Sayyed Mohammad Hashemi

Fault type classification (FTC) is a major unit of industrial distance relays that affects some other protective schemes such as single-pole tripping and reclosing, fault location and etc. Traditional FTC techniques make use of either phase changes between current symmetrical components or magnitude differences between superimposed currents. Since inverter-based resources (IBRs) have different current signatures than those of synchronous generators, conventional FTC approaches suffer from misrecognition when applied to a transmission line emanating from an IBR. The fault current contribution of IBRs is determined by the host grid code (GC) and the internal controller. Therefore, this paper demonstrates the limitations of the conventional FTC methods employed in industrial applications for protection of lines that originate from IBRs under modern host GCs. First, the influence of various GCs on the classic FTC techniques is analyzed based on the negative-sequence control strategies. Then, some experimental tests are executed to evaluate the accuracy of industrial FTC methods in the attendance of IBRs. After that, various newly proposed FTC methods in the presence of IBRs are studied, and their advantages and disadvantages are discussed. Lastly, potential research gaps in the area of FTC with IBRs are noted for further study and investigation in academic circles.

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.

Journal of Iranian Association of Electrical and Electronics Engineers نشریه مهندسی برق و الکترونیک ایران

Reliable voltage measurement is a pre-requisite for correct operation of a relay's voltage-dependent functions. The secondary circuit of a relay's voltage transformer (VT) is usually fuse-protected. The blowing of a VT's three-phase fuses prevents correct voltage measurement, commonly referred to as the loss-of-voltage (LOV) condition. Relays are equipped with different methods to detect the LOV conditions and avoid confusing them with grid faults. However, this paper shows that existing LOV detection methods are prone to misoperation in the presence of inverter-based resources (IBRs). The paper's findings are corroborated by hardware-in-the-loop testing of relays with the state-of-the-art LOV detection methods. This paper also develops a new LOV detection method for transmission system relays that addresses the unveiled problem. The proposed method considers the fault behavior of IBRs and detects LOVs by examining certain conditions in three stages, namely phase-voltage-check, phase-current-check, and current-transients-check. Simulation studies are used to verify the dependable and secure operation of this new method for different LOVs, faults, IBRs, and VT configurations. The obtained results demonstrate that this method performs successfully regardless of the type of generation units. Moreover, it is sufficiently fast to prevent relay misoperation during LOV conditions and does not require extra hardware.

The high penetration of residential air conditioners (RACs) poses a growing concern in emerging fault‐induced delayed voltage recovery (FIDVR) in power systems. FIDVR is expected to be a significant threat to the stability and reliability of future power grids. Hence, the system planners should carry out appropriate simulation studies to mitigate the severe consequences of FIDVR events. A key question to implement these studies is how to determine the worst condition which results in FIDVR. Most of the actual FIDVR events have been experienced in the hot hours of the day and this issue makes one curious to think about the relationship between the FIDVR events and the ambient temperature. In this regard, a novel temperature‐dependent RAC model is presented and verified by using laboratory tests. Furthermore, two cases with different power system loading patterns, i.e. the peak temperature hour and the peak demand hour, are examined. The proposed RAC model is implemented on the IEEE 118‐bus test system. Moreover, an actual FIDVR event reported in Iran has been reproduced employing the proposed RAC model. Implemented simulations reveal that to precisely reproduce the recorded FIDVR event, it is necessary to consider the ambient temperature when the fault has been occurred.

Stalling of residential air conditioners (RACs) following a transient fault can delay the voltage recovery ranging from 3 to 20 seconds. This phenomenon is referred to as fault-induced delayed voltage recovery (FIDVR). Several aggregated RAC models have been presented to replicate the actual FIDVR events. However, they usually have two main drawbacks as: i) considering independent stalling voltage and stalling time for all RACs, ii) resulting in only two ultimate modes; either 100% stalled or 100% normal running. This paper amends the abovementioned shortcomings by proposing a simple and effective performance-based RAC model. The proposed model utilizes a simple explicit relation between the stalling voltage and its required time to stall the RAC, furthermore, it can stall a fraction of RACs based on the voltage dip characteristics. The experimental results support the proposed model and computer simulations employing the IEEE 118-bus test system and Iran's electricity grid reveal the effectiveness of the proposed model.

Load dynamics play an important role in the voltage stability. Grid‐side short‐circuit faults may induce severe voltage drops at motor load buses. Once the fault is cleared, depending upon its clearing time, the load bus voltage may either return to its permissible range or degrade gradually until it collapses. From the short‐term voltage stability viewpoint, the former is a stable phenomenon, while the latter is an unstable circumstance and the load should be shed in order to prevent voltage instability from being spread over the grid. To cope with this problem, this study presents a new under‐impedance load shedding (UILS) scheme. A quadratic distance relay is used as the load shedding element. The trajectory of load impedance is monitored by the proposed UILS relay. Following the grid‐side fault clearance, if the impedance trajectory enters the load shedding zone and remains inside it for a predefined time, voltage instability is detected and the load is curtailed by the UILS relay. The proposed approach is tested on various networks, including a real power system model. The obtained results approve the efficiency of the proposed UILS scheme.

Line differential protection provides the most selective protection scheme for transmission lines. It has an acceptable performance in situations which are challenging for the legacy distance protection. Following large disturbances, two or more areas of a power system may lose their synchronism and go out-of-step (OOS) which appears often as unstable power swings in some transmission lines. Existing OOS detection methods are based on the impedance trajectory seen by distance relays and conventional line differential protection cannot detect this condition. This paper introduces a new out-of-step detection method using the current phasors measured at both ends of a transmission line. Rigorous mathematical analyses and illustrated simulation study results are presented to substantiate the efficiency of the proposed method. The obtained results approve that the proposed method can be served as an efficient OOS detection method for line differential protection schemes.