Introduce in detail what is ADSS fiber optic cable - Optic-Electric

An all-dielectric (metal-free) optical cable is independently hung on the inside of the power conductor along the transmission line frame (the position of the suspension is mainly determined by factors such as the electric field strength at the suspension place, ground distance, construction and maintenance convenience conditions, etc. Hanging below the power wire) to form an optical fiber communication network on the transmission line, this optical cable is called ADSS.

When the transmission line has been set up with a ground wire, and the remaining life is still quite long, it is necessary to build an optical cable system at a low installation cost as soon as possible, and at the same time avoid power outages.

Structures of ADSS optical cable

At present, there are mainly two kinds of ADSS optical cables.

Central tube structure:

The optical fiber is placed in a PBT (or other suitable material) tube filled with water blocking ointment with a certain excess length, wrapped with suitable spun yarn according to the required tensile strength, and then extruded into PE (≤12KV electric field strength) or AT (≤20KV electric field strength) sheath.

The central tube structure is easy to obtain a small diameter, and the ice wind load is small; the weight is also relatively light, but the excess length of the optical fiber is limited.

Layer twist structure:

Stranded ADSS Optical Cable

The fiber optic loose tube is wound on the central reinforcement (usually FRP) at a certain pitch, and then the inner sheath is extruded (it can be omitted in the case of small tension and small span), and then wrapped according to the required tensile strength Suitable spun yarn, then extruded into PE or AT sheath. The cable core can be filled with ointment, but when the ADSS works with a large span and a large sag, the cable core is easy to "slip" due to the small resistance of the ointment, and the loose tube pitch is easy to change . It can be overcome by fixing the loose tube on the central strength member and the dry cable core by a suitable method, but there are certain technological difficulties.

The layer-stranded structure is easy to obtain a safe optical fiber excess length, although the diameter and weight are relatively large, which is more advantageous in medium and large span applications.

Characteristics of ADSS cable

Structural characteristics of ADSS optical cable

The ADSS optical cables that have been produced can be divided into two types: layer-stranded type and central beam-tube type. Among them, the layer-stranded optical cable has a FRP reinforcing core, and its weight is slightly heavier than that of the beam-tube type. Under the environment, according to the electric field strength, it can be divided into AT sheath galvanic corrosion resistance type and PE sheath standard type.

The characteristics of ADSS cable are as follows:

Specially designed for power system, it is a self-supporting aerial optical cable with full insulation medium, its structure does not contain any metal material;
The fully insulated structure and high withstand voltage index are conducive to the installation of overhead power lines in live operation, without affecting the line operation;
The use of anti-fiber material with high tensile strength can not only withstand strong tension, meet the long-span requirements of overhead power lines, but also prevent bird pecking and artificial shooting;
The thermal expansion coefficient of ADSS optical cable is small. When the temperature changes greatly, the radian change of the optical cable line is small, and its weight is light, and its ice walking and wind load are also small.

ADSS Optical Cable-Aramid Yarn

The ADSS optical cable has a different structure from the overhead conductor, and its tensile strength is borne by the aramid rope. The elastic modulus of the aramid rope is more than half smaller than that of the steel, and the thermal expansion coefficient is a fraction of that of the steel, which determines the arc of the ADSS optical cable. The vertical is more sensitive to external load changes. The elongation of ADSS optical cable can reach 0.6[%] in the ice-covered state, while the wire is only 0.1[%]; the sag is relatively slow to temperature changes, and the sag remains basically unchanged when the temperature changes; under strong wind conditions, its The wind deflection angle is very large. When the wind speed is 30m/s, the wind deflection angle can reach 80°, and the wind deflection angle of the wire is only about half of that of the optical cable.

in addition:

Strong ability to withstand extreme severe weather (strong winds, icing, etc.).
The outer sheath of ADSS optical cable is made of AT or PE material, which runs in a strong electric field and has the problem of electrical corrosion.
ADSS fiber optic cables are subject to wind vibration. Smooth and stable lateral wind blows to the optical cable, wind vibration will occur, and fatigue damage will occur at the hanging point.
ADSS optical cable has a certain resistance to pressure and can withstand the large grip force of the tension clamp.

Lifepsan of ADSS cable

ADSS optical cables are erected on high-voltage transmission lines, and their general lifespan is more than 25 years, and there are many factors that affect their lifespan. The main factors are:

The gradient of the high-voltage induced electric field near the tower changes greatly? The high-voltage induced electric field has strong electrical corrosion to the optical cable? Generally, the PE type is used for overhead power lines of 35KV and below, and the AT type is used for 110KV and above lines;
For double-circuit towers, due to the power failure of the primary circuit or the reconstruction of the circuit, it should be considered when selecting the hanging point;
When the line passes through the working area with salt spray acid gas, the chemical substance will corrode the outer skin of the optical cable, and its electric-resistant protective cover will be damaged, which is vulnerable to arc damage;
Improper construction causes damage or wear to the outer skin, etc., and its surface is easy to corrode when it operates in a long-term high-voltage electric field, and the optical cable with a smooth and smooth outer sheath can effectively reduce electrical corrosion and prolong life.

Selection principle of optical cable hanging point

According to the calculation results of the electric field strength of various towers, the hanging points that meet the requirements of the electric field strength can be divided into three ways: high, medium and low hanging points.

High hanging points are generally difficult to construct and inconvenient to operate and manage;
The low hanging point has some problems in the safety distance to the ground, and is prone to theft;
Generally, in the information network project, the way of hanging point is adopted.

For example: 110KV line tension pole, gate pole, double-circuit iron tower, steel pipe single pole, cement single pole, etc. The optical cable can be hung between 300 and 500mm under the first layer of the cross arm.

Among them, the size of the high-voltage induced electric field is generally calculated by the ADSS optical cable manufacturer according to the preliminary design of the Electric Power Design Institute, and the electric field strength and distribution diagram of different tower types are given, and combined with the specific difficulty of construction, the hanging point of the optical cable is finally determined. Location.

In the special application software, as long as the phase line coordinates of the tower, the phase line diameter, the ground wire type, and the voltage level of the line are provided according to the established coordinate system, an induced electric field distribution diagram can be obtained. Therefore, in the preliminary design In the preparation stage, the detailed and reliable line data is the guarantee of the quality of the whole project.

The optical cable should be suspended in a position with low electric field strength, that is, AT type sheath ≤ 20KVm PE type sheath ≤ 20KVm;
The projection of the optical cable in the horizontal and vertical directions should not cross the conductor and the ground wire, so as to avoid whiplash when the wind deviates and swings;
The optical cable should not rub and collide with the tower;
Optical cables must maintain a safe distance from residential areas, railways, highways, communication lines and other power lines;
The hardware for suspending the optical cable must be installed on the tower material that can withstand the lateral tension of the tower, so as to minimize the force on the tower;

The distribution of ADSS optical cable

The distribution of optical cables is an important issue in the construction of optical cables. When the lines and conditions used are clear, the distribution of optical cables must be considered.

The factors that affect the allocation are :

Because ADSS optical cable can not be connected arbitrarily like ordinary optical cable (because the core of optical fiber cannot bear the force), it must be carried out on the tension tower of the line, and because the conditions of the connection point in the field are poor, the coil length of each coil of optical cable should be controlled as far as possible. 3 ~ 5Km. If the coil length is too long, it will be inconvenient for construction; if it is too short, the number of connections will be large, and the attenuation of the channel will be large, which will affect the transmission quality of the optical cable.
In addition to the length of the transmission line being the main basis for the length of the cable reel, the natural conditions between the towers should also be considered, such as whether the tractor is convenient to travel, whether the tensioner can be placed, etc.
Due to the error of the line design, the following empirical formula can be used for the distribution of the optical cable: the length of the optical cable plate = the length of the transmission line × the coefficient + the length of the construction consideration + the length of the welding + the line error; Usually, the "coefficient" includes the line sag, the Over-drawing length, etc., the length considered in construction is the length used for traction during construction.
The minimum distance from the ADSS optical cable hanging point to the ground is generally not less than 7m. When determining the distribution plate, it is necessary to simplify the distance difference in order to reduce the type of optical cable, which can reduce the number of spare parts (such as various hanging hardware, etc.), and it is convenient construction.

Basic requirements for ADSS optical cable installation

The construction of ADSS optical cable is usually carried out on live line towers. Insulated non-polar ropes, insulating safety belts, and insulating tools must be used in the construction. The wind force should not be greater than level 5, and a safe distance from lines of different voltage levels must be maintained, that is, 35KV greater than 1.0 m, 110KV greater than 1.5m, 220KV greater than 3.0m safe distance;
Because the fiber core is easily broken, the tension and lateral pressure during construction should not be too large; (3) During construction, the fiber optic cable should not rub and collide with other objects such as the ground, houses, towers, and the edge of the cable tray;
The bending of the optical cable is limited, the bending radius of the general operation is ≥ D, D is the diameter of the optical cable, and the bending radius is ≥ 30 D during construction;
The optical cable will be damaged when twisted, and longitudinal twist is strictly prohibited;
The fiber core of the fiber optic cable is easy to break due to moisture and water, and the end of the cable must be sealed with waterproof tape during construction;
The outer diameter of the optical cable is matched with the representative span, and it is not allowed to adjust the disk arbitrarily during construction, and at the same time, the hardware corresponds to the outer diameter of the optical cable, and it is strictly forbidden to use it indiscriminately;
After the construction of each reel of optical cable is completed, there is usually enough excess cable reserved for hanging and splicing at the tower, and installing the optical fiber distribution frame in the substation.

About the sag tension table

The sag tension meter is an important data material that reflects the aerodynamic performance of ADSS optical cables. A complete understanding and correct use of these materials is a necessary condition to improve the quality of the project. Usually manufacturers can provide sag tension meters under three constant conditions, namely installation The sag is constant (the installation sag is a fixed percentage of the span); the installation tension is constant and the load tension is constant. These three types of tension gauges describe the sag tension performance of ADSS optical cables from different sides.

It is only used to illustrate the sag tension characteristics of ADSS optical cable products under given conditions of use, which are different from actual engineering applications and must be paid attention to.
It should be noted that the span in the sag tension table is the actual span, to be precise, the actual span of the isolated file, that is, the span when the tension section has only one segment.
In practical engineering, the representative span of the tensile section should be obtained first, and then the sag and tension data corresponding to the one with the same or similar value of the representative span should be found from the sag tension table. Remember At this time, the sag is generally compound sag. Through the wind deflection angle, the horizontal sag and vertical sag are obtained. Here, it represents the sag, the tension, and the theoretical value of the span, and the actual data is calculated. In the control conditions, the wind load control is related to the mechanical properties of the ADSS optical cable. It usually occurs in the large span of more than 600m, and in the case of strong winds of more than 30 ms, the weight of the ADSS optical cable is lighter than that of the wire, and its wind deflection angle is greater than that of the wire. The wind deflection angle is easier to elongate. This may cause the ADSS optical cable to collide with the wire in the strong wind.

Although the design calculation is more complicated, in the case of small spans, such as when the representative span is less than 100m, the sag of the erection line is usually taken as 0.5 m, which means that when the span is between 100m and 120m, the sag of the erection line is usually taken as 0.5 m. For 0.7m, the lowest point of the sag of the ADSS cable should not be lower than the lowest point of the sag of the wire.
In actual construction, in the continuous gears of the tension bar, the middle gear or a larger gear distance close to the middle gear is often selected, and the one with the smaller suspension point height difference is used as the observation gear. If the number of gears is 7 to 15 gears, the Select 2 observation files at both ends.
Common observation methods include equal-length method and different-length method to observe sag, and tension measurement method can also be used to observe sag. Conclusion ADSS optical cable engineering design and construction is a complex system engineering, involving mechanical, electrical, meteorological conditions, construction personnel In many aspects, such as the quality of the staff, it is necessary to have both a scientific attitude and effective working methods.
With the continuous progress of the power information network project, more and more construction and daily maintenance experience will be accumulated, so that the application of ADSS optical cable will be further developed.

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ADSS cable introduction