Cross‐linked polyethylene is a chemically stable polymeric dielectric material with high dielectric strength, low dielectric constant and a small dissipation factor. Because of these excellent dielectric properties, cross‐linked polyethylene is used as an insulating material for electric power cables. Based on the results of much research working as an engineer of a cable manufacturer and in academia, this article describes the outline of charge generation under DC voltage stress and electrical degradation occurring in the material under AC voltage stress. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.