-Variability in arc ratings of fabrics poses challenges for end users, manufacturers and test laboratories. In this article a test laboratory, a manufacturer, and a large US electric utility ...partnered and performed repeat tests on fabrics to study variability in arc ratings. The work included cross-referencing data from testing performed on control fabrics and comparison of results from different laboratories. The results help gain an understanding of factors that influence arc rating to improve test methods and standards, guide users to select appropriate PPE to match their hazards and enable manufacturers to validate claims on their products. Lastly, the paper gives recommendations to end users regarding best practices to accommodate arc rating variability in their programs.
Abstract
Tension remains between the observed and modeled properties of substellar objects, but objects in binary orbits, with known dynamical masses, can provide a way forward. HD 72946 B is a ...recently imaged brown dwarf companion to a nearby, solar-type star. We achieve ∼100
μ
as relative astrometry of HD 72946 B in the
K
band using VLTI/GRAVITY, unprecedented for a benchmark brown dwarf. We fit an ensemble of measurements of the orbit using
orbitize!
and derive a strong dynamical mass constraint
M
B
= 69.5 ± 0.5
M
Jup
assuming a strong prior on the host star mass
M
A
= 0.97 ± 0.01
M
⊙
from an updated stellar analysis. We fit the spectrum of the companion to a grid of self-consistent
BT-Settl-CIFIST
model atmospheres, and perform atmospheric retrievals using
petitRADTRANS
. A dynamical mass prior only marginally influences the sampled distribution of effective temperature, but has a large influence on the surface gravity and radius, as expected. The dynamical mass alone does not strongly influence retrieved pressure–temperature or cloud parameters within our current retrieval setup. Independently of the cloud prescription and prior assumptions, we find agreement within ±2
σ
between the C/O of the host (0.52 ± 0.05) and brown dwarf (0.43–0.63), as expected from a molecular cloud collapse formation scenario, but our retrieved metallicities are implausibly high (0.6–0.8) in light of the excellent agreement of the data with the solar-abundance model grid. Future work on our retrieval framework will seek to resolve this tension. Additional study of low surface gravity objects is necessary to assess the influence of a dynamical mass prior on atmospheric analysis.
This paper presents a method to limit the arc energy and hence the hazard risk category value according to IEEE 1584 by using a system of two oppositely connected multi-sectional thyristor branches. ...A test circuit for testing the effectiveness of a thyristor arc eliminator was designed and constructed. Arc ignition inside electrical switchgear can be a source of danger for technical personnel. The arc energy calculated according to the algorithms in IEEE 1584 can be significantly reduced by using multi-sectional arc eliminator MSAE. For the actual measuring object, the calculation of the hazardous arc flash zone and the hazard category was carried out for the system not equipped with an arc eliminator, and then the same was performed in a system with an arc eliminator. In parallel, the pressure inside the closed polyvinyl chloride (PVC) electrical box enclosure was measured and then compared with the calculated pressures that could occur during an arc fault. It was found that a Multi-Sectional Arc Eliminator (MSAE) effectively protects devices supplied from low voltage networks against the effects of short circuit or arc fault, such as the sudden increase of gas pressure inside the switchboard, which may cause it to break, significantly reduce the loss of electrode material, limit the spread of hot electrode material outside the switchgear, and also significantly reduces the energy of the electric arc.
In arc flash hazards calculations, protection boundary can be used to gain insight in personnel protection against thermal injuries. Although IEEE 1584-2002 has provided the calculation guide based ...on tests with the arcing electrodes in a vertical plane, applications where the traditional vertical arrangement is not directly applicable have been drawing more attention over the past few years. Due to the varied thermal behaviors of arc under different equipment configuration and the varied bus connection mode, for the purpose to achieve the adequate protection on arc flash thermal injury, it is necessary to analyze the effect of different electrode geometries on arc flash protection boundary (AFPB). According to the prior work on the development of IEEE 1584-2018, this article fully discusses the impact of electrode geometry on incident energy exposure level and AFPB. With the multiple electrode geometry designed tests, thermal behaviors of arc under different electrode orientation, gap distance, and equipment configurations have been analyzed. According to test results, correction equations were derived under each typical electrode geometry to adjust the AFPB calculation model of IEEE 1584-2002. Through the comparisons, the corrected model can better reflect the actual effects of electrode geometry, meanwhile showing a good ability to provide reasonable AFPB for practical uses.
A simplified arc-flash analysis technique that allows for the determination of the settings of overcurrent protective devices and selection of arc-rated personal protective equipment (PPE) based on a ...reference constant incident energy boundary area is presented in this article. The reference areas are created based on the equations of IEEE Standard 1584-2018 1, taking into consideration potential variation in the input parameters described in the standard. The method presented in this article provides an efficient and straightforward means to simultaneously consider the effects of varying input parameters on arc-flash calculation results by plotting areas of constant incident energy on a time-current plot. Actual power distribution equipment may have multiple electrode configurations, gaps between conductors, operating voltages, as well as a range of available bolted short-circuit currents and variation in the size of equipment enclosures. The multiple combinations require dozens of simulations to determine the worst-case incident energy levels. Unlike previous implementations of incident energy curves, which were typically single line representations of the incident energy, the plotting of bounded areas (C-area plots) allows for multiple parameter sweeps to determine a band of variation within a defined set of parameter combinations.
The 2018 update to the IEEE Std. 1584 Guide for Performing Arc-Flash Hazard Calculations has introduced new electrode configurations that can drastically affect incident energy calculations and ...labeling. The electrode configurations discussed in this article are: vertical conductors/electrodes inside a metal box/enclosure (VCB), vertical conductors/electrodes terminated in an insulating barrier inside a metal box/enclosure (VCBB), and horizontal conductors/electrodes inside a metal box/enclosure (HCB). It is generally understood that at typical working distances, HCB will produce a higher incident energy than VCBB, which will produce a higher incident energy than VCB with all other parameters equal. However, there is a counter-intuitive trend for the arc-flash boundary, such that the boundary distance for HCB is often lower than the boundary for VCBB and VCB. The electrode configuration will also affect the magnitude of arcing current, which may result in varying fault clearing times depending on which electrode configuration is selected. This article will discuss arcing fault current, incident energy, and arc-flash boundary results for each enclosed electrode configuration that challenge the assumption that HCB will always yield the worst-case incident energy and arc-flash boundary. The results of 50 arc flash studies have been surveyed and presented in this article to supplement and validate observations and conclusions.
The integration of renewable generation systems into electricity distribution grids is becoming increasingly com-mon. New generation plants are commonly connected to electricity grids by modifying ...their design and operating conditions. Photovoltaic plants are being integrated into large transmission grids, limiting their capacity and altering the conditions for which they were designed. Electricity distribution grids must also cope with the connection of new photovoltaic installations for self-consumption, which can range from a few kW for domestic use to several MW for large industries. For this analysis we focus exclusively on the phenomenon of arc flash (AF) in alternating current (AC) because most AF accidents happen in this type of AC systems, and distribution networks worldwide operate with this type of current, even though they do it at different frequencies. IEEE 1584™-2018 has increased the calculation accuracy to determine the incident energy of power systems. Nevertheless, the changing dynamics of power systems due to the connection of new installations and the uncertainty associated with the design parameters has pushed us to develop this study focused on the behavior of AF. This article studies the impact of certain parameters on the calculation of incident energy, as well as on the arc flash boundary (AFB) in an electrical distribution network where a 4 MW photovoltaic generation plant is connected. The most interesting objective of this analysis is to determinate the behavior of the electrical distribution network, considering certain design parameters that may vary throughout its useful life. In particular, the variability of the short-circuit impedance of power transformers and their impact to the distribution network where they are connected has been studied. Other variables such as the opening time of the circuit breakers and the length of the cables are also analyzed, considering a photovoltaic generation plant integrated in the distribution network. Each of the parameters analyzed are extremely important in current power transmission networks. So far, AF analyses do not assume the errors due to the inaccuracy of the data used to parameterize the simulation model. Thanks to this analysis, it will be proven how the variability of certain parameters affects the accuracy of AF analysis in a real distribution network, demonstrating to society the importance of having real, updated and accurate data before proceeding to simulate the system under study.
أوضحت الدراسة إن مشكلة روسيا الأساسية بحكم موقعها الجغرافي أنها معزولة وبعيدة عن طرق التجارة والملاحة العالمية لا تملك سواحل بحرية إلا على المحيط المنجمد الشمالي وهو بحر جليدي تتجمد مياهه معظم أيام ...السنة، وعلى بحر البلطيق والبحر الأسود وكلاهما مغلقان لذلك اختطت روسيا سياسة خارجية الانفتاح على البحار وإيجاد منفذ خارجي من خلال السيطرة على البحار لا سيما بحر البلطيق وبحر قزوين والبحر الأسود من أجل الوصول إلى المياه الدافئة. أظهر القيصر ايفان الرابع مقدرة مشهودة كرجل دولة مؤهل وقدير، امتاز بسعة الاطلاع والإحاطة بخفايا السياسة وبمواهب مشهودة ومثابرة وإصرار في محاربة إعداء الدولة الروسية ولا سيما السويد وبولندا التي تسيطر على بحر البلطيق والحرص على مصالحها السياسية والاقتصادية واهتم بتقوية الجيش وتسليحه بالأسلحة النارية من أجل تنفيذ مخططاته العسكرية وسياسته التوسعية لفتح نافذة لدولته تطل على البحار لتخليص دولته من العزلة الجغرافية. كشفت الدراسة إن القيصر ايفان الرابع حقق نجاحا سياسيا نتيجة استيلائه على الأراضي الواسعة الخصبة المتاخمة للفولغا قازان واستراخان، وبذلك أصبح نهر الفولغا من منبعه إلى مصبه قناة روسية بحتة تسهل الوصول إلى بحر قزوين ومهدت الطريق للروس لاحتلال ما وراء الأورال، واهم طريق تجاري لموسكو، الأمر الذي أعطى دفعة جديدة لتطور الدولة الروسية. اتبع القيصر ايفان الرابع سياسة العنف والقسوة وقام بقتل ونهب كل المدن التي مر بها وجرد رجال الدين من جميع امتيازاتهم ورجح طبقة معينة على طبقة أخرى، دون مراعاة مطاليب أفراد المجتمع الروسي وقيد حرياتهم السياسية والثقافية ما يهمه سوى جمع المال بأية وسيلة كانت لا سيما وجود مواطنين روس في معظم المدن التي استولى عليها، لتقوية المؤسسة العسكرية على حساب الآخرين، مما أدى إلى بث التفرقة والحقد والعداوة بين أبناء شعبه، كان من المفروض أن يبذل جميع مساعيه من أجل تحقيق التضامن والمحبة بين طبقات المجتمع الروسي، لأن التضامن وتلبية احتياجات أبناء دولته يؤدي إلى سيادة الأمن والاستقرار وتحقيق الوحدة تقود إلى كسر شوكة الأعداء الطامعين في أراضي الدولة الروسية. بينت الدراسة إن القيصر الروسي بذل جميع مساعيه من أجل تحقيق طموحات روسيا السياسية فقد خاض الحرب الليفونية التي استمرت خمسة وعشرين عاما (1558- 1583م) للحصول على منفذ إلى بحر البلطيق كانت حصيلتها فقدان الروس أراضيهم التي تطل على خليج فنلندا، واتضح أن الدولة الروسية لم تكن آنذاك على درجة من القوة كافية لتحقيق نجاحا سياسيا ضد تجمع الدول الأوروبية ضدها، فضلا عن خيانة القادة العسكريون الروس في ساحات الحرب الذين تركوا القيصر وانحازوا إلى عدوه وازدادت كراهيتهم للسياسة الاستبدادية المطلقة للحكومة القيصرية. واستمرت روسيا بجهود القياصرة وقادتها وشعبها تواصل حروبها ضد الأعداء لتحقيق طموحاتها السياسية وتنفيذ مخططاتها التوسعية باتجاه البحار للتخلص من العزلة الجغرافية، وتعزيز علاقاتها الدبلوماسية والسياسية والاقتصادية مع دول العالم.
A Graphical Approach to Incident Energy Analysis Lutz, Rick; Charbonneau, Maximilian; Garcia, Michael
IEEE transactions on industry applications,
2018-Jan.-Feb., 2018-1-00, Letnik:
54, Številka:
1
Journal Article
Recenzirano
The goal of an incident energy analysis is to determine the largest incident energy that a worker could be exposed to at a piece of electrical equipment. This is most commonly done using the IEEE ...1584 method. It is a common observation when performing this analysis that minor variations in fault current can result in large changes in a protective device's operating time and the resulting incident energy. This would not be a problem if it was possible to remove all errors from the bolted fault calculation and the arcing fault calculation. Unfortunately, the arcing fault current calculation has some margin of error and the data used in arc flash models are often estimated. A graphical approach to determining the incident energy circumvents these problems and ensures that the worst-case incident energy is determined. This graphical approach is derived from graphs of incident energy based on protective device time-current curves. An examination of the resultant graphs reveals a few maximums in the incident energy curve. These maximums are caused by the protective devices curve, the minimum and maximum arcing fault currents, and any time limitations that are applied. As a result, the locations of these maximums are easily predicted allowing the maximum incident energy to be determined by performing the IEEE 1584 calculation at a few key current values.
El presente trabajo se propone estudiar las vicisitudes editoriales del Lisardo enamorado de Alonso de Castillo Solórzano (Valencia, 1629) y de su primera versión, los Escarmientos de amor ...moralizados (Sevilla, 1628), pasando revista a los elementos lingüísticos e ideológicos que los distinguen e identificando las modalidades de reelaboración empleadas por su autor.
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