Characterization of Conduction Properties of DC Cable Dielectric Materials

Modern power systems are undergoing a grand transformation towards a wide area transmission network, publicly known as “Smart Grid” and “Super Grid”, for technical and economic advantages. Regional systems have been built-up towards national grids and later interconnected with neighboring countries. High voltage direct current (HVDC) is emerging rapidly as an effective and efficient solution for grid interconnection, island electrification, urban grid decongestion, renewable off-shore wind energy integration. Despite the emerging opportunities, significant technical challenges persist for HVDC/MVDC technology, namely in DC cabling and accessories, DC breakers and DC diagnosis and monitoring. The major challenge for DC cabling resides in the insulation due to performance deterioration by space charge accumulation. DC cable dielectrics require optimization of materials that meet a desired property which differs from AC cable dielectrics. In this comprehensive study, the properties needed for the insulation system intended for DC cables and the approach to the design and development of DC formulation with proper balance between key electrical properties, have been investigated. A formalism which includes the correlation between the conductivity and space charge based on two physical materials parameters, activation energy and mean trap separation, has been developed, based on which the role of chemical defects and physical disorder in controlling the conductivity of polymers as well as their implication on practical material design and development are discussed. Basic understanding of those two physical parameters may bring the ability to engineer desirable DC material as well as improved capability to understand the physical basis of aging and other phenomena in dielectrics. These findings contribute towards tailored polymeric insulation materials with superior electrical performance of DC cables for future energy efficient power grids.