A protection device for a power cable that includes a central conductor surrounded by insulation based on paper impregnated with material based on impregnation oil may include a sheath around the insulation, a first portion of the cable stripped of the sheath, an adjacent portion of the cable stripped of both the insulation and sheath, the adjacent portion penetrating the connector; an outer protection extending over at least the first and adjacent portions, and extending over the connector; and/or a plug of high-permittivity mastic material filling an axial space extending along the adjacent portion. The outer protection may include a barrier layer in contact with the insulation along at least part of the first portion. The barrier layer may include elastomer material that is virtually impermeable to the oil. The plug may axially separate the barrier layer and connector to prevent migration of the oil into the connector.