To assess the condition of oil paper insulation using the X-Y model simulation, a model transformer with the alternative geometry structure has been designed. Equivalence between X-Y model simulation and field frequency domain spectroscopy measurement is verified in this paper. Then the influences of geometric structure, oil conductivity, water content of pressboard and aging condition on the frequency domain spectroscopy results of oil-paper insulation system are investigated respectively. Results show that a "hump" is visible in the frequency spectroscopy of tanδ when the oil conductivity is higher. The frequency where the maximum value of the "hump" appears shifts to higher value with the increment of oil conductivity, but the maximum tanδ values are the same. The frequency of the maximum value of the "hump" also shifts to higher with the increment of X or Y value of the insulation structure, meanwhile the amplitude of the "hump" decreases. The frequency range influenced by water content of pressboard is related to oil conductivity. With the degradation of oil paper insulation, the frequency spectroscopy of tanδ shifts to higher frequency. A new method using X-Y model simulation to assess the ageing condition of transformer insulation is optimistic.
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