. The street railway review . xperienced soonafter the introduction of electrical apparatus for street rail-way service, and it was evident that some means must betaken to preserve the armatures of generators and motorsfrom damages by electric storms. The first types werequite simple, consisting simply of two serrated surfaces witha short air gap. The air gap was not of proper length andthe arresters were not placed as they should be, consequentlythey were ineffective. A number of designs were evolvedfor station, car and line service. With the air gap it wasfound that after a stroke of lightni
. The street railway review . xperienced soonafter the introduction of electrical apparatus for street rail-way service, and it was evident that some means must betaken to preserve the armatures of generators and motorsfrom damages by electric storms. The first types werequite simple, consisting simply of two serrated surfaces witha short air gap. The air gap was not of proper length andthe arresters were not placed as they should be, consequentlythey were ineffective. A number of designs were evolvedfor station, car and line service. With the air gap it wasfound that after a stroke of lightning the arc was maintainedby the dynamo current; to prevent this a fuse was introducedinto the earth circuit. As soon as the fuse would blow thearrester was useless, and when another discharge quicklyfollowed the first, as is often the case, the apparatus wasunprotected. The air gap was employed in preference toother resistance, as it is a good insulator under ordinary cir-cumstances, but offers very much less impedance to the. S- FIG. I. G. E. TYPE MU ARRESTER. passage of a stroke of lightning than anv other kind ofinsulation, and is instantly restored to normal. The oscillatory character and the disruptive discharges oflightning give rise to complicated phenomena and makeabsolute immunity from danger almost impossible. Theline may receive a direct stroke, or excessive current may beinduced from a primary discharge quite apart from the the line has received the discharge there are what areknown as nodal points, or points which, because of theoscillatory character of the lightning, are at a very muchlower potential than other parts of the line. For thisreason arresters must be distributed at intervals. The suecessful operation depends largely upon the systematicarrangement of the arresters and choke coils, and also theinstalling of short and straight earth connections. Thenumber of pulsations of a lightning discharge is so greatthat a few turns in the circuit over whi
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Keywords: ., book, bookcentury1800, bookdecade1890, booksubjectstreetrailroads
