Determination of waiting times between successive breakdown experiments

Abstract

A common duty in high voltage engineering is the experimental determination of the breakdown voltage probability distribution of gaseous insulated electrode configurations. Due to electron detachment from negative ions in the case of electron attaching gases, the breakdown probability does not only depend on the gas and its density, but also on the ion density in the gas. If a disruptive discharge occurs in a gas gap, the number of ions in the gap is significantly increased compared to the equilibrium state at zero voltage. If the time until the next voltage application is too short, the statistical time lag will be decreased and, as a consequence, the probability of breakdown will be increased. To perform statistical independent breakdown experiments it is necessary to ensure identical ion densities in the gas gap before every new voltage application. In the literature waiting times mostly around six minutes are proposed as sufficient for ion density equalization in sulfur hexafluoride (SF 6 ). However, simulations of the behavior of SF 6 performed for the present contribution reveal that six minutes are not always sufficient to achieve statistical independent results. Especially at higher pressures longer waiting times are necessary. To investigate this problem, measurements of the natural ion pair generation in SF 6 were performed at different laboratories. Based on this data the temporal development of the ion distribution in the gas is calculated. Two cases are of interest: the changes in ion density after a disruptive discharge and in case the gap withstood the applied voltage and therefore all ions are swept out. After transformation of the temporal ion density into breakdown probability curves it is possible to estimate the necessary waiting time.

Partial discharges and breakdown in C3F8

“…But, to the authors' knowledge, for C 3 F 8 only autodetachment from metastable parent anions is reported [18,19] with lifetimes in the range of 10 −11 s to 10 −8 s [20], but no detachment rates are available. The calculation of the theoretical lower limit of the statistical time lag by the volume V crit exceeding the critical field strength at the given applied voltage and the ion production rateṅ 1 (measured for SF 6 at our laboratory [49])…”

Peak Voltage Measurements Using Standard Sphere Gap Method

“…Various studies have been made over the time concerning the time gap between two consecutive breakdowns [14,15]. For the scope of the present work this time gap has been set to at least one minute.…”

An Efficient Procedure to Identify and Quantify New Molecules for Insulating Gas Mixtures

“…A certain electrode arrangement, typically needle-plane, coaxial or parallel planes, is chosen, and the breakdown voltage level is measured for a particular wave shape. A large number of breakdown experiments has to be carried out to properly account for the statistical nature of the breakdown process and it has to be ensured that each measurement is independent of the previous ones [12,13,14]. The resulting information is only valid for this configuration and wave shape and cannot be generalized or otherwise transferred.…”