Measurement of Volumetric Current and Estimation of Nonlinear Dielectric Impedance of LDPE

In Low-Density Polyethylene (LDPE) insulation, the non-linear nature of volumetric current - time characteristics were often attributed to its complex space charge dynamics, apart from temperature and electric field dependence. However, a scanty attention is given to the measurement related issues of volumetric current in the literature. In this paper, the authors have presented experiments conducted on measuring circuits used in electrometer as well as with the commercial electrometer, to investigate the measurement related aspects on the current characteristics of LDPE. Matching the time constants of measuring circuit impedance with the dielectric under test, would typically offset all the errors of the measurement. However, LDPE with the non-linear variation of its impedance characteristics, makes it difficult for accurate measurement, as it dynamically deviates from the fixed time constant of the measuring circuit impedance. Hence, the true volumetric current characteristics and a novel circuit model for the impedance of LDPE are proposed. Interestingly, they are observed to corroborate well with the Transient Space Charge Limited Current (TSLC) theory.