Evaluation of apparent trap-controlled mobility and trap depth in polymeric HVDC mini-cables

Polymeric insulation materials have not been used in HVDC cable systems until recently because of the tendency of polymers to deplete accumulated charges very slowly. Research on space charge injection, conduction and trapping mechanisms can reveal information about which materials are the best candidates for HVDC cable insulation. In this paper, space charge de-trapping and extraction processes are evaluated in polymeric mini-cables consisting of several different XLPE based insulation materials and PE based semi-conductive layers. The main difference between the materials can be found in the type and concentration of additives. De-trapping and extraction of accumulated space charge in the insulation is investigated with the help of depolarization measurements, which are performed with the Pulsed Electro-Acoustic (PEA) method for cable geometry objects.