1,721,099 research outputs found
The magic of the conductors current density in the time and in the space
No full textThis paper outlines and simplifies a couple of composite quantities the “I 2 t”, related to the let-through energy produced in a conductor by a current I and the “I l” related to the ohm voltage drop in the conductor, defining the load current torque. The current density δ=I/S in the two above mentioned quantities expressed as “δ 2 t” and “δ l” characterizes, in a general way, the heating and the voltage drop of a conductor that is its intrinsic behavior to the flowing of a current. Steady density values support the sizing of conductors for their continuous operation in the time and their configuration in the load “space” of the system. Withstand densities, related to the short time duration of one second, define the cables behavior to overloads and the short-circuit currents that the cables are capable to withstand
Density of currents and of withstand electric charges admissible for the conductors
No full textThe designer of electrical power systems needs rules of thumb to maintain a full understanding of the circuits sizing and of the results obtained adopting available software programs. At this aim, it appears useful to consider characteristic current densities for the conductors in a tentative of a new approach. Steady current densities support the criteria of sizing the circuits for their continuous operation in the time and for their configuration in the load “space” of the system. Transient current densities characterize the cables withstand behavior. The paper identifies withstand electrical charge densities for overcurrents in relation to assigned intervals of overtemperature. For each assumed transient time, the current densities in the conductors are admissible until they accumulate a charge density not greater than the withstand value
Ethics and eco-design for complex uses of energy
No full textA new scope of the electrical engineering shall be the ethical design and management, the environmental sensitivity. The technical implication of electrical engineers is increasingly to promote a methodology of development, growth and progress towards the innovations of electrical technologies. Eco-design of power systems has to balance active intelligence of system components with passive intelligence of system structures. It has to combine energy saving and rational use of energy with the exigencies of service continuity, energy quality and electrical safety with a unitary and coordinated vision of the other non-electrical needs. The technological innovations of Internet of Things and digitization determine a complex spatial-temporal reality consisting of structured microsystems and virtual-dynamic systems. Their complex interactions operate in a simple way with a local management based on the principle of adjacency of the flock logic. It is urgent the human society becomes aware of the electrical ethical rights and claims them before their complete compromise. Essential electrical rights of the users are, in synthesis, system and equipment ownership, sustainable innovations, use of equipment life cycle, good operability, micro approach design, defense of electrical structuration, energy communities, society of things, socialized process, reparability and unification, auto protection of special exigencies of appliances
Virtual society of IoT Robosats and emancipation of electrical utilization
No full textIoT can offer to each person monitored automata, robosats (robot satellites), as extension of the personal domain of action. These robosats can establish a virtual society of things in a connected dynamic system that is constitute 'virtual' structures of microsystem chains of many megawatts. Considering that the average use of household electricity reaches more than 20% of total energy consumes, the prospective influence of IoT on the electrical energy utilization can start an epochal evolution in the structure/operation of power systems. IoT can permit an efficient establishment of electrical microgrids and the pursuit of sustainability objectives. At this aim it is necessary a new approach and adequate regulatory changes
Integrated grounding systems: an unavoidable opportunity for users in urban and industrial areas
No full textIn the IEC approach, a global ground system by definition ensures the safety of interconnected MV / LV ground facilities, but the utility only can validate its existence. An integration between adjacent ground systems of users, such as in urban and industrial areas, assists to ensure that the safety conditions prescribed by the standards are met regardless of requiring recognition from the utility. This solution can contribute to promote the upgrade to the global ground system with the final adhesion of the utilities overcoming the problem of validating the global ground system and promoting the common interest of safety
A simplified method for arc flash assessment in low voltage A.C.
No full textVarious software are existing to assess the risk of Arc Flash complying with the model provided by the IEEE1584-2018 guide. The empirical model interpolates intermediate values of average arc current, incident energy, and arc-flash boundary to determine final results, corrected by factors for enclosure size and arc current variation. It becomes relevant to have a physical understanding of the phenomenon, examining singularly the various parameters that effect it, such as the arc-flash in air or in enclosure, electrode gap, the box size. In this way, the paper proposes a simplified method to be able to diagnose the computerized results. At first, it proposes the calculation of arc fault currents in the same way than the short circuit currents, analyzing and highlighting the influence of the fault current power factor. Then, this paper proposes a tentative criterion in low voltage a.c.≤600V. It suggests reference values for the arc current in the maximum power transfer condition and so for the incident energy to adopt in the arc-flash boundary evaluation and in the selection of the adequate PPE. The numerical results on case studies obtained with the proposed model and adequate coefficients, considering the arc gap and the box size, are completely consistent with the results obtained with IEEE1584-2018 guide
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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