Short-circuit conditions can occur unexpectedly in any
part of a power system at any time due to various physical problems. Such situations cause a large amount of fault current flowing through some power system apparatus. The occurrence of the fault is harmful and must be isolated promptly by a set of protective devices. Over several decades, protective relaying has become the brain of power system protection [1].Its basic function is to monitor abnormal operations as a "fault sensor" and the relay will open a contractor to separate a faulty part from the other parts of the network if there exists a fault event. To date, power transmission and distribution systems are bulky and complicated. These lead to the need for a large number of protective relays cooperating with one another to assure the secure and reliable operation of a whole. There-fore, each protective device is designed to perform its action dependent upon a so-called "zone of protection" [2]From this principle, no protective relay is operated by any fault outside the zone if the system is well designed. As widely known that old fashion analog relays are inaccurate and difficult to establish the coordination among protective relays, the relay setting is typically conducted based on the experience of an expert or only a simple heuristic algorithm. However, with the advancement of digital technologies, a modern digital protective relay is more efficient and flexible to enable the fme adjustment of the time-dial setting (TDS) different to that of the old fashion electromagnetic one.