The assessment of the degree of paper aging and remaining life of fluid-filled paper-insulated high voltage underground transmission cables through wet-tensile strength

The assessment of the degree of paper aging and remaining life of installed fluid-filled paper-insulated high voltage cables, which constitute considerable utility investment, has received a great deal of attention. The traditional methods consist of the determination of the mechanical properties of paper as it ages with time. Such properties include tensile, folding, burst and tear strengths as well as elongation. The proper application of this approach requires a knowledge of the initial mechanical properties, but this is not readily available. However the application of wet-tensile strength, which is extensively used in the paper and pulp industries but has never been considered in the electrical industry, does not require such prior knowledge. Unlike the traditional mechanical properties that gradually decrease with aging, wet-tensile strength initially increases to a peak and then decreases as aging occurs. This peak, which is characteristic of wet-tensile strength for all cellulosic paper, is singularly governed by temperature and time. The wet-tensile strength results relating to investigations performed on fluid-impregnated paper tapes thermally aged under laboratory conditions are presented, including wet-tensile strength data on cable pieces removed from service. Laboratory and field studies indicate the potential of this novel physical property as a cable aging marker.