1、 Definition and Core Values

24 core non-metallic optical cable is an optical communication transmission medium that excludes metal materials. Through the precise integration of 24 independent optical fibers, a full dielectric structure without metal reinforcement and armor layer is constructed. This type of optical cable is designed for two high-risk scenarios: first, power transmission corridors with strong electromagnetic interference, and second, environments that require the elimination of flammable and explosive materials such as mines and petrochemicals caused by electric sparks. The essence of its technology is to achieve mechanical substitution of traditional metal components through synthetic materials, while retaining the high bandwidth and low loss characteristics of optical fiber communication.

In the intelligent transformation of ultra-high voltage power grids and the construction of smart mines, the 24 core configuration is particularly critical - compared to the capacity limitations of 12 core optical cables and the complex operation and maintenance of 48 core cables, 24 core achieves a balance between transmission capacity and economy, becoming the gold standard for backbone routing at the distribution layer.

2、 Structural Analysis and Material Innovation

（1） Hierarchical structure design

Sheath system: The outer layer is made of black high-density polyethylene (HDPE) or low smoke halogen-free flame-retardant polyolefin (LSZH). The thickness of HDPE sheath usually reaches 2.0mm or more, providing excellent moisture and corrosion resistance; The LSZH sheath is crucial in enclosed spaces such as mines, with an oxygen index of over 32% and a smoke transmittance of over 60% during combustion, far superior to ordinary PVC materials. The surface of the sheath adopts a circular convex design to enhance its resistance to rodent gnawing.

Mechanical reinforcement layer: The core tensile unit is composed of two layers of composite materials. The central reinforcement is made of glass fiber reinforced plastic (FRP) with a diameter of 2.5mm, which has a tensile strength exceeding 600MPa and an elastic modulus exceeding 50GPa; The outer layer of FRP is spiral wrapped with aramid fiber bundles, with aramid accounting for no less than 30% of the cross-sectional area and a maximum breaking force of 20kN. This composite structure has tensile properties comparable to steel cables while being insulated, and has the advantages of light weight (40% lighter than metal cables) and fatigue resistance.

Fiber core integrated system: 24 G.652D single-mode optical fibers are accommodated in loose tubes and arranged in a layer twisted arrangement of 6 tubes x 4 fibers. Each 250 μ m coated optical fiber is suspended in a polybutylene terephthalate (PBT) sleeve filled with thixotropic fiber paste. The thermal expansion coefficient of PBT material is highly matched with that of fiber glass, and it can effectively suppress micro bending loss in temperature cycling from -40 ℃ to+70 ℃. The loose tube is wrapped around the FRP reinforcement in a SZ twisting manner, and the twisting pitch is optimized to ensure that the strain of the fiber during bending does not exceed 0.15%.

3、 Key performance and reliability verification

1. Optical performance: At a working wavelength of 1550nm, the attenuation coefficient of standard 24 core non-metallic optical cables is controlled within 0.22dB/km, and some models can be reduced to below 0.19dB/km; The zero dispersion wavelength range is 1300-1324nm, and the dispersion slope does not exceed 0.092ps/(nm ² · km). These indicators meet the requirement of 80 kilometers without relay transmission, exceeding the requirements of the conventional communication standard YD/T 901-2018.

2. Mechanical reliability: Ensure service stability through a three-stage verification system:

Tensile performance: Long term allowable tension up to 6kN (equivalent to hanging a vertical span of 1000 meters), short-term ultimate tension exceeding 12kN

Flattening test: After withstanding a pressure of 300kg/10cm, the additional loss increment of the optical fiber is ≤ 0.03dB

Bending cycle: Repeatedly wound 1000 times under a bending radius of 15 times the diameter, with no degradation in transmission performance

Temperature adaptability: After gradient testing from -50 ℃ (freezing) to+85 ℃ (thermal cycling), the attenuation fluctuation range is less than 0.05dB/km

3. Special protective capabilities: The all dielectric structure endows it with two major advantages

Electromagnetic immunity characteristics: In a 50Hz 3000A/m magnetic field environment, there is no phase disturbance in the optical signal

Lightning protection capability: Through a 150kA lightning current impulse test (simulating direct lightning strikes), the optical cable structure remains intact

Explosion proof safety certification: The surface resistance of the sheath is greater than 1 × 10 ¹⁰ Ω, meeting the GB 3836.1-2020 explosive environment standard

4、 Core Technologies for Engineering Implementation

1. Three elements of laying control

Traction force limitation: The tension is always controlled within 20% of the rated tensile strength. It is recommended to use anti twist traction heads combined with rotary torque reducers for the installation of power towers

Bending radius management: Maintain ≥ 20 times the diameter of the optical cable during dynamic laying, ≥ 15 times the diameter in a fixed state, and install guide roller sets at the corners of the tunnel

Wear protection measures: A 50mm quartz sand cushion layer is laid at the bottom of the trench for the buried section, and a silicon core pipe with an inner diameter of 35mm or more is selected for the pipe penetration section

2. Continuation and testing procedures

Fusion splicing process: Using ribbon fiber fusion splicing technology, 4-core fiber array splicing is completed in one go, with a single point fusion splicing loss of ≤ 0.03dB. The splicing sequence strictly follows the TIA-598 chromatographic specification: blue, orange, green, and brown color ring identification management.

Protection scheme: use stainless steel joint box with double sealing structure, fill silicon gel inside to achieve IP68 waterproof, and set stainless steel fasteners outside to resist mechanical impact

Acceptance testing: Conduct dual wavelength testing at 1550nm and 1625nm using OTDR, with a requirement that the difference in attenuation consistency between fiber cores is less than 0.02dB/km, and the fault location error is within ± 1 meter.