External Damage: Cables are susceptible to external damage during storage, transportation, installation, and operation. Direct-buried cables, in particular, are highly vulnerable to damage caused by ground-level construction work for other projects. Such incidents account for approximately 50% of all cable-related failures. To prevent these, it is essential not only to ensure high-quality standards throughout the storage, transport, and installation phases but, more importantly, to strictly enforce protocols for any ground-excavation work.
Corrosion of the Protective Layer: Electrochemical corrosion-caused by stray underground currents-or chemical corrosion from non-neutral soil can compromise the protective layer, rendering it unable to safeguard the cable's insulation. Solutions include installing drainage equipment for stray currents in areas where they are concentrated. If the soil surrounding a cable contains chemicals that could damage its lead sheath, the affected section should be placed inside a conduit, cushioned and covered with neutral soil, and coated with bitumen.
Overvoltage and Overload Operation: Improper voltage selection, sudden high-voltage surges during operation, or prolonged overloading can degrade the cable's insulation strength, leading to dielectric breakdown. These issues must be addressed through more rigorous inspections and the improvement of operating conditions.
Water Ingress in Outdoor Terminations: Poor construction-such as failing to completely fill a termination with insulating compound-can lead to water ingress, potentially resulting in an explosion. It is therefore critical to strictly adhere to construction specifications, conduct thorough inspections upon completion, and maintain regular monitoring and timely repairs. Oil leakage from a termination compromises its sealing structure, causing the impregnating agent at the cable end to drain away and dry out. This increases thermal resistance, accelerates the aging of the insulation, facilitates moisture absorption, and ultimately leads to thermal breakdown. If oil leakage is detected at a termination, inspection frequency should be increased; in severe cases, the power must be cut off and the termination rebuilt.
