Symmetrical components theory, presented by Fortescue in 1918, and its analysis of the time domain presented by Lyon in 1954, have been widely used for fault analysis and power system protection algorithms. In recent times, applications in time domain have been deeply studied given their potential for getting a quicker failure detection, there are two main techniques which apply signal processing methods in the time domain: Travel-wave and incremental quantities. The theoretical background of symmetrical components to fault analysis is well recognized. Currently, the fault protection algorithms using symmetrical components are based on frequency domain. This paper presents a theoretical analysis of the use of symmetrical components in time domain, particularly in asymmetrical faults. A Signal processing algorithm to obtain the instantaneous symmetrical quantities from phases quantities are presented. A study case is simulated to validate the time domain technique and fault analysis permits show the potential of the results to develop protection algorithms.