SELECTION OF DISTANCE RELAYING SCHEMES WHEN PROTECTING DUAL CIRCUIT LINES

The difficulties associated with the distance protection of dual circuit transmission lines is well known and appropriate schemes have been implemented worldwide that enable reliable protection of these assets. However, the application of these schemes usually fail to consider the more extraordinary fault occurrences that can plague transmission systems. This paper considers the application of various faults to a simulated dual circuit transmission line. The observations have shown that inter-circuit faults may be undetectable in the instantaneous zone of protection when lines incorporate some of the presently used distance schemes. These faults can present impedances to both line terminals that are larger than those required for Zone 1 operation. Such an event has the potential to lead to a loss of major loads, mal-operation of single pole tripping schemes and even system instabilities based on the critical clearance requirements. 1