24,438 research outputs found
Study of resonances in 1 x 25 kV AC traction systems with external balancing equipment
Š 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.AC traction systems are 1 à 25 or 2 à 25 kV/50 Hz single-phase, nonlinear, time-varying loads that can cause power-quality problems, such as unbalanced or distorted voltages. To reduce unbalance, external balancing equipment is usually connected to these systems, forming the Steinmetz circuit. Parallel resonances can occur in these types of circuits, exciting the harmonic emissions (below 2 kHz) of railway-adjustable speed drives. This paper studies these resonances at pantograph terminals and provides analytical expressions to determine their harmonic frequencies. The expressions are validated from several traction systems in the literature and PSCAD simulations.Postprint (author's final draft
Modeling Inverter Losses for Circuit Simulation
Transformer-like inverter models can represent a very good alternative to common switch-diode models for simulation, reducing convergence problems and/or calculation time. They may also provide easier insight into the converter operation and power loss effects, at least from the point of view of the applicants, aiding for design and teaching purposes. The paper shows how conduction and switching losses can be incorporated in the transformer-like inverter model in a simple and intuitive way, which requires very few parameters and allows for separate modeling of lossless behavior, conduction losses and the switching losses. Loss models are proposed in some versions differing for the accuracy and simulation easiness. In any case, the resulting inverter lossy model is very compact and can be implemented by just a pair of nonlinear controlled sources as basic building blocks, available in any circuit simulation program, as the free of charge and widely used PSpice student version
Nuclear Magnetohydrodynamic EMP, Solar Storms, and Substorms
In addition to a fast electromagnetic pulse (EMP), a high altitude nuclear
burst produces a relatively slow magnetohydrodynarnic EMP (MHD EMP), whose
effects are like those from solar storm geomagnetically induced currents (SS
GIC). The MHD EMP electric field E < 10^-1 V/m and lasts < 10^2 sec, whereas
for solar storms E > 10^-2 V/m and lasts >10^3 sec. Although the solar storm
electric field is lower than MHD EMP, the solar storm effects are generally
greater due to their much longer duration. Substorms produce much smaller
effects than SS GIC, but occur much more frequently. This paper describes the
physics of such geomagnetic disturbances and analyzes their effects.Comment: 29 pages, 14 figures, 5 table
NumerickĂĄ analĂ˝za a simulace RogowskĂŠho cĂvky
This work illustrates an analysis of Rogowski coils for power applications, when operating under non ideal measurement conditions. The developed numerical model, validated by comparison with other methods and experiments, enables to investigate the effects of the geometrical and constructive parameters on the measurement behavior of the coil and we also study the behavior of Rogowski coils coupled with bar conductors under quasi-static conditions. Through a finite element (FEM) analysis, we estimate the current distribution across the bar and the flux linked by the transducer for various positions of the primary conductor and for various operating frequencies. Simulation and experimental results are reported in the text.Tato prĂĄce ilustruje analĂ˝zu rogowskĂ˝ch cĂvek pro energetickĂŠ aplikace pĹi provozu v podmĂnkĂĄch bez ideĂĄlnĂho mÄĹenĂ. VyvinutĂ˝ numerickĂ˝ model, ovÄĹenĂ˝ porovnĂĄnĂm s jinĂ˝mi metodami a experimenty, umoĹžĹuje zkoumat vliv geometrickĂ˝ch a konstrukÄnĂch parametrĹŻ na chovĂĄnĂ mÄĹenĂ cĂvky a takĂŠ studujeme chovĂĄnĂ rogowskĂ˝ch cĂvek spojenĂ˝ch s tyÄovĂ˝mi vodiÄi za kvazi-statickĂ˝ch podmĂnek . PomocĂ analĂ˝zy koneÄnĂ˝ch prvkĹŻ (FEM) odhadujeme rozloĹženĂ proudu pĹes tyÄ a tok spojenĂ˝ snĂmaÄem pro rĹŻznĂŠ polohy primĂĄrnĂho vodiÄe a pro rĹŻznĂŠ provoznĂ frekvence. SimulaÄnĂ a experimentĂĄlnĂ vĂ˝sledky jsou uvedeny v textu.410 - Katedra elektroenergetikydobĹ
Analysis of energy dissipation in resistive superconducting fault-current limiters for optimal power system performance
Fault levels in electrical distribution systems are rising due to the increasing presence of distributed generation, and this rising trend is expected to continue in the future. Superconducting fault-current limiters (SFCLs) are a promising solution to this problem. This paper describes the factors that govern the selection of optimal SFCL resistance. The total energy dissipated in an SFCL during a fault is particularly important for estimating the recovery time of the SFCL; the recovery time affects the design, planning, and operation of electrical systems using SFCLs to manage fault levels. Generic equations for energy dissipation are established in terms of fault duration, SFCL resistance, source impedance, source voltage, and fault inception angles. Furthermore, using an analysis that is independent of superconductor material, it is shown that the minimum required volume of superconductors linearly varies with SFCL resistance but, for a given level of fault-current limitation and power rating, is independent of system voltage and superconductor resistivity. Hence, there is a compromise between a shorter recovery time, which is desirable, and the cost of the volume of superconducting material needed for the resistance required to achieve the shorter recovery time
Stability analysis of electric power systems for âmore electricâ aircraft
This paper presents a comprehensive assessment of small-signal stability for a âmore-electricâ
aircraft power system consisting of a synchronous variable-frequency generator which supplies several power
electronic controlled loads via an 18-pulse autotransformer rectifier unit (ATRU) for AC-DC conversion.
Functional models for key power system components and loads are derived. Numerical tools employed for the
automatic calculation of linearized equations and operating points are described, and the influence of leading
design and operational parameter on system stability is evaluated
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