Innovative monitoring system for power transmission link elements

Sheath voltages limiters (SVL´s - see Fig.1) are used to protect the sheath sectionalising insulators of joints or terminations for specially bonded cable systems. Their purpose is to minimize the transient voltage that is produced across the sectionalising insulator during switching surges or lightning strikes and to reduce the risk of them flashing-over. These SVL´s are normally located within link-boxes which can be accessed fairly easily but for cable systems located in tunnels the SVL´s are normally in air and to gain access to the SVL´s it is necessary to enter the tunnel. Many utilities wish to restrict third party tunnel access (for security reasons) and hence there is a requirement to monitor these SVL´s from outside the tunnel. This document describes such a monitoring system.