Effects of Magnetic Field on Dielectric and Insulation Properties: A Review

The rapid development of electromagnetic energy equipment requires a strict evaluation of insulation performance under strong magnetic fields. Due to the influence of magnetic fields on charges, traditional insulation design principles are likely to be inappropriate. This article discusses the influence of magnetic fields on the dielectric and insulation properties of polymer materials. The key experimental phenomena and conclusions are as follows. Magnetic fields can significantly alter charge dynamics and material properties. At a magnetic flux density of 12 T, the conductivity of dielectric materials such as polypropylene increased by 152%–474%, attributed to enhanced charge injection and shallow well density. The excitation of charges and the energy level splitting caused by magnetic fields are considered to be the reasons for reducing trap depth. The dielectric constant decreases with increasing magnetic field strength, especially at low dielectric frequencies. The polarization relaxation process is modulated by the field orientation—parallel magnetic fields tend to accelerate relaxation, while vertical magnetic fields tend to prolong relaxation. Partial discharge (PD) characteristics exhibit magnetic field dependence. Due to Lorentz-driven charge accumulation and local field distortion, the PD inception voltage (PDIV) decreased by 7%–15% under a 12 T magnetic field. The phase-resolved PD (PRPD) pattern reveals changes in the discharge phase distribution. Under the magnetic field, the inception probability of electrical trees in dielectrics increases, and their growth rate accelerates. As the magnetic field increases, the electric tree trees transform from branch-like structures to bush-like structures. Nonuniform magnetic fields can guide the development direction of the electric tree toward high magnetic field areas. The breakdown strength of solid dielectrics decreased, which is caused by the excitation and aggregation of charges and the activation of free radicals.