Safety issues related to the connection of MV and HV grounding systems outside substations

In recent years, there has been an explosive growth of mobile telephone systems. In urban areas, antennas are seen on tall buildings and structures. In rural areas, the options are limited and high voltage (HV) towers represent an interesting alternative. Antennas started to appear in HV towers two to three years ago and their number will increase rapidly over the next few years. Different safety related questions arise from these installations. The antenna system requires both power and a link to the telephone system. The system is fed from a MV line. The question arising from feeding mobile telephone systems in HV towers is whether the connection of MV and HV grounding systems should extend outside substations or an isolation transformer be used; the main concern is related to touch voltages in MV and LV installations during a fault on the HV tower. This question had led Hydro Quebec to initiate a project aimed at determining the most appropriate method to feed loads in HV towers. It includes a computer analysis and field tests.