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Breakdown of cable insulation may occur due to
Thermal instability
Puncture
Tracking
Any of above
Any of above
Breakdown of cable insulation is a failure in the dielectric strength of the insulating material, which can be triggered by thermal, electrical, or chemical degradation. Because all three listed phenomena—thermal instability, puncture, and tracking—are recognized mechanisms that cause such insulation failure, option D is the correct answer.
Breakdown of cable insulation is a failure in the dielectric strength of the insulating material, which can be triggered by thermal, electrical, or chemical degradation. Because all three listed phenomena—thermal instability, puncture, and tracking—are recognized mechanisms that cause such insulation failure, option D is the correct answer.
Wd=V2ωCtanδ — Dielectric loss formula representing the heat generated in the insulation
Ebreakdown=dV — Electrical field stress causing puncture when it exceeds the material limit
Thermal instability is prevalent in high-voltage cables where dielectric loss increases with frequency and voltage.
Puncture can occur due to manufacturing defects like voids or gas bubbles in the insulation.
Tracking is common in outdoor cable terminations and joints exposed to environmental moisture and pollution.
Insulation failure leads to a catastrophic reduction in insulation resistance (Rins).
High Voltage Underground Transmission
Power Distribution Infrastructure
Tracking is sometimes referred to as 'surface discharge' which creates carbonized paths on the surface.
Puncture is usually permanent and leads to immediate fault current tripping.
D is correct — All listed options are primary physical mechanisms by which the insulation integrity of an underground cable is compromised.
Always remember that in power systems, insulation failure is rarely caused by a single factor; environmental conditions and electrical stress interact to accelerate material degradation.