<p style="text-align:justify"><span style="font-size:14px">We have already discussed that some minimum voltage is required for the operation of the directional relay. The numerical directional relay provides the facility of voltage memory in such a case where voltage available to relay is small. The relay measures the voltage available at relaying point and if it is less than certain pre-set value (usually 15 % of 110 V, the rated voltage), the voltage memory function is activated. The relay, in this case, uses the memorized pre-fault voltage.</span></p>