Water Tightness Testing and Evaluation of Composite Interface Structures in Cable Joints

Moisture is one of the most serious causes of cable joint failures in the distribution network, which can invade cable joints through the composite interface structures. Enhancing the sealing performance of interface structures is an important initiative that should be focused on, but the relevant aspects are lacking in the design and selection of cable accessories. In this work, a detection and evaluation method applicable to the water tightness of composite interface structures in distribution cables is proposed, and the water ingress process at different temperatures and interfacial pressures is measured. Two indexes, namely the time constant of penetration T
p
and the water resistance coefficient K
r
, are defined and calculated to evaluate the water tightness of cable joints. Experimental results show that increasing temperature and decreasing interfacial pressure have accelerated effects on the water ingress process, resulting in a worse water tightness of cable joints. When the temperature increases from 25°C to 75°C, T
p
decreases to a minimum of 16.7% and K
r
decreases to 49.8%. As the interfacial pressure decreases from 0.14 MPa to 0.015 MPa, T
p
decreases to a minimum of 7.22% and K
r
decreases to 55.2%. Similar results are obtained for water immersion environment and humid environment with 95% relative humidity. The proposed method is effective and accurate for testing and evaluating the water tightness of cable joints and can provide important guidance for the design and selection of cable accessories.