On-line monitoring of transformer via transfer function

Frequency response analysis method is one of the most frequently used diagnostic tools for investigating coil deformation. Transfer function is unique for each system and it changes with a variation of the system parameters. On-line measured transfer function with a suitable transformer model and the estimation of parameters can support the diagnostic. Condenser bushings rated 115 kV and above are usually provided with taps and this can be used for on-line monitoring of the transfer function. A new technique for on-line transfer function monitoring of power transformer through its bushing taps or non-invasive capacitive sensors installed on the surface of transformer bushing is presented. To evaluate the feasibility of this method, the transfer functions of a 13 kV / 230 kV / 400 kV, 500 MVA auto transformer are monitored in frequency domain in offline conditions.