Cable bridge connects to underground
Cables from a bridge or overhead structure are connected to underground systems using specialized terminations, joints, and transfer stations to ensure safe, insulated, and reliable power transmission.
Transition Components
When a cable bridge connects to an underground system, several key components are involved:
- Cable Terminations: These are used to connect the end of a cable to another element, such as a transformer, switchgear, or the underground network. Terminations can be indoor, outdoor, or separable connectors, depending on exposure to weather and UV radiation .
- Joints (Splices): Joints connect cable sections together. They can be straight (same type of cable), transition (different cable types), or branch joints (to create a link to another cable), .
- Cable Transfer Stations: These are constructed at points where cables enter or exit the ground, allowing for safe transition from overhead or bridge-supported cables to underground conduits .
Cable Structure and Insulation
Underground cables consist of a conductor, an insulating layer, a wire shield, and a cable sheath. The conductor, usually copper for high-voltage applications, carries the current. The insulation, often cross-linked polyethylene (XLPE), prevents electrical leakage. The wire shield manages fault currents and contains the electric field, while the sheath protects against moisture .
Installation Considerations
- Thermal Management: Underground cables generate heat, so spacing, trench design, and sometimes water cooling are used to maintain safe operating temperatures .
- Protection Against Water: Water ingress is a major cause of failure. Accessories and terminations must be sealed properly to prevent electrical breakdown .
- Accessibility for Maintenance: Some joints and terminations are designed to allow external access for monitoring and testing .
Practical Process
- Cable Routing: Cables are brought from the bridge or overhead line to a transfer station.
- Termination Installation: The cable end is fitted with a termination suitable for underground connection.
- Jointing: If the underground cable is delivered in sections, joints are installed to connect the segments.
- Entry into Underground Conduit: The cable is routed into a trench or tunnel, ensuring proper insulation, spacing, and protection.
- Monitoring and Testing: Grounding joints and monitoring stations may be installed to ensure safe operation and detect faults . This system ensures that electrical power can safely transition from elevated structures to underground networks while maintaining reliability, insulation integrity, and protection against environmental hazards.
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