This paper examines the behavior of single phase and three phase transformers with internal faults under sinusoidal and non- sinusoidal operating conditions. The terminal behavior of the transformer was investigated by coupling the finite element transformer's physical model and external electric circuit simulations. Such a model would allow the efficient representation of the transformers with internal faults. A Discrete wavelet transforms (DWT) was then used to extract the different harmonic components of the transformer currents. The key advantages of the DWT are its ability to provide a local representation (in both time and frequency) of the current signal for normal and faulty modes, as well as its applicability to nonstationary signals.
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