Views: 0 Author: Site Editor Publish Time: 2026-01-30 Origin: Site
What Makes Medium Voltage Submarine Cables Different from Other Types
Medium voltage submarine cables are specially designed for underwater power transmission. Compared with standard land cables, submarine cables must withstand hydrostatic pressure, corrosion, mechanical impact, and long-term exposure to moisture.
MV submarine cables are typically designed in either single-core or three-core construction depending on installation requirements and project conditions.
Key Structural Characteristics
Medium voltage submarine cables usually include the following layers:
Conductor (copper or aluminum, class 2 or compacted conductor per IEC 60228)
Conductor screen
XLPE insulation (water tree retardant type)
Insulation screen
Metallic screen (copper wires or copper tape)
Longitudinal water-blocking layers
Radial water barrier (lead sheath or corrugated aluminum sheath)
Bedding layer
Single or double steel wire armoring
Outer serving layer (PE or PP)
Each layer serves a specific technical purpose, ensuring electrical reliability and mechanical protection under submarine conditions.
Three-Core vs Single-Core Design
Three-core submarine cables are commonly used for medium-voltage three-phase distribution systems. This configuration reduces installation complexity and is suitable for nearshore or shorter route applications.
For higher current ratings or longer transmission distances, single-core submarine cables installed in trefoil formation are often preferred due to better thermal dissipation and reduced electromagnetic interaction.
Insulation Selection
Water tree retardant XLPE is the most commonly used insulation material for MV submarine cables. It offers:
High dielectric strength
Excellent thermal performance
Long service life
Good resistance to water tree aging
EPR insulation may be used where higher flexibility is required, but XLPE remains the dominant choice for most submarine power applications.
Water Protection System
Unlike land cables, submarine cables require multi-layer water protection:
Longitudinal water blocking (water swelling tapes or powder)
Radial water barrier (lead sheath or corrugated aluminum sheath)
Outer serving for additional environmental protection
This structure prevents moisture penetration and ensures long-term operational reliability.
Mechanical Protection
Steel wire armoring provides tensile strength for laying operations and protects against external mechanical damage such as anchors, fishing gear, or seabed abrasion.
Double armoring is often used in shallow water or high-risk zones.
Medium voltage submarine cables primarily use two insulation systems: TR-XLPE (Tree-Retardant Cross-Linked Polyethylene) and EPR (Ethylene Propylene Rubber).
Both materials are suitable for submarine environments when combined with proper water-blocking systems.
Insulation Type | Advantages | Considerations |
TR-XLPE | Low dielectric losses, high dielectric strength, excellent thermal performance, strong resistance to water tree aging | Slightly lower flexibility compared to EPR |
EPR | Higher flexibility, good resistance to mechanical stress, good dielectric performance | Higher dielectric losses compared to XLPE |
In modern MV submarine cable design, TR-XLPE is widely adopted due to its lower dielectric losses and excellent long-term aging performance.
It is important to note that water ingress protection is achieved through dedicated water-blocking systems and metallic sheaths rather than by the insulation material alone.
Conductor Materials
Medium voltage submarine cables can use either copper or aluminum conductors, depending on project requirements.
Copper Conductors
Higher electrical conductivity
Smaller conductor cross-section for same current rating
Higher tensile strength
Suitable for high-current applications
Aluminum Conductors
Lower density (lighter weight)
Cost-effective for long-distance transmission
Commonly used in offshore wind farm export and array cables
The choice between copper and aluminum depends on:
Current rating
Installation conditions
Cable weight limitations
Budget considerations
Project technical specifications
Proper connector design and installation practices ensure reliable performance for both conductor types.
Water-Blocking and Armoring System
Submarine cables require comprehensive water protection to ensure long-term reliability under hydrostatic pressure.
Water protection in MV submarine cables is typically achieved through:
Longitudinal Water Blocking
Prevents water migration along the cable axis in case of sheath damage.
Common methods include:
Water-swellable tapes
Water-blocking powder
Water-swellable yarns
Swelling cords
These materials expand upon contact with water and seal the damaged area.
Radial Water Barrier
Prevents water penetration from outside to inside the cable.
Radial water barriers typically consist of:
Lead sheath
Corrugated aluminum sheath
These metallic layers provide complete radial watertightness and corrosion resistance.
Armoring System
Armoring provides mechanical strength and external protection.
Functions include:
Tensile strength during laying operations
Resistance to seabed abrasion
Protection against fishing activities and anchors
Impact and crush resistance
Armoring types:
Single wire armoring (SWA)
Double wire armoring (DWA)
Double armoring is commonly used in shallow water or high-risk zones.
Medium voltage submarine cables are multi-layer engineered systems. Each layer performs a specific electrical or mechanical function.
Layer | Technical Function |
Conductor | Copper or aluminum conductor (IEC 60228), carries rated current |
Conductor Screen | Semi-conductive layer controlling electric field distribution and eliminating stress concentration |
Insulation | TR-XLPE or EPR insulation providing dielectric strength and voltage withstand capability |
Insulation Screen | Semi-conductive layer ensuring uniform electric field and interface to metallic screen |
Metallic Screen | Copper wires or copper tape providing fault current path and electromagnetic shielding |
Water-Blocking Layer | Prevents longitudinal water migration |
Radial Water Barrier | Lead sheath or corrugated aluminum sheath ensuring radial watertightness |
Bedding Layer | Provides mechanical separation and protection before armoring |
Armoring | Steel wire armoring providing tensile strength and mechanical protection |
Outer Serving | HDPE or PP outer layer for environmental protection |
Submarine cables typically incorporate additional structural and protective layers compared to land cables in order to withstand:
Hydrostatic pressure
Mechanical impact
Seabed abrasion
Installation tensile forces
In some projects, submarine power cables may integrate fiber optic units for communication and monitoring purposes.
Cable outer diameters vary depending on voltage level, conductor size, and armoring type, and may exceed 50 mm for MV applications.
Submarine cables require comprehensive protection systems to ensure long service life in marine environments.
Protective Element | Technical Function |
Insulation System | TR-XLPE or EPR providing dielectric strength and thermal performance |
Metallic Screen | Provides fault current path and electromagnetic shielding |
Longitudinal Water Blocking | Prevents water migration along cable length |
Radial Water Barrier | Lead sheath or corrugated aluminum sheath ensuring radial watertightness |
Bedding Layer | Mechanical separation before armoring |
Armoring | Steel wire armoring providing tensile strength and external mechanical protection |
Outer Serving | HDPE outer layer providing environmental and abrasion protection |
Submarine cable protection is significantly more robust than standard land cable construction due to the harsh marine environment.
Submarine cables are manufactured using controlled extrusion and cross-linking processes to ensure uniform insulation quality.
Factory joints (FJ) or Factory Vulcanized Joints (FVJ) are used to connect long production lengths. These joints maintain:
Electrical integrity
Mechanical strength
Water tightness
Jointing procedures typically include:
Conductor welding
Reconstruction of conductor screen
Re-crosslinking of XLPE insulation
Restoration of insulation screen
Reapplication of metallic sheath and water barriers
Electrical routine testing in accordance with IEC standards
Quality assurance is critical in submarine cable manufacturing. Production follows strict inspection and testing procedures in accordance with IEC standards such as IEC 60502-2 (for MV cables).
Testing typically includes:
Conductor resistance measurement
Partial Discharge (PD) testing
AC voltage withstand testing
Sheath integrity testing
Dimensional inspection
X-ray inspection for welded metallic sheaths or factory joints
Submarine cables undergo more stringent quality controls compared to land cables due to their limited accessibility after installation.
Aspect | Submarine Cables | Land Cables |
Design Environment | Designed for marine and underwater conditions | Designed for terrestrial installation |
Production Process | Includes water-blocking systems, metallic sheaths, heavy armoring | Typically no radial water barrier |
Mechanical Strength | Designed for high tensile loads during laying | Limited tensile requirements |
Installation | Laid by cable-laying vessels with controlled tension | Installed in trenches or ducts |
Armoring | Single or double steel wire armoring depending on seabed conditions | Often unarmored or lightly armored |
Performance Requirements in Submarine Environments
Hydrostatic pressure increases approximately 0.1 MPa per 10 meters of water depth. Submarine cables must maintain structural integrity and electrical performance under these external pressures.
Radial water barriers and robust armoring ensure long-term reliability even at significant depths.
Submarine cables must balance flexibility and mechanical strength to withstand:
Installation bending during laying
Seabed irregularities
Thermal expansion during operation
External mechanical aggression
Proper cable design ensures compliance with minimum bending radius and maximum allowable tensile load requirements.
Marine environments expose cables to:
Saline corrosion
Abrasion from seabed materials
External impact from fishing gear or anchors
HDPE outer serving and corrosion-resistant armoring protect the cable system over long service life.
Corrosion Protection of Submarine Cables
Submarine power cables operate in aggressive marine environments where saltwater, hydrostatic pressure, and mechanical impact can severely affect service life. Therefore, corrosion protection and water blocking design are critical for long-term reliability.
A typical submarine power cable includes the following protective elements:
1. Metallic Water Barrier
Submarine cables are usually equipped with a continuous metallic water barrier, such as:
Lead sheath
Corrugated copper sheath
Corrugated aluminum sheath
This layer provides:
Radial water tightness
Protection against moisture ingress
Mechanical reinforcement
Unlike textile serving layers, the metallic sheath is the primary barrier preventing water penetration into the insulation system.
2. Radial and Longitudinal Water Blocking
To prevent water migration along the cable length in case of external damage, submarine cables incorporate:
Water-swelling tapes
Water-blocking compounds
Longitudinal sealing structures
This ensures that any local damage does not lead to progressive failure along the cable.
3. Outer Sheath
The outer sheath is typically made of high-density polyethylene (HDPE) or similar marine-grade materials. It provides:
Excellent resistance to seawater corrosion
High mechanical strength
Abrasion resistance during laying and seabed contact
Polypropylene yarn serving may be applied as an additional protective layer, but it is not the primary corrosion barrier.
4. Steel Wire Armoring
Galvanized steel wire armoring provides:
Tensile strength for installation
Mechanical protection against impact and fishing activities
Resistance to external mechanical stress
Depending on installation depth and seabed conditions, cables may use:
Single-wire armoring (SWA)
Double-wire armoring (DWA)
In deep-water applications, armor design is optimized to balance weight and tensile performance.
5. Cathodic Protection (Project-Specific)
Cathodic protection systems are generally used for offshore pipelines and large steel structures.
For submarine cables, corrosion resistance is primarily achieved through:
Galvanized armoring
Protective outer sheath
Metallic water barrier
Cathodic protection may be considered in specific project designs, but it is not a standard feature of all submarine cables.
With proper structural design, high-quality materials, and correct installation methods, submarine power cables can achieve a service life of 25–40 years or more in harsh offshore environments.
Submarine Cable Applications
Submarine power cables are used where overhead lines or underground land cables are not feasible.
They are widely applied in:
Offshore wind farm grid connections
Inter-island power transmission
Cross-sea interconnection projects
Offshore oil and gas platforms
Marine infrastructure and subsea facilities
These cables are engineered to operate under:
High hydrostatic pressure
Strong ocean currents
Seabed movement
Long-term saltwater exposure
Proper route survey, burial depth assessment, and protection design are essential to ensure long-term system reliability.
Significance of International Standards Compliance
Compliance with internationally recognized IEC standards ensures that submarine power cables meet strict requirements for electrical performance, mechanical strength, and long-term reliability.
Each standard plays a specific role:
IEC 60228 ensures conductor quality and electrical efficiency.
IEC 60502 / 60840 / 62067 define insulation structure, type testing, and voltage performance requirements.
IEC 60229 guarantees outer sheath integrity and protection against moisture ingress.
IEC 60287 ensures accurate current rating calculations to prevent overheating.
IEC 60853 defines performance under cyclic and emergency loading conditions.
IEC 60092 supports compliance with offshore and marine electrical requirements.
By complying with these standards, submarine cable systems achieve:
Enhanced operational safety
Extended service life
Reduced maintenance costs
Improved project approval and bankability
Reliable performance in harsh marine environments
Submarine cables have more layers than land cables. These layers keep water out and stop sea animals from hurting the cable. They also protect the cable from strong pressure under the sea. Land cables do not need all these layers. Submarine cables use special materials to stop rust and damage.
No, you cannot use regular cables underwater. Regular cables do not block water or have strong armor. They will break fast if put underwater. Always pick cables made for submarine use.
Most submarine cables last between 25 and 40 years. Good installation helps them last longer. Strong materials also make them last more years. You should check the cable often to keep it safe.
Aluminum makes the cable lighter than copper. This helps when putting cables in deep water. Copper is better for carrying electricity, but it is heavier and costs more.
