Discussion at Spring convention: Lightning arrester application from the economic standpoint

K. B. McEachron: In the fourth paragraph in the first page, the statement is made that the relief voltage of the aluminum arrester for 6.6-kv. service is 18 kv., and for a certain distribution arrester is 28 kv. In the next paragraph is stated that the station type auto-valve has a relief voltage of 21 kv. instantaneous value. It is also stated that the comparison is well shown by the curves in Fig. 1. If the relief voltage is taken as that at which current first begins to flow then, according to the figure referred to, the distribution type (Curve 2) has a relief value of zero volts and the type S V and L V, 10 and 24 kv. respectively. From an examination of the curves, is it not true that these curves do not represent test results, but rather calculated curves based on theoretical considerations It is stated that the station type “closely parallels the electrolytic and therefore no curve is shown.” As shown, however, this cannot be the case, since as stated in Mr. Atherton´s paper before the Institute in 1923, the arrester is designed for a so-called counter voltage of 25 per cent above the crest value of the rated voltage of the arrester. In this case, this gives about 13,000 volts, which is the value given in the paper. It should be remembered that this critical voltage is without the series line gap which adds materially to the voltage at which discharge begins.