Locating transformer faults through sensitivity analysis of high frequency modeling using transfer function approach

The online condition monitoring of power transformer insulation can give early warning of electrical failure and could prevent catastrophic losses. Transfer function analysis offers the additional advantage of fault identification and location. High frequency resonance in a transformer can be modeled by analogue distributed winding concepts. Every transformer has an unique transfer function independent of the shape of the input waveform and can be evaluated through sweep and impulse tests. Results show that this transfer function changes by winding deformation, displacement, ground leakage, local breakdown and partial discharges etc. Digital simulation of impulse and variable frequency transient responses together with their fast Fourier transform spectral analysis are used in this paper to identify transformer faults and characterize their influence on transfer function. Sliding faults through the winding revealed changes in the transfer function to help locate the fault´s location. This paper contributes to the development of a high frequency transformer model capable of studying faults including partial discharges, deriving condition assessment of a previously untested transformer from the varied characteristic plots to assess remaining life of a power transformer