Thermal Influence on Space Charge Accumulation in Multilayer Dielectric Insulation for HVDC Systems

Accumulation of space charge within the dielectric material who is used in high-voltage direct –current (HVDC), is estimated from measured space charge distribution as a function of temperature using the pulsed electro acoustic (PEA) technique. A sandwich structure constituted by two nonidentical dielectric films Fluorinated Ethylene Propylene (FEP) and Low Density Polyethylene (LDPE) was subjected to an electric stress level of +14.3 kV/mm at three temperatures: 20 °C, 40 °C, and 60 °C. Space charge and electric field distributions were investigated for combinations of LDPE/FEP flat specimens. The time dependence of the space charge distribution was subsequently recorded at different temperatures under field (polarization) and short circuit conditions (depolarization). Experimental results demonstrated that temperature plays a significant role in space charge dynamics at the dielectric interface. The increase in temperature may result in an enhancement of charge injection from the electrodes, and increase the activation energy of charge, which in turn enhances charge mobility and conductivity. A great quantity of interfacial charge is introduced at high temperatures. The increase of the temperature increases charge injection, charge mobility, electrical conductivity, and filling of the trap, and the formation of the shallow trap.