Breakdown of Gases Below Paschen Minimum: Basic Design Data of High-Voltage Equipment

Abstract

For the region pd<(pd)min, breakdown characteristics U2 = f(pd) are presented for both the noble and the more important molecular gases He, Ne, A, Kr, Xe, N2, H2, NH3, air, CO2, O2 (and Hg), particularly giving the probability of breakdown on which they are based, so that they can be used for dimensioning the relevant equipment. The design of vessel and electrode geometry which were introduced to determine these characteristics, and which have been tested up to a peak voltage of several hundred kilovolts, made it possible to study and describe the shape of the breakdown and flashover voltages relative to one another at pressures down to high vacuum (region of vacuum breakdown). They also provide an overall picture of the constructional facilities existing within the four following regions of ultimate stress, in which the breakdown voltage is determined by the ultimate electrical stressing of 1) the electrode surface (vacuum breakdown), 2) the insulator inside wall (internal flashover), 3) the insulator outside wall (external flashover), and 4) the gas path (Paschen breakdown). To express the probability of breakdown between 100 percent certainty (W = 1) and complete freedom from breakdown (W = 0), Poisson's formula may be used for the various breakdown mechanisms, i. e., for values of pd close to the respective kink and in the kinked part of the lefthand leg of the Paschen curve (regions 1-4 in Fig. 2), the value μbeing proportional to the peak value of the applied voltage Û.