The fault location task is usually undertaken with the help of saved transient records of currents
and voltages during the fault. These records may be analog oscillographic records, digital fault
records or records available from many of the digital computer-based relays. In the case of analog
recordings, the calculation is based upon the reading of the current and voltage phasors from the
analog tracings, while with the digital records a direct calculation of the phasor quantities could be
made from the data samples. A convenient method of finding the fundamental frequency phasor
from one cycle of a waveform sampled at N samples per cycle is to use the discrete Fourier
transform formula