Interaction Between Partial Discharge and Generated Bubbles Under Repeated Lightning Impulses in Transformers Using a Complex Structure Model

The focus of this research is on the insulation structure where radial and axial spacers connect in a power transformer. The interaction between the occurrence of partial discharge (PD) and the generation of bubbles using a model that is very similar to the real structure in a transformer is studied. The inception voltage of the PD caused by the oil gap created by the axial and radial spacers might lower than that caused by a metallic impurity. However, PD caused by the metallic impurity was more likely to generate bubbles because of its higher discharge energy. It is also found that the residual space charge on the insulation surface prevents the occurrence of PD and also affects the generation of bubbles under repeated lightning impulse voltage. Moreover, it is found that generated bubbles do not affect the occurrence of PD. One reason for this is that the bubbles disappear during the interval time between repeated impulses. The effect of the residual space charge is considered to be another reason.