Phenomenon of secondary reverse streamer in an ester transformer liquid under lightning impulse voltage

Secondary Reverse Streamer (SRS) was investigated in a natural ester transformer liquid under standard negative lightning impulse voltage. SRS represents a streamer that occurs well after the termination of the primary streamer (PS) propagation under a single lightning impulse, and it holds an opposite polarity to that of the PS and the impulse voltage. As an example when negative impulses are applied, all the SRSs have positive polarities. Although both streamers' stopping lengths increase with the applied voltage, the stopping length of SRS is always shorter than that of PS. The average propagation velocity of SRS is approximately 1.25 km/s regardless of applied voltages. The maximum light intensity of SRS is lower than that of PS. The formation of SRS is likely caused by the reserve electric filed induced by residual space charges.