209 research outputs found
Currents Passing Through the Human Body: The Numerical Viewpoint
No full textIn the case of direct or indirect contact with electrically energized parts, an electric current circulates through the body. When the magnitude and duration of the current through the heart exceed the ventricular fibrillation thresholds, the cardiac muscle starts uncoordinated contractions, greatly jeopardizing the life of the subject. Technical standards on electrical installations describe the protective measures against direct and indirect contact necessary to minimize the probability of inception of ventricular fibrillation. Safety considerations are based on experiments made in the past on animals, but the extrapolation of results to human beings is complex and rather questionable. The purpose of this study is to analyze the body factors that affect the distribution of currents passing through the human body with virtual anatomical models. A set of 16 models of individuals is used to simulate different electric contacts. The use of virtual models of a diverse population (i.e., eight males and eight females, ten adults and six children) provides a statistical support to the results. The obtained heart-current factors, are compared with values present in the literature. This paper provides a novel viewpoint on the problem, and supports the ongoing research activity and efforts to improve the electrical safety of persons
Special issue on grounding systems
No full textThe articles in this special section focus on grounding systems for industrial, commercial, and residential installations
Electrical Safety Of Aeronautical Ground Lighting Systems
No full textAeronautical ground lighting (AGL) systems have been developed to deliver warnings and status indications to pilots and maneuvering area vehicle drivers on runways. Their role in preventing the hazard of runway incursions, present in the aviation industry, is therefore crucial. AGL systems basically consist of a primary series lighting circuit, which is supplied at constant current and high voltage (e.g., 5 kV), and AGL transformers supplying ground lights at their secondary sides. Protection of persons against electric shock in AGL systems cannot be conveyed by disconnection of supply as ground faults would cause the out-of-service of the lighting system, thereby compromising the safety of aerodromes; alternative protective measures are therefore employed. In this paper, the authors examine the electrical safety issues present during maintenance of AGL systems, often performed live in order to guarantee the continuity of the service. Experimental measurements on AGL isolating transformers have been also reported in this paper, and possible solutions to improve the electrical safety of operators are proposed
Analysis of causation of a flour dust explosion in industrial plant
No full textCommon solids (e.g. flour, sugar, etc.) can be suspended and transported in air via pneumatic conveying systems. Finely divided solid substances dispersed into a dust cloud (e.g. into a silo) can form a potential explosive atmosphere, if in the right concentration with the oxidizing agent (e.g. air). In addition, it is known that the pneumatic handling of substance, which allows its transport at a certain velocity, can generate static charges; thus, a possible competent ignition source may be also created. In this paper, the causation of an actual dust explosion involving a flour silo being loaded from a tank truck through pneumatic conveying systems in an industrial plant is analyzed. All the mechanisms of static discharge applicable to the case in question are discussed, in light of both actual empirical data collected at the incident site, and theory. To fully explain the events that led to the explosion, plausible hypotheses, alternative to static discharge, were also evaluated
An effective semi-analytical method for simulating grounding grids
No full textThe analytical study of grounding systems is only possible for basic electrodes, i.e., hemispherical and spherical electrodes, rods, and horizontal wires. However, it is normal practice to employ more complex earthing systems, such as grounding grids integrated with rods, in order to obtain lower resistances to ground and improve the electrical safety of substations. This paper introduces a semianalytical (or seminumerical) method, consisting of an analytical approach integrated with a numerical solution, to study grounding grids of complex geometry and their effects on non stratified soils. The algorithm that was created and realized with MATLAB allows the determination of all the quantities of interest for the design and the analysis of such grounding systems, i.e., ground resistance, ground potentials, and distribution of the ground-fault current along the grid's components (i.e., horizontal wires and rods). The model is based on the assumption that conductors forming grids have very small radii if compared with their lengths and that the wires can be considered equipotential cylindrical elements. A verification of the proposed algorithm through a finite-element method has been also carried out to confirm the validity of the results. Exemplary calculations of the ground resistance of grids are included in this paper
Electrical safety in arc welding processes
No full textManual metal arc welding can be a hazardous practice if proper precautions are not taken. The welding procedure uses an open electric arc between an electrode and the metals to be joined. Besides the obvious risks of burns and inflammation of the cornea, which are prevented by using proper personal protective equipment, the operator may also be subject to the risk of electric shock from the exposed parts of the welding circuit, both the electrode and the workpiece. In addition, the welding current, by straying from the intended path, can cause localized heating of parts, with the risks of triggering fires and/or explosive atmospheres. Because of the high current required by the arc welding equipment, operators are exposed also to strong electromagnetic fields. This paper seeks to clarify the aforementioned issues, especially in light of the fact that the risk associated with electric shocks may be unknown to welders and their supervisors
Electrical safety of plug-in electric vehicles: shielding the public from shock
No full textThis article discusses fundamental electrical safety issues, especially protection against electric shock, for those interacting with electric vehicles (EVs). The safety of users may be challenged by the vehicle's increased operating voltages, at different frequencies, possibly making the protection against direct and indirect contacts more complex. The article examines vehicles' electrical safety under both normal operating conditions and in the case of electrical and/or mechanical failure. Safety during charging in reference to different charge modes is also discussed. Furthermore, solutions are proposed for improving safety in light of applicable technical standards and the evolution of the technology
Inductive power transfer for automotive applications: State-of-the-art and future trends
No full textThe paper discusses the status of the development status of the inductive power transmission for automotive applications. This technology is, in fact, gaining the interest of electric vehicle manufacturers as an effective strategy to improve the market penetration of electric mobility. Starting from the origin of this technology, the paper presents an overview of the current state-of-the-art as well as the current research and industrial projects. Particular attention is devoted to the description of a prototypal system for the dynamic inductive power transmission whose goal is to extend the battery range by a fast partial recharging during the movement of the vehicl
Electrical model of building structures under ground-fault conditions. Part I
No full textBuilding structures are systems of connected parts designed to support continuous persons' occupancy. Safety of persons against electrical indirect contact under ground-fault conditions depends on the potential gradient established by the fault current within the structure. In buildings, persons are in contact with floors, but also with walls and/or conductive objects, thus ground-fault potentials not only depend on the configuration and location of the grounding system with respect to the point of touch, but also on the construction type of the structure, as well as on the floor material. In this paper, through both analytical models and field measurements involving different types of buildings (i.e. masonry, reinforced concrete), the authors have investigated the main factors that affect the distribution of ground potentials in structures
Interferences phenomena between separate grounding systems
No full textOne of the main purposes of grounding systems is to safely inject fault currents into the soil; such currents flow through any buried conductive objects (e.g., other earth electrodes) eventually present along their path to the source. As a result, even though grounding systems may be metallically isolated, they become coupled due to the flow of the earth-current and interferences occur. Due to this unwanted coupling, dangerous potentials may arise over the 'passive' electrode, which may expose persons to the risk of electric shocks. This paper proposes a semianalytical approach to evaluate mutual interactions among grounding systems at low frequency, and establishes criteria to evaluate their actual independence. A significant case study of interactions between the substation grid and the safety ground bed in a mining installation is quantitatively discussed
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