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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]

This paper presents a new approach to wide-area out-of-step (OOS) protection through predicting the power and rotor angle curves by the autoregressive moving-average (ARMA) method. To reduce the computation burden of ARMA, its parameters are estimated using an extended Kalman filter. The predictive feature of the proposed approach results in saving hundreds of milliseconds before the actual instability occurs, which can be served to activate appropriate countermeasures against wide-spread system instability. The OOS condition is detected using the extended equal area criterion developed for multimachine power systems, in which the single-machine infinite-bus model of the system is built using wide-area measurements. The proposed approach is adapted with the communication requirements of IEEE Std. C37.118, and thus, it can be used as a practical wide-area OOS protection scheme. The IEEE 39- and 118-bus systems are used to evaluate the efficiency of the proposed approach. The obtained results demonstrate the effectiveness of the proposed scheme in predicting OOS phenomena. [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]

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]

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]