In gas-insulated high-voltage direct current (HVDC) devices

micro partial discharges (PD) caused by micro-protrusions or surface roughness on conductors or enclosures  may not cause immediate insulation system failure due to their weak discharge intensity. However

the continuous charging of carriers generated by the discharges to the insulator is one of the potential triggers of surface flashover of insulators. This work investigates the micro PD characteristics in SF6 at 0.1–0.7 MPa

which is below the lower limit of conventional detection methods

via a highly sensitive micro-discharge measurement platform. The experimental results show that the micro PD exhibits a strong polarity effect. With increasing pressure

the mean amplitude and mean repetition rates exhibited an extremum at 0.3 MPa. As the applied voltage increased

the mean amplitude shifted from negative polarity dominance over positive polarity to positive polarity dominance over negative polarity. Time-resolved PD (TRPD) and pulse sequence analysis (PSA) patterns indicate that the micro PD is characterised by clustered bursts and amplitude stratification. Furthermore

the negative polarity micro PD is more stable than the positive polarity counterpart. The results of this work can provide references to guide the optimized design of gas-insulated HVDC devices.