Using superimposed principles (Delta) in protection techniques in an increasingly challenging power network

Superimposed techniques also called Delta or Incremental techniques have been used for more than 30 years in protective relays. Directionality for distance relays has been implemented in different ways and has/is widely used. Directional Comparison relays were popular in the 80s and 90s and sometimes they were called “Directional Wave relays” meaning the relays detect the origin direction of travelling waves. Some of those relays use to quote operating time as little as 2-5 ms. As well as directionality, phase selection based on superimposed quantities has been used for similar amount of time. The principle has the advantage of calculate very fast fault direction and phase selection as well as an increased sensitivity due to the removal of prefault conditions.