Surface flashover of solid insulators in atmospheric air and in vacuum

Abstract

The surface flashover of Teflon, plexiglass, quartz, Pyrex glass, Macor glass-ceramic, and sapphire solid insulators has been measured in vacuum (∼10−8 Torr, ∼10−6 Pa) and in atmospheric air using dc, ac (60 Hz), and 1.2/50-μsec lightning impulse voltages. The dependence of the flashover voltage on the following parameters is investigated: (1) spacer material, (2) diameter of the spacer, (3) spacer length, (4) number of spacers stacked in series, (5) air pressure in the range 10−6–105 Pa, (6) electrode material, (7) spark conditioning, and (8) the external resistance in series with the gap. At a fixed insulator length the flashover voltage decreases with increasing spacer diameter. The withstand voltage of spacers stacked in series increases with increasing the number of spacers. The dc flashover voltage of different insulating materials is theoretically calculated in vacuum as a function of the length of the insulator and compared with the experimentally obtained results. Good agreement is obtained.

The effects of performing isometric training at two exercise intensities in healthy young males

“…In the present study the mean peak HR (during the final 30 s of exercise in the incremental isometric exercise test) was 122.6 ± 19.0 b min -1 . This was similar to a mean peak HR of 125 b min -1 , derived from five previous double-leg isometric exercise studies (Lewis et al 1985;Misner et al 1990;Fujisawa et al 1996;Smolander et al 1998;Wiles et al 2008). The selection of 95% and 75% peak HR was based on pilot work which showed that the minimum %HR peak that could be elicited successfully, when using EMG, was 75%HR peak .…”

Increased surface flashover voltage in microfabricated devices

“…Unfortunately, there is only a limited amount of information regarding M cr , c, and v 0 , with measurements ranging over several orders of magnitude for different experimental setups, [26][27][28][29] and A 1 is only known for a handful of common dielectrics. 30 Therefore, we will treat u as a fitting parameter to compare between static and rf measurements and between different fabrication processes.…”

Ferroelectric Thin-Film Devices

“…We describe its experimental characteristics, together with a simple model, for barium-titanate based MLCs with nickel electrodes. The dependence of flash-over breakdown field E FB on dielectric length L is found to satisfy the Pillai-Hackam Law [8,9] E FB (L) = a L 1/2 . However, other details support the more complex model of Le Gressus et al [10][11][12][13], including the treeing on the insulator surface and parallel fracture lines.…”

“…But at much lower voltages, typically 30% of that required for such direct breakdown, flashover or arcing can cause failure. The basic mechanism is that of Pillai and Hackam [8,9], and a more detailed semiconductor-based model is given by Le Gressus' group [11][12][13].…”