Analysis of Fault Detection Algorithms Used in Line Differential Protection (87L)

Recently, the use of optical communications systems along with modern numerical relays made the application of the current differential protection (CDP) function possible even for long transmission lines. Longitudinal differential protection is among the crucial protection mechanisms for protecting the lines. Line differential protection has shown better performance in conditions that are challenging for legacy distance protection. Longitudinal current comparison protection has been used in the industry for many decades, yet there is still room to improve the reliability and sensitivity in more challenging events. Specifically, in time-critical situations where the faulty condition might damage the network if it lasts more than a few milliseconds. To inspect, an MV testbed with two different variations equipped with some well-known fault detection algorithms is designed to be used to represent any given MV transmission network. Then some mathematical and performance methods are collected to be examined on the two suggested testbeds to extract the features and trajectory patterns of calculated values. Among these algorithms, in this study, Alpha plane as one of the famous phasor-based methods and Clarke transform as one of the methods using instantaneous values of the currents have been analyzed in the accuracy and sensitivity in various given scenarios. This study helps the body of knowledge around designing multipurpose testbeds, discussing the performance of methodologies suggested in the literature, and investigating the prospect of using a time-domain-based method such as the Clarke transform to break free from the delay associated with the full-cycle observation window needed for a valid phasor estimation employed predominantly in Alpha plane characteristic and similar strategies.