Space charge analysis in enamelled wires by using thermally stimulated depolarization current (TSDC)

This paper reports on measurements of thermally stimulated depolarization current (TSDC) that is applied to characterize changes in the large motors and generators enamelled wires that have been exposed to aging under steep-front pulse voltage waveforms. The thermoelectrets are prepared at various polarizing fields, EP, and measurements of TSDC are carried out both as a function of time and temperature over the range of 23–200 °C. In addition, various TSDC parameters such as activation energy, ɛa, characteristic relaxation time, τ and the released charge, Q during the relaxation process have been determined by applying initial rise method. The experimental results for TSDC spectra of wire specimens have shown that the total stored charge in the insulation bulk increases significantly, as the number of insulation layers increases on the wire. The reason for such a higher concentration of trapped charges is more likely due to the presence of a broad distribution of the traps, which are occupied by the injected charges.