Epoxy resin insulators are key components in DC GIL/GIS

and are subjected to complex operational conditions such as DC electric fields

temperature gradients

polarity reversal operation

and DC superimposed impulses

existing to unpredictable dynamic electric field distortion and surface discharge problems. Nonlinear conductive materials

whose conductivity increases nonlinearly with electric field

are considered to have the function in adaptively relaxing DC electric field distortions. We first review the related researches on nonlinear conductive epoxy composites

covering the electrical conduction mechanisms

formulation processes

and electrical properties. Taking into account factors such as nonlinear conductivity

breakdown strength

and the physical settling characteristics of fillers like zinc oxide (ZnO) and silicon carbide (SiC)

we regard epoxy/SiC composites as a superior choice for nonlinear conductive insulators. Subsequently

we review the development of nonlinear conductive insulators for DC-GIL/GIS in recent years

with the technical approach evolving from the initial "bulk doping" to the current "surface modification". Compared to the bulk-doped insulators with overall nonlinear conductivity

the surface nonlinear conductive insulators exhibit superior performances in regulating surface electric field and reducing conductive loss

without degrading the electrical and mechanical properties of the insulator bulk. This paper aims to provide insights for researchers and professionals in the DC GIL/GIS field

with the hope of advancing the application of nonlinear conductive insulators in engineering from laboratory research.