Tests were initially carried out at 60 Hz in order to provide a baseline for the comparison of results at higher frequency and also to validate the results with those found in literature. Figure 4 shows the variation of the breakdown voltage as a function of humidity for several gap lengths. It shows a slight increase of the breakdown voltage with humidity and that the variation is nearly linear. Table 1 presents the trend in breakdown voltage with humidity for the gap lengths evaluated. The data is presented as percentage increases on the breakdown voltage per unit of absolute humidity and RH. The data reveals an increasing humidity effect as the gap length increases.