Influence of polarity on breakdown voltage of gases in divergent electric field under lightning impulse voltages

Abstract

This paper deals with the influence of the polarity of voltage of different gases (N 2 , dry Air, SF 6 and CO 2 ) and mixtures (SF 6 -N 2 , SF 6 -dry air and SF 6 -CO 2 ) on breakdown voltage (U BDV ) in a sphere-plane and point-plane electrode arrangements under standard lightning impulse voltage stress. It's shown that in point-plane electrode geometry, the negative breakdown voltage U NBDV is always higher than the positive one (U PBDV ) for all investigated gases. While in a sphere-plane electrode system, this rule is not respected. Depending on the electrode gap, the type of gas and its pressure, U NBDV can be either lower than U PBDV (dry air), or first higher and then lower or yet first lower and then higher; the inversion appears at a given pressure that it's not the same according to the gas, gap and polarity. For gas mixtures, U NBDV is always higher than U PBDV whatever SF 6 content.

Clarifications on the Behavior of Alternative Gases to SF6 in Divergent Electric Field Distributions under AC Voltage

“…According to the pre-breakdown current measurements (see Figure 8) and the optical observations (see Figures 3 and 8), the negative glow streamer mode was identified as the breakdown mechanism for compressed N2. These findings agree with previous investigations [10][11][12][13][14][15]. Figure 9 summarizes the negative and the positive-inception voltage and AC breakdown measurement for 12.77% O2-87.23% CO2 at various pressures up to 10 bar abs.…”

“…For Ei between 3.5 eV and 10 eV, SF4 − , SF3 − and SF2 − anions are produced. The previous dissociative attachment patterns in SF6 result in multiple polarity reversal (at least 2) (+)/(−) and (−)/(+) as a function of the maximum electric field given by Equation (1) [7,8,14,29,30]. Only one polarity reversal happens in C4F7N/CO2 mixtures and pure CO2.…”

Experimental Investigation of the Breakdown Voltage of CO2, N2, and SF6 Gases, and CO2–SF6 and N2–SF6 Mixtures under Different Voltage Waveforms

“…Similar to the trend observed for SF 6 with an electrode gap of 10 mm, we first observed, at 0.5 bar, that the positive DC BDV was higher than the negative DC BDV, and then we observed the inverse: that the negative DC BDV became higher (Figure 6). Such a variation has been reported in previous work in SF 6 under LI voltages [12]. This inversion phenomenon has also been observed with a 3.7% Fluoronitriles-96.3% CO 2 mixture [4].…”

Electrical Breakdown Study in CO2 and CO2-O2 Mixtures in AC, DC and Pulsed Electric Fields at 0.1–1 MPa Pressure

“…For positive impulse, the breakdown has a small linear increase in the 40-60 kV range with increasing pressure. The differences in breakdown voltage due to polarity in strongly non-homogeneous fields (point-plane) is similar to that observed in air [21]. Several mechanisms could be responsible for this behaviour:  Streamer to leader transition in CO 2 above 0.1 MPa [7]: when the needle is stressed with positive polarity, leaders were observed with optical diagnostics.…”