SF6-N2 mixtures for explosion-protected motors

With the aim to use SF₆-N₂ mixtures as purging and protective gases for explosion-protected machines, the PD inception voltage in the gas gaps of the end winding spaces was investigated. The PD was measured between two coils and between coils and earthed parts of the motor case for different pressures and SF₆ concentrations. The investigations focused on the electrical safety margin that could be reached with relatively small SF₆ admixtures. Conclusions have been drawn for the practical dimensioning of end winding spaces in high-voltage machines