Moisture‐dependent interface and bulk behaviour of space charge in DC‐stressed oil‐impregnated pressboard insulation

Abstract

Abstract In this paper, the effect of moisture on the charge behaviour in oil‐impregnated pressboard is analysed based on the characteristics of the interface and the bulk. Space charge behaviour and infrared spectra are acquired from a sample with a high moisture content of 1.92% and another with low moisture content of 0.13%. The results show that a greater number of hydrogen bonds form in the high‐moisture sample. The threshold fields of charge injection are 1 and 0.6 kV/mm in the low‐ and high‐moisture samples, respectively. The dynamic charge transport in bulk is significantly accelerated by moisture. The drop in the injection barrier at the interface and the accelerated transport of charge in bulk in the high‐moisture sample may be associated with the mediating effect of a water layer at the interface and the lower trap energy in bulk caused by the hydrogen bonds, respectively. The combined changes in the interface and the bulk led to the dominant position of negative charges inside the high‐moisture sample, regardless of the distribution area or the charge amount.

Keywords

• Organic insulation
• Engineering materials
• Transformers and reactors