Simulation and Modelling of Transient Electric Fields in HVDC Insulation Systems Based on Polarization Current Measurements

Abstract

Simulating and modelling electric field dynamics in the insulation of medium- and high-voltage DC electrical systems is needed to support insulation design optimization and to evaluate the impact of voltage transients on ageing mechanisms and insulation reliability. In order to perform accurate simulations, appropriate physical models must be adopted for the insulating material properties, particularly conductivity, which drives the electric field in a steady-state condition and contributes to determining the field behavior during voltage and load transients. In order to model insulation conductivity, polarization, and conduction, mechanisms must be inferred through charging and discharging current measurements, generally performed at different values of electric field and temperatures in flat specimens of the material under study. In general, both mechanisms are present, but one of them may be predominant with respect to the other depending on type of material. In this paper, we showed that models based on predominant polarization mechanisms were suitable to describe impregnated paper, but not polymers used for HV and MV DC insulation. In the latter case, indeed, trapping–detrapping and conduction phenomena were predominant compared to polarization, thus conductivity models had to be considered, in addition to or as a replacement of the polarization model, in order to carry out proper electric field simulations.

Circuital Modeling of Polarization and Depolarization Currents in Polymeric Materials Under Low Electric Fields

“…As an example, Fig. 19 shows the match between the space charge measured from XLPE at 20°C and its estimate from (24).…”

“…The samples were thermally pre-treated and had goldsputtered electrodes with a diameter of 26 mm and a guard ring. The system has a resolution of 0.001 pA, with a background noise of 0.1 pA. More details on the setup are given in [24].…”

“…During depolarization 𝐵 ̇ plays the major role, as the deep traps release the captured carriers. The polarization processes, 𝐶𝑣̇s and 𝑖 sp , take place for both short and long times, even if in the long-term they may be overwhelmed by trapping and detrapping [24].…”

Electrical Conduction Mechanisms in Ethyl Cellulose Films under DC and AC Electric Fields

“…The conduction mechanisms controlled by the bulk are complex and have several origins. The orientation of electrical dipoles (permanent or induced) by the effect of an external electrical field produces a current that can be measured [ 15 , 16 ]. Additionally, the injection of electrons can be evaluated through an electric current.…”