Modified Paschen curves for non-uniform fields in air based on a rod–plane electrode geometry

Abstract As more-electric and all-electric aircraft concepts are developed, there is a growing research interest in the effects of electrical discharges under low-pressure conditions due to the associated damaging effects and safety concerns. Paschen curves allow understanding how gas insulation systems behave in uniform field gaps under different pressure conditions. However, most real-world insulation systems generate non-uniform fields, which behave differently. For example, corona discharges (PDs) occur at lower voltages than those required for complete air gap breakdown. Although conventional Paschen curves for uniform field gaps show that the complete breakdown voltage U b is a unique function of the pressure–distance product ( p·d ), this paper shows that under non-uniform field conditions, PDs under 50 Hz sinusoidal supply can occur at significantly lower voltages than those required for complete air gap breakdown, particularly at high p·d values. It also demonstrates that each pressure has a unique curve relating the breakdown voltage to the p·d product. The results presented here demonstrate that, due to the non-uniformity of the electric field distribution at high p·d values, partial discharge activity may occur at much lower voltage levels than those predicted by conventional Paschen curves. However, as the p·d product decreases, due to the uniformity of the electric field, the obtained curves tend to overlap with the Paschen curves based on uniform field gaps. Additionally, this paper shows that complete breakdown discharges can occur in non-uniform fields well below the voltage value predicted by the original Paschen curve. However, such differences diminish as p·d values approach the quasi-uniform field condition.