Safety issues in tunnel installation of EHV power cables

This paper deals with tunnel installations of extra high voltage (EHV) power cables. Cross-bonding of the screens remains the usual earthing arrangements of cable systems, if their extension is greater than 1,5 km approximately. Such EHV cable systems need a functional earthing along the route in correspondence of each major section, at the sending and at the receiving ends. Given the difficulties involved with the realization of these earthing systems, other techniques should be sought for. In this paper two different methods to earth the cable screens are taken into account: the former is obtained by means of one or more earth continuity conductors (ECCs), whereas the latter relies on the tunnel steel reinforcement (TSR) itself. Each method is discussed and analyzed both in terms of safety issues and stray currents.