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access icon free Effects of the charge carrier elimination process on oil conductivity decrease under high electric field intensity

© The Institution of Engineering and Technology
Received 19/03/2020, Accepted 19/10/2020, Revised 09/10/2020, Published 08/01/2021

The DC conductivity of insulating oil is key to converter transformers, in which AC and DC electrical fields simultaneously exist. Research on the influence of the electric field on oil conductivity can optimise the insulation design of converter transformers. Although numerous studies have been conducted on the conductance mechanism of non-polar liquids, the explicit mechanism and properties of oil conductivity under a high electrical field remain unclear. This study developed an optimised conductance model considering charge carrier elimination, dissociation, and charge injection process. Thereafter, the authors chose three types of oils for converter transformers and measured the variations in oil conductivity and ion mobility under different electric fields with 0–10 kV/mm range. The result indicates that ion mobility will increase under a high electric field owing to the EHD effects. The conductivity of the insulating oil follows a U-shaped pattern with an increasing electric field, thereby generally matching the optimised theoretical model. Therefore, the decrease in conductivity is mainly the result of the elimination process of free ions, whereas the increase is the result of the injection process that occurs on the electrodes.

Inspec keywords: insulating oils; electrical conductivity; ion mobility; electrohydrodynamics; charge injection

Other keywords: oil conductivity; DC conductivity; nonpolar liquids; EHD effects; DC electrical fields; charge carrier elimination; conductance mechanism; dissociation; electric field intensity; AC electrical fields; insulating oil; ion mobility; electrodes; converter transformers

Subjects: Electrical conductivity of insulators; Organic insulation

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