Introduction of Types of Underground Cables
Underground cables are vital in today’s electrical systems. They are the best way to transmit and distribute electricity in crowded or sensitive areas. Unlike overhead lines, underground cables are buried. This protects them from strong winds, lightning, and extreme weather. These hazards shorten the lifespan of power cables. So, underground cables last longer and are more reliable. There are many types of underground cables.
Underground cable connections are vital for public safety. They reduce the risk of accidental contact and electrocution. Also, they stop disruptions from animals or weather. So, they are resilient in bad conditions. High-voltage underground cables reduce transmission losses, which can be high in overhead lines. They also enhance the beauty of modern urban areas. They remove the need for visible poles and wires, which helps maintain the landscape.
These connections are vital in high-reliability, high-safety areas. These include city centers, residential neighborhoods, and industrial zones. Underground cables are weather-resistant and low-maintenance. They are a sustainable, low-visibility power transmission solution.
Classification of Underground Cables
You can classify underground cables by several criteria. They include the number of conductors, voltage rating, construction, insulation, and installation methods. Each types of underground cables highlights traits that make a cable suitable for specific uses and environments.
Classification Based on the Number of Conductors
Single Core Cable:
A single-core cable has a single conductor. It is insulated by layers of suitable materials. It is mainly used in applications needing one conductor, like simple electrical installations. These cables are favored for their simplicity and easy installation. They are ideal where only a few conductors are needed. Single-core cables are often used in underground systems. They provide robust, reliable performance.
Advantages of single-core cables include:
- Simplicity: Easier to install and manage due to the presence of only one conductor.
- Flexibility in Use: Suitable for various applications, including both underground and overhead installations.
- Cost-effective: They are usually cheaper. They use fewer materials than multi-core cables.
Three Core Cable:
A three-core cable contains three separate conductors, each insulated from the others. These cables are used in three-phase power systems. Each conductor carries one of the three phases. They are also used in other applications. These include circuits needing a live, neutral, and earth connection.
Advantages of three-core cables include:
- Efficiency: Ideal for balanced three-phase systems, reducing the need for extra cables.
- Versatility: They work in both low and high-voltage apps. So, they’re suitable for many installations.
- Space-Saving: It combines three conductors in one cable. This reduces the space needed for wiring.
- Applications: Preferred for systems up to 66 kV. For higher voltages, the insulation makes the cable too bulky. Therefore, single-core cables are used instead.
Classification Based on Voltage Rating
The voltage rating of types of underground cables dictates their application in different power systems. Cables are categorized as follows:
Low Tension Cables:
Low Tension (LT) cables are electrical conductors. They operate at low voltages, typically 660 to 1,100 V. These cables are for residential, commercial, and industrial use where lower voltage is needed.
Key characteristics of LT cables include:
- Voltage Rating: LT cables are used for systems with voltages below 1 kV.
- Current Carrying Capacity: These cables can carry high currents. So, they suit various low-voltage electrical systems.
- Short Circuit Rating: LT cables can handle short circuits with high currents, up to 250 °C, for a short time.
High Tension Cables:
HT cables send high-voltage power, usually 11 kV to 33 kV. These cables are vital. They safely carry high electrical energy over long distances. HT cables have thick insulation and conductors. They withstand higher voltages. They are often used in power and industrial applications.
Super Tension Cables
Super Tension Cables can handle voltages up to 33 kV. These cables are used where higher voltages are needed. They are for medium-distance power transmission and distribution. Super Tension Cables have reinforced insulation. It ensures the safe and efficient transmission of electricity at high voltages.
Super Tension Cables are common in underground and overhead transmission systems. They help to cut energy loss and ensure stable power delivery.
Extra High Tension Cables:
EHT Cables send power at high voltages, from 66 kV to 220 kV. These cables are for long-distance power transmission. They need strong insulation and construction to handle high voltages. This ensures safe and efficient power delivery.
EHT cables are vital in the power transmission network. They distribute power over long distances, cut energy loss, and stabilize the grid.
Extra Super Voltage Cables:
ESV Cables are for very high voltage use, above 132 kV. These cables are vital for long-distance power transmission. Efficiency and reliability are key. They are built to handle very high voltages. They connect major power generation sources with vast distribution networks.
These cables must have advanced insulation and construction. They are to be safe and perform well under high voltage. They often send electricity from power plants to substations.
Classification Based on Cable Construction
Types of underground cables are affected by their construction. It impacts performance, reliability, and their use in different environments. Common construction types of underground cables include:
Belted Cables:
- Construction: Three conductors are bunched together. An insulating paper belt wraps them. The gaps between the conductors are filled with fibrous materials, like jute or hessian.
- Limitations: They degrade over time. So, they are unsuitable for voltages above 11 kV due to tangential electric stresses.
Screened Cables:
- H-Type Cables: M. Hochstadter introduced these cables. They have individually insulated cores, covered by a metallic screen. The screens are then bundled and surrounded by a lead sheath. This provides excellent electric stress distribution and heat dissipation.
- L. Type Cables: Like H-type cables but with individual lead sheaths for each core. This eliminates the need for a sheath. This design minimizes core-to-core breakdowns and improves flexibility.
- S.L. Type Cables: A mix of H-type and S.L. type cables. Each core is insulated and has a separate lead sheath. This boosts reliability.
Pressure Cables:
- Oil-Filled Cables: For voltages above 66 kV, these cables use pressurized, circulating oil to prevent voids and insulate. The oil also helps in dissipating heat effectively.
- Gas-Filled Cables: They use pressurized gas, usually dry nitrogen, to cool and insulate the cables. These cables can handle higher voltages and currents. But they are more costly to install and maintain.
Classification Based on Insulation Type
The insulation in the types of underground cables is critical to their performance. It must resist high temperatures and have strong dielectric strength. Common insulation materials include:
| Insulation Material | Max. Operating Temperature |
|---|---|
| PVC Type A | 75°C |
| PVC Type B | 85°C |
| PVC Type C | 85°C |
| XLPE | 90°C |
| Rubber | 90°C |
| Rubber (EPR, Silicon) | 150°C |
Rubber Insulation:
- Common in flexible cables and those requiring high-temperature resistance, such as silicone-insulated cables.
PVC Insulation:
- Widely used due to its durability, chemical resistance, and ease of installation. Variants like Type B and C resist higher temperatures. They suit more demanding applications.
XLPE Insulation:
- Offers superior electrical properties and high-temperature resistance, making it ideal for high-voltage applications.
Installation Practices for Underground Cables
We must install underground cables. They will protect our electrical infrastructure from damage, weather, and other environmental factors. Common installation techniques include direct burying, duct installation, and tunneling. Each has unique uses and benefits.
Direct Burying
Direct burying is a cost-effective and straightforward method of cable installation. In this process:
A trench is dug, typically around 1.5 meters deep and 0.45 meters wide, depending on the required depth and location.
A layer of sand is laid at the bottom to protect the cables from stones and moisture.
The cable is placed and covered with sand. Then, a warning tape is added above the cable to prevent accidental digging.
This method is often used in areas with minimal external threats, such as rural or suburban locations.
Duct Installation
Duct installation involves laying cables within protective ducts or conduits. The procedure includes:
Installing protective ducts of PVC, concrete, or steel in pre-dug trenches adds security. It also allows for easier cable replacement or repair.
It is important to place the cables in these ducts and seal them. This will prevent water and other environmental hazards from getting in.
This method is useful in urban areas with frequent digging. It allows for easy cable access without needing to dig up entire sections.
Tunneling
In densely populated or environmentally sensitive areas, tunneling is a preferred technique. This process requires:
Creating a dedicated tunnel underground that houses various utility lines, including high-voltage cables.
The tunnel must be safe. It needs ventilation, drainage, and access points for maintenance.
Tunneling is very safe. It is best for areas where urban development may block other methods.
Safety Guidelines for High-Voltage Installations
When installing high-voltage underground cables, several safety guidelines must be followed. They protect workers and the infrastructure. Key safety considerations include:
PPE: Workers must use gloves, safety glasses, and insulated tools to reduce the risk of electric shock.
Grounding: Properly ground cables and equipment to avoid static buildup and accidental discharge during installation.
Testing and Inspection: Inspect regularly during and after installation. This is to ensure that safety standards are met and that the cables are undamaged.
Clearance: Keep safe distances from other utilities. Ensure clearances are adequate to reduce the risk of damage or interference with other systems.
Advantages and Disadvantages of Underground Cables
Underground cables are better than overhead lines. They need less maintenance and are more durable. However, they come with specific drawbacks that can make installation and repairs challenging. Here’s an in-depth look at both the benefits and drawbacks.
Benefits of Underground Cables
Reduced Maintenance: Underground cables generally require much less maintenance than overhead lines. Being buried protects them from damage, like falling tree branches. So, fewer inspections and repairs are needed.
Resistance to Weather: Underground cables are below ground. So, they resist weather like storms, high winds, and lightning. This makes them a more reliable option for a continuous power supply in areas prone to severe weather.
Aesthetic Appeal: Underground cables are invisible, unlike overhead power lines. They reduce visual clutter and improve the look of residential and urban areas. This benefit is particularly valuable in scenic or historic locations where preserving the view is a priority.
Drawbacks of Underground Cables
High Installation Cost: One of the main drawbacks of underground cables is the high installation cost. Burying cables requires specialized equipment, planning, and skilled labor. This raises the cost compared to overhead lines.
Difficulty in Fault Detection: When faults occur, it is complex and time-consuming to find issues in underground cables. Unlike overhead lines, faults in underground systems are harder to find. They require specific equipment to locate issues, which takes longer to repair.
Complex Repairs: Repairing underground cables is often challenging due to their buried nature. Accessing cables requires excavation. This can be disruptive and costly, especially in cities with other buried infrastructure. Additionally, complex repairs may increase the overall downtime and labor requirements, affecting reliability.
Common Applications and Use Cases of Underground Cables
Underground cables are a reliable, efficient way to transmit electricity in various sectors. Below are key applications in residential, commercial, industrial, and public infrastructure settings:
Residential Areas
In crowded cities, underground power systems keep the landscape neat. Underground cables reduce visual clutter and outage risks. Severe weather and disturbances often affect overhead power lines. This setup also contributes to higher levels of safety and reliability for urban residents.
Commercial and Industrial Facilities
For large-scale operations, underground power supply provides a stable and protected electrical system. In places like factories, data centers, and warehouses, power must be continuous and uninterrupted. Underground cables reduce exposure to damaging external factors. These include corrosion and interference from nearby machines. So, facilities benefit from using them. This app helps keep a clean, organized space. It’s critical for efficiency and safety.
Public Infrastructure
In vital public infrastructure, like airports and hospitals, a reliable underground power supply is key. These facilities can’t afford frequent power outages. So, underground cables are ideal. This method better protects infrastructure from hazards and disruptions. It ensures public safety and maintains critical services. Airports use these systems to power various components. They include runway lighting and communication systems. This boosts efficiency and security.
Conclusion:
Types of underground cables are better than overhead lines. They are more reliable and resilient to weather. This is important in densely populated, high-demand areas. These systems have several types of underground cables for different voltages and uses. They meet both residential and industrial needs. As power demands rise, advanced types of underground cables can help. They cut transmission losses and ensure a constant power flow, even in tough conditions. They support sustainable energy delivery.
The future of underground power connections is in new tech. It promises higher efficiency, durability, and less maintenance. New cable-laying and insulation technologies improve power systems. They boost their longevity and stability. This aligns with energy transition goals and urban infrastructure needs. Using advanced types of underground cables in urban planning is vital. They will help build a strong power grid. It must meet rising demand and cut the environmental impact of power distribution.
