Reliability of HVDC Cable Joints – Today and Future Challenges by Hansjörg Gramespacher

Due to the large number of joints in land-based HVDC cables, which can easily reach over 1000 in a single system, failure rate of joints plays a decisive role in overall system performance. Unfortunately, routine tests in the case of HVDC cable joints may not be sufficient to guarantee high reliability during operation. This is because electric field in some regions within an HVDC joint during operation can be much higher than seen during routine testing due to the fact that field distribution in such a joint is highly sensitive to temperature. Therefore, to properly cover field distribution in the joint at higher conductor temperatures, additional electrical testing may be needed. This presentation explains how simulation has shown that fields in some parts of an HVDC joint can be higher during operation than seen during the DC routine test according to IEC 62895. That means that not all critical defects in a joint can be detected during routine tests, which will increase failure rate during operation in the field. Performing an additional DC routine test with higher temperature is recommended.