Studies on the effects of moisture and ageing on charge de‐trapping properties of oil‐impregnated pressboard based on IRC measurement

Abstract

The dielectric properties of oil-paper insulation degrade due to moisture ingression and ageing. This degradation significantly impacts the space charge accumulation and charge trapping behaviour in the insulation, which are vital parameters for insulation health under the high-voltage direct current environment. In this work, an improved model based on the isothermal relaxation current (IRC) has been developed to study the charge trapping behaviour of an oil pressboard under the influence of moisture and ageing. The conventional IRC model considers the total relaxation current because of charge de-trapping only. However, in the case of a composite dielectric like oil pressboard, dipolar relaxation also affects the relaxation current. In this work, a methodology has been proposed to investigate charge de-trapping behaviour of oil-pressboard insulation considering the dipole relaxation process from IRC measurements. For this purpose, frequency domain spectroscopy measurements and IRC measurements have been performed on oil-impregnated pressboard specimens carefully prepared in the laboratory having different ageing conditions and moisture contents. Results presented in this work depict that charge trapping parameters, i.e. the trap depth and trapped charge distribution are highly affected both by ageing and moisture. It was observed that ageing leads to the generation of deeper traps, while moisture mainly enhances the density of shallow traps.

Improved space charge transport model in bi‐layer dielectrics—considering carrier dynamic equilibrium

“…In solid dielectrics, carriers are governed by a set of self-consistent equations as following [9][10][11][12][13][14]17]. The current continuity equation:…”

“…In solid dielectrics, carriers are governed by a set of self‐consistent equations as following [9–14, 17].…”

Investigations on the effect of ageing on charge de‐trapping processes of epoxy–alumina nanocomposites based on isothermal relaxation current measurements

“…From the time at which the particular amount of charge is extracted ( t n ), the trap depth ( E tn ) for that corresponding time can be calculated from the following equation: The trap density ( N t ) at the trap depth E t can be evaluated from Using (5) and (6), the trap density ( N t ) at trap depth E t can be calculated easily. In this present work, the values of υ and f 0 have been adopted as 6.2 × 10 12 and 0.5, respectively[21].…”

“…Using (5) and (6), the trap density (σ t ) at trap depth E t can be calculated easily. In this present work, the values of υ and f 0 have been adopted as 6.2 × 10 12 and 0.5, respectively [21].…”

“…The method employed for obtaining trap distribution is isothermal relaxation current (IRC) [21][22][23] measurements with certain modifications in the analysis methodology. This modification is the inclusion of polarisation-depolarisation current (PDC) measurements in the IRC model.…”