Innovative probabilistic approach to reduce zone-2 time delay setting of distance relays

Abstract

The time delay of distance relay zone-2 has considerable impacts on the protection system performance. Traditional deterministic techniques for adjustment of this parameter only consider the worst cases, even with a low probability of occurrence. This leads to the increment of the fault clearing time for most of the high-probability scenarios and endangers the system's stability. To diminish this issue and achieve a suitable tradeoff between protection system selectivity and operation time, a novel probabilistic framework is proposed in this paper for proper adjustment of zone-2 time delay. This framework includes two major parts; the fault and protection system are appropriately modeled in the first part, and then in the second part, the Monte Carlo method is employed as the computational engine for analyzing the system attributes under different conditions considering local and pilot protection schemes. Finally, two indices are proposed for the quantitative assessment of operation speed and selectivity of the protection system. The simulation studies fairly reveal that the operation speed of zone-2 is significantly improved using the proposed settings. In addition, the obtained results indicate that the proposed probabilistic approach not only improves the dependability, but also does not endanger the security of the protection system.