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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. [ABSTRACT FROM AUTHOR]

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 OOS 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

It is commonly assumed that power swings are symmetrical phenomena that impose almost identical effects on the three-phase voltages and currents of the power system. However, there is another type of power swings which is asymmetrical and occurs mainly during single-pole tripping. In the nowadays heavily loaded power systems, the likelihood of occurrence of this phenomenon is increased considerably. Although the effects of symmetrical power swings on distance protection are widely analyzed in the literature, asymmetrical power swings have been less studied so far. This paper focuses on this type of power swings and their effects on distance protection. Besides, two new techniques are proposed to detect faults during asymmetrical power swings and enhance performance of power swing blocking schemes. The first technique is based on the rate of change of zero sequence current, while the second one is based on the magnitudes of voltage and current in each phase, as well as their relative phase angle. The presented analyses and proposed methods are validated using two benchmark test systems and promising results are obtained. [ABSTRACT FROM AUTHOR]

Synchronous generators of any size require protection against loss of excitation because it can cause harmful effects to the generator and power grid. This paper proposes a new setting-free approach to detect loss of excitation in synchronous generators. Unlike the conventional method, which requires demanding work to set the relays, the proposed method does not require any threshold to act. It will be shown that after loss of excitation, the rate of change of resistance measured by relay 40 (ANSI Code for protection against loss of excitation) will become negative and remain negative for a while. On the other hand, it will be shown that during the slowest power swings, the rate of change of resistance cannot remain negative for more than 1.7 s. This, therefore, can be used as a criterion for detecting the loss of excitation of a synchronous generator. The main advantages of the proposed method are that it is setting-free and meanwhile acts faster than the most famous method introduced in 1949. [ABSTRACT FROM PUBLISHER]

This study presents a new protective scheme for transmission lines which are compensated by thyristor‐controlled series capacitor (TCSC). Employing the averages of voltage and current, a new criterion is introduced to discriminate between the forward and reverse faults. The validity of introduced criterion is tested for the inductive and capacitive modes of TCSC. During normal conditions, the averages of voltage and current are almost zero. While, following a short‐circuit fault, they change from zero to non‐zero values. The concept of fault superimposed components is used to extract the mathematical equations of the proposed scheme. Various case studies are considered to evaluate the performance of the proposed scheme. Computer and experimental simulations approve the efficiency of proposed method in high‐speed protection of TCSC‐compensated transmission lines. [ABSTRACT FROM AUTHOR]

This study presents an adaptive phasor estimation approach for fast numerical distance protection. The proposed method is based on signal condition assessment and choosing the proper phasor estimation method. Effects of errors caused by decaying DC component and coupling capacitor voltage transformer transients, as the main problems for distance relay impedance measurement procedure, are alleviated using the proposed adaptive method. Meanwhile, a new short window DC removal method is introduced. Thanks to the fast DC value estimation method, a short window phasor estimation method is utilised for current phasor estimation. Using the proper phasor estimation method based on voltage and current signal conditions results in more accuracy, fast decision making procedure and consequently a more reliable protection scheme. To verify the performance of the proposed method, numerous simulation studies are carried out. The results assert that the proposed adaptive method not only accelerates the relay operation, but also improves the relay accuracy which enhances numerical distance protection from security and dependability viewpoints. [ABSTRACT FROM AUTHOR]

Differential protection is able to provide the most selective protection compared with other protective schemes. In this paper, a new differential scheme is proposed for pilot protection of transmission lines. The concept of differential impedance (Zdiff) is introduced using the synchronous voltages and currents of both terminals of the line. The proposed scheme is capable of fast discriminating between the internal and external faults, even in the worst operating conditions. The dependence on the line capacitive charging current and the source strength are common problems in conventional pilot protection methods which have been removed in the proposed scheme. Moreover, compared with the conventional differential protection, the proposed scheme can exactly determine the fault location. Both computer and experimental simulation studies have been performed to evaluate the proposed scheme. The obtained results approve the high efficiency of the proposed scheme as powerful pilot protection. [ABSTRACT FROM PUBLISHER]

In this study, a novel scheme is proposed for pilot protection of transmission line based on the fault component integrated power (FCIP). An appropriate definition is proposed for FCIP. The proposed scheme is able to quickly discriminate the normal condition, internal fault and external fault situations, even in severe operating and emergency conditions. This FCIP‐based scheme is not affected by the line charging capacitive and, therefore it does not need to be compensated for the capacitive current. Hence, this novel pilot protection scheme, based on FCIP, can be used for long distance high‐voltage transmission lines. The faulty phase/phases can also be detected by the proposed scheme. Moreover, compared with a newly‐introduced protective scheme which is based on the fault component integrated impedance, the proposed FCIP‐based scheme has faster operation speed. The efficiency of the proposed protective scheme is evaluated and approved over extensive simulation studies. [ABSTRACT FROM AUTHOR]

BACKGROUND: Cardiovascular diseases are the major causes of mortality worldwide and acute myocardial infarction (AMI) is the leading cause of mortality among cardiovascular diseases. Thrombolytic therapies, especially during the first few hours after the disease onset, can significantly reduce AMI-related mortality. METHODS: The current study aimed to determine the prevalence and causes of non-administration of thrombolytic therapy for AMI patients admitted to Hajar Hospital, Shahrekord, Iran, from May until November 2000. Non-probability convenient sampling method was used to select 106 subjects with Q-wave AMI. Data was collected by completing a questionnaire, reviewing medical records, and interviewing with patients. SPSS7.5 was for data analysis. RESULTS: A total number of 106 AMI patients were studied among whom 62 (59%) individuals received thrombolytic therapy. Delayed referral to the hospital was the major cause of failure to provide thrombolytic therapy. The cause of non-treatment could not be identified in 15 (19.5%) subjects eligible to receive therapy. CONCLUSION: Training general practitioners and individuals involved in this regard along with accelerating the process of patient referral to hospitals can reduce AMI-related mortality. [ABSTRACT FROM AUTHOR]

herosclerosis has a high prevalence in systemic lupus erythematosus (SLE) patients and vascular endothelial dysfunction is the earliest stage of atherosclerosis. The aim of this study was to evaluate the prevalence of vascular endothelial dysfunction and its risk factors in SLE patients and to identify its correlation with disease activity, duration and concomitant conditions in these patients. A total of 84 female SLE patients and 18 healthy young women were included. The vascular endothelial function was evaluated via ultrasonographic assessment of the brachial artery diameter to determine flow-mediated dilation (FMD) and post-TNG dilation-FMD gap (PFG) indexes. FMD indexes of one standard deviation lower than mean FMD of the control group were considered as impaired, and PFG indexes of one standard deviation more than mean PFG of the control group were defined as impaired. SLE patients had a higher prevalence of impaired FMD than healthy subjects (48.8 vs. 5.5%). The prevalence of impaired PFG in SLE cases and healthy subjects was 25 and 5.5%, respectively. FMD and PFG impairment did not have any significant correlation with disease activity, duration, presence of anti-dsDNA, anticardiolipin antibodies, antiphospholipid syndrome and history of receiving cyclophosphamide pulses. Vascular endothelial dysfunction is very common in SLE patients and no single specific factor can explain this finding. We recommend the application of brachial artery Doppler ultrasound as a screening test for detection of early stages of atherosclerosis in SLE patients. [ABSTRACT FROM AUTHOR]

• Establishing the sequence impedances of the IBRs on the analytical basis showing the main differences between the IBRs and their predecessors in the sequence network. • Suggesting a single-ended fault location scheme which is independent of the pre-fault data in the presence of IBRs. • Estimating the remote source impedance by means of the healthy line records,. • Providing fault location results for all asymmetrical short circuit faults in the presence of IBRs. • Extending the suggested fault location scheme for long transmission lines including considerable charging current. This paper aims to reveal conventional impedance-based fault location methods' shortcomings in the presence of inverter-based resources (IBRs) through an analytical framework established for the analysis of the IBR sequence impedances. Thereafter, a single-ended method is put forward in order to accurately specify the fault location in the lines emanating from the IBRs. The proposed fault location formulation utilizes the negative and zero sequence currents as alternative polarizing currents, therefore it is independent of the pre-fault data, and it can be applied for all kinds of asymmetrical short circuit fault. Furthermore, the established formulation is further amended to make it applicable to long transmission lines. The suggested method also provides acceptable accuracy in various conditions, such as different fault resistances, different host grid codes, and dynamic behavior of the fault resistance. The performance of the proposed scheme is scrutinized using the PSCAD/EMTDC software with an extensive number of simulations. The obtained results reveal the effectiveness and efficacy of the proposed fault location method in the presence of IBRs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary: A wide‐area backup protection (WABP) method is proposed in this paper based on the zone status of distance relays. The time difference between the operation of zone‐3 and wide‐area based methods makes it possible to employ wide‐area data for improvement of zone‐3. In case of zone‐3 is directly backup for zone‐1, the proposed method can decrease the time delay of zone‐3 with a complete reliability. Moreover, the proposed method is capable of discriminating between the actual faults and power system stressed conditions. Considering the operational time of wide‐area methods, the algorithm could also be applied for zone‐2 backup protection. The proposed method is also developed to consider the availability of wide‐area data for all busses within the disturbance area, as well as data missing for one or two adjacent busses, which are remarkable advantages over the existing WABP methods. Meanwhile, the wide‐area data used in the proposed method are only the pickup/release status of distance relays zones which are binary data and can be communicated readily through existing wide‐area infrastructures. Simulation results on the IEEE 57‐bus test system demonstrate the effectiveness of the proposed method as a promising WABP in improving the performance of zone‐3 in distance protection schemes. [ABSTRACT FROM AUTHOR]

This paper introduces a new approach, based on faster-than-real-time (FTRT) analysis, to predict out-of-step (OOS) condition of a turbine-generator (T-G) unit subsequent to a fault scenario. The proposed FTRT analysis is based on 1) solving a state-space model of the T-G electromechanical system and corresponding controllers without the need for online measurements, and 2) an estimated Thevenin equivalent of the rest of the power system. The measurement-free FTRT analysis is carried out after the Thevenin parameters are estimated subsequent to the fault clearance instant. Equal area criterion is applied on the predicated variables to detect OOS condition. A reliable decision can be made based on this approach, since it does not involve simplifying assumptions contrary to the existing approaches. The FTRT approach accurately considers the impacts of the detailed model of the generator, automatic voltage regulator, prime mover, governor system, and the host power system. This paper provides detailed mathematical formulation for the proposed OOS detection method and verifies its feasibility and accuracy based on single machine and large test systems. The proposed approach is also implemented on an industrial platform and evaluated. The results confirm that the proposed approach can accurately identify OOS conditions, earlier than the rotor angle noticeably increases. [ABSTRACT FROM AUTHOR]

• Proposing a new fault classifier which correctly classifies the fault type in the presence of IBRs. • Acceptable performance regardless of IBR internal controllers, prefault condition, fault location and fault resistance. • Compatibility of the proposed method with the traditional and modern grid codes. • High security due to the variety of input signals. Fault type classification is a critical stage in modern distance relays for activating the effective phase and ground distance elements. It is also used for some supplementary functions such as single-pole tripping and reclosing, teleprotection, and fault location. Traditional fault type classifiers are based on the symmetrical or superimposed components of the current signal. However, owing to the unconventional behavior of inverter-based resources (IBRs) compared to the synchronous generators, traditional methods are not reliable in the presence of IBRs. For example, modern grid codes impose some restrictions in terms of injected current during asymmetrical fault which put the accuracy of conventional fault classification methods in danger. Fault resistance could also affect the accuracy of fault type classification method. In this paper, first, the fault current signature of IBRs is analytically derived. Then, impacts of modern grid code and fault resistance on the conventional fault classification are properly evaluated by executing some simulation studies. Finally, a new fault classifier is proposed which is based on symmetrical components of the local voltage and current during asymmetrical faults. The proposed classifier presents a satisfactory degree of security in the faulted phase identification in the presence of IBRs under different host grid codes. Performance of the proposed method is properly analysed with different simulation scenarios such as different fault locations, fault resistances, pre-fault condition, test systems, and host grid codes in PSCAD/EMTDC software. [ABSTRACT FROM AUTHOR]

• Proposing a new non-pilot solution to speed up the second zone protection of distance relays. • Detecting the remote circuit breaker operation (RCBO) using the healthy phases data. • Developed method for both single- and three-pole circuit breaker (CB) mechanisms. • Investigating the proposed algorithm with various simulations besides some experimental tests. • Proposing an immune scheme to the CT saturation and CVT transients. Nowadays, power systems are operated closer to their stability margins and therefore, the need for faster protection algorithms is escalated. The second zone of distance protection is conventionally set to operate with some lengthy delay, which increases the fault clearing time for the end part of the protected line. Therefore, the acceleration of zone-2 for internal faults can remarkably increase the speed of line protection. This practice is traditionally performed by pilot protection systems, which rely on communication channels. This paper proposes a new non-pilot solution to this challenge using only local measurements. A phasor-based algorithm is proposed to detect the remote circuit breaker operation (RCBO) using the healthy phases data. The proposed method has been developed for both single- and three-pole circuit breaker (CB) mechanisms, which makes it practical for transmission and sub-transmission lines. Thanks to using the healthy phases data, the proposed method is immune to the current transformer saturation and capacitor voltage transformer transients. The performance of the proposed method is simulated and investigated in various critical situations besides some experimental tests. The obtained results approve the efficiency and robustness of the proposed method for different scenarios, e.g. noisy conditions, evolving faults, and parallel lines. [ABSTRACT FROM AUTHOR]