Why are completely metal-free fiber optic cables used on high-voltage power towers? OFSCN®
In high-voltage power towers and corridors, the use of optical cables with no metal components (i.e., All-Dielectric Self-Supporting Cables, abbreviated as ADSS cables) or non-metallic optical cables is driven by extremely high safety, physical, and engineering design considerations. The core reasons are mainly reflected in the following physical and engineering principles:
1. Electrical Tracking Corrosion (Electromagnetic Induction) under Strong Alternating Electromagnetic Fields
Around high-voltage and ultra-high-voltage power transmission lines (such as in 110\text{ kV}, 220\text{ kV}, or 500\text{ kV} systems), extremely strong alternating electromagnetic fields exist.
If the optical cable contains metal components (e.g., steel wire strength members, metal sheaths, or moisture-proof aluminum tapes):
- The metal acts as a conductor and generates an induced electromotive force in the spatial electromagnetic field, creating an induced voltage of hundreds of thousands of volts, forming a high potential difference between the metal layer and the ground (or tower).
- When the optical cable surface is contaminated by airborne dust, salt mist, rainwater, etc., its surface resistance decreases.
- Under the action of the induced voltage, a weak leakage current is generated on the cable surface, leading to micro-arc discharges (i.e., “dry band arcing”) in discontinuous dry bands.
- This continuous localized high-temperature discharge burns the outer sheath of the optical cable, gradually carbonizing to form a dendritic conductive path, ultimately destroying and breaking the cable. This phenomenon is physically known as Electrical Tracking.
Using all-dielectric optical cables that contain no metal components fundamentally eliminates the generation of induced potential differences, thereby removing the hidden danger of electrical tracking.
2. Avoiding High-Voltage Breakdown and Flashover Discharge
The air gaps and insulation distances of insulators at high-voltage transmission towers are precisely calculated.
- If the optical cable contains metallic materials, it introduces a “dielectric body” between the high-voltage conductors and the grounded tower, altering the electric field distribution around the tower.
- During thunderstorms or in environments with high humidity, it is extremely easy to cause flashover discharge (arcing) or insulation breakdown from the high-voltage conductors to the metallic components of the optical cable. This not only burns out the optical cable but can also directly cause short-circuit tripping of the high-voltage transmission line, leading to widespread power outages.
3. Lightning Protection (Lightning Arresting Characteristics)
Tall high-voltage towers are natural focal points for lightning strikes.
- Any cable or optical cable with metal material will attract lightning like a lightning rod (flash receiving).
- The instantaneous extreme heat generated by the powerful lightning current passing through the internal metal strength members of the optical cable will not only instantly melt the internal optical fibers but also cause extreme instantaneous potential backlash to the grounding system of the supporting tower, damaging surrounding power facilities.
- Pure non-metallic materials (composed of dielectric materials such as glass fibers, aramid, PE sheathing, etc.) are “invisible” to lightning and do not attract strikes, greatly enhancing the lightning strike safety of communication links and power grids.
4. High Tensile Strength, Lightweight, and Large Span (Application of Aramid Materials)
The distance between high-voltage towers is typically hundreds of meters, and in special terrains like mountainous areas, the span can exceed one thousand meters. The optical cable must be self-supporting without additional support.
- Although traditional metal reinforcing steel wires have high tensile strength, they are extremely heavy (high specific gravity). If used for long-distance spans, they are not only prone to breaking due to gravity and ice accumulation but also impose a huge mechanical load on the high-voltage towers, potentially even causing tower collapse.
- Non-metallic optical cables use high-modulus aramid fibers (Aramid Yarn, such as Kevlar) as tensile strength members. The density of aramid fiber is only one-fifth that of steel wire, but its tensile strength and modulus far exceed that of steel wire. This makes the optical cable not only extremely lightweight but also capable of withstanding extreme tension, wind loads, and ice loads, perfectly adapting to large-span installations.
5. Immunity to Electromagnetic Interference (EMI)
Optical fibers use photons to transmit signals in silica glass ( \text{SiO}_2 ), rather than electrons, inherently possessing resistance to electromagnetic interference. Combined with the all-dielectric (non-metallic) cable body design, the entire optical communication system is completely immune to electromagnetic coupling or electrostatic induction noise even under high-frequency, strong electromagnetic radiation up to hundreds of kilovolts, achieving absolute signal isolation and high-fidelity transmission.
Special Sensing Solutions in High-Voltage, High-Strength Electromagnetic Environments
In the internal state monitoring of smart grids and high-voltage electrical equipment (such as transformer windings, high-voltage busbar joints, reactors, etc.), the same challenges of strong electric fields and electrical insulation are faced.
Beijing Dacheng Yongsheng Technology Co., Ltd. utilizes insulation design principles similar to those of all-dielectric optical cables to develop and produce non-metallic, high-insulation, anti-electromagnetic interference Fiber Bragg Gratings (FBG) temperature sensors that can perform absolute safe, non-energized temperature monitoring in strong electric field environments:
1. OFSCN® Ceramic Encapsulated FBG Temperature Sensor
This sensor uses a metal-free, highly insulating ceramic material for encapsulation, capable of withstanding high voltages and strong electromagnetic environments, preventing high-voltage breakdown and flashover discharge.
OFSCN® Ceramic Encapsulated FBG Temperature Sensor
2. OFSCN® 150°C Low-Voltage Insulated FBG Temperature Sensor
Designed specifically for insulation monitoring in low, medium, and high-voltage electrical environments, it features an all-dielectric sheath and structural encapsulation, containing absolutely no metal, ensuring the safety of electrical isolation.
OFSCN® 150°C Low-Voltage Insulated FBG Temperature Sensor
These all-dielectric and insulated fiber optic sensors share the same physical objective as the non-metallic optical cables used on high-voltage power line poles. While achieving high-precision, rapid physical parameter sensing, they completely eliminate safety threats such as sparks, flashovers, short circuits, and electromagnetic interference within the electrical system.