the data in the paper

Transformers, especially dry-type transformers, which nowadays are going to be employed instead of oil-type transformers, are one of the major equipment in the generation, transmission and distribution network of electric energy. The transformer insulation strength may reduce due to partial discharge (PD) occurrence, and this can finally result in its insulation failure. In order that the insulation of a subtransmission dry-type transformer becomes immune against partial discharge effect, the electric field intensity in the insulation should be kept less than the PD inception electric field intensity. Measurement and determination of PD inception parameters provide the necessary information for warning the users. The two main partial discharge inception parameters to be investigated are the partial discharge inception voltage and the partial discharge inception electric field intensity. These two parameters are also important in the insulation design of transformers. This paper proposes a combined method using the experimental and the finite element (FEM) modeling to determine the partial discharge inception parameters. In the presented comprehensive experimental model, the detailed dimensions of the transformer winding as well as the grounded transformer core and the insulating spacers are modeled. therefore, the experimental modeling resembles the actual working conditions of the dry-type subtransmission transformer under test. As a result, the accuracy in modeling the partial discharge inception parameters increases. In the proposed method, the partial discharge inception voltage under ac stress and the approximate discharge inception time are experimentally determined by using ultra high frequency (UHF) antenna. Then by simulating the proposed electrode structure in Comsol software, the electric field distribution and the partial discharge inception electric field intensity is obtained.