Field Tests on Thyrite Lightning Arresters Using Artificial Lightning of 1,500,000 Volts

The impulse characteristics of thyrite station type arresters of various ratings have been studied when connected to a 45-mile transmission line. The surges were supplied by a 1,500,000-volt impulse generator. The volt-timle curves for arresters of various ratings were obtained under the conditions corresponding to the arrester on each incoming circuit, on the bus with two incoming circuits and on the bus with one incoming and one outgoing circuit. The oscillograms were found to check the calculations closely. With the arrester 90 ft. from a nearby tower the effect of tying arrester and tower grounds together was studied, and also the effect on flashover at nearby towers. The effect of flashover at a tower 1,660 ft. away on the operation of the arrester was determined. Oscillograms are given comparing the protective characteristic of a single-stack arrester with that of a two-stack arrester of the same rating. There is no discernable difference between the two characteristics. It has been proposed that line insulation for a distance of one-half mile from the station should be limited. Oscillograms are given for two arrester ratings, showing that, for the waves used, no protection is offered by the arrester at a distance of 2,180 ft. and a large part is lost at 500 ft. It is concluaded that the insulation should be limited at the arrester if the arrester is to protect it safely. The effect of the length of arrester connections is given, showing that on the 69-kv. arrester a loop 30 ft.