Earthing of 130 kV power lines-effects on dependability and line cost

Power lines without overhead shield wires have low investment costs and their dependability in areas with low lightning incidence has been accepted. However, requirements for higher availability, improved power quality and lower maintenance costs may change the choice of line design as discussed in this paper. Results are presented from a comparison of three different 130 kV power line designs, with and without shield wires, with respect to lightning performance, ground-return currents, dependability and costs. The lightning performance is analysed by EMTDC-simulations and the probability for line-to-line and line-to-ground faults are calculated. The severity of resulting voltage dips, and the corresponding outage cost for sensitive customers are discussed. Fault current distributions for different grounding designs are calculated and required safety precautions and protective measures, on the power line or adjacent installations, are discussed. In conclusion: shielded lines have low outage costs, and show advantages in most technical aspects