Discussion of "Testing EHV Station Insulation for Performance in Contaminated Conditions" [with authors' reply

Abstract

There are some results reported in the paper that the discussor (B. Macchiaroli) would like to consider, namely the data of Table VII concerning tests conducted to observe the influence of drying time on flashover voltage on 30-inch station post insulator elements. It is noted that the flashover voltage decreased in excess of 20% from the time the insulator was thoroughly wet to the point where the lowest flashover voltage was observed with the insulator partially dry. The corresponding curves are reproduced. Since the discussor does not know whether, in the interim time, the authors have found the reasons for this apparently unusual behavior, he proposes a possible explanation. In replying the original authors note that Mr. Macchiaroli presents the interesting observation that, in his testing experience, it is necessary to wait some period of time for a saline solution, depending upon the amount of sodium chloride in solution, before the conductivity stabilizes at its highest value. The higher the salt concentration, the greater the length of time required to reach the point of stabilization. The data given in Table VII of the original paper, as plotted in Fig. 1 of this discussion, show a reduction in flashover voltage much greater during drying of the contaminant containing salt, then in the saltfree test. Admittedly, one set of test data is not sufficient for drawing definite conclusions, but this comparison between salt-free and saline contaminant may lend support to the discusser's theory. It may even introduce another ingredient to investigate-not only length of time for stabilization to occur, but also the magnitude of change in conductivity due to the salt content of the contaminant.