The total length of my country's power transmission lines ranks second in the world. According to statistics, there are 310,000 kilometers of existing 110KV and above lines, and there are a large number of 35KV/10KV old lines. Although the domestic demand for OPGW has increased sharply in recent years, the demand for ADSS fiber cable is still rising steadily.
ADSS optical cable is an "addition" to the old line. ADSS fiber cable can only try to adapt to the original line conditions, which include (but not limited to) meteorological load, tower strength and shape, original conductor phase sequence arrangement and diameter, sag tension and span and safety spacing. Although ADSS fiber cable looks similar to ordinary "all-plastic" or "non-metallic" optical cable, they are two completely different products.
1. Representative structure
At present, there are two main types of ADSS fiber cables popular at home and abroad.
1. Central tube structure:
ADSS Cable the optical fiber is placed in a PBT (or other suitable material) tube filled with water-blocking grease with a certain excess length, and is wrapped with suitable spun yarn according to the required tensile strength, and then extrude PE (≤12KV electric field strength) or AT (≤20KV electric field strength) sheath.
The central tube structure is easy to obtain a small diameter, with a small ice wind load; the weight is also relatively light, but the excess length of the optical fiber is limited.
2. Layer-twisted structure:
The optical fiber loose tube is wound on the central reinforcement (usually FRP) with a certain pitch, and then the inner sheath is extruded (which can be omitted at low tension and small span), and then wrapped with suitable spun yarn according to the required tensile strength, and then extrude PE or AT sheath. The cable core can be filled with grease, but when the ADSS works at a large span and with a large sag, the cable core is easy to "slide" due to the small resistance of the grease, and the pitch of the loose tube is easy to change. The problem can be overcome by fixing the loose tube to the central reinforcement and the dry cable core with a suitable method, but there are certain process difficulties.
The layer-twisted structure is easy to obtain safe excess fiber length. Although the diameter and weight are relatively large, it is more advantageous when used in medium and large spans.
2. Main technical parameters
The ADSS fiber cable works in an overhead state with two points of support over a large span (usually hundreds of meters, or even more than 1 kilometer), which is completely different from the traditional concept of "overhead" (the overhead suspension line hooking program of the post and telecommunications standard has an average of 1 support point for the optical cable every 0.4 meters). Therefore, the main parameters of the ADSS cable are in line with the regulations of the power overhead line.
1. Maximum allowable tension (MAT/MOTS)
Refers to the tension to which the optical cable is subjected when the total load is theoretically calculated under the design meteorological conditions. Under this tension, the optical fiber strain should be ≤0.05% (layer twisted) and ≤0.1% (central tube) without additional attenuation. The excess fiber length is just "eaten" at this control value. According to this parameter, meteorological conditions and controlled sag, the allowable span of the optical cable under this condition can be calculated. Therefore, MAT is an important basis for sag-tension-span calculation, and is also an important evidence for characterizing the stress-strain characteristics of ADSS cables.
2. Rated tensile strength (UTS/RTS)
Also known as ultimate tensile strength or breaking force, it refers to the calculated value of the sum of the strengths of the bearing section (mainly nylon). The actual breaking force should be ≥95% of the calculated value (the break of any component in the optical cable is judged as cable breakage). This parameter is not optional, and many control values are related to it (such as pole tower strength, tension fittings, earthquake protection measures, etc.). For optical cable professionals, if the ratio of RTS/MAT (equivalent to the safety factor K of overhead lines) is inappropriate, even if a lot of nylon is used, and the available optical fiber strain range is very narrow, the economic/technical performance ratio is very poor. Therefore, the author recommends that industry insiders pay attention to this parameter. Usually, MAT is approximately equivalent to 40% RTS.
3. Annual average stress (EDS)
Sometimes called daily average stress, it refers to the tension of the optical cable under theoretical load calculation under windless and iceless conditions and the annual average temperature, which can be considered as the average tension (stress) of ADSS during long-term operation. EDS is generally (16~25)%RTS. Under this tension, the optical fiber should have no strain and no additional attenuation, that is, it is very stable. EDS is also the fatigue aging parameter of the optical cable, and the vibration-proof design of the optical cable is determined based on this parameter.
4. Ultimate operating tension (UES)
Also known as special use tension, it refers to the maximum tension of the optical cable during the effective life of the optical cable when it may exceed the design load. It means that the optical cable allows short-term overload, and the optical fiber can withstand strain within a limited allowable range. Usually, UES should be >60%RTS. Under this tension, the strain of the optical fiber is <0.5% (central tube) and <0.35% (layer twisting), and the optical fiber will have additional attenuation, but after this tension is released, the optical fiber should return to normal. This parameter ensures the reliable operation of the ADSS cable during its life.
3. Matching of fittings and optical cables
The so-called fittings refer to the hardware used to install optical cables.
1. Tension clamp
Although it is called "clamp", it is actually better to use spiral pre-twisted wire (except for small tension and small span). Some people also call it "terminal" or "static end" fittings. The configuration is based on the outer diameter and RTS of the optical cable, and its gripping force is generally required to be ≥95%RTS. If necessary, it should be tested with the optical cable.
2. Suspension clamp
It is also better to use spiral pre-twisted wire type (except for small tension and small span). Sometimes it is called "mid-range" or "suspension end" fittings. Generally, its gripping force is required to be ≥ (10-20)%RTS.
3. Vibration damper
ADSS optical fiber cables mostly use spiral dampers (SVD). If EDS ≤ 16%RTS, vibration prevention can be ignored. When EDS is (16-25)%RTS, vibration prevention measures need to be taken. If the optical cable is installed in a vibration-prone area, the anti-vibration method should be determined through testing if necessary.
For more ADSS cable technology, please consult: Whatsapp/Phone:18508406369
Company official website link: www.gl-fiber.com