Space charge measurements by the thermal-step-method and TSCD in polymeric materials

Several methods are available for studying the space charge inside an insulating material. The thermal step method (TSM) is operative to locate and measure the space charge in samples from various thicknesses and geometries such as films, sheets, slabs and cables. This nondestructive method is based on the measurement of the thermodilatation current after applying a thermal step on one side of the sample. We have performed TSM measurements in association with thermally stimulated discharge currents (TSDC). The coupling of both methods is an efficient tool: TSM gives the localisation of charges while TSDC gives the energy levels. In this paper, space charge formation in polyethylene terephtalate thin films has been investigated and we present some results obtained from the coupling of both methods. Polyethylene terephtalate (PET) polyester films are a common dielectric used in film capacitors.