Generator fault detection technique using detailed coefficients ratio by daubechies wavelet transform

An AC (alternating current) generator is one of the important components in producing a electric power and so it requires highly reliable protection relays to minimize the possiblity of demage occurring under fault conditions. Conventionally, a RDR (ratio differential relaying) based on DFT (discrete Fourier transform) has been used for protecting the stator winding of a generator. However, when DFTs based on Fourier analysis are used, it has been pointed out that defects can occur during the process of transforming a time domain signal into a frequency domain one which can lead to loss of time domain information. This paper proposes the adoption of a protection algorithm for the stator by applying a WT (wavelet transform) to overcome the defects in the DFT process. Moreover, a new ratio equation is proposed for easy utilization of the detailed coefficients by DWT (Daubechies wavelet transform) through the course of MLD (multi-level decomposition) using MATLAB. For the case studies reported in the paper, a model system was established for the simulations utilizing the ATP (alternative transient program), and this verified the effectiveness of the proposed technique through various off-line tests carried out on the collected data. The propose method is shown to be able to rapidly identify internal faults and did not operate a miss-operation for all the external faults tested.