RESEARCH ARTICLE Improvement of distance relay zone‐3 security using fault and breaker opening generated traveling waves Akbar Sharafi | Majid Sanaye‐Pasand | Peyman Jafarian School of Electrical and Computer Engineering, College of Engineering, University of Tehran, Tehran, Iran Correspondence Akbar Sharafi, School of Electrical and Computer Engineering, College of Engineering, University of Tehran, Tehran, Iran. Email: a.sharafi@ut.ac.ir Funding information University of Tehran, Grant/Award Number: 8101064-1-10 Summary This paper presents a new algorithm for discrimination of short‐circuit faults from power system stressed conditions. The proposed algorithm is based on the combination of distance relay zone‐3 operation and traveling waves gener- ated by either the fault or circuit‐breaker switching. By pick‐up of the distance relay zone‐3, the algorithm looks for traveling waves arriving from the fault point in the first stage. If a fault generated traveling wave is detected, it would be concluded that a fault has occurred. Otherwise, the algorithm enters the next stage and waits for arriving traveling waves caused by open‐switching of the faulted line remote circuit‐breaker. If any traveling wave is detected, the system is under fault condition. Otherwise, the reason of zone‐3 pick‐up is due to a stressed condition. Training a decision tree‐based classifier with the proposed fea- tures and simulating the method demonstrate that the proposed algorithm is able to provide a reliable remote back‐up scheme for protection of transmission lines. KEYWORDS back‐up protection, circuit‐breaker switching, decision tree, stressed condition, traveling wave 1 | INTRODUCTION Selective operation of protection system plays a significant role on the stability of power system. Maloperation of protective relays has been one of the main contributors to degradation of power system security in most of wide area disturbances throughout the world. Spurious operation of back‐up protective relays due to misinterpretation of stressed system conditions such as power swing, heavy loading, and voltage instability as a fault event has been the cause of many large‐scale blackouts worldwide. 1,2 One of the widely used protection techniques for transmission lines is distance relaying which operates based on the impedance between the fault point and the relay location estimated using local voltage and current waveforms. Commonly, zone‐3 of a distance relay is used to provide remote back‐up protection during failure of the primary protection at the next substation and is typically set to cover approximately 120% of the longest following line. One of the advantages of the zone‐3‐based back‐up protection scheme is that it is completely based on local measurements, and hence, its performance is not depen- dent upon the communication system. Because the reach of zone‐3 might be extended close to the transmission line load limit to consider in‐feed effects, during stressed con- ditions such as power swing, load encroachment, and voltage instability, the impedance trajectory might enter Symbols: Z c , Line surge impedance; R f , Fault resistance; V f , Instantaneous magnitude of the voltage at the fault moment; k, Portion of TW which passes the fault point; n, Sample number; j, Decomposition level; dj, Detail coefficient of wavelet transform; SE f , Signal energy for fault TWs; Th f , Threshold for fault TWs; SE b , Signal energy for breaker opening TWs; Th b , Threshold for breaker opening TWs Abbreviations: CB, Circuit breaker; DWT, Dyadic wavelet transform; GPS, Global positioning system; PMUs, Phasor measurement units; PSB, Power swing blocking; SE, Signal energy; TWs, Traveling‐waves Received: 5 December 2016 Revised: 5 April 2017 Accepted: 14 July 2017 DOI: 10.1002/etep.2414 Int Trans Electr Energ Syst. 2017;e2414. https://doi.org/10.1002/etep.2414 Copyright © 2017 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/etep 1 of 12