Lightning induced overvoltages, improvement in quality of service in MV distribution lines by addition of shield wires

One important cause of disturbances in distribution systems is lightning that determines permanent or transient faults in overhead lines by direct or, more frequently, indirect strokes. The trouble caused to customers, because of the susceptibility of some loads, may be very severe even in the case of transient faults, i.e. those which disappear after the opening and high-speed reclosure of protective breakers. This paper provides an assessment of the reduction in the number of faults caused by the lightning activity to an MV distribution system by the addition of a shield wire. The effect of an increase in the insulation level is also analysed.