Space charge estimation in epoxy-based nanodielectrics using complementary techniques

Abstract

One of the major problems of polymeric insulation is their tendency to accumulate space charge at higher electric fields, especially in HVDC (High Voltage DC) applications. Nanodielectrics are an emerging area of research because of their potential as a novel insulating material in electrical apparatus and systems. Understanding space charge behavior in these new materials is crucial to their application in high field environment. In the present work, space charge behavior in epoxy alumina nanocomposites is investigated by using Pulse Electro Acoustics (PEA), Conduction Current (CC), and Electroluminescence techniques in conjunction. The PEA technique is used to measure accumulated charge density, and maps the space charge distribution in the volume of the dielectric. Polarization- Depolarization current measurements are carried out to extract conduction current density, dc conductivity, and permittivity. Electroluminescence measurements are related to injection and impact ionization of charge carriers. Space charge density, conduction current density, and electroluminescence counts, show a transition above a certain electric field. The electric field above which all three characteristics undergo a transition is associated with the threshold field for accumulation of space charge. Nano-dielectrics show lower space charge, and lower conductivity at higher fields than neat epoxy. The permittivity of the nanodielectrics is seen to be higher than neat epoxy at lower electric fields. At higher fields their permittivities are comparable. The complementary findings from all three techniques prove to be effective in characterizing the space charge in the nano dielectrics.