer of strands of OPGW should be made of the same material, and the outer monofilament should be made of aluminum-clad steel monofilament, and the diameter should not be less than 3.0mm.

1.3 OPGW parameters and representation

OPGW is mainly composed of optical unit (optical fiber, protection tube) and grounding unit (aluminum-clad steel wire, aluminum alloy wire). Its three most important parameters are cable diameter, rated tensile strength and short-circuit current capacity.The specific meanings of the OPGW parameters are as follows:

D--diameter (mm), affecting the horizontal load of the tower

S--section (mm ² ), affecting cable strength and heat capacity level

G--unit weight (kg/km), depending on the material of the cable and the ratio of aluminum to steel, affecting the vertical load of the tower

RTS-- rated tensile strength (KN), affecting the mechanical properties of the cable and the force of the tower

R--DC resistance (Ω/km, 20°C), depending on the material of the cable and the ratio of aluminum to steel, affecting the shunt performance

E--Modulus of elasticity (GPa), a basic parameter in mechanical calculation

---linear expansion coefficient (/°C), a basic parameter in mechanical calculation

I ² t-- short current capacity (kA ² .s), depending on the material and section of the cable

The OPGW model specification consists of four parts, each part is represented by a code or a number (refer to DL/T 832-2003)

as follows:

OPGW-24B1-80[100;32.8]

Parameter Description:

24-core,

B4—non-zero dispersion shifted single mode fiber

80-fiber cable total section ( mm ² );

100-rated breaking force (kN);

32.8 - Short circuit current capacity (kA ^2. S).

2 OPGW technical standards

International standards:

IEEE 1138-2009 Construction standards for composite optical fiber overhead ground wires for electric power lines

Optical fibre cables - Part 4-1: Combination specification - Aerial optical fibre cables for transmission lines.

Chinese national standard

GB / T 7424.4-2003: cable - Part 4: specification OPGW

Chinese industry standards:

Power industry standard DL/T 832-2016 fiber composite overhead ground wire

Mechanical industry standard JB/T 8999-2014 optical fiber composite overhead ground wire

3 OPGW electrical characteristics design

3.1 Split calculation formula

In order to ensure the safe operation of the OPGW, the design of the OPGW also requires another ground wire to have a strong shunting capability, which can effectively split the power system in the case of single-phase grounding short-circuit and lightning strike accidents. The current distribution of the OPGW and another ground line can beapproximated by the following formula:

I _OPGW / I _{shunt ground} = (Z _{shunt ground} - Z _{mutual resistance} ) / (Z _OPGW - Z_{mutual resistance} )

In the middle

The I _{of OPGW} --OPGW the current, kA ;

I _{split ground wire}- current in the shunt ground , kA ;

Z _OPGW - resistance of _OPGW , ( Ω /km);

Z _{shunt ground}- the resistance in the shunt ground , ( Ω /km);

Z _{mutual resistance} - the mutual inductance between two parallel ground lines (OPGW and another ground), ( Ω / km).

3.2 Single-phase grounding short-circuit current distribution

The short-circuit current flowing through the ground line is usually the largest at the exits of the power plants and substations at both ends, and the short-circuit current at the center of the line and the shunt coefficient flowing through the ground line are sharply attenuated. In the long line (generally 80km or more can be regarded as long line, the same below), in order to save investment, different ground wire combination methods can be used, such as large cross section, low impedance, short circuit current capacity in a short distance from the line exit. The large OPGW selects the OPGW with less cross-section and short-circuit current capacity in the center of the line. The single-phase short-circuit current at each point of the line can generally be based on the "single-phase grounding zero-sequence short-circuit current curve of the transmission line".

For overhead lines with dual ground lines, the following grounding lines can be used: When using OPGW, a good conductor should be selected to share the return current flowing through the ground wire (usually aluminum-clad steel strands) to reduce flow. The short-circuit current of the OPGW, at this time, the good conductor ground is called the shunt ground or shunt. At this time, the OPGW and the good conductor shunt ground wire , and the heat capacity of the OPGW and the common ground wire should be checked at the same time . In the long line, combined with the terrain and meteorological conditions, another ground wire can also be combined with different structures, sections and materials.

In the general calculation, the bus short-circuit current is often regarded as the short-circuit current of the first ground wire on the terminal tower. In fact, in the first line ground of the terminal tower, a small part of the current flows through the earth back to the neutral point of the transformer. According to the software calculation results of Tsinghua University, the current flowing through the first ground wire only accounts for 70% of the short-circuit current (when the line length is 25km). If the line is regarded as infinitely long, the short circuit flows through the first ground. Current will account for the vast majority. When the line length is from 0 to 200 km, the short-circuit current flowing through the first ground wire is between 70 and 90%.

In the calculation, in order to leave enough room, it is recommended that the short-circuit current flowing through the first ground wire accounts for 95% of the short-circuit current. That is, 5% of the short-circuit current returns to the neutral point of the transformer through the earth.

3.3 OPGW short-circuit current capacity

Calculating the short-circuit current of the transmission line shall be determined according to the plan of the development of the power system for 5 to 10 years or a long-term vision plan, according to the maximum operation mode of the system.

When the OPGW or the shunt ground wire material is determined, the heat capacity of the material is constant. The short circuit capacity of the OPGW and the shunt ground wire is related to the short circuit current and the short circuit time. The specific relationship is as follows:

Short circuit current capacity = short circuit current ² × short circuit current duration

The duration of the short-circuit current should be determined according to the system voltage level, protection configuration, and so on. For 500kV lines, the short-circuit current duration is recommended to be 0.25s; for 110kV-220kV lines, it is usually 0.30 seconds.

The capacity of the system short-circuit current flowing through the OPGW must be less than its allowable short-circuit current capacity. The allowable temperature of the OPGW when checking the thermal stability of the short-circuit current shall be determined according to the data provided by the manufacturer or by experiment, and is generally considered at 200 °C.

When the OPGW branch is designed, the short-circuit current capacity should be fully verified, and the branch cable should meet the technical requirements of the corresponding line.

3.4 Selection and configuration of OPGW and shunt ground

Both the OPGW and the shunting ground wire shall meet the requirements of the design specifications of GB 50061-2010, GB 50545-2010, GB 50665-2011 and GB 50790-2013 for the mechanical and electrical use conditions of the ground wire, while having sufficient mechanical strength. It also has sufficient current carrying capacity to meet thermal stability requirements. The shunt ground should be able to effectively share the short-circuit current flowing through the ground. The model of the OPGW and the split ground wire and its segmented distribution scheme should be combined with the thermal stability check of the OPGW and determined by technical and economic comparison.

When selecting the PGW and the shunting ground structure, it is best to match the tension and the design sag characteristics as much as possible .

3.5 OPGW and shunt ground wire are thermally stable

a) OPGW and shunt ground wire should meet the requirements of mechanical strength and thermal stability.

For overhead transmission lines with dual ground lines, the thermal stability of the ground wire combination shall be verified at the same time, and measures such as erecting coupling lines may be taken when necessary.

According to Appendix E of the Code for Grounding Design of AC Electrical Installations (GB T50065-2011), the thermal stability formula is as follows:

C-constant. Steel core aluminum wire-120; steel strand-70; aluminum-clad steel strand - 20% IACS-73, 27% IACS-80, 30% IACS-83, 35% IACS-89, 40% IACS-95.

b) When calculating the single-phase grounding short-circuit current in the OPGW and the shunt ground, consider the shunt flowing through the earth. Generally estimated by 5 to 10%.

c) Select the off-grid ground of OPGW from the point of view of lightning strike resistance

(1) Broken core caused by thermal effect: lightning current causes instantaneous heat generation through the ground wire, and the lightning current is very large, reaching 120~200kA, but the passage time is very short, within tens of microseconds, the lightning impulse voltage wave head time is 1.2 microseconds, wave tail 50 microseconds, when the lightning current take 200kA, heat capacity was only 2 kA ² S. Therefore, although the lightning current is large, the duration is very short, which does not affect the thermal stability of the OPGW.

(2) Lightning strike broken core: Due to the large lightning current and short acting time, it has a strong electromagnetic impact effect, which causes the OPGW or the shunting ground wire to break and break the core.

3.6 Grounding of OPGW and shunt ground

The OPGW requires a dedicated grounding wire to be reliably grounded. It cannot be grounded only with a metal fitting. Thermostable check, when the ground has requested streaming effect, should be grounded shunt ground; the rest of the ground segment splitless claims, the insulating segment may be employed a single point grounding , the use of a single graded insulation Point grounding method, the insulation length should not exceed 5km . The purpose of the ground segment segmentation insulation is mainly to reduce the energy loss of the ground wire. The ground wire energy loss is composed of two parts: the inter-line circulation component and the ground component. The inter-line circulation component is much larger than the ground component. In the operation of the line, only one ground wire is insulated, which can eliminate the circulating current component between the wires, thereby greatly reducing the energy loss of the ground wire. Double insulator strings should be used for grounding insulation.

In order to ensure the operation safety of the OPGW, in the case that the short-circuit capacity of the OPGW meets the requirements, it is recommended to use the ground segment segment insulation and the OPGW full-line linear grounding operation mode; the OPGW can also adopt the segmented insulation single-point grounding method.

Since the OPGW in operation has a strong induced current, when the OPGW is not connected with the grounding line of the substation (the station) or the contact is poor, the OPGW is not fixed in the OPGW and the structure during the release of the charge. An electrical contact will create an electrical arc, causing discharge burns and melting of the OPGW. In order to avoid such a situation, the OPGW should be reliably electrically connected to the frame by grounding wires at the top and the middle of the frame. In order to ensure that the OPGW and the frame are not fixed contact points, and the OPGW and the frame gap discharge hazard are eliminated, the OPGW along the frame should adopt the down-conductor clamp with the insulating phase pad, and the closest distance between the OPGW and the frame member should be not less than 20mm. . The joint box and the grounding portion of the residual cable frame should also be insulated from the frame. In addition, in order to reduce the induced current on the OPGW, the other shunt ground and the structure should be reliably grounded during the normal operation of the line.

4 Mechanical properties of the OPGW

4.1 Design safety factor of OPGW

The design safety factor of the OPGW should not be less than 2.5 and should be greater than the design safety factor of the wire.

The maximum tension of the OPGW at the lowest point of the sag shall be calculated as follows:

T _max ≤ T _P / T _C

In the formula:

T _{max —} the maximum tension of the OPGW at the lowest point of the sag, N;

T _P — rated breaking force of OPGW, N;

K _C — The design safety factor of the OPGW.

The design safety factor of the suspension point should not be less than 2.25.The OPGW, which is mounted on the pulley, should also calculate the additional tension caused by the local bending of the suspension point. Under the meteorological conditions of rare wind speed or rare ice coating , the maximum tension of the OPGW at the suspension point should not exceed 66% of the rated breaking force.On the same line, when the calculation condition is +15 °C and there is no wind, the OPGW matches the design sag characteristics of the shunt ground, which should be consistent.

4.2 OPGW anti-vibration measures

The average operating tension of the OPGW should not be greater than 20% of the rated breaking force, and the corresponding anti-vibration measures should be taken according to the upper limit of the average operating tension.

The OPGW's annual average operating tension limit and corresponding anti-vibration measures shall be provided and accounted for by the suppliers of OPGW and supporting fittings. Anti-vibration measures for optical cables include shock-proof hammers and spiral dampers (anti-vibration whip).

a) Anti-vibration hammer: Anti-vibration hammer is a kind of adjusting frequency damper. It has very effective anti-vibration effect for large-diameter wires. The basic principle is to absorb energy dynamically. In general, the frequency damper has a specific frequency characteristic range. Commonly used in light ice areas, installation must be equipped with protective lines.

Number of anti-vibration hammer installations:

The installation distance of the anti-vibration hammer can be calculated as follows:

S1=0.4 × D ×( T/M ) ^1/2 ( mm );

S2=0.7S1;

S3=S4=S5=...=0.6S1

among them:

D―——outer cable diameter (mm);

T―--annual average running tension (N);

M―——the unit weight of the optical cable (g/mm);

Precautions:

(1) According to the calculation, if the anti-vibration hammer calculation installation position falls on the inner skein, it is not necessary to install the guard line, and it can be directly installed.

(2) If the anti-vibration hammer calculation installation position falls on the OPGW cable, it is necessary to install the guard line, and note that the end of the guard line is at least 50-80 mm from the end of the inner skein.

(3) If the anti-vibration hammer calculation installation position falls on the outer skein, it is directly installed on the inner skein, and the center of the anti-vibration hammer is 50-80 mm from the end of the outer skein.

b) Helical damper (anti-vibration whip): anti-vibration whip (spiral anti-vibrator) is a commonly used shock damper, anti-vibration whip for small cable diameter transmission line and fiber line high frequency vibration reduction The vibration is very effective. The anti-vibration whip dissipates the vibration energy through the impact with the cable, thereby achieving the effect of weakening the line vibration. This type of damper is very effective for anti-vibration of small diameter wires, and its damping effect depends on the relationship between the quality and frequency of the anti-vibration whip and the wire. The heavy ice area cable line is characterized by large ice wind load and high material consumption. An effective anti-vibration measure for heavy ice areas is the use of a spiral vibration isolator.

(1) Anti-vibration measures in heavy ice areas

Since the anti-vibration hammer has anti-vibration failure in the case where the ice layer is thick, in addition, since the ice-skiping phenomenon is often accompanied by uneven de-icing, a spiral damper is used. It can play a good protective role for the dancing and jumping of the line.

(2) Anti-vibration scheme when using anti-vibration whip

Anti-vibration whip (spiral anti-vibrator) is currently the most commonly used impact damper, made of high-strength engineering plastic with impact resistance and anti-aging. The spiral vibration isolator consists of a clamping section and a vibration damping section. The clamping section grips the optical cable and dissipates the vibration energy through the impact of the vibration reduction section and the optical cable, thereby achieving the effect of weakening the line breeze vibration.

(3) Determination of the number of spiral dampers

Determine according to the line spacing:

When 0m < span ≤ 250m, install 6 (that is, install 3 on each side of the fitting)

When 250m

When 500m

When 750m

(4) Installation method

The installer sees the following figure:

The spiral damper is installed in the same position on the tension clamp or the suspension clamp. Generally, the first anti-vibration whip is installed at 150mm from the end of the inner skein, and the second is installed at 150mm from the end of the first anti-vibration whip. Where. This method is installed in series; it can also be installed in parallel or two stacked together, and the two installation methods have the same effect.

4.3 OPGW plastic elongation treatment

The plastic elongation of the OPGW after erection is determined according to the data provided by the manufacturer or by experiment. The influence of plastic elongation on the sag should be compensated by the cooling method. If there is no data, refer to the line GB.50545-2010. regulations, the author generally lower 15 ℃ more .

4.4 Other mechanical properties of OPGW

The calculation of OPGW mechanics is consistent with the calculation of the grounding line of overhead transmission lines. The parameters are not detailed here. If there is any problem, please leave a message to Xiaobian or join the 72468968QQ group for communication.

5 OPGW's distribution (length) calculation

The OPGW's distribution is a key part of the design process and determines the length of each OPGW. The arrangement of the distribution plate is directly related to the arrangement of the fiber optic connector. It also determines the installation interval of the OPGW and, if necessary, the direction of deployment.

5.1 OPGW distribution principle

The distribution plate shall obey the tensile section of the line. To reduce the fiber joint, two adjacent smaller tensile sections may be combined. Joints should be avoided in unfavorable terrain such as paddy fields, swamps, ponds, hilltops, and deep valleys, based on route data or site surveys. Joints should be arranged as far as possible in a location with convenient transportation and easy access to utilities. When there are two or more 90° rotation angles or more than four 45° rotation angles in the line, the discs should be divided as much as possible, and the joints should be arranged on these corner towers.

5.2 OPGW disk length

The distribution plate shall obey the tensile section of the line. To reduce the fiber joint, two adjacent smaller tensile sections may be combined. Joints should be avoided in unfavorable terrain such as paddy fields, swamps, ponds, hilltops, and deep valleys, based on route data or site surveys. Joints should be arranged as far as possible in a location with convenient transportation and easy access to utilities. When there are two or more 90° rotation angles or more than four 45° rotation angles in the line, the discs should be divided as much as possible, and the joints should be arranged on these corner towers.

In the plain area, a single plate of 3 to 5 km is a better choice. For example, in a mountainous area with complex terrain, it should be controlled as much as possible at a length of 3 km, so that a construction team can be discharged in one day. The length of the OPGW single disc also depends on the diameter of the monofilament of the stranded single wire, since the length of the single wire that can be accommodated on the work plate on the stranding machine is limited. When the long-length tensile section or the maximum single-disc length cannot meet the requirements of the tensile-resistant section, one treatment method is to reduce the diameter of the monofilament under the premise of maintaining the original aluminum-steel ratio, diameter and cross-section (to ensure The lightning protection performance, the diameter reduction is limited) is changed to multi-layer armor.

5.3 OPGW distribution length calculation

According to the relevant manufacturer's experience and the actual inspection of the relevant project, the length of the distribution plate can be calculated according to the formula:

D _L =A×L+2(H+h)+2B

In the formula:

D _L -- distribution length (m);

L -- line length (m);

A - length reserved coefficient: plain: 1.02 ~ 1.03; hills: 1.03 ~ 1.04; mountain area: 1.04 ~ 1.05;

H -- the height of the construction pulley from the input end of the cable (m) ;

h -- the height of the construction pulley off the ground at the output end of the cable (m) ;

B -- traction reserved length, usually 6 ~ 10m.

Due to the different geographical conditions of the area in which the cable is erected, the length of manufacture shall be determined on a case-by-case basis. The length of each OPGW is subject to manufacturing, transportation, construction and the limit of the site along the line, generally within 5km.

5.4 Reserved length of OPGW cable

In the maintenance work of the optical cable, the optical cable needs to be extended when the reconnecting box is partially moved. Therefore, reservations should be made in appropriate places during construction. This reserved length should be considered in the design length of the cable.

In the cable engineering, two reservation modes are usually adopted, one is the ordinary reservation mode (above figure a), which is used for telescopic bending on the pole . In areas with relatively wide terrain, this method is adopted, and the length is reserved. Within 5m; the other is the disc mode, which can be used when the terrain is limited or the reserved length is greater than 5m. The radius R of the curvature of the disk 6 is not to be less than the allowable radius of the cable, and the minimum bending radius of the cable is not to be less than 20 times the diameter of the light. Generally, the length of the cable for overhead erection and pipeline laying is 6~12m.

6 OPGW cable fittings

6.1 Configuration of OPGW fittings

The OPGW must use a dedicated pre-twisted fitting. The rated breaking strength and grip strength of the tensile-resistant fittings are both greater than 95% RTS. Under this tension, the fittings and OPGW are not allowed to have relative slip. The inner diameter of the pre-twisted wire of the sheet metal is directly related to the outer diameter of the cable. The outer diameter tolerance of the cable should be emphasized. The inner diameter of the pre-twisted wire of the fitting should be configured as far as possible according to the negative tolerance of the outer diameter of the OPGW. The holding force of the overhang (excluding the overhanging tensile) to the cable (horizontal sliding load) is generally 10 to 20% RTS.

In fitting configuration and selection, the tower selection of a set of terminal / base Clamp, strain tower use two sets / groups Strain line clip, straight tower selection of a set / group catenary clamp.

6.2 Design safety factor of fittings

The safety factor of the fittings shall comply with the requirements of the corresponding design rules for the transmission line. For general lines, the safety factor of the strength of the fittings should not be less than the following values (GB 50545-2010 6.03):

Maximum load condition 2.5

Disconnection, disconnection, check calculation 1.5

For large span lines, the safety factor of the strength of the fittings should not be less than the following values (DL/T 5485-2013 8.0.2):

Operation status 3.0

Wire break condition 2.0

Checking the situation 1.5

6.3 OPGW hanging metal string

The OPGW overhanging metal string is used to hang the OPGW on the linear tower. The pre-twisted type suspension clamps should be used. The pre-twisted suspension types are divided into single suspension clamps and double suspension clamps . The overhanging string must meet the load requirements and the short circuit current requirements of the line design .

Single suspension clamp

The single suspension clamp technology is characterized by a double-layer structure that provides greater protection for long-term unbalanced load-running cables, better dynamic stress tolerance, and improved grip. Due to the large contact area of the suspension clamp , the stress distribution is uniform, and there is no stress concentration point, which enhances the rigidity of the cable installation point and has a good protection effect on the optical cable. The materials selected have strong corrosion resistance, oxidation resistance and aging resistance, which greatly extend the service life. The structure is simple, the installation is very convenient, no special tools are needed, and maintenance is free.

Double suspension clamp

Double suspension clamp mainly for large span rivers, high drop of valleys and other special places, the line of OPGW and ADSS turn angle in the tower of 25 ° ~ 60 °.

6.4 OPGW resistant sheet metal string

The OPGW sheet is used to withstand the tension of the OPGW. The OPGW is connected to the tension-resistant tower, and a pre-twisted type tension clamp is generally used. The tensile string must meet the load requirements and the short circuit current requirements of the line design .

The OPGW sheet metal fitting adopts a gold steel sand structure between the inner and outer stranded wires to increase the friction force, has a good protection effect and damping effect on the optical cable, and reduces the damage to the optical cable due to the dancing. Due to the large contact area, the stress distribution is uniform, and there is no stress concentration point, which has a good protection effect on the optical cable. The materials selected are highly resistant to corrosion, oxidation and aging. The structure is simple, the installation is very convenient, no special tools are needed, and maintenance is free.

6.5 OPGW anti-vibration hammer ( whip )

The OPGW anti-vibration hammer is used to control the breeze vibration of the OPGW caused by the wind. The anti-vibration hammer itself shall not cause stress concentration that causes damage to the OPGW, and the guard line shall be used at the installation position on the OPGW.

The anti-vibration measures in the heavy ice area adopt a spiral damper (anti-vibration whip). Spiral damper, commonly known as shockproof whip in engineering. It is a line protection device, which is used to eliminate or reduce the vibration generated by the laminar wind during operation of the optical cable to prevent damage to the metal fittings and the optical cable. The spiral damper is generally made of a high-strength PVC material in a spiral shape. A section with a small aperture is called a tightening section, and a section with a large aperture is called a damping section.

The factors that cause the cable vibration are: the length of the gear, the size of the tension, the wind speed, the wind direction, the topography and the structural size of the cable.

6.6 OPGW grounding down conductor

The OPGW should be reliably grounded, and another ground wire with shunting requirements should be reliably grounded.

Both the OPGW suspension string and the tensile string need to have a grounding lead, and the grounding lead should have a good mechanical and electrical connection with the OPGW and the tower.

When the OPGW is connected to the substation structure, the grounding line is reliably connected between the OPGW and the grounding grid connection point at the top of the substation structure. The cross-sectional area of the grounding line is the same as the OPGW cross-sectional area. In addition, between the OPGW connection box and the grounding point at the top of the frame, the OPGW and the substation frame transverse metal platform member grounding grid connection point or the substation ground grounding grid connection point are reliably connected by the grounding wire to ensure the OPGW and The substation grounding grid has a reliable second grounding point, and the grounding wire section is the same as the OPGW section.

6.7 OPGW connector box and down conductor

The OPGW splice box should be easy to install and maintain on the transmission line tower and easy to weld.

The joint box in the line should be installed on the designated tower and installed at a position 7m above the ground to prevent the destruction of mammals or artificial birds. The joint box on the side of the substation frame should be installed on the frame pillar. The installation position should be suitable for the operation personnel. The distance between the equipment and the live equipment in the station should meet the requirements of relevant regulations.

The down-conductor clip of the tower OPGW fiber should be installed on the tower leg without the nail; the fiber on both sides of the tension tower is led to the junction box through the double-slot down-clamp; the installation distance of the lower-clamp is : for the cross-arm part is about 1 meter, for the tower body part is about 1.5 meters; the front and rear side of the fiber-optic down-conductor line along the ground line cross-bearing slope main material into the inside of the tower body, leading to the 7 ~ 9 m from the ground After the surface, the remaining cable is placed in the remaining cable frame, and the bending radius of the remaining cable is more than 2 times the allowable bending radius; the optical fiber down-conductor has no hard bend and chamfer, and the down-conductor, the remaining cable frame and the junction box are firmly installed. The allowable bending radius of the OPGW down conductor at the bend should not be less than the value provided by the manufacturer.

The lead hoop of the OPGW fiber of the frame shall be installed on the frame; the cable shall be led to the remaining cable rack at 2.5 m from the ground to be welded by the lower clamp; the installation distance of the down clamp shall be 1.5 m, and the turn may be appropriate. Adjust the installation distance; note that the lower clamp should be installed firmly to ensure that the OPGW does not touch the steel;

6.8 OPGW residual cable rack

The OPGW residual cable frame is required to be easily installed and maintained on the transmission line tower. The minimum coil diameter of the remaining cable frame should not be less than the value provided by the OPGW manufacturer.

6.9 OPGW Optical Cable Distribution Frame (ODF)

The optical cable distribution frame is used for connecting and distributing the optical fiber cable and the FC/PC single-core optical fiber after the optical cable enters, and the optical path is wired and dispatched by the adapter. The technical requirements shall comply with the relevant provisions of YD/T 778-2011 "Fiber Distribution Frame".

When the cable is introduced into the rack, the bending radius should be no less than 15 times the diameter of the cable. When the cable fiber passes through the hole of the metal plate and turns along the sharp edge of the structural member, the protective cover and the gasket should be installed. When the fiber and pigtail are bent, the bending radius should be no less than 37.5mm.

7 frame to ODF frame guide cable selection design

7.1 Selection and structure of guiding cable

The ODF frame optical cable of the substation (station) to the communication equipment room should be made of non-metal ( high-voltage occasion ), good flame retardancy (substation fire protection requirements), layer- wound optical cable, and generally GYFTZY non-metal flame-retardant optical cable, as shown below.

The figures in the figure indicate:

1 Cable medium center reinforcement: Insulation rod with high tensile strength made of glass fiber reinforced plastic ( FRP ) , the tensile Young's modulus is not less than 50Gpa, and the bending Young's modulus is not less than 45Gpa. The rate is not less than 2% , and no joint is allowed within the manufacturing length of the cable.

2 fiber .

3 loose tube: The loose tube buffer tube made of high elastic thermoplastic material contains multiple optical fibers, and the tube is filled with water blocking compound, which has high waterproof and moisture resistance.

4 Filler: Made of highly elastic thermoplastic material, the color should be distinguished from the loose tube and can replace the loose tube in the core. The loose tube and the filler are stranded in a single layer around the central reinforcement.

5 cable core water blocking: the expansion material is used to prevent the longitudinal water intrusion of the cable core.

6 wrapped core: The stranded cable core is wrapped with moisture-proof belt to further strengthen the moisture-proof performance of the cable.

7 inner sheath: extruded with polyethylene, tightly wrapped fiber optic cable

⑧ cable strengthener: torsional torque balanced cable strengthener, high modulus aramid negative thermal expansion about the twisted wire spiral from the inner sheath to be opposite to the stranding direction aramid adjacent, outermost layer should be a right Spin. The Young's modulus is not less than 90 Gpa, and each bundle of aramid does not allow joints within the manufacturing length of the cable.

9 outer sheath: flame retardant / etch resistant polyethylene material .

7.2 Guide cable laying

The non-metallic guide cable should be placed in the semi-rigid plastic sleeve (PE or PVC material), and laid on the cable trench cable bracket in the station. In order to avoid misalignment, it should be fixed once every 2m, and ensure that the static bending radius of the cable is not less than The cable has 20 times the cable diameter, and the dynamic bending radius during construction is not less than 20 times the cable diameter. If a single-layer armored structure of the guiding cable is required, the design must consider good grounding at both ends, and if necessary, ground or multi-point grounding, and ensure that current is not introduced into the communication equipment.

In addition to the regulations mentioned in the reference text, this paper also refers to the " Design Depth and Technical Regulations of Optical Fiber Composite Overhead Ground Wire " of Guangdong Power Grid and the " Design of Optical Fiber Communication Lines for Power Systems" compiled by Yunnan Electric Power Design Institute.