Research on thickness ratio and multilayers effect on the oil and paper space charge distribution

Under the HVDC condition, the formation of the space charge in the oil paper system could affect the electric field distribution for converter transformers. Therefore, it is important to analyze the factors that determine the space charge behavior such as the temperature, moisture, electric field, oil paper thickness ratio and multilayers such as (Oil+Paper+Oil+Paper) structure. This paper focuses on the space charge distribution affected by the multilayers (O+P+O+P) oil paper structure and different oil paper thickness ratios. The pulsed electroacoustic method (PEA) was used to measure space charge distributions. It is found that increasing oil thickness could facilitate charge injection. However, the increase of pressboard thickness could prevent the charge injection. It is also found that the same oil paper thickness ratio could lead to similar space charge injection within the oil paper sample under the same 10 kV/mm electric field. Therefore, based on the same oil paper thickness ratio, space charge measured from the thinner thickness sample were further applied to the thicker thickness sample to estimate electric field distribution using COMSOL software, which cannot be measured by the PEA system directly.