Space Charge Accumulation at Material Interfaces in HVDC Cable Insulation Part II—Simulations of Charge Transport

Abstract

Extruded high voltage direct current (HVDC) cable systems contain interfaces with poorly understood microscopic properties, particularly surface roughness. Modelling the effect of roughness on conduction in cable insulation is challenging, as the available results of macroscopic measurements give little information about microscopic charge distributions at material interfaces. In this work, macroscopic charge injection from interfaces is assessed by using a bipolar charge transport model, which is validated against a series of space charge measurements on cable peelings with different degrees of surface roughness. The electric field-dependent conduction and charge trapping effects stimulated by the injection current originating from rough surfaces are assessed. It is shown that by accounting for roughness enhanced charge injection with the parameters derived in part I of the paper, reasonable agreement between computed and measured results can be achieved at medium field strengths (10–40 kV/mm).

Biaxially oriented silica–polypropylene nanocomposites for HVDC film capacitors: morphology-dielectric property relationships, and critical evaluation of the current progress and limitations

“…The first TSDC peak was systematically observed around T g for all the films (trap depth ∼0.75 eV). For the silica compounds however, the TSDC spectra above T g became more pronounced and complex, indicating higher presence of shallow (or rather, “inter-level” 87 ) traps with trap depths in the 0.7–0.9 eV range in comparison to neat BOPP. In the high temperature region (∼90 °C and above), the unfilled BOPP films exhibited strong TSDC peaks corresponding to charges released from deep traps (in the range of 1.1–1.3 eV), often being anomalous in the sense that the current flow was in the same direction as the polarization current (polarity reversal) which is a result from drifting of thermally de-trapped charge under the internal field caused by the space charge.…”

Impact of nanometric processes linked to charge generation on the macroscopic behaviour in polyethylene

“…Simulations have been performed in the presence of a surface roughness at the anode only. Previous studies [3,5] have shown that concave defects increase the local electric field to a larger extent. To account as simply as possible for surface roughness, protusions having an elliptic shape have been simulated on a length of 10µm at the anode.…”

“…Charges, generated at the electrodes or inside the bulk, disturb the electric field distribution, leading to local field enhancements, and potentially to an early breakdown. Bipolar charge transport models, also called BCT or mesoscopic models [1][2][3], have been developed this last two decades to predict the electric field distribution within such insulating materials. Electronic charges generation (electrons or holes) at the electrodes are generally described as charge injection, either using the thermionic -i.e.…”

“…These physical hypotheses are however too simple, and do not account for the particular material structure of the material at an interface, directly related to barrier injection, and/or energy states, and lastly to surface roughness. Experimental [1][2] and theoretical researches [3][4][5] have focused on this particular interface behaviour, but a lot remains to do. In the present paper, we propose a 2D charge transport model developed to account for different physical processes related to the interface: surface roughness, variation of the injection barrier height along the x axis related to a variation of the material structure, and an interfacial zone of 1 µm where the energy states are deeper and with a higher density.…”

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

“…Modern methodologies for the simulation of electric fields in solid dielectrics do not consider polarization processes, but focus on bipolar charge transport (BCT) models (see, for example, [14][15][16][17]). These models describe the motion of two charge carriers (electrons and holes) through the bulk of the dielectric by means of the drift-diffusion equations.…”