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It is possible to produce electrical signals proportional to symmetrical component (sequence) quantities from directly measurble phase quantities in three-phase power circuits. This paper presents details of a simple sequence filter design using the operational amplifier as its basic component. Such signals can be used in the laboratory or in a classroom demonstration, in situations which provide the student with clear insight into the nature and properties of symmetrical components. This paper presents some representative applications which demonstrate how the educational mission of the filter can be achieved, including pure sequence excitation and fault detection. Extending the design to N-phase applications is also discussed.