Assessment of Electric Shock Hazard Coming From Earth Continuity Conductors in 110 kV Cable Lines

Abstract

There has been a growing demand of electric power in many urban agglomerations. To address this demand, 110-kV power networks are regularly expanded inside and around cities in Poland. These power networks are often constructed as underground cable lines. The 110-kV cable lines are usually designed as three single-core cables laid in a common route. In case of long 110-kV cable lines, the cross-bonding method is applied to the connection of metal sheaths of these cables. Additionally, one or more earth continuity conductors are laid along the main cable line and earthed at both their ends. These earth continuity conductors can be uninsulated and can cause electric shock hazard (danger step voltages). The problem defined in this paper consists of an attempt to calculate the expected step voltages for different considered earth continuity conductor arrangements in 110-kV cable lines and to compare the obtained results to admissible values of the voltages found in an appropriate standard. Protection against electric shock, calculation of earthing resistance, and step voltages, as well as simulation studies in case of sample 110-kV cable lines have been described in the paper. The results show the analyzed layouts of 110-kV cable lines have significant impact on the values of voltages occurring in and around earth continuity conductors. The maximum values of earth electrode voltage (and in this way expected touch voltages), as well as step voltages occur in the layout of single cable line and single earth continuity conductor arranged in parallel.