1. What is ADSS fiber optic cable?
ADSS fiber optic cable is All-dielectric Self-supporting Optical Cable.
An all-dielectric (metal-free) optical cable is independently hung on the inside of the power conductor along the transmission line frame to form an optical fiber communication network on the transmission line, this optical cable is called ADSS.
All-dielectric self-supporting ADSS fiber optical cable, due to its unique structure, good insulation, high-temperature resistance, and high tensile strength, provides a fast and economical transmission channel for power communication systems. When the ground wire has been erected on the transmission line, 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. In this scenario, the use of ADSS optical cables has great advantages.
ADSS fiber cable is cheaper and easier to install than OPGW cable in many applications. It is advisable to use power lines or towers nearby to erect ADSS optical cables, and even the use of ADSS optical cables is necessary in some places.
2. Structure of ADSS fiber optic cable
There are two main ADSS fiber optical cables.
- Central tube ADSS fiber optic cables
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 spinning 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 ADSS fiber optic cables
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 fiber excess length, although the diameter and weight are relatively large, which is more advantageous in medium and large span applications.
3. The characteristics of ADSS fiber optic cable
- Specially designed for power systems, it is a self-supporting aerial optical cable with full insulation medium, and its structure does not contain any metal materials
- 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 materials with high tensile strength can not only withstand strong tension, meet the large span requirements of overhead power lines, but also prevent birds pecking and artificial shooting
- ADSS cable sag is sensitive to external load changes. In the state of ice coating, the elongation of ADSS optical cable can reach 0.6%, while the wire is only 0.1%
- The outer sheath of ADSS optical cable is made of AT or PE material. When it runs in a strong electric field, it has the problem of electrical corrosion
- ADSS fiber optic cables are subject to wind vibration. The 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
4. Advantages of ADSS fiber optic cable
- Strong ability to withstand extreme weather (strong wind, hail, etc.).
- It has strong temperature adaptability and small linear expansion coefficient, which can meet the needs of harsh environmental conditions.
- The optical cable is small in diameter and light in weight, which reduces the impact of ice and strong wind on the optical cable, and also reduces the load of the power tower and maximizes the use of tower resources.
- The ADSS optical cable does not need to be attached to the power line or the bottom line, it can be erected on the tower independently, and the construction can be carried out under the condition of no power outage.
- The performance of the optical cable under the high-intensity electric field is extremely superior, and it will not be subject to electromagnetic interference.
- It is independent from the power line and easy to maintain.
- It is a self-supporting optical cable, and does not require auxiliary hanging wires such as hanging wires during installation.
5. The main application of ADSS fiber optic cable
- It is used as the lead-in and lead-out optical cable of the OPGW system relay station. Based on its safety properties, the power isolation problem can be well solved when introducing and extracting the repeater station.
- As the transmission cable of the optical fiber communication system in the high voltage (110kV-220kV) power network. Especially in many places, it is very convenient to use it when retrofitting old communication lines.
- Used for optical fiber communication system in 6kV~35kV~180kV distribution network.
6. Main technical parameters of ADSS fiber optic cable
ADSS optical cables work in an overhead state supported by two points with a large span (usually hundreds of meters, or even more than 1 km), which is completely different from the traditional concept of “overhead”. Therefore, the main parameters of ADSS optical cables are in line with the regulations of power overhead lines.
- Maximum allowable tension (MAT/MOTS)
It refers to the tension of the optical cable when the total load is theoretically calculated under the design meteorological conditions. Under this tension, the fiber strain should be ≤0.05%(layer twist) and ≤0.[% (center tube) with no additional attenuation. According to this parameter and meteorological conditions and the controlled sag, the allowable use span of the optical cable under this condition can be calculated. Therefore, MAT is an important basis for the calculation of sag-tension-span, and it is also important evidence to characterize the stress-strain characteristics of ADSS optical cables.
- Rated tensile strength (UTS/RTS)
Also known as ultimate tensile strength or breaking force, it refers to the calculated sum value of the strengths of the bearing cross-section (mainly textile fibers). The actual breaking force is greater than or equal to 95% of the calculated value (the breakage of any component in the optical cable is judged as the cable breakage). This parameter is not optional, and many control values are related to it, such as tower strength, tensile fittings, anti-vibration measures, etc. Suppose the ratio of RTS/MAT (equivalent to the safety factor K of overhead lines) is not appropriate, even if a lot of fiber is used, and the available optical fiber strain range is very narrow. In that case, the economic/technical performance ratio is very poor. Typically, MAT is approximately equivalent to 40% RTS.
- Everyday Stress (EDS)
It refers to the tension of the cable under the theoretical calculation load under no wind, no ice and annual average temperature, which can be regarded as the average tension of the ADSS during long-term operation. EDS is generally 16~25% RTS. Under this tension, the fiber should be strain-free, without additional attenuation, i.e. very stable. EDS is also the fatigue aging parameter of the optical cable, and the anti-vibration design of the optical cable is determined according to this parameter.
- Ultimate operating tension (UES)
Also known as the special service tension, it refers to the maximum tension that the cable is subjected to when the load exceeds the design load during the effective life of the optical cable. It means that the optical cable is allowed to be overloaded for a short time, and the optical fiber can withstand strain within a limited allowable range. Usually, the UES should be > 60% RTS. Under this tension, the fiber strain is <0.5% (center tube) and <0.35% (layer twist), and the fiber will experience additional attenuation, but after the tension is released, the fiber should return to normal. This parameter ensures the safe operation of the ADSS cable during its lifetime.
7. ADSS fiber optic cable hardware
- Tension clamp
Although it is called “clamp”, it is actually better to use a spiral pre-twisted wire (except for small tension and small span). It is also called “terminal” or “static end” fittings. The configuration is based on the outer diameter and RTS of the optical cable, and its holding force is generally required to be greater than or equal to 95% RTS. When necessary, it should be tested with the optical cable.
- Suspension clamp
It is also better to use the spiral pre-twisted wire type (except for small tension and small span). Sometimes referred to as “mid-range” or “overhanging” fittings. Generally, its holding force is required to be ≥ (10-20) % RTS.
- Vibration isolator
ADSS optical cable mostly adopts spiral vibration dampers (SVD). If EDS≤16% RTS, anti-vibration can be ignored. When EDS is (16-25) % RTS, anti-vibration measures should be taken. If the optical cable is installed in a vibration-prone area, the anti-vibration method should be determined by testing if necessary.
8. Basic requirements for ADSS fiber optic cable construction
- The construction of ADSS optical cables is usually carried out on live line towers. Insulated non-polar ropes, insulated safety belts, and insulating tools must be used during 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, the safety distance of 35KV is greater than 1.0m, 110KV is greater than 1.5m, and 220KV is greater than 3.0m;
- Since the fiber core is easily brittle, the tension and lateral pressure cannot be too large during construction;
- During construction, the optical cable cannot rub and collide with other objects such as the ground, houses, towers, and the edge of the cable reel;
- The bending of the optical cable is limited, and the bending radius of the general operation is ≥D. D is the diameter of the optical cable, and the bending radius is ≥30D during construction;
- The optical cable will be damaged when twisted, and longitudinal twist is strictly prohibited;
- The fiber core of the optical 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. It is not allowed to adjust the disk at will during construction. 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 cables 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.
9. The service life of ADSS fiber optic cable
ADSS optical cable is erected on high-voltage transmission lines, and its general life is more than 25 years, and there are many factors affecting its life. 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 on the optical cable. Generally, the PE type is used for overhead power lines of 35KV and below, and the AT type is used for lines of 110KV and above;
- For the double-circuit tower, 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 and acid gas, the chemical substance will corrode the outer skin of the optical cable, and its electric-resistant protective sheath will be damaged, which is vulnerable to arc damage;
- Damage or wear of the outer skin caused by improper construction, and the surface is easy to corrode when running in a long-term high-voltage electric field, and the optical cable with a flat and smooth outer sheath can effectively reduce electrical corrosion and prolong life.
10. Selection of ADSS fiber optic cable
- Select ADSS fiber optic cable according to mechanical strength
ADSS optical cable is fully self-supporting and requires good mechanical properties. For optical cable manufacturers, it is mainly ensured by adding spinning yarn. When manufacturing an optical cable, first calculate the mechanical strength requirements of the optical cable according to the span of the power line, the sag of the optical cable, the weather conditions, and the icing, and then calculate the amount of spinning yarn used.
Since the design life of ADSS optical cable is more than 25 years, it is also necessary to consider that the surface of the optical cable will be attached to some dirt and increase the load during long-term use.
- Select ADSS fiber optic cable according to electrical corrosion
As far as the causes of electrical corrosion are concerned, first of all, the capacitive coupling potential between the power phase line and the earth will generate leakage current on the surface of the wet optical cable; secondly, when there is a dry point on the surface of the optical cable, an arc will occur between the dry point and the wet point. The resulting heat will erode the outer sheath and cause cracks and, in severe cases, cable breakage.
AT (Anti Tracking) and PE (Polyethylene Sheath) in ADSS cable refer to the sheath of the cable. Currently, AT-sheathed ADSS cables can operate in a safe environment with induced potentials not greater than 25 kV. Generally, PE sheathed optical cables are used for overhead power lines of 35 kV and below; AT sheathed optical cables are used for 110 kV and above lines; ADSS optical cables are not suitable for power lines above 220 kV.
- Select ADSS fiber optic cable according to structure
Compared with the layered structure, the central tube structure has the advantages of small outer diameter and lightweight, and is generally suitable for areas with thick ice coating, strong wind force and small span. The layer-twisted structure can obtain a larger tensile and has better bending performance, so the layer-twisted structure is selected for medium and large spans.
The above is the basic introduction to ADSS fiber optic cable. Bonelinks is an ADSS fiber optic cable supplier. Our products adopt strict quality standards in production and inspection, ensuring excellent operation performance and good product stability. For needs or more questions, please contact us.