الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Transformers are a critical and expensive component of the power system. Due to the long lead time for repair of and replacement of transformers, a major goal of transformer protection is limiting the damage to a faulted transformer. Some protection functions, such as over excitation protection and temperature-based protection may aid this goal by identifying operating conditions that may cause transformer failure. The comprehensive transformer protection provided by multiple function protective relays is appropriate for critical transformers of all applications.
The main object of this work is to discriminate between internal faults and those due to power transformer magnetizing inrush current. This would introduce a novel method for recognizing the different natures of power transformer currents. The proposed technique is based on stationary wavelet transform. The algorithm is based on evaluating the SWT coefficients of the fifth and six level details. The diagnosis criterion for discrimination is evaluated for each sliding window. The resulting wave shape and its time locations represent the needed signatures to identify the type of the investigated currents. Many study cases were used for testing the algorithm of discrete wavelet transform DWT and it showed to be effective and reliable assessment. But we used SWT to give more capability and dealing with electrical power system.
The simulation study cases introduced in the thesis are generated by using the PSCAD/EMTDC software then the simulated output currents are transferred via an interface block to data file which go to a matrix in the developed MATLAB software. Wavelet transform is then applied from the wave menu to extract the discriminating criterion. All the simulation results showed fast, accurate, discriminative and reliable capabilities of the SWT to identify different natures of currents flowing in a power transformer under different operating conditions.
Different outputs come from MATLAB which can show the difference between the inrush current and internal fault current.
Different fault types are examined and tested and the SWT developed technique has showed to be an effective tool with high selectivity. The developed technique when compared to other methods, showed to be superior with more accuracy, higher speed and selectivity.