220kV power line optical cable connection method

Optical cables on 220kV power lines are typically connected using OPGW installation techniques involving tension clamps, insulated supports, splicing, and grounding according to ITU-T standards.

Overview of OPGW Installation

Optical Ground Wire (OPGW) cables serve a dual purpose: they act as a ground wire for high-voltage lines and carry optical fibers for communication. These cables are installed along the tops of transmission towers and require careful handling due to their mechanical and electrical functions .

Mechanical Connection Methods

1. Tension and Dead-End Clamps: OPGW cables are secured at tower heads using tension clamps or dead-end fittings. These clamps provide a uniform grip on the cable, preventing distortion and ensuring mechanical stability under wind and ice loads . Preformed wire grips are commonly used for both small and large spans, providing corrosion resistance and high tensile strength.
2. Insulated Supports: On tangent and strain towers, OPGW cables are often insulated from the tower structure using insulator assemblies. This prevents unwanted current flow through the cable while maintaining mechanical support .
3. Transposition and Segment Insulation: In some 220kV lines, OPGW segments are insulated at specific points with single-point grounding and middle transposition to reduce induced currents and energy losses. This method also minimizes lightning stroke risks and improves cable running conditions .

Splicing and Optical Fiber Connection

1. Fusion Splicing: Optical fibers within the OPGW are typically joined using fusion splicing, which provides low-loss, permanent connections. Splicing is performed in controlled environments, often in junction boxes or splice enclosures mounted on towers .
2. Staggered and Fixture Joints: For multi-conductor cables or branch connections, staggered splices or fixture joints are used to prevent bulkiness and maintain mechanical integrity. Knotted tap joints or wire nut splices may be applied for smaller branch connections .

Vibration and Stress Management

1. Spiral Vibration Dampers: These are installed on spans to reduce conductor vibrations caused by wind, which protects both the mechanical and optical integrity of the cable .
2. Suspension Clamps: Aluminum or compatible material suspension clamps are used to reduce static and dynamic stresses at support points, ensuring the cable remains secure and undamaged .

Grounding Considerations

OPGW cables are grounded at specific points to ensure safety and proper operation. In some designs, the cable is grounded at transformer substations or at tower points with higher short-circuit currents. Proper grounding reduces induced voltages and energy losses along the line .

Standards and Guidelines

Installation should follow ITU-T L.151 recommendations and IEC 60794-4-10 standards, which cover cable characteristics, handling, stringing, splicing, and grounding procedures. These standards ensure both electrical performance and mechanical reliability .

Summary

The connection of optical cables on 220kV power lines involves a combination of mechanical clamping, insulated supports, splicing, vibration damping, and strategic grounding. Following international standards and using proper installation hardware ensures the cable performs reliably as both a ground wire and a communication medium. Proper handling, tensioning, and splicing are critical to maintain the integrity of the optical fibers and the safety of the high-voltage system.