Long Time Evaluation of Cable Joints in Water by Stefan Kühnel / Stefan Kornhuber

To ensure reliable medium voltage distribution networks, it is important that cable components can withstand a range of electrical, mechanical, thermal and ambient stresses. Water is one of the main factors behind degraded insulation. If the tightness of cable joints or cable shielding is not assured, moisture ingress can adversely affect the inner interface and lead to internal puncture. Several construction methods are used to protect this critical inner joint system and a special water stress test procedure has been developed to ensure correct tightness and functionality. As part of this process, a special test stand was designed to expose joints without outer protection systems to combined stress with water and medium voltage and several joints were investigated over a period of up to 10 years. Some joints were stressed with continuous voltage while others were stressed electrically at prescribed intervals. During the continuous stress by water and voltage, breakdown voltage tests, PD tests and visual examination after dismantling were performed. This presentation outlines the test set-up and different test objects studied, reviews results after the long-term evaluation and offers key conclusions.