1929 Lightning Experience on the 132-Kv. Transmission Lines of the American Gas and Electric Company

A record of the 1929 lightning performance of a 1,200-mile 132-kv. transmission net workis given, and compared with the record of the system during the previous three years. The system is almost entirely of steel tower construction with conductors in vertical configuration; and on most lines one ground wire is employed. It is shown that some 75 per cent of high-voltage transmission line outages on this system are due to lightning. Lightning performance of lines being dependent on the severity of lightning conditions, a record of these conditions should be kept from year to year if records are to be compared. Data are presented on relative yearly lightning intensity, line outages, damage found to insulators and hardware, performance of double circuit lines, lines with and without ground wire, and with two ground wires, and also with and without grading shields. The apparent part tower footing ground resistance plays in line outages due to lightning is also given. The conclusions are drawn that 1. Two circuit lines are far more reliable, from a lightning point of view, than single circuit lines. 2. One ground wire offers considerable protection against lightning, and two ground wires considerably more. 3. Grading shields properly applied do not reduce line outages but decrease the damage to insulators, hardware, and conductors. 4. Both direct and induced lightning strokes have to be considered on these lines. 5. Flashovers do not always concentrate on high tower footing resistance towers. 6.