Effects of Gradient Magnetic Field on Electrical Tree Growth Characteristics in Silicone Rubber

In this article, the positive and inverse gradient symmetric magnetic field and the asymmetric magnetic field with different angles are constructed. The influence of the magnetic field distribution on the electrical tree characteristics is investigated. The experimental results show that both the positive and the inverse gradient magnetic fields can promote the deterioration of the electrical trees. Under the symmetrical $\Delta 1.5$ T gradient magnetic field, the tree initiation probability increases from 55% to 100%, and the breakdown time decreases by 67.5%. Under the $\Delta $ -1.5 T, the tree initiation probability increases from 55% to 75%, and the breakdown time declines by 57.5%. The morphology of the electrical trees is largely affected by the distribution of the magnetic field. The dispersion of the degradation channels increases with the enhancement of the magnetic field. Under the asymmetric magnetic field, the deterioration process is also accelerated, with the increase of the magnetic field. More importantly, the growth direction of the electric trees shifts to the side with the higher magnetic flux density. The magnetic field enhances the local electric field and promotes the occurrence of partial discharge by exerting a deflection force on the charges. Consequently, the growth rate and morphology of electrical trees are affected.