Overhead Transmission vs Underground Transmission | difference between Overhead transmission and Underground transmission

This page compares Overhead Transmission vs Underground Transmission and mentions difference between Overhead transmission system and Underground transmission system.

The electrical power system is categorized into two parts transmission system and distribution system.
• Transmission System: The transmission lines of it connect electric plants to substations and other power plants and other utilities at higher voltages. It carries electricity at high voltages (69KV) and carry electric power over longer distances from central station to main substations.
• Distribution System: It distributes electricity to each of the customer premises, businesses and industrial plants ar low voltage ratings. It carries electricity at low voltages (12 KV to 44 KV). It is used to distribute power from high voltage transmission systems to end customers or subscribers.

Underground Transmission System

Underground Transmission System

From above discussion, Underground transmission lines are less common while underground distribution lines are more common. In common terms, the laying of cables below the earth surface for purpose of transmission of electric power is known as underground transmission system. This is depicted in the figure-1. They are typically 3-5 feet below the ground.

Following are the characteristics or features of Underground Transmission System.
• It is generally used or preferred in densely populated urban areas where sufficient right of way is not available to install transmission lines.
• Space for laying cables to be dug initially.
• Dewatering is needed in wet areas before construction.
• This system has significant impact on surrounding properties.
• The system requires longer construction time frame.
• Cleaning of equipments is essential in vaults.
• Though there are few outages compare to overhead system, if is difficult and time consuming maintenance tasks in case of failure.
• Underground transmission costs are higher (8 to 10 times) compare to Overhead transmission.
• Typical life span of underground transmission system is less (about one half) compare to overhead transmission system.
• It provides better protection from storm or wind damage and improves reliability of power supply.
• 4-cable system needed to enhance reliability of the system further.
• The underground lines are installed closer as they are insulated with plastic, rubber or oil.
• Few EMF (Electro Magnetic Field) issues are observed in underground cabling.

Overhead Transmission System

Overhead Transmission System

In common terms, the laying of cables above the earth surface for purpose of transmission of electric power is known as Overhead transmission system. This is depicted in the figure-2. It is installed in the areas where wider right of way is available. The entire structures are install much above the ground.

Following are the characteristics or features of Overhead Transmission System.
• It is easy to install Overhead cables in this transmission system type.
• It is easier to locate the damage and repair the system.
• It has lower system loss compare to underground system.
• It has increased life expectancy.
• The system is easy to maintain.
• It has higher likelihood of accident or attack.
• Environment concerns are to be handled at appropriate situations to be safe.
• Overhead lines are installed further apart as air is used as an insulator.

• EMF (Electro Magnetic Field) or corona issues are serious concerns in Overhead transmission lines.

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Refer following links to know more on various transmission systems.
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