Modified concentric power swing blocker applicable in UPFC compensated line

Flexible AC transmission systems (FACTS) devices have adverse impacts on the performance of distance relays (DRs) due to the fast intervention of the controllers of these devices during power swing. Power swing blocker (PSB) as the complementary part in a DR is designed to distinguish a fault from a power swing; meanwhile its performance in compensated lines needs to be investigated. The performance of concentric PSB (CPSB) is studied in transmission lines compensated by unified power flow controller (UPFC). It is shown that fast responses of proportional-integral (PI) controllers of UPFC, reduce recorded time by CPSB significantly (it decreases by 90% of uncompensated condition) which makes DR to issue trip command during power swing condition. Detailed model of UPFC is simulated in three-machine and New England power systems to show the deficiency of CPSB in compensated condition. In order to overcome the deficiency of the CPSB in UPFC-compensated line, two remedial actions are proposed. The first method is based on modifying CPSB to solve the problem and the second method is based on modifying control loop of UPFC to prevent the problem. Both methods show their efficiency to overcome the deficiency.