Field Investigation of the Characteristics of Lightning Currents Discharged by Arresters

Data have been obtained during the past three years on the magnitude and wave shape of lightning currents discharged by arresters in service on several solidly grounded neutral circuits of the American Gas and Electric Company system. Correlated measurements have been obtained with the cathode-ray oscillograph, the fulchronograph, and the surge-front recorder. The maximum arrester-phase leg current recorded in this investigation was 9,600 amperes with 70 per cent of the currents less than 1,000 amperes. The wave fronts of the low-magnitude currents were, in general, abrupt. For crest magnitudes of over 1,000 amperes they ranged from two to over 25 microseconds to crest. The maximum rate of rise recorded was 2,500 amperes per microsecond. The components in all discharges were of relatively short duration, with times to half value averaging 25 microseconds and with no measurable durations in excess of 500 microseconds. Of the 18 arrester-phase legs studied, all but one discharged at least once during the investigation. Nineteen of the 21 separate records of discharges in three-phase arrester banks had currents which, if arresters had not been installed, would have produced voltages in excess of the standard basic impulse level for the voltage class of the apparatus involved, so that failure of unprotected equipment might have occurred.