Introduction: Replacing an aging overhead ground wire with OPGW cable is a mechanical and communications upgrade that starts at the tower, not at the fiber count.
Grid modernization teams often inherit a shield wire that has spent decades at the top of a transmission line. It may still look intact from the ground, but corrosion, vibration fatigue, lightning damage, and loose strands can reduce its ability to carry fault current and protect the phase conductors. When the same line also needs a communication path for SCADA, teleprotection, or substation links, replacing the old ground wire with optical ground wire (OPGW) cable solves two problems in one asset. The difficult part is not choosing 24 fibers. The difficult part is matching the new cable to the existing towers, ground wire sag, tension limits, and stringing conditions without creating a clearance or loading problem.
Why aging ground wires are replaced with OPGW cable instead of a separate fiber line
An aging ground wire is replaced because it is no longer a reliable part of the transmission line’s lightning and fault-current path. Steel shield wires lose strength and conductivity over time through atmospheric corrosion, vibration fatigue at clamps, and lightning arc damage. A visual inspection may show rust or broken outer strands, while the real concern is the loss of mechanical margin and current-carrying capacity. If the utility replaces it with another plain ground wire, the line regains protection but gains no communication. A separate fiber line would require its own route, supports, attachments, and inspection plan, adding another infrastructure system along the same corridor. OPGW cable changes that equation because it occupies the existing ground wire position. The cable is a metallic composite: a metallic loose-tube optical unit holds the fibers, and aluminum-clad steel and aluminum alloy stranded wires form the outer strength and conduction layers. That construction lets the cable act as the overhead ground wire while carrying single-mode fibers inside the same package. For grid modernization work, a 24-core G. 652D OPGW cable provides a practical fiber count for substation links, teleprotection channels, and smart-grid communication without turning the ground wire into a phase conductor. The replacement sequence is straightforward in concept: survey the old ground wire, compare diameter, sag, tension, and tower clearances, design the OPGW cross-section, then plan stringing and fiber splicing. The fiber count is the easy part; mechanical compatibility is what decides whether the replacement works.
How existing tower loads and ground wire sag shape mechanical matching during replacement
Existing towers were designed around a specific ground wire diameter, unit weight, everyday tension, maximum tension, and sag profile. A new OPGW cable rarely matches all those values by accident. It may be heavier or lighter, stiffer or more flexible, and different in thermal expansion. Tower load is affected in several directions: vertical load at the ground wire attachment, transverse load during wind, longitudinal load from unbalanced tension, and clearance between the ground wire and phase conductors. If the OPGW is installed too tight, tower members and foundations may see higher loads than the original design intended. If it is too loose, sag increases and clearance to the phase conductors or ground may shrink. Both outcomes matter on a high voltage line. Ground wire sag is therefore the central mechanical check in a replacement. The design team compares the old ground wire sag in the ruling span with the proposed OPGW sag at everyday tension and maximum working tension. They also review short-circuit capacity because a fault current heats the cable and can change sag after the event. The outer aluminum-clad steel and aluminum alloy strands must provide the required tensile strength and fault-current capacity, while the metallic loose-tube optical unit protects the G. 652D fibers from radial pressure and moisture. A fiber optic ground wire manufacturer can customize span, RTS, short-circuit capacity, and drum length, but those values follow the project inputs. The old ground wire diameter, sag, tension, and tower clearances must be checked before any replacement design is frozen. The matching process also affects hardware. Suspension clamps, tension clamps, armor rods, and vibration dampers must fit the new OPGW diameter and grip the cable without crushing the optical unit. If the fittings are chosen only by nominal size, field installation can create slip, concentrated stress, or fiber attenuation. This is why the mechanical review comes before the communication review. The communication upgrade is valuable, but it only works if the cable survives tension stringing and years of wind and fault events on the existing tower line.
How fiber routing and tension stringing shape the replacement work
Fiber routing and stringing are not separate from the mechanical design; they are the field expression of it. OPGW is installed by tension stringing, where the cable is pulled through sheaves under controlled tension and then sagged to the design value. The fibers inside the metallic loose tube are protected during this process, but only if pulling tension, bend radius, sheave geometry, and drum handling stay within limits. The final splice locations also depend on drum length and access. A replacement plan that ignores these details can produce a mechanically acceptable cable with unacceptable fiber losses.
1. Tension Stringing Limits Define How the New OPGW Is Pulled
Tension stringing sets the pulling tension, back tension, and speed used to move the OPGW from the drum, through stringing sheaves, and across each span. IEEE 1812 provides useful background on stringing methods, pulling equipment, and bend radius rules for overhead conductors and OPGW. The practical point for grid modernization staff is that the cable cannot be dragged over rough surfaces or pulled over sheaves that are too small. Excessive tension can stretch the metallic strands and stress the optical unit; a sharp bend can force the fibers against the tube wall. The stringing plan should define pulling grips, running boards, sheave groove size, and tension limits for each span. After the pull, the crew tensions the OPGW to the design sag and installs dampers where vibration risk is high. The fiber link is only as reliable as the stringing control behind it.
2. Bend Radius and Drum Handling Affect Field Splice Placement
Drum length affects how many field splices are needed and where they can be placed. A longer drum reduces splice count but creates a heavier reel that is harder to transport and handle on uneven terrain. A shorter drum is easier to move but adds splice closures, which must be accessible and weatherproof. Bend radius matters at the reel, during payout, through sheaves, and inside the splice box. The 24 G. 652D fibers need slack and orderly routing in the splice tray so that closure assembly does not create microbends. Field splices are usually placed at tension towers or other accessible points rather than mid-span. After splicing, optical time-domain reflectometer testing confirms attenuation and splice quality. Drum length, bend radius, and splice placement are therefore part of the same replacement sequence, not afterthoughts.
Conclusion
Replacing an aging overhead ground wire with OPGW cable works best when the project follows the physical order of the line. First, confirm why the old ground wire needs replacement and whether the communication upgrade justifies a combined asset. Next, compare the existing tower loads, ground wire sag, tension, and clearances with the proposed OPGW design. Then plan tension stringing, drum length, bend radius, and field splice locations around the cable’s mechanical limits. A 24-core G. 652D OPGW cable with a metallic loose-tube optical unit and aluminum-clad steel and aluminum alloy strands can serve both protection and communication functions, but span, RTS, short-circuit capacity, and drum length remain project-specific. For teams reviewing replacement options, JIQIAN Fiber Optic Cable’s 24-core G. 652D OPGW product data can serve as a useful reference for the parameters that must be matched before construction begins.
FAQ
Q：Why replace an aging overhead ground wire with OPGW cable instead of installing a separate fiber line?
A：An aging ground wire already needs replacement to restore lightning protection and fault-current capability. Using OPGW cable in the same position adds fiber communication without building a separate fiber route, separate supports, or a second inspection system. The line gets a renewed ground wire and a utility communications path in one asset, provided the OPGW’s diameter, sag, tension, and tower loading match the existing structures.
Q：How does ground wire sag affect OPGW replacement on an existing tower?
A：Ground wire sag controls clearance to phase conductors and ground, and it reflects the tension placed on the tower. A replacement OPGW that sags more than the old ground wire may reduce clearance; one that is pulled too tight may increase tower loads and vibration risk. The design comparison should use the ruling span, everyday tension, maximum working tension, and short-circuit heating effects to keep the new sag within acceptable limits.
Q：What cable features matter most when replacing an old ground wire on a high voltage line?
A：The most important features are diameter, unit weight, rated tensile strength, everyday and maximum tension, short-circuit capacity, and fiber protection. A metallic loose-tube optical unit with 24 G. 652D fibers, plus aluminum-clad steel and aluminum alloy stranded wires, gives the cable its ground wire and communication roles. Span, RTS, short-circuit capacity, and drum length should be customized to the actual line and tower conditions.
Sources / References
G.652: Characteristics of a single-mode optical fibre and cable
Related Examples
OPGW 24-Core G652D Fiber Optic Ground Wire for Overhead Transmission Lines
Comments
Post a Comment