What Are Submarine Power Cables?

Submarine power cables are specialized electrical cables designed to transmit high-voltage electricity across bodies of water, such as oceans, seas, straits, or large lakes, typically beneath the water’s surface. Unlike terrestrial cables, they are engineered to withstand harsh marine environments, including high pressure, seawater corrosion, and mechanical stresses from currents or anchors. Used for voltages from 35 kV to 500 kV or higher, these cables connect offshore renewable energy sources, power remote islands, and link national power grids for international energy trading. Their robust design, incorporating materials like cross-linked polyethylene (XLPE) insulation and steel armoring, ensures reliability over a typical 25-year service life, aligning with the durability of marine cables discussed previously.

Construction of Submarine Power Cables

Submarine power cables are complex assemblies built to endure extreme underwater conditions. Their construction includes:

• Conductor: Typically copper or aluminum for high conductivity. Copper is preferred for its efficiency, while aluminum is lighter and increasingly used for cost savings. Conductors are stranded for flexibility and corrosion resistance.
• Insulation: Materials like XLPE, polyethylene (PE), or paper-impregnated insulation (for oil-filled or mass-impregnated cables) prevent current leakage. XLPE is common for voltages up to 420 kV due to its thermal stability and low power loss, similar to MV cables discussed earlier.
• Shielding: Conductor and insulation shields (e.g., metallic foil or braid) reduce electromagnetic interference (EMI) and ensure even electric field distribution, especially in AC cables.
• Waterproofing: Lead sheathing or polyethylene layers prevent water ingress, critical for long-term immersion in high-salinity seawater.
• Armoring: Steel wires or tapes protect against mechanical damage from anchors, fishing trawls, or seabed abrasion. Non-magnetic armoring minimizes magnetic field losses in AC cables.
• Outer Jacket: A durable polyethylene or PVC sheath resists corrosion, UV radiation, and biological fouling.
• Optical Fibers: Modern cables often integrate optical fibers for data transmission or temperature monitoring, enhancing operational efficiency.

This layered design, resembling a coaxial cable, ensures durability and performance in depths up to 8,000 meters, contrasting with the simpler construction of multi-conductor or multi-pair cables.

Types of Submarine Power Cables

Submarine power cables are categorized by current type and core configuration, each suited to specific applications:

• Alternating Current (AC) Cables:
  • Three-Core AC Cables: Contain three insulated conductors in a single cable, ideal for lower-power applications like nearshore wind farms. Common for voltages up to 220 kV.
  • Single-Core AC Cables: Used in sets of three (one per phase) for high-power transmission. A fourth spare cable is often included for redundancy. Suitable for longer distances but limited to under 100 km due to capacitive losses.
• Direct Current (DC) Cables:
  • High-Voltage Direct Current (HVDC) Cables: Preferred for long distances (over 100 km) due to lower resistive and reactive losses. Used in projects like the 580-km NorNed cable. HVDC cables support voltages up to 500 kV and capacities like 1 GW in the Black Sea cable.
• Specialized Cables:
  • Oil-Filled Cables: Use low-pressure oil for insulation, suitable for high-voltage applications but pose environmental risks if damaged.
  • Mass-Impregnated Cables: Feature paper insulation with viscous compounds, reliable for deep-sea HVDC systems without oil leakage risks.

AC cables are cost-effective for shorter distances, while HVDC cables excel in long-distance, high-capacity transmission, similar to the specialized roles of LSOH or Teflon cables in other contexts.

Applications of Submarine Power Cables

Submarine power cables serve critical roles in global energy systems:

• Offshore Renewable Energy: Connect offshore wind farms, tidal, or wave energy facilities to onshore grids. For example, the London Array wind farm uses AC cables to transmit power from turbines to substations.
• Interconnectors: Link national power grids for energy trading and supply stability. The NorNed cable (700 MW) connects Norway and the Netherlands, while the planned Black Sea cable (1 GW) will transfer green energy from Azerbaijan to the EU.
• Remote Power Supply: Deliver electricity to islands or coastal communities without local generation, replacing inefficient diesel generators. Examples include cables powering islands in the St. Lawrence River.
• Offshore Platforms: Supply power to oil, gas, or ocean science observatories, requiring robust cables like marine-grade wires discussed previously.

These applications highlight the cables’ role in renewable energy integration and global energy security, akin to the versatility of custom cables.

Installation Process

Installing submarine power cables is a complex process requiring specialized equipment and planning:

• Pre-Laying Survey: Underwater detectors map seabed topography, currents, and obstacles to determine the safest cable path.
• Cable Design: Engineers select insulation (e.g., XLPE for corrosion resistance) and armoring based on water depth and environmental factors.
• Laying Process: Cable-laying vessels equipped with dynamic positioning (DP) systems deploy cables, often burying them 1–2 meters under the seabed in shallow waters (up to 2,000 meters) to protect against anchors or fishing. In deep waters, cables rest on the ocean floor.
• Jointing and Termination: Cables are spliced with water-tight joints and connected to onshore or offshore substations, ensuring seamless power transfer.
• Post-Installation Testing: Continuity, insulation resistance, and voltage tests verify performance before commissioning.

The process demands precision to avoid damage, similar to the careful installation of ABC or photovoltaic cables, with a focus on environmental and mechanical challenges.

Environmental and Maintenance Considerations

Submarine power cables face unique environmental and maintenance challenges:

• Environmental Impact: Cables produce electromagnetic fields (EMFs) that may affect marine species’ migration, though burial mitigates exposure. Oil-filled cables risk leaks (e.g., up to 2,500 gallons of dielectric fluid), posing environmental hazards if damaged. Modern XLPE cables are inert and safer.
• Corrosion and Durability: Long-term exposure to seawater requires corrosion-resistant materials like tinned copper and polyethylene, similar to marine-grade wires.
• Maintenance: Damage from anchors or fishing trawls requires costly repairs using remotely operated vehicles (ROVs) or cable ships. A typical cable lifespan is 25 years, but economic obsolescence may lead to earlier retirement.
• Regulatory Compliance: Installations must adhere to standards like those from the International Submarine Cable Protection Committee, ensuring minimal impact on marine ecosystems and navigation.

These considerations emphasize the need for robust design and careful monitoring, aligning with the safety focus of LSOH or mineral-insulated cables.

AC vs. DC Submarine Power Cables Comparison Table

Choosing between AC and DC submarine power cables depends on distance, power capacity, and cost. The table below compares their key attributes:

Note: Consult NEC or international standards for project-specific requirements.

Tips for Designing and Selecting Submarine Power Cables

Selecting submarine power cables requires careful planning to ensure performance and safety:

• Assess Distance and Power Needs: Use AC cables for distances under 100 km (e.g., nearshore wind farms) and HVDC for longer spans (e.g., 580-km NorNed cable).
• Choose Materials: Select XLPE insulation for environmental safety and copper conductors for efficiency, similar to preferences in custom cables.
• Consider Environmental Conditions: Specify armoring and waterproofing for deep-sea or high-current areas, akin to PUR’s durability in harsh environments.
• Plan for Redundancy: Include spare cables (e.g., a fourth single-core AC cable) to ensure reliability if damage occurs.
• Verify Compliance: Ensure cables meet UL, IEC, or ICPC standards for safety and environmental impact, especially in regulated marine zones.
• Use Simulation Tools: Employ numerical modeling (e.g., EMS AC Electric solver) to optimize cable design and minimize EMF exposure.
• Engage Experts: Consult marine engineers and licensed electricians for surveys, installation, and maintenance to navigate complex seabed conditions.

These steps ensure cables meet project demands while minimizing risks, similar to selecting multi-conductor or multi-pair cables.

Conclusion

Submarine power cables are vital for global energy transmission, enabling offshore renewable energy integration, inter-country power sharing, and remote power supply. Constructed with robust materials like XLPE insulation, copper conductors, and steel armoring, they withstand harsh marine environments for up to 25 years. Available as AC (three-core or single-core) or HVDC cables, they cater to diverse applications, from nearshore wind farms to long-distance interconnectors like the Black Sea cable. Installation requires meticulous planning, including seabed surveys and specialized vessels, while environmental considerations like EMF and oil leakage risks demand careful design. By selecting appropriate cable types, materials, and installation methods, and consulting professionals, stakeholders can ensure reliable, safe, and efficient power transmission across seas, building on the precision of custom cables and the durability of marine-grade wires.