Frequency response analysis (FRA) is a technique for evaluating the mechanical integrity of power transformers. This paper proposes a methodology to locate inter-disc fault in a transformer winding through FRA measurements. A core-type three phase transformer is used for simulating faults on several locations along the interleaved winding, from top to bottom end. Correlation coefficient, vector fitting and Nyquist plot are employed to assist in the analysis. By drawing the transfer function of the winding response on Nyquist plot, key information is extracted and two equations are developed to locate the fault.