Accurate Estimating Algorithm of Transfer Function for Transformer FRA Diagnosis

Frequency response analysis (FRA) is an effective tool to detect winding deformation. If variation occurs to the FRA trace, a fault may be indicated. A new method to estimate the transfer function from FRA measurement results on large
bandwidth is proposed. A MATLAB program is developed to auto-process the measured data and to obtain the transfer function expression. Measurement results from large frequency ranges are divided into several ranges, and key information is abstracted from each range to form a new transfer function. Afterwards, correction is still needed to eliminate the difference between estimated transfer function and measured data. This method is verified as valid for estimation of transfer functions of 48 groups of FRA data of a 400/275 kV auto-transformer.