The principle of the current correlation differential protection based on the correlation integration was analyzed further in this paper. Through the analysis

we found that this criterion has disadvantages in some system conditions. Aiming to the applied requirement in the field

an improved applied correlation criterion was proposed. The power system models of different structures using ATP were built to simulate the improved criterion completely. Simulation studies show that the improved criterion preserves the advantages of correlation criterion

which is simple

fast and not effected by the distributed capacitance

more sensitive and reliable

easy to set. Pilot studies prove that the improved criterion is very suitable for the protection of EHV/UHV transmission lines.