Abstract
AbstractApplying environmentally friendly ester liquids in high‐voltage direct current (HVDC) converter transformers is a technological ambition that requires research on their performance under DC voltages. This paper researched ester liquid‐impregnated Kraft paper through experimentally investigating space charges and dielectric properties under HVDC fields. The study focused mainly on the influence of cellulose degradation. Hence, Kraft papers of different degree of polymerisation impregnated with fresh ester liquid and fresh mineral oil were tested, and their space charges, electric field distortion, conductivity and permittivity were evaluated. Strong correlations were found between these parameters. Electric field distortion in fresh ester liquid‐impregnated paper (ELIP) was higher than that in fresh mineral oil‐impregnated paper (MOIP) but remained almost constant with paper‐ageing. However, electric field distortion increased noticeably in MOIP with paper‐ageing and became higher than that in ELIP. Thus, electric field distortion resulted from space charges and conductivity mismatch under new and ageing conditions must be considered in designing the insulation systems of converter transformers.
Published Version
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