Influence of Microbubbles Motion State on Partial Discharge in Transformer Oil

To study the influence of microbubbles motion state on partial discharge (PD) in transformer oil, an experimental platform of suspended microbubbles in transformer oil is established. Deformations of suspended microbubbles in mobile and stationary states are observed. The Ultra-high frequency (UHF) and pulsed current methods are applied to detect the PD of mobile and stationary microbubbles. In addition, the time-frequency characteristic of different PD is analyzed, and an Phi-U-N map is constructed. A deformation parameter (c) of microbubble is defined, and the electric field distribution is analyzed with the change of c. The results show that oil flow has a significant influence on the PD of microbubbles. When the motion state of microbubble changes from stationary to mobile, we find that the stretched shape of microbubble changes from horizontal ellipsoid to vertical one, the PD inception voltage increases, and the electric field strength inside microbubble decreases. Therefore, mobile microbubbles are harder to lead to PD than stationary microbubbles, signifying that increasing the oil flow helps to enhance the dielectric strength of oil.