Polarity Limits of the Sphere Gap

Impulsive Flashover Characteristics and Weibull Statistical Analysis of Gas-Solid Interfaces With Varying Relative Humidity

“…That is, the field distribution at the electrode edges can be classified as quasi-uniform, similar to that of the sphere gaps tested in [9] and [10]. In [9] and [10], it is shown that, for different ratios of gap spacing, S, to sphere diameter, D, the breakdown behaviour of a geometrically-symmetrical electrode arrangement is not always electrically symmetrical. The ratio S/D determines the mechanism of the electrical breakdown, and the resultant breakdown voltage of the system.…”

“…These design criteria resulted in asymmetrical electrical behaviour of the geometrically-symmetrical electrode arrangement, including in the case when the electrodes were not bridged by a solid spacer. For such open air gaps, this behaviour is due to the ratio of the inter-electrode gap spacing and the diameter of the electrodes, as shown in [9], and discussed further in [10]. Based upon the discharge regimes discussed in [9] and [10], the dimensions of the electrode system used herein, where the discharges generally occur at the rounded edges of the electrodes for no-spacer tests, fall within the 'low positive spark over range' from [10], due to the ratio of the diameter of the electrode edge (20 mm) to gap distance (40 mm) being 200%; this is discussed further in section V.…”

“…Using the same method, S/D for the current system is calculated to be ~2. From [10], it is seen that this system falls within the 'low positive sparkover range', which results in a higher negative breakdown voltage.…”

“…When comparing negative and positive breakdown voltages at <10% RH, the differences between the voltages at each pressure are statisitically significant to one standard deviation. This has been discussed in [9] and [10], where the specific electrode diameters and gap spacings result in a difference in the positive and negative breakdown voltages, for sphere-sphere gaps, with one electrode grounded. The dimensions used in the present study, displaying the asymmetric field distribution shown in Fig.…”

“…The dimensions used in the present study, displaying the asymmetric field distribution shown in Fig. 2 and using the same process as [9], [10], mean that the current electrode system can be categorised in the 'low positive spark over range,' resulting in a higher negative breakdown voltage. However, when adding moisture to the system, the breakdown voltages at ~50% RH and at >90% RH showed an increasingly-symmetrical performance, with the negative and positive breakdown voltages being closer in magnitude.…”