What is the main drawback of the underground transmission system compared to the overhead transmission system?  

Explanation:

Drawback of Underground Transmission System

Statement: What is the main drawback of the underground transmission system compared to the overhead transmission system?

Correct Option: 2) Heavy initial cost

Detailed Solution:

The underground transmission system and overhead transmission system are two distinct types of power transmission systems used to transfer electrical energy over long distances. While underground transmission systems offer several advantages, such as reduced visual impact, minimal exposure to atmospheric hazards, and enhanced safety, they also come with significant challenges. Among these, the heavy initial cost is the primary drawback when compared to overhead transmission systems.

Let us delve deeper into the reasons why heavy initial cost is the main drawback of underground transmission systems:

1. Cost of Installation:

• Underground transmission systems involve extensive excavation, trenching, and preparation of the ground to lay cables. These processes require advanced machinery and skilled labor, resulting in high installation costs.
• Overhead transmission systems, on the other hand, involve erecting poles or towers and stringing cables, which is relatively simpler and less expensive.

2. Cable Material:

• The cables used in underground systems are more complex and expensive compared to those used in overhead systems. They need to be insulated to withstand high voltages, protected against moisture, and designed to dissipate heat effectively.
• Specialized materials, such as XLPE (Cross-Linked Polyethylene) or oil-filled cables, are often used, which significantly increases the cost.

3. Additional Infrastructure:

• Underground systems require ancillary infrastructure, such as cooling systems, jointing bays, and manholes, to ensure proper operation and maintenance.
• These additional components add to the overall cost of the system.

4. Maintenance and Repair:

• While underground systems are less prone to external damage, any fault in the system is challenging to locate and repair. Specialized equipment and expertise are required, resulting in higher maintenance costs over time.
• In contrast, faults in overhead systems are easier to detect and repair, leading to lower maintenance costs.

5. Longevity and Upgrades:

• Underground systems have a longer lifespan compared to overhead systems, but this comes at a higher initial investment.
• Upgrading underground systems to accommodate higher loads or new technologies is more complex and costly compared to overhead systems.

Conclusion:

The heavy initial cost of underground transmission systems is their most significant drawback when compared to overhead transmission systems. While underground systems provide benefits such as improved reliability and aesthetics, their high cost often limits their widespread adoption. This factor must be carefully considered during the planning and implementation of power transmission projects.

Important Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Exposure to lightning

This option is incorrect because underground transmission systems are not exposed to atmospheric hazards such as lightning. Overhead systems are prone to lightning strikes due to their elevated position, but underground systems are safely insulated and buried, eliminating this concern.

Option 3: Exposure to atmospheric hazards such as smoke, ice, wind

This option is also incorrect. Underground systems are protected from atmospheric hazards like smoke, ice, and wind because they are buried beneath the ground. Overhead systems, on the other hand, are more vulnerable to these environmental factors, leading to potential damage or interruptions.

Option 4: Induction interference between power and communication circuits

This option is not the primary drawback of underground transmission systems. While induction interference can occur in both overhead and underground systems, it is more commonly associated with overhead systems due to their proximity to communication lines. Proper cable shielding and spacing can mitigate this issue in underground systems.