Design, testing and application of moisture impervious cable

Moisture barriers can effectively protect the insulation of medium voltage cables from water treeing. Activities to study and qualify the performance of moisture barrier cable have progressed on a global scale. Design concepts for three types of moisture barrier cable are presented. One design includes wire neutrals with a separate moisture barrier over the neutrals and under the jacket. In the second design, the moisture barrier acts as both a radial water block as well as a shield. Materials for the sheath, such as plastic coated metals, water-blocking tapes, cushion layers for thermal expansion, and adhesives for sealing, are discussed. The third design utilizes a thin lead/plastic laminate placed directly over the insulation semiconducting screen. This is called an on-core design. Standardization activities for watertight cable are proceeding on an international scale. Application of watertight cables in several power systems indicates reduced fault rates and lack of failures associated with treeing