Substation cabling

Eindhoven University of Technology and the Dutch power Distribution Company NUON, carry out a joint research project on global earthing. In this project we treat different faults and various interference sources e.g. lightning and switching events together.

In September 1998 we analysed the consequences of a fault in a medium voltage network on the grounding systems at LV-side. To study the current distribution and to verify the models, we deliberately introduced one phase to ground faults in the 10 kV floating MV network. The selected site was the end of a 2 km long buried MV cable feeding a small group of houses; the soil there had a high resistivity. The fault current was 127 A. The current distribution and the relevant voltages were measured at several positions in MV and LV net.

We compare the results for a TT and a quasi-TN earthing system in the houses, also taking the telecom cable into account. The distribution of the fault current over the MV cable, measured at another MV station at 2.2 km distance, are in agreement with calculations, based on a model which includes the contact of the lead shield of the MV cable with the ground. Current and voltage data were compared with calculations.