While underground lines are more reliable, their installation and operation present specific challenges at the transmission level:

• Heat Dissipation: At EHV levels, the cables generate immense heat. Unlike overhead lines that are air-cooled, underground cables rely on the surrounding soil to dissipate heat. Special thermally conductive backfill materials must be used to prevent the insulation from overheating and failing.

• High Pulling Tension: The sheer weight of a long, heavy transmission cable means that immense pulling force is required. This necessitates professional-grade hydraulic cable pullers that are capable of delivering several tons of controlled tension without damaging the cable's sensitive core.

• Cable Joints and Terminations: These are the most vulnerable points in an underground transmission system. Splicing a 230kV cable is a highly specialized task that must be performed in a clean, controlled environment to prevent voids and contaminants that could lead to electrical breakdown.

• Capacitive Effects: Unlike overhead lines, underground cables have a high capacitance, which can create a voltage rise along the line. This requires expensive and complex reactive compensation equipment to manage and maintain stable grid voltage.