Initiation of breakdown in strings of bubbles immersed in transformer oil: Paschen curves and proximity of bubbles

Recent experiments¹ have shown that bubbling the transformer oil with air or sulfur hexafluoride leads to the decrease of breakdown voltage by 34% and 19%, respectively. To lend an insight to how streamers are initiated in an isolated bubble or strings of bubbles filled with air or SF₆ and immersed in transformer oil, we computationally investigated the role of randomly distributed initial seeds of electrons inside bubbles of various size.