A Lightning Stroke Pathfinder

Extra-high-voltage transmission lines, designed in accordance with the AIEE lightning outage estimation method published in 1950, have actually experienced several times the outages predicted. Recent studies, based on new concepts of the lightning stroke mechanism, strongly indicate that lightning strokes to the phase conductors, or shielding failures, account for this sharp discrepancy. A low-cost instrument, rugged in design and readily installed, has been developed to discriminate between strokes to the shielding system or a phase conductor. Signals are easily read either from the ground or from a helicopter. Power follow current is similarly indicated. A minimum of 100 records are deemed essential to firmly allocate lightning outages to phase conductor or shield wire stroke terminations. To secure these records, it is recommended that a field study be conducted on a suitable mile-year sample of transmission lines. With this information available, the engineering prediction of the lightning performance of transmission lines can be placed on a much sounder basis and lines can be designed to a preselected level of tripout probability.