Abstract:
In this thesis, a novel approach for the protection of transmission lines which utilizes only coefficient energy for both detection and classification is proposed. The fault current signals generated by workspace on MATLAB simulation model have been analyzed using Daubechie-4 (d4) mother wavelet at 7th level decomposition with the help of Wavelet Toolbox embedded in MATLAB. A case study of 132kV, 160km transmission line has been used to test the novel approach. The value of the coefficient energy of the current signals gives the indication of fault and no-fault conditions. The energy of the three phase current signal (A,B,C) at 7th level decomposition were calculated as 0.1559x10-5, 0.1328 x10-5, 0.1737 x10-5 (for normal condition), 6.4200 x10-5, 1.7730 x10-5, 1.6660 x10-5 (for A-G fault), 667.1000 x10-5, 700.9000 x10-5, 0.7860 x10-5 (for AB-G fault), 677.8000 x10-5, 689.9000 x10-5, 0.1740 x10-5(for A-B fault), 885.6000 x10-5, 898.3000 x10-5, 832.7000 x10-5(for ABC fault). Also, the coefficient energy ratios were calculated to help classify the faults. The total ratio of the coefficient energies of the three phases were found to be approximately 3.4819 (for normal condition), 5.9177 (for A-G fault), 1741.4580 (AB-G fault), 7861.3448 (for A-B fault), 3.1423 (for ABC fault). Like the coefficient energy, the ratio was found to be increasing as the severity of the fault increases, except for L-L-L fault. Hence, both coefficient energy and ratio were employed in fault classification. With the approach presented in this work, ten classes of fault (A-G, B-G, C-G, A-B, B-C, A-C, AB-G, BC-G, AC-G & ABC) could be correctly identified and classified within fault duration of 0.085 seconds. The results therefore, demonstrate the proposed approach to be fast and reliable.
