Discrimination between 3-phase fault currents and circulating currents measured at the source of 11 kV radial feeders

The 11 kV feeders which are supplied from 33 kV/11 kV substations are usually operated in radial mode. However due to operational necessitates the remote ends of any two feeders are often closed. When this occurred, circulating current could be established between the two feeders independently whether they belong to the same substation or to two different substations. Such current could cause the maloperation of source protection specifically designed to protect 11 kV feeders and their associated distribution transformer. This is because of the similarity between the circulating current under consideration and a 3-phase fault current. The aim of this paper is to investigate the similarities and differences between circulating currents through 11 kV distributors and 3-phase fault currents with the view to establish some sort of criteria to help source protective schemes to differentiate between the two types of currents