Interruption Failure Research Articles

Analysis of Single Server Markovian Queueing Model with Differentiated Working Vacation, Vacation Interruption, Soft Failure, Reneging of Customers

This article investigates the reneging of customers in M/M/1 model with differentiated working vacation, vacation interruption and soft failure. The customers come with rate λ and receives service during busy period with rate μ, where λ and μ obeys markovian distribution. In this model two distinct vacations are considered: one has been taken just after serving all customers in busy period with slow service rate θ as some soft failure occurs during working vacation (Vacation I). At an epoch of completion of working vacation, if any customers are present in the system, then the server moves to busy period for serving customers otherwise move to vacation II. During vacation II if customer comes then interruption is assumed to occur in the vacation and server returns to busy period otherwise remain in vacation .When an arriving customer finds server is on working vacation, it makes customer impatient and it start up an impatient timer T0 with an exponentially distributed rate α0 If service does not begin before T0 expires, the customer might renege with probability p without getting served or wait for their turn with probability 1-p=q. By using PGF technique we have derived different steady state probabilities and various system performances analytically. Effect of few parameters on different system performances have been shown numerically and illustrated graphically.

Study on the influence of mechanism dispersion on transient recovery voltage distribution of modular DC vacuum circuit breakers

AbstractA simulation analysis and an experiment are carried out to investigate how the gap difference between the breaks of a direct current vacuum circuit breakers with multi‐breaks (MB‐DC VCB) caused by the mechanism dispersion of the breaker influences the distribution of TRV among the breaks. An interruption model of MB‐DC VCB, combining the continuous transition model, is established to analyse the rising rate of transient recovery voltage and the dielectric strength recovery speed of the breaks for MB‐DC VCB under different gap difference conditions. Based on the experimental platform of dual break DC vacuum circuit breaker breaking, the correctness of the simulation model is verified on a DC VCB with the double‐breaks interruption experimental platform. Moreover, a model is applied to the non‐synchronous interruption simulation of a DC VCB with three‐breaks. The relationship between the TRVs of the breaks under different gap difference conditions is analysed using the comparative analysis method, obtaining the maximum gap difference at the moment of breaking failure. The results of this study show that large‐gap breaks have a higher TRV than small‐gap breaks (the fracture of the action delay module), with double fractures reaching 1.4 times and triple fractures reaching a maximum of 1.52 times; the ability of small‐gap breaks to withstand TRV is weak, giving rise to re‐breakdown or even interruption failure; as the number of fractures increases, the maximum gap difference also increases. Improving the synchronous interruption ability of the MB‐DC VCB is conducive to improving the interruption performance and interruption success rate of this type of a circuit breaker.

THE PROBLEM OF RELIABILITY OF GEODESIC NETWORKS

Nowadays, the theory of reliability is widely used in the construction industry, and it is also used in the field of geodesy. By abstracting its position, it can be successfully transferred to systems that, it would seem, are not in a dynamic state. Let's take, for example, the points of the polygonal (leveling) network in the city. It would seem that such a network is in a static state, but over time it undergoes changes, that is, it is in imperceptible dynamics and its reliability gradually decreases.
 Reliability in the broadest sense of the word means the ability of a technical device (system, network) to operate without interruption (failure) for a given period of time under certain conditions. Such a period of time is usually determined by the time of execution of some task, which is carried out by the device or system and is part of the general operational task.
 Currently, the problem of reliability is becoming one of the central problems of engineering and management organization. Ensuring the reliable operation of all system elements is of primary importance.
 The modern interpretation of the term "reliability" in geodesy is associated with Baard's reliability theory, according to which reliability is defined as "the ability of the network to self-monitor against gross errors [1]. One of the indicators of reliability is the minimum amount of gross error that can be detected after statistical analysis of the corrections obtained after equalization. On this path, many difficulties arise, most of which remain unsolved, namely the impossibility of localizing a gross error, quantitative assessment of reliability, methods of designing reliable geodetic networks. The unsatisfactory state of reliability theory limits its practical application, but at the same time, the problem of product reliability is the main one in modern production and its importance is growing all the time. In this regard, there is an acute problem in highlighting new views on solutions to this problem in the field of designing and creating geodetic networks.
 A new scheme for constructing the theory of reliability of geodetic measurements is proposed. Its basis is a probabilistic determination of reliability, a system of tolerances, and methods of localizing gross errors. Reliability is defined as a probabilistic measure of the homogeneity of measurements that have passed control. Quantitative reliability is estimated by three indicators: differential, integral and the minimum gross error. The Neumann-Pearson criterion is recommended for establishing tolerance. This theory makes it possible to design geodetic networks with a given reliability.

Study on impact of gap difference on plasma distribution of direct current vacuum circuit breaker with double-break

During the fault current breaking process of a mechanical direct current vacuum circuit breaker (DC VCB) with double-break (DB), the mechanism’s dispersion can result in a gap difference between the two breaks. A DB DC VCB breaking experiment platform is constructed in order to investigate the impact of gap difference on plasma distribution during the DB DC VCB breaking process. During the experiment, a high-speed camera is used to capture the vacuum arcing process at the two breaks under varying gap difference conditions. Then, the arc feature parameters and their variations during the zero-zone process are extracted using image processing techniques, and the distribution patterns of plasma and arc energy at the two breaks are analyzed and compared. When there is no gap difference between the two breaks of the experimental DB DC VCB, there are no significant differences in arc energy and the sizes of high-, medium-, and low-temperature plasma zones between the two breaks. When there is a gap difference between two breaks, the break with the smaller gap has larger high and medium-temperature plasma zones, more concentrated arc energy, higher particle concentration, lower arc diffusion velocity and arc energy decay velocity, and a greater amount of residual plasma after the extinguishing of the arc. When the gap difference exceeds a certain threshold, energy spots appear on the contact surfaces, and a high concentration corridor of residual particles remains between the contacts after the current crosses zero, forming a breakdown weak point that eventually leads to arc re-ignition (hence interruption failure) under the action of transient recovery voltage.

Lifetime estimation and surface degradation of MCCB contact tips due to multiple electrical interruptions

This paper presents the surface degradation analysis of contact tips of commercial (20A, 110 V) molded case circuit breaker due to multiple electrical interruptions during experimental electrical test. In the experimental electric test, and according to the post arc current observation, the arc voltage and current were categorized. Multiple high-current interruption has been identified, and the phenomena that regulate the interruption failure have been established. Also, post-arc current sprinted for a short period of time (10–200 µs) during multiple electrical interruptions. These interruptions cause the failure of the contact tips of MCCB. The metallurgical changes were also observed on the contact tips. The braze joints between contacts tips and copper base is also affected by thermal and electrical conductivity during the electrical interruptions. The optical microscope reveals the typical metallurgical changes that occur during a breakdown, such as surface degradation, wear, cracks adjacent to the braze interface, oxide layer formation, cracks on the contact tips, and cracks that penetrate into the copper base. The experimental investigation of the factors influencing the post arc current was carried out to learn more about the link between the post arc current and the degradation of the interruption characteristics. This investigation’s primary objective is to explore the interruption performance and failure analysis of commercial MCCBs.

Cost Effective Reliability Improvements in 33kV/11kV Electricity Distribution Networks – A Case Study in Western Province South 1, CEB, Sri Lanka

Electricity Distribution system in Sri Lanka consists of 33 kV, 11 kV and LV (400V/230 V) networks. Providing reliable supply to the end user is a challenging task to any utility. Therefore, utility is committed to develop its network to provide reliable supply to electricity users by investing in system developments. In this research, a methodology is introduced for selecting cost-effective solutions to improve the reliability of the 33 kV and 11 kV distribution systems among different proposals. Improvement of conductor, its insulation and protection of short duration faults are focused to develop the system in this research. Part of the method developed includes a software tool (named as DisFeeRIA) to analyse the reliability indices and economic parameters for the relevant proposal. Database of the DisFeeRIA software tool includes failure rate improvement, mean time to repair and costing of each option under consideration. Medium Voltage Underground Cable (MVUGC), Medium Voltage Aerial Bundle Conductor (MVABC), Medium Voltage Covered Conductor (MVCC), Room Temperature Vulcanizing (RTV) Si-R coating on existing bare overhead line ceramic insulators are considered as options for improving conductor and its insulation. One of the latest and innovative technologies used in distribution network, Pulse Closing Technology, is used to reduce short duration faults (momentary interruptions) and enhance the lifetime of the equipment used in distribution networks. Developed tool and method were tested by a case study done for distribution network in Western Province South – 01 of Ceylon Electricity Board (CEB). Three (03) feeders were selected in different areas from Urban, Coastal and Rural for this purpose. MVCC and RTV Si-R coating for existing Medium Voltage Bare Overhead lines can be used for improving the reliability of Coastal, Urban and Rural distribution feeders in a cost-effective manner after proper analysis, based on technical and economic aspects. However, depending on the safety concerns, MVUGC or MVABC can be used irrespective of the economical aspect. Intelirrupter pulse closers can be used to replace traditional auto recloses, especially with MVUGC, MVABC and MVCC in rural feeders. It helps to reduce momentary interruption failures and enhance the equipment lifetime by reducing thermal and mechanical stress on all distribution equipment and cables. Furthermore, it improves the power quality of the system.

開極タイミング変化時におけるアーク温度の解析

The gas circuit breakers have the problem of re-ignition after current zero. The instantaneous voltage drop causes enormous damage in the case of current interruption failure. Therefore, it is the responsibility of circuit breaker to interrupt the current quickly and reliably. Efficient cooling of the arc temperature is important in order to prevent the re-ignition caused by the transient recovery voltage. In this paper, the arc temperature as a function of opening electrodes timing was analyzed. As a result, the three-dimensional transition of arc temperature to current zero for each current interruption timing at each sine wave time was obtained. In addition, the opening electrodes timing that decreases the arc conductance at current zero was elucidated.

Anti-corrosion behaviour of TiO2-nanocomposites coated stainless steel

• This research work discussed the corrosion behavior of Nano coatings on stainless steel by measuring the corrosion rate via the weight loss method. • As a result, the plating of the nanocomposite based on thin-film technology establishes high-performance functional Nano coatings for corrosion resistance. Thus, minimize the costs of repairs due to corrosive damage, avoid service retardation and operation failure of the equipment, and save lives from injuries caused by weathered equipment and facilities. • The plating of the nanocomposite through the dip-coating method based on thin-film technology provides good corrosion resistance. The three-component mixtures of titanium dioxide, zinc oxide, and polyamide were formed in various ratios. • The thin film of nanocomposite was characterized by Scanning Electron Microscopy (SEM), and Fourier Transforms Infrared Spectroscopy (FTIR) from various researchers. TiO2: ZnO: Polyamide mixture ratio (0.276:0.200:0.524) indicates the minimum weight loss in the corrosive environment (0.921), so it was selected as the optimum mixture for coatings. The present study reports the corrosion behavior of Nano coatings on steel substrate (304L SS) by measuring the corrosion rate via the weight loss method. The morphology and chemical constituents of the nanocomposite thin film were characterized by Scanning Electron Microscopy (SEM), and Fourier Transforms Infrared Spectroscopy (FTIR) from various researchers. TiO 2 : ZnO: Polyamide (PA) mixture ratio (0.276:0.200:0.524) indicates the minimum weight loss in the corrosive environment (0.921), so it was selected as the optimum mixture for coatings. As a result, the plating of the nanocomposite based on thin-film technology creates high-performance functional Nano coatings for corrosion resistance. Thus, minimize the costs of repairs due to corrosive damage, avoid service interruption and operation failure of the process equipment, and save lives from injuries caused by weathered equipment and facilities.

Resilience Assessment of an Urban Metro Complex Network: A Case Study of the Zhengzhou Metro

An urban metro network is susceptible to becoming vulnerable and difficult to recover quickly in the face of an unexpected attack on account of the system’s complexity and the threat of various emergencies. Therefore, it is necessary to assess the resilience of urban metro networks. However, the research on resilience assessment of urban metro networks is still in the development stage, and it is better to conduct said research using a technique which combines many attributes, multiple methods, and several cases. Therefore, based on the complex network modeling and topological characteristics analysis of metro systems, a metro network’s robustness and vulnerability measurement method under node interruption and edge failure is proposed for the first time in this study. Then, considering the three cases of general station interruption, interchange station interruption, and traffic tunnel failure, a quantitative resilience assessment model of metro networks is put forward, and the corresponding recovery strategies are discussed. Finally, a case study of the Zhengzhou Metro Network (ZZMN) under an extreme rainstorm is conducted to demonstrate the viability of the proposed model. The results show that ZZMN possesses scale-free and small-world network properties, and it is robust to random interruptions but vulnerable to deliberate attacks. ZZMN still needs to improve its effectiveness in information transmission. The centrality distribution for each node in the ZZMN network differs significantly, and each node’s failure has a unique impact on the network. The larger the DC, BC, and PR of a node is, the lower the network’s robustness after its removal is, and the stronger the vulnerability is. Compared with the three cases of general station interruption, interchange station interruption, and traffic tunnel failure, the network loss caused by tunnel failure was the lowest, followed by general station interruption, and the interruption at interchange stations was the most costly. Given the failures under various cases, the metro management department should prioritize selecting the optimal recovery strategy to improve the resilience of the metro network system. This study’s findings can assist in making urban metro systems less vulnerable to emergencies and more resilient for a quick recovery, which can provide scientific theoretical guidance and decision support for the safety and resilient, sustainable development of urban metro systems.

Integrated optimization of a regional integrated energy system with thermal energy storage considering both resilience and reliability

The regional integrated energy system (RIES) is widely adopted from the viewpoints of energy saving, emissions reduction and resilience enhancement. Especially, in case of external energy supply interruption caused by extreme events, a RIES can survive and ensure energy supply by multi-energy coupling and reserve capacity. Moreover, the resilience and reliability of a RIES can be further enhanced by employing energy storage equipment. In this study, an integrated optimization framework has been proposed for a RIES including thermal energy storage accounting for both resilience and reliability. Firstly, a rolling optimization model is developed to calculate the minimum capacity of backup thermal energy storage at each time. Following which, the day-ahead economic scheduling is carried out based on the constraint of backup energy. The Monte Carlo method based on the Markov process is used to simulate the system reliability. The reliability model can also reflect the increase of operation costs caused by backup thermal energy. As an illustrative example, a regional energy system located in Shanghai, China has been selected for analysis. According to the simulation results, the backup thermal energy storage improves both resilience and reliability of the RIES system, and ensures the load supply in case of external energy interruption or equipment failure. There are nine load-shedding periods with improved energy satisfaction rate under external energy interruptions in summer and five in winter. Furthermore, under 10,000 days of operation simulation, the supply interruptions due to equipment failure decrease from 47 to 15 in summer and 22 to 4 in winter.

Performance Analysis of Passive Resonance Circuit Breakers in HVDC Systems

High voltage direct current (HVDC) systems have been increasingly employed to provide a connection amongst various energy sources, especially renewable energies. In order to switch the load current in these systems, the passive resonance breaker (PRB) is employed as a transfer switch. The interruption capability of the PRBs is highly dependent on the dynamic behavior of the arc in this system. Accordingly, this article presents a black-box high-degree of freedom arc-model based on Schwarz and the genetic algorithm as a heuristic optimization to follow the characteristics of the static and quasi-static arc regarding the oscillation frequency of the interruption current. The model has been verified by the published experiments. Subsequently, the PRB operation has been quantified based on the state-space approach along with an accurate dynamic arc model to follow in a wide frequency range of the arc current. The results are indicated that the amplification coefficient alone is insufficient to determine the interruption capability of these protection tools. Therefore, this article attempts to quantitatively determine the interruption capability curve by introducing criteria, such as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Δt_PZ</i> (peak to zero time-interval), <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">arc</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">/dt_CZ^-</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">du</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">arc</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">/dt_CZ⁺</i> to obtain the origins of the interruption failure probabilities and dimensioning of the PRBs with respect to the interruption limits for gas blast CBs.

Impact of cyber attacks on distributed compressive sensing based state estimation in power distribution grids

Modern power distribution grids suffer from multiple vulnerabilities due to the tight integration between the physical system and the cyber infrastructure. Sophisticated and malicious cyber attacks continue to adversely impact the grid operation leading to performance degradation, service interruption, and grid failure. State estimation plays an essential role in grid monitoring and advancing cyber-attack situational awareness. In this regard, this paper first proposes a distributed compressive sensing (CS) state estimation approach for an unobservable distribution grid. The proposed distributed CS approach divides the distribution grid into sub-areas to perform local state estimation. Then an alternating direction method of multipliers (ADMM) based iterative information exchange among neighboring areas is employed to complete the estimation process. In this estimation process, the impact of loss of measurement data, false data injection (FDI), replay, and neighborhood cyber-attacks is analyzed. Extensive simulations are performed on the IEEE 37-bus and IEEE 123-bus standard networks to demonstrate the algorithm’s robustness to the aforementioned cyber-attacks. A quantitative analysis of computational complexity and simulation time of the distributed CS based approach is also presented.

Effectiveness of Prophylactic Use of Hepatoprotectants for Tuberculosis Drug-Induced Liver Injury: A Population-Based Cohort Analysis Involving 6,743 Chinese Patients.

Background: Tuberculosis drug-induced liver injury (TB-DILI) is a common and potentially severe adverse drug reaction leading to treatment interruption and treatment failure. The real-world preventive effectiveness of hepatoprotective agents for DILI is not well described. The aim of the study was to evaluate the patterns of prophylactic therapies in real-world settings and risks of DILI among adult TB patients without known risk factors for DILI. Methods: This is a population-based retrospective cohort study of patients receiving first-line anti-tuberculosis drugs in the Chinese Center for Disease Control and Prevention (CDC) TB registry linked to the Ningbo Regional Health Care Database (NRHCD) between 2015 and 2020. The primary exposure was any use of chemopreventive agents including silymarin and/or glycyrrhetinic acid during the 30-day period prior to TB diagnosis (index date). The main outcome measure was the occurrence of newly onset DILI following TB treatment. Eligible patients were followed until the earliest of any DILI, treatment discontinuation, death, or end of the study period (30 June 2020). Marginal structural competing risk models and Cox models via inverse probability treatment weights using high-dimensional propensity scores were used to estimate subdistribution hazard risks (SHR) and 95% confidence intervals (CIs) for DILI risks, with adjustment for age, sex, TB-related characteristics, and comorbidities. Results: We identified a cohort of 6,743 adult patients with TB (mean age of 47.1 [SD 18.7] years; 65.80% male), of whom 2,886 (42.8%) patients received hepatoprotective agents. A total of 895 DILI events and 111 all-cause death events without DILI were observed over a median follow-up of 367 days post-TB diagnosis. The incidence rates of composite outcomes combining DILI and all-cause mortality were 248.9 and 222.3 per 1,000 person-years in the hepatoprotective agent exposed and unexposed groups (relative hazard ratio 1.35, 95% CI 1.11–1.64), respectively. The incidence rates of DILI were 223.7 and 196.1 per 1,000 person-years in the hepatoprotective agent exposed and unexposed groups (relative hazard ratio 1.38, 95% CI 1.12–1.71), respectively. Patients with any chemopreventive agent use had comparable liver function changes as evidenced by laboratory tests. Conclusion: A non-trivial number of adult patients received chemopreventive agents for TB-DILI. However, prophylactic utilization of hepatoprotective agents was not associated with a reduction in TB-DILI risks.

Realizacija besprekidnog napajanja komandno-upravljačkog centra u sistemu OOiU

The emergency and notification warning system has the task to, in accordance with legal regulations, rules and observances, perform all necessary measures in order to monitoring, inform, and if necessary, partial or general public alerting of the population in the endangered area. The emergency and notification warning system, which is, among other things, very important for the Emergency management sector of the Republic Serbia, is managed from the command-control center. The importance of this system is evidenced by the fact that it has data transmission on two transmission paths (WiFi and UHF). Based on the above, it follows that it is very important to ensure robust, reliable and uninterrupted operation of the CCC and thus the smooth operation of the emergency and notification warning system. Uninterruptible power supply (UPS) plays a significant role in ensuring reliable, uninterrupted and autonomous operation of the entire system. The role of BPN is very important, because in case of loss of mains power 230 V, 50 Hz, it should take over the power supply of the system. The control system should provide a very fast switching (switching time ≤10 ms) to the backup power supply without interruption and voltage failure of the entire system. When working on a battery bank, the autonomy of the designed system in the absence of mains power is 48 hours. The paper will present the practical implementation of such a system, as well as the experimental results obtained during the operational commissioning of the UPS system. The solution is in use in the CCC-Valjevo of the emergency and notification warning system, starting from June 30, 2020.

Secure State Estimation and Control of Cyber-Physical Systems: A Survey

Cyber-physical systems (CPSs) empower the integration of physical processes and cyber infrastructure with the aid of ubiquitous computation resources and communication capabilities. CPSs have permeated modern society and found extensive applications in a wide variety of areas, including energy, transportation, advanced manufacturing, and medical health. The security of CPSs against cyberattacks has been regarded as a long-standing concern. However, CPSs suffer from extendable vulnerabilities that are beyond classical networked systems due to the tight integration of cyber and physical components. Sophisticated and malicious cyberattacks continue to emerge to adversely impact CPS operation, resulting in performance degradation, service interruption, and system failure. Secure state estimation and control technologies play a vital role in warranting reliable monitoring and operation of safety-critical CPSs. This article provides a review of the state-of-the-art results for secure state estimation and control of CPSs. Specifically, the latest development of secure state estimation is summarized in light of different performance indicators and defense strategies. Then, the recent results on secure control are discussed and classified into three categories: 1) centralized secure control; 2) distributed secure control; and 3) resource-aware secure control. Furthermore, two specific application examples of water supply distribution systems and wide-area power systems are presented to demonstrate the applicability of secure state estimation and control approaches. Finally, several challenging issues are discussed to direct future research.

Interrupter Size Effect of High‐Voltage Gas Circuit Breaker on Thermal Interruption Performance and Current Zero Properties

Small model interrupters are convenient to investigate interrupting performance of high‐voltage gas circuit breakers in terms of efficiency. However, the equivalence of interruption phenomena of small model interrupters (e.g., interrupting performance, interruption criteria, and geometric sensitivity) to product‐scale interrupters has not been clarified. Interrupting tests with small and large model interrupters were carried out with the dimensions of the interrupter as parameters to clarify the effects of modified interrupter dimensions on blast pressure and interrupting performance. Arc voltage and arc conductance were measured to acquire detailed electrical behavior in the thermal interrupting phase. In the results, small model interrupters showed the same performance trends as geometrically modified large model interrupters. By introducing an interrupter size factor, the boundary of the extinction peak of the arc voltage and arc conductance at 200 ns before current zero that distinguishes the success and failure of interruption for both small and large models agreed well. Moreover, the arc parameters determined by Cassie and Mayr arc models were analyzed with consideration to interrupter size factor. In conclusion, the interrupter size factor was validated from the point of arc phenomena and an equivalence of small model to product‐scale interrupter was confirmed. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Comparison of the Interrupting Capability of Gas Circuit Breaker According to SF6, g3, and CO2/O2 Mixture

In the study, an interrupting performance test on the 145 kV gas circuit breaker is performed according to three different gases: SF6, g3 (5% NovecTM4710 with 95% CO2), and CO2(70%)/O2(30%) gases. Thanks to research advancements, it is confirmed that CO2 and g3 (5% NovecTM 4710) gases, respectively, have 40% and 75% dielectric strength, compared to that of SF6 gas. The filling pressure and transient recovery voltage criteria of each gas were determined differently in order to compare the maximum interrupting performance of each gas. The pressure of SF6 gas was determined to be 5.5 bar, which is typically used in circuit breakers. The pressure of the other two gases was determined to be 8.0 bar (the maximum available pressure of the test circuit breaker) to find the maximum interrupting performance. Moreover, the rate-of-rise of transient recovery voltage of SF6 was determined as 10 kV/μs, which is the value at the state of maximum interrupting performance of the test circuit breaker with SF6. On the other hand, the rate-of-rise of transient recovery voltages of g3 (5% NovecTM4710 with 95% CO2) and CO2(70%)/O2(30%) gases were, respectively, determined as 4∼5 kV/μs to find the interruption available point. The characteristics of arc conductance, arc current, and arc voltage near the current zero, and post-arc current are analyzed to compare the interrupting performance, according to different arc-quenching gases. The arc current is measured using a current transformer (Rogowski coil), and a signal processing method of the arc current and arc voltage is introduced to increase the reliability of the interrupting performance results. As a result of the test, it is confirmed that the critical arc conductance for all test conditions converged within a certain range and the value is around 0.7 mS. In addition, the critical current slope just before the current zero-crossing during the interrupting process is shown to be 1.8 A/μs between interruption success and failure. Consequently, it is verified that the CO2(70%)/O2(30%) mixture and g3 (5% NovecTM4710 with 95% CO2) have a similar arc extinguishing performance and SF6 has a relatively higher extinguishing performance than that of CO2(70%)/O2(30%) mixture and g3 (5% NovecTM4710 with 95% CO2) under the aforementioned filling pressure and TRV conditions.

Fault Location in Solar Farms

Power delivery interruption and catastrophic failures are some of the potential consequences of undetected faults in photovoltaic (PV) arrays. A voltage protection scheme with the minimum number of sensors which is capable of detecting, classifying, and locating line-to-line (intrastring and cross string), line-to-ground, and open-circuit faults in a utility-scale PV array is proposed in this article. The proposed protection scheme consists of three steps. In the first stage, by a simple and efficient algorithm occurrence of any disturbance in the system is detected using some voltage sensors. At this stage, faulty strings in the PV array are also identified. In the second step, using a new least squares-based method, fault and shading conditions are discriminated from each other. Finally, in the third step, the faults inside the faulty string are located using a new method based on multiclass artificial neural networks. Fault location methods that have been developed so far require a large number of sensors or additional equipment for the exact location of faulty modules inside the fault string, but in the proposed method, only one sensor is used per string for fault localization. The proposed scheme for detection and location of faults is evaluated by simulating a typical system in different conditions.

Mesh topology based clock synchronization technique for pseudolite systems

Clock synchronization is critical for synchronous pseudolite systems. Wireless synchronization methods are desirable for their flexibility in system deployment, and most of them build a tree topology of time information flow based on master-slave synchronization between pseudolites. A slave pseudolite can receive signals broadcast by multiple pseudolites; however, existing methods usually utilize one signal and ignore others in which the time information could improve synchronization precision and reliability. We present a mesh topology based clock synchronization (MTCS) technique by utilizing all received signals. MTCS builds a mesh topology of time information flow, which can keep synchronization in case of link interruption or pseudolite failure. The coupling relationship of slave clocks is derived, and the influence of measurement biases is analyzed. As shown by both analysis and simulations, MTCS has better clock synchronization precision. When link interruption or pseudolite failures occur, MTCS is more robust than tree topology based methods.

A randomized controlled trial evaluating general endotracheal anesthesia versus monitored anesthesia care and the incidence of sedation-related adverse events during ERCP in high-risk patients

ERCP is a complex procedure often performed in patients at high risk for sedation-related adverse events (SRAEs). However, there is no current standard of care with regard to mode of sedation and airway management during ERCP. The aim of this study was to assess the safety of general endotracheal anesthesia (GEA) versus propofol-based monitored anesthesia care (MAC) without endotracheal intubation in patients undergoing ERCP at high risk for SRAEs. Consecutive patients undergoing ERCP at high risk for SRAEs at a single center were invited to participate in this randomized controlled trial comparing GEA and MAC. Inclusion criteria were STOP-BANG score≥3, abdominal ascites, body mass index≥35, chronic lung disease, American Society of Anesthesiologists class >3, Mallampati class 4 airway, and moderate to heavy alcohol use. Exclusion criteria were preceding EUS, emergent ERCP, tracheostomy, unstable airway, gastric outlet obstruction or delayed gastric emptying, and altered foregut anatomy. The primary endpoint was composite incidence of SRAEs: hypoxemia, use of airway maneuvers, hypotension requiring vasopressors, sedation-related procedure interruption, cardiac arrhythmia, and respiratory failure. Secondary outcomes included procedure duration, cannulation success, in-room time, and immediate adverse events. Two hundred patients (mean age, 61.1 ± 13.6 years; 36.5% women) were randomly assigned to GEA (n= 101) or MAC (n= 99) groups. Composite SRAEs were significantly higher in the MAC group compared with the GEA group (51.5% vs 9.9%, P< .001). This was primarily driven by the frequent need for airway maneuvers in the MAC group. Additionally, ERCP was interrupted in 10.1% of patients in the MAC group to convert to GEA because of respiratory instability refractory to airway maneuvers (n= 8) or significant retained gastric contents (n= 2). There were no statistically significant differences in cannulation, in-room, procedure, or fluoroscopy times between the 2 groups. All patients undergoing GEA were successfully extubated in the procedure room at completion of ERCP, and Aldrete scores in recovery did not differ between the 2 groups. There were no immediate adverse events. In patients at high risk for SRAEs undergoing ERCP, sedation with GEA is associated with a significantly lower incidence of SRAEs, without impacting procedure duration, success, recovery, or in-room time. These data suggest that GEA should be used for ERCP in patients at high risk for SRAEs (Clinical trial registration number: NCT02850887.).