Sequence filters: A critical review of sequence filters, analysis of design principles and an experimental investigation of the transient response of selected filters

Although individual sequence filters, developed for specific purposes, appear from time to time in the relevant literature, there has been no comprehensive treatment of them to date. In existing published work there has been little indication of the importance of correct detail design. Sequence filters were developed from the mathematical theory of symmetrical components. Filters are systematically reviewed on this basis. Initially the elements required for the construction of filters are considered. Generalised theories for the basic filters are developed and design principles established. A new design for an efficient negative sequence filter with a smaller frequency error than any previous filter is given. The performance of -ve sequence filters during 3-ph symmetrical S.C. conditions in the power system have been analysed mathematically and investigated experimentally with good agreement in the results, The development of complex filters from the basic types is considered and finally the roles performed by sequence filters in line protection is reviewed.