Application of high voltage (HV) live-line working techniques - Hot stick in HV/MV substation maintenance -A case study

EDP Distribuição is the Portuguese public electricity distribution network operator, managing 413 substations, 83.713 km km of high voltage (HV) and medium voltage (MV) overhead and underground lines, and 66.003 low voltage substations. EDP Distribuição started live-line working (LW) on MV overhead lines during the 1970s and progressed to HV lines (60 kV) in 1998. The LW techniques (hot stick) have also been applied in substations, first in MV and, for more than a decade, in HV, mainly in the establishment of temporary circuits, in the removal or placement of bus bar sections, and also in connection of MV or HV equipment, always with the aim of not interrupting the power supply to customers. The present paper describes a replacement of two poles of a HV isolator suffering from overheating on different metal contact zones, and carried out by EDP Distribuição teams during the summer of 2013. The option of using LW techniques was imposed by the particular conditions of that substation. It was a site without redundancy in HV feeders, with sensitive industrial loads and with limited capacity to support the loads by MV lines.