Prevention Method for Inter-Wire Insulation Failures in Cable Terminal Box Using Humidity-Controlling Polymer

摘要

A mechanism model for the inter-wire insulation failure in cable terminal boxes was fabricated, and verified by the field investigation together with a supplemental experiment. Cracks are generated in the polyethylene (PE) insulation coating of wires due to the thermal oxidation. The water condensation, combined with the deposited sea-salt, form conductive pathways among the cracks. We found that the relative humidity (RH) inside the terminal box synchronously followed that of the outdoor air and often reached 100% RH, which can cause water condensation. We propose a promising method for alleviating the insulation failure by controlling the humidity inside the terminal box. For this purpose, we have employed a water-absorbent polymer. We monitored the inter-wire resistance in the terminal box that was placed in the 100% RH atmosphere. Without the polymer, the resistance significantly decreased and fiercely fluctuated. With the polymer, the resistance was stabilized above a satisfactory level. This demonstrates that the proposed method effectively works as proposed.