High voltage cables, also known as HVCs, are the backbone of modern power transmission systems – enabling the safe and efficient delivery of electricity across vast distances and challenging environments.
Whether they’re carrying power from a hydroelectric dam to a bustling city, connecting offshore wind farms to the grid, or supporting high-speed rail networks, HVCs are essential for keeping the world energized and connected.
But have you ever wondered how these robust and specialised cables are made?
The manufacturing process of high voltage cables combines precision engineering, advanced materials, and rigorous testing. This post dives into the step-by-step process of how HVCs are designed, constructed, and prepared, along with an explanation on what they actually are and how they work.
What are high voltage cables?
High voltage cables are specialised power cables designed to transmit electricity at high voltages – typically above 1,000 volts (1 kV). These cables are a critical component in power transmission and distribution systems, connecting power generation facilities, substations, and end-user infrastructure.
Where are high voltage cables used?
High voltage cables are used in various applications where efficient and safe transmission of electricity is required over long distances or under challenging conditions. Below are the primary use cases for HVCs:
1. Power transmission
High voltage cabless are often used in the form of aerial conductors to transmit electricity from power generation stations (e.g., thermal, nuclear, hydroelectric) to substations. They can also be used in urban areas where space is limited, or overhead lines are impractical, and as such, HVCs are laid underground.
2. Power distribution
Everywhere needs power distribution, from substations to industrial facilities, commercial buildings, and residential areas. High voltage cables can support localised high voltage power requirements and connect to step-down transformers for further distribution.
3. Renewable energy systems
High voltage cables are often found to connect and transmit power from renewable energy systems. This can include wind farms, where HVCs connect offshore and onshore wind turbines to the grid, solar power plants, to transmit electricity generated to the main grid or substations through solar cables, and hydroelectric plants, to transmit power generated from remote hydropower stations to cities or industries.
4. Marine Cables
The properties of high voltage cables are often found in marine cables, used to transmit power across bodies of water, such as oceans, seas, rivers, and lakes. This is common when connecting islands to mainland power grids and in cross-border power exchanges between countries.
5. Industrial and commercial applications
High voltage cables are often more common than we think – found everywhere from industrial facilities and data centres to hospitals and critical infrastructure. Whether they need high voltage electricity to power large machinery, high voltage data cables to meet the massive demands of modern data transmission, or simply a stable and uninterrupted supply of power, HVCs will be hidden in plain sight.
6. Urban infrastructure
In metropolitan areas, underground high voltage cables can be used to reduce visual clutter from overhead lines. This can help to support mass transit systems, such as metros and trams, that require high-voltage electricity.
7. High-speed rail and electric transport
Beyond metropolitan areas, HVCs can also supply power to railway systems, including high-speed trains, which operate on high-voltage systems.
8. Grid interconnectors
High voltage cables can be used to create links between regional or national power grids, to allow electricity trade and stabilise energy supply. This often involves marine or underground HVCs for long-distance transmission.
9. Emergency power supply
Temporary or mobile high voltage cables can also be used during emergencies, to quickly restore power after natural disasters or equipment failure.
10. Specialised environments
High voltage cables may also be needed in specialised environments, such as military bases and oil rigs. The military may require high voltage defense cables to power advanced systems and operations in remote locations, whereas oil rigs may have offshore platforms that use HVCs for power supply and transmission.
Components in high voltage cables
Wondering what cables are made of? High voltage cables are designed with multiple layers, to ensure they can safely and efficiently transmit electricity at high voltages. The key components in a HVC are installed in this order:
Conductor → Conductor shield → Insulation → Insulation shield → Metallic screen → Bedding → Armour (if present) → Outer sheath
1. Conductor
The conductor of a high voltage cable is at the very core, and its purpose is to carry the electrical current through the cable. HVC conductors are typically made of copper or aluminium – chosen for their high electrical conductivity – and can be solid or stranded for flexibility and enhanced performance.
2. Conductor shield
The conductor shield goes around the conductor, providing a smooth interface between the conductor and the insulation, reducing electrical stress concentration. Cable shielding made with a semi-conductive material, typically a blend of the conductor and insulation materials used.
3. Insulation
Next is the insulation layer. There are many benefits of wire insulation, however in high voltage cables, it is primarily used to prevent electrical discharge and contain the high voltage within the cable.
Often, insulation is made from either cross-linked polyethylene (XLPE) – for thermal stability in high temperature cables – or ethylene propylene rubber (EPR) – used for flexible cables and harsh environment cables.
4. Insulation shield
Then, the cable is shielded once again with an insulation shield. This works with the conductor shield to create a smooth, uniform electrical field, made of the same materials, and to provide a safe pathway for fault currents to flow to the ground.
5. Metallic screen
High voltage cables also often have a metallic screen, to provide a shield against electromagnetic interference (EMI) and a return path for fault currents – alongside enhancing the cable’s overall mechanical strength and grounding. This can be made with various conductive materials – most commonly copper tape, braided copper, or aluminium.
6. Bedding
To protect the metallic screen from mechanical damage and moisture, a soft protective layer, known as bedding, is wrapped around it. This is often made from PVC or polyethylene.
7. Armour (optional)
For additional mechanical protection and tensile strength, particularly in harsh environments such as underground or underwater cable installations, HVCs can be armoured. This is done by applying steel or aluminium wires or tape around the cable.
8. Outer sheath
Finally, an outer sheath is applied to the outside of the cable – also known as cable jacketing or cable sheathing – which serves as the first line of defence in exposed conditions and protects the cable from environmental factors such as water, chemicals, UV radiation, and physical damage. Cable sheathing is made from durable materials like PVC, polyethylene, or other weather-resistant polymers.
9. Other optional components
Depending on the application of the high voltage cable, some also feature moisture barriers and/or cooling systems. Moisture barriers prevent water ingress in underground and marine cables, whereas cooling systems can help to manage heat in high-capacity installations.
How do high voltage cables work?
High voltage cables work by transmitting electrical energy at high voltages, typically over long distances, whilst ensuring minimal energy loss, electrical safety, and reliability.
Why “high voltage”?
Power is the product of voltage and current. To transmit large amounts of power efficiently, increasing voltage allows the current to be reduced. Lower current reduces resistive losses in the cable, making high-voltage transmission more efficient.
Principles of operation
Electricity flows through the conductor, driven by a potential difference (voltage) between the cable ends – as all cables do. High voltage cables generate strong electric fields when this electricity follows, but their insulation and shielding layers manage these fields to prevent dielectric breakdown. What’s more, as the electricity flows, resistance in the conductor generates heat, however HVCs are designed to manage this heat, either passively (through materials that withstand high temperatures) or actively (with integrated cooling systems).
Installation methods
High voltage cables can work differently, depending on how they are installed – typically overhead, underground or underwater.
1. Overhead HVC cables
For aerial transmission, high voltage cables use minimal insulation and rely on air as the primary insulator.
2. Underground HVC cables
Insulated and sheathed high voltage cables are buried to avoid overhead clutter and ensure safety in urban or environmentally sensitive areas.
3. Marine HVC cables
Specially armoured and insulated for durability, these high voltage cables transmit electricity across oceans and rivers.
How are high voltage cables manufactured?
Unsure about the cable manufacturing process? The manufacturing of high voltage cables is a meticulous process that involves multiple stages, to ensure the cables can handle high electrical stresses, environmental conditions, and long-term operation.
Here’s a detailed explanation of the HVC manufacturing process:
Step 1: Cable design
The first step in manufacturing any type of cable is cable design. There are many steps that go into cable design, including understanding what the cable will be used for and deciding how that fits into the materials and methods used.
Step 2: Material selection
Once the cable design is complete, the cable manufacturer will then select the appropriate materials needed for the cable. This includes the conductor, insulation, shielding, sheathing and armouring (if applicable) materials.
Step 3: Conductor manufacturing
With the correct materials to hand, the conductor can then be manufactured. This will either be done by wire drawing, where the conductor material rods are drawn through dies to achieve the desired diameter, or stranding, where multiple thin wires are twisted or stranded together to form the conductor.
Step 4: Cable extrusion
The next part of this process is cable extrusion.
First, the conductor needs to be shielded. Using a semi-conductive layer, the material is extruded around the conductor.
Then, as part of the above extrusion process, the wire insulation is also extruded onto the conductor – on top of the shielding. For XLPE insulation, the material is chemically or physically cross-linked into the cable.
The final part to the extrusion process is to apply another shielding layer, of the same material as the conductor shielding, over the insulation.
Step 5: Metallic screen and bedding application
Next, the metallic screen – whether it be tape or wires – is applied over the insulation shield. To protect the metallic screen, bedding is applied over the top of it.
Step 6: Outer sheathing
As the final part of the “actual” manufacturing process, the cable sheathing or jacket is applied around the cable. If you need your HVC to be a specific colour, here is where it will be added.
Step 7: Armouring (optional)
If your high voltage cable required additional protection, or is being manufactured for underground or underwater use, you would then apply metal armouring around the cable sheath.
Step 8: Quality control and testing
Once the cable has been manufactured, it needs to be tested. This also ensures that the cable meets international standards such as IEC, IEEE, or local regulations to ensure they are safe, efficient, and reliable.
HVCs typically go through 3 tests to check for quality control: high voltage testing, mechanical testing, and thermal testing.
1. High voltage testing
Here, the HVC undergoes electrical testing, including partial discharge, dielectric strength, and insulation resistance tests, to ensure it meets safety and performance standards.
2. Mechanical testing
This tests the cable for tensile strength, flexibility, and impact resistance.
3. Thermal testing
High voltage cables are subjected to high temperatures, to assess their thermal stability.
Step 9: Final assembly
Finally, now that the cable manufacturing process has completed, and the cables are certified “fit for use”, they are ready to be spooled onto large reels and packaged for delivery.
When it comes to cables, we’re the experts you can trust. To learn more about cable manufacturing and how each different cable works, find more resources and information available on our blog, or get in touch with our helpful team today for tailored advice.