LAUSR

Breakdown phenomena in the Hydrofluoroolefin 1234zeE gas (HFO) are studied under impulse voltage in moderately divergent field, with field enhancement factor $\eta < 10$ . The first breakdown voltage recorded in new HFO with clean electrodes is higher than in SF6. However, the degradation of HFO by discharges induces the formation of soot deposited on electrodes, which strongly facilitates the inception of subsequent prebreakdown leaders: both inception field and statistical delay to inception are reduced. As a consequence, the breakdown voltage of HFO with polluted electrodes drops and becomes lower than in SF6 in identical conditions. This deleterious effect is not recorded in negative polarity.