Space charge polarization in insulating mineral oil

Dielectric spectroscopy is a powerful tool to study dipole relaxation, electrical conduction and structure of materials. Space charge polarization, as a parasitic effect due to the blocking of charge carriers in the vicinity of electrode, can mask dielectric response of the sample at low frequencies. In this paper, the frequency response of three different kinds of mineral oils have been measured and compared with the simulation based on a classic space charge polarization model. Since the creation of charge carriers in mineral oil is not only from dissociation but also injection from electrode, a modified model with injected part could describe the measurement result more accurately. The dielectric response due to electrode polarization has been simulated considering both the movement of internal charge carriers and injected charge carriers. According to the simulation results, the frequency-dependent curve of complex dielectric permittivity calculated from the polarization model could fit the experimental data well. The amount of the injected charge carriers increases with the aging time. A better fit can be obtained when high mobility charge carriers are taken into account. The present model of space charge polarization enables one to obtain a better understanding of electrical conduction in mineral oil.