Study of creeping discharges propagating over epoxy resin insulators in presence of different gases and mixtures

This work shows that the discharges pattern and final length, L_f, of creeping discharges depend on the amplitude and polarity of the voltage, the type of gas (mixture) and pressure similarly as in the case of the materials we investigated previously. L_f is longer when the point is positive than when it´s negative; this is likely due to the influence of space charge on the electric field. L_f increases quasi-linearly with the voltage; it´s reduced when the pressure is increased. L_f is shorter in SF₆ than in CO₂ or N₂. On the other hand, the increase of SF₆ content in SF₆-CO₂ mixture leads to a significant decrease of L_f. Therefore the addition of small concentration of SF₆ in a given gas mixture improve the dielectric strength of insulating structure.