| Transient based protection uses transient fault components to realize the protection,and it has a high speed. So it can do well in settling the conflict between speediness and reliability in traditional protection for EHV transmission line. Started from theory of MM and transient protection,several aspects of transient protection are displayed in this thesis, this paper discusses MM principle and its applications in detecting signal transient energies. The transient current generated by the internal and external faults in EHV transmission lines contains different high frequencies because of the line traps and bus-bar capacitance. The difference is extracted and amplified by Multi-resolution Morphological Gradient (MMG) to construct a novel non-unit transient current protection scheme. Based on analyzing the characteristics of modulus current components on different types faults occurred in EHV transmission lines, a transient current based fault phase selection algorithm is also presented. The schemes and algorithms mentioned above were proved to be correct and effective by lots of simulations in this paper.
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