IEEE 1425:2001 pdf free.IEEE Guide for the Evaluation of the Remaining Life of Impregnated Paper-Insulated Transmission Cable Systems.
To achieve the dielectric strength required for operation at transmission voltages, the impregnated paperinsulation must be kept under hydraulic pressure using a dielectric fluid(mineral oil, synthetic liquid, ornitrogen gas).Jacketed metallic enclosures are used to contain the fluid: a steel pipe for HPFF and HPGFcables and,usually, a lead, copper, or aluminum sheath for SCLF cables. These enclosures,when buried,may be subjected to corrosive environments and damage from external sources.
A weakened enclosure will eventually result in leakage of dielectric fluid and potential partial discharge andmoisture ingress into the insulation,ultimately leading to cable failure.As the costs of repair and cleanup,and the loss of revenue associated with cable unavailability,can be substantial, it is imperative that theintegrity of pressure containment components be maintained.
Some of the external factors that may cause damage to a cable system include excavation, boring, excessiveground loading or vibration, settlement of the soil and substrate, and corrosive soils. Mechanical protectionis required to prevent accidental cable contacts and cable damage, and it is critical to cable system reliabilityand length of service. Although damaging the cable may result in service interruption and have potentiallyserious environmental and cost implications, contacting an energized cable may represent a grave hazardand should be avoided.
To protect against accidental contact, the first line of defense could be to provide clear，visible，above-ground markers indicating both the presence of high-voltage cables, the name of the utility, and the“OneCall” phone number. In addition, some utilities install a buried cautionary marker tape above the cables andstrong barriers such as casing pipes, steel plates, concrete slabs and side walls, or reinforced concrete ductbanks.
Patrolling cable routes，monitoring excavation by third parties，and participating in Public UtilitiesCoordinating Committees that coordinate work on public road allowances, are the most efficient means ofensuring the continued mechanical protection of cables.IEEE 1425 pdf download.