Reliability of Transmission Links Consisting of Overhead Lines and Underground Cables

Underground cables will be applied more often within new connections of the extra-high-voltage (EHV) transmission network. Since EHV underground cables are a relatively new technology, not much is known about their behavior in large transmission networks. Underground cable connections (consisting of cables, joints, and terminations) are, in general, less reliable than traditional overhead lines, mainly because of their much longer repair time. This can negatively influence the reliability of the transmission network as well. It is therefore of interest to study the reliability of underground cable connections in detail. This paper concentrates on the reliability of EHV underground cable and overhead line connections. Based on actual failure statistics of individual components, the reliability of a connection is analyzed, and which factors are of influence and what measures can be taken to improve the reliability are studied. An optimized cable repair process and a configuration with additional disconnectors are two solutions.