Power transmission and distribution

D. W. Roper: This report calls attention to some of the lightning arresters and distribution circuits in Chicago. For fear that the readers might get a wrong impression, I want to add a little to what appears in the report. The lightning-arrester records of the several types appeared to indicate that the results obtained were not quite what were expected. Further investigation of that point has brought out an interesting feature, somewhat unlooked for, in that some of these burn-outs which have been recorded and which have affected our results were due to lightning entering via the secondary circuits. The lightning arresters we have are on the primary circuits. The primary distribution, in general, occupies the top arm and the secondary ordinarily the next lower arm. Sometimes it is on the same arm with the primary circuits. As the lightning potentials which appear on the line are in proportion to the height from the ground, it is seen that the secondary circuits have been getting almost the same lightning effects as the primary.