Abstract: Abstract:The directional element is a major part of relay protection function elements. The memory voltage of directional element is used to ensure the right action during threephase outlet fault. Based on Fourier algorithm, the influence of the frequency deviation of the power system on amplitude and phase of the current and voltage were analyzed. The action features of the positive sequence directional element were discussed in depth. Aiming at the problems of memory voltage of directional element during fault occurrence of power system with frequency deviation, a rational solution was given.

Key words: Keywords:directional element, memory voltage, frequency deviation, phasephase shortcircuit fault