As an essential component of power transformer, transformer bushing’s reliable operation does not only impact the safety of transformer itself but also other equipment located nearby. To prevent bushing failures, it is therefore important to routinely assess bushing insulation and pin-point the potential problem as early as possible. In this paper, fault diagnosis and tear-down analysis of five 500kV oil-impregnated paper (OIP) transformer bushings are presented. Results of different field and laboratory diagnostic tests are discussed and compared. Key features of partial discharge-led defect with x-wax deposits are analysed. The effectiveness of adopting frequency domain spectroscopy (FDS) in combination with dissolved gas analysis (DGA) as supplementary field diagnostic test is then demonstrated.
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