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The power swing detection (PSD) block plays an important role in the security and dependability of distance relays. In most commercial distance relays, power swing is detected using the concentric characteristics method. On the one hand, incremental demand for electrical energy has led that the load area gets closer to the relay operational zones in the R-X plane. Meanwhile, some grid codes requirements, such as detecting high-resistance faults, necessitate that distance operational zones (particularly zone-3) become larger in the resistance direction of the R-X plane. Considering these points, the resistive distance between the load area and distance relay zones, and accordingly, the setting time of the conventional concentric characteristics method decreases. Consequently, the correct operation of PSD function under different conditions, e.g., heavy loadings, fast power swings, fault resistance variations during the fault, evolving faults, and the effect of instrument transformers transients, would be faced with some challenges. In this article, a new PSD method is proposed by investigating the impedance trajectory during power swing conditions. A novel index named the ratio of resistance variation speed is suggested, which improves not only the security of distance relays for fault conditions including the transient behavior of current and voltage transformers and fault resistance variations, but also their dependability for power swing conditions during heavy loadings and fast swings (up to 7 Hz). The method's efficiency is evaluated on two single-machine and three-machine test systems using the PSCAD/EMTDC software. The obtained results verify the superior performance of the proposed method in different scenarios.

Fast and accurate fault location is vital for maintaining the reliability of power systems at an acceptable level. In this article, a generalized equivalent circuit (GEC) is proposed for fault location in transmission systems based on voltage and current phasors of one end of the transmission line. Based on the proposed GEC, a generalized fault location algorithm (GFLA) is designed that can be implemented for finding the location of both symmetrical and unsymmetrical faults in single/double circuit, coupled/uncoupled, and transposed/untransposed transmission lines. The proposed method can accurately obtain the location of faults without any knowledge of the fault type, faulted phase (s), and without applying sequence networks for a specific fault type. Moreover, it does not require the source impedance as an input and it is robust against uncertainties such as fault impedance. Although the proposed GFLA is iterative, it is very fast and not sensitive to the initial guess of the fault location. The simulation results show the generality and accuracy of the proposed method, which makes it suitable for various fault location applications.

Distance relay based pilot protection schemes are commonly employed in industrial relays to provide fast tripping of the faulty transmission lines. However, the probable communication link failure or interruption can make these schemes ineffective. Therefore, some non-pilot methods are addressed in the technical literature which cannot offer an appropriate performance in the presence of inverter-based resources (IBRs) owing to the unconventional fault behavior of IBRs as compared with that of synchronous generators. Thus, an analytical non-pilot method is established for the accelerated tripping (AT) of the second zone of distance relay in the presence of IBRs. At the first place with the proposed method, the faulted phase is identified through a fault classification scheme. Within the second phase, using the strength of the variations existing in the negative and zero sequence components of both voltage and current signals, the remote breaker status is realized. Finally, according to the remote breaker status, the AT or delayed tripping decision is decided. Performance of the established methodology is examined for different simulation scenarios, such as different fault locations as well as fault resistances, employing the PSCAD/EMTDC software. The obtained promising results obviously approve the efficiency of the proposed framework.

Due to the increment of network loads and also incredible costs of installing new transmission lines, the loading of transmission lines has been increased considerably. Therefore, determining critical transmission lines is quite important for the secure operation of power systems and enhancing situation awareness. This article offers a novel algorithm to identify critical lines from the synchronous generator oscillations (SGOs) viewpoint. The proposed method can identify both intra- and interarea transmission lines. Using the proposed method, linearization of the system's equations is performed to estimate the behavior of SGOs after a line outage. Using the developed state-space-based technique, critical lines are determined without requiring to solve the differential equations of the system and to perform time domain simulation studies. To do this, a novel dynamic index is introduced which is strongly correlated with both generator's oscillations overshoot and settling time indices. The proposed method can determine both critical intra- and interarea lines for each generator and area, respectively. The performance of the proposed method is evaluated on different test systems including the IEEE 118-bus system and some of the obtained results are reported. The numerous simulation results thoroughly verify the effectiveness and high efficiency of the proposed method.

The ultimate goal of power transformer protection system is to quickly and reliably detect internal faults while remaining stable for external faults and transients. Since in the conventional protection system, each relay decides about the transformer condition independently, it can be considered that the output signals of relays are logically “OR”ed with each other. In this case, confirming internal fault condition by more than one relay does not increase the confidence level of decision-making and consequently the operation speed, while maloperation of one function causes the failure of overall protection system. To cover this drawback, this article introduces a new protection paradigm based on fusing the decision of independent protection functions. The fundamental concepts along with an application of this approach are proposed in the article. Besides, to improve the fusion performance, a probabilistic approach for the protection functions is suggested. Results of the comprehensive evaluations and field data verifications demonstrate that the proposed approach not only increases the operation speed and dependability of protection system, but also improves its security by accurately detecting the transformer status even in cases where a protection function maloperates for a transient condition.