Electrical Breakdown Experiments in Air for Micrometer Gaps Under Various Pressures

Abstract

In gases the breakdown voltage was defined by Paschen (1889) to be proportional to the product of pressure p (or to be more exact density ρ) and electrode spacing d. This has been widely accepted to be true independent of the actual values of pressure and electrode spacing. Paschen himself on the other hand only validated this ”law” for gap sizes of .01 cm to .15 cm with atmospheric pressure and .1 cm to 2 cm with pressures of 2 cmHg to 75 cmHg, i.e. 26.67 mbar to 1 bar. It was never confirmed, that the breakdown dependence from the product p · d really applies to electrode distances below 100 µm. All measurements done in the past to obtain the p · d values in the range below .1 bar-mm as presented by Dakin et al. (1971) were performed at small pressures but rather large gaps. Nevertheless it is widely accepted to use these p · d values for atmospheric pressure and gap widths below 100 µm. As Germer (1959), Boyle and Kisiluk (1955) and Hartherz et al. (2000) have shown, the general assumption of the so called ”Paschen Minimum” for small gaps below 10 µm is not applicable in general. Especially the increase of the breakdown voltage for p · d values below 8 bar-urn does not apply to air pressures in the range of 1 bar.