Space Charge Diagnostics in Aged Polymeric Insulation

Condition assessment of DC insulation systems is important from the point of view of operation and reliability. Under DC field, space charge accumulates within the bulk of the insulation in polymeric insulators. These accumulated charges cause local field intensification within the volume of the insulator, and subject the material to additional stresses, promoting aging. Therefore assessment of space charge in DC insulation is important. In this work, we study the effect of thermal aging on space charge accumulation in polyethylene, epoxy, and epoxy based nanocompositesunder DC applied field. From space charge measurements, trap depth and trap controlled mobility are estimated. Further, dielectric loss factor is estimated from depolarization current characteristics using Hamon approximation. Thermal aging causes the material to become increasingly lossy, and this is seen to be accompanied by a proportional change in space charge characteristics i.e. accumulated charge density, trap depth, and mobility.