Experimental study on safety aspects of cellular phone systems in HV towers

Since 1991, NUON has applied a TN system for their LV network, low voltage clients are then no longer required to have a separate ground electrode. To guarantee safety for LV clients not only faults in the LV network, but also ground faults in HV or MV grids should be considered, since they may cause large touch voltages in the LV network. A particularly interesting example is a LV system in a HV tower, as is the case with a mobile phone base station. A safety problem may occur in the low voltage network after a flashover of the HV insulators. A fraction of the 50 Hz current will flow into the LV grid. We studied the problem both with an experiment and simulations. In this paper we give a detailed description of our measurements. A new guideline to protect persons and electronic equipment is discussed