Overhead vs. Underground Transmission: A Detailed Comparison

This article compares overhead and underground transmission systems, highlighting their key differences. The electrical power system consists of two main parts: the transmission system and the distribution system.

• Transmission System: Connects electric plants to substations, other power plants, and utilities at higher voltages (typically 69kV and above). It’s responsible for carrying electricity over long distances from central stations to main substations.
• Distribution System: Distributes electricity to customer premises, businesses, and industrial plants at lower voltage ratings (usually 12kV to 44kV). It delivers power from high-voltage transmission systems to end consumers.

Generally, underground transmission lines are less common than underground distribution lines.

Underground Transmission Systems

Underground transmission systems involve laying cables below the earth’s surface for electric power transmission. These cables are typically buried 3-5 feet deep.

Underground Transmission System

Here are the characteristics of underground transmission systems:

• Urban Areas: Preferred in densely populated urban areas where there isn’t enough space to install overhead lines.
• Installation: Requires digging to lay cables.
• Dewatering: Necessary in wet areas before construction.
• Environmental Impact: Significant impact on surrounding properties during construction.
• Construction Time: Longer construction timeframe.
• Maintenance: Cleaning of equipment is essential in vaults.
• Outages and Maintenance: Fewer outages compared to overhead systems, but repairs are more difficult and time-consuming in case of failure.
• Cost: Higher costs (8 to 10 times) compared to overhead transmission.
• Lifespan: Typically shorter lifespan (about half) compared to overhead transmission systems.
• Protection: Better protection from storms and wind damage, improving power supply reliability.
• Redundancy: 4-cable systems are often used to enhance system reliability.
• Proximity: Underground lines can be installed closer together because they are insulated with plastic, rubber, or oil.
• EMF: Fewer EMF (Electromagnetic Field) issues observed compared to overhead lines.

Overhead Transmission Systems

Overhead transmission systems involve laying cables above the earth’s surface for electric power transmission.

Overhead Transmission System

Here are the characteristics of overhead transmission systems:

• Installation Areas: Installed in areas where wider right-of-way is available.
• Installation: Easier to install cables.
• Maintenance: Easier to locate damage and repair the system.
• Losses: Lower system loss compared to underground systems.
• Lifespan: Increased life expectancy.
• Maintenance: Easy to maintain.
• Safety: Higher likelihood of accidents or attacks.
• Environment: Environmental concerns need to be addressed to ensure safety.
• Spacing: Overhead lines are installed further apart as air is used as an insulator.
• EMF/Corona: EMF (Electromagnetic Field) or corona issues are serious concerns.