1,721,068 research outputs found
Compliance of non-sinusoidal or pulsed magnetic fields generated by industrial sources with reference to human exposure guidelines
No full textIn this paper theory and methodology to analyze non-sinusoidal/pulsed fields created by industrial sources in the low frequency range are presented. The methodologies to analyze non-sinusoidal fields are introduced by recalling the fundamental electrostimulation mechanisms. Finally, a case study of a resistance spot welding gun is considered and the results are discussed. Regarding the resolution of the human model, it is found that using a 1 × 1 × 1 mm3 discretization and then apply a spatial averaging in a volume of 2 × 2 × 2 mm3 is almost equivalent to the direct use of a resolution equal to 2×2 × 2 mm3. Furthermore, several metrics to remove numerical artifacts are also tested. Some of them are based on the percentile filtering whereas others are based on a statistical procedure aimed to filter out the outliers in the numerical solution. It is pointed out that, for a localized exposure, the statistically based approaches goes in the direction to define a metric able to adapt to each specific exposure condition, the 99th percentile can underestimate the actual maximum that, on the contrary, it is better estimated by the 99.9th percentile
Uncertainty quantification in the assessment of human exposure to pulsed or multi-frequency fields
Full text linkObjective: pulsed fields or waveforms with multi-frequency content have to be assessed with suitable methods. This paper deals with the uncertainty quantification associated to these methods. Approach: among all possible approaches, the weighted peak method (WPM) is widely employed in standards and guidelines, therefore, in this paper, we consider its implementation both in time domain and frequency domain. For the uncertainty quantification the polynomial chaos expansion theory is used. By means of a sensitivity analysis, for several standard waveforms, the parameters with more influence on the exposure index are identified and their sensitivity indices are quantified. The output of the sensitivity analysis is used to set up a parametric analysis with the aim of evaluating the uncertainty propagation of the analyzed methods and, finally, also several measured waveforms generated by a welding gun are tested. Main results: it is shown that the time domain implementation of the weighted peak method provides results in agreement with the basilar mechanisms of electromagnetic induction and electrostimulation. On the opposite, the WPM in frequency domain is found to be too sensitive to parameters that should not influence the exposure index because its weight function includes sharp variations of the phase centered on real zeros and poles. To overcome this issue, a new definition for the phase of the weight function in frequency domain is proposed. Significance: it is shown that the time domain implementation of the WPM is the more accurate and precise. The standard WPM in frequency domain has some issues that can be avoided with the proposed modification of the phase definition of the weight function. Finally, all the codes used in this paper are hosted on a GitHub and can be freely accessed at https://github.com/giaccone/wpm_uncertainty
Chassis influence on the exposure assessment of a compact ev during wpt recharging operations
Full text linkIn this study, the external magnetic field emitted by a wireless power transfer (WPT) system and the internal electric field induced in human body models during recharging operations of a compact electric vehicle (EV) are evaluated. The magneticfield is calculated with a hybrid scheme coupling the boundary element method with the surface impedance boundary conditions in order to fit the multiscale open-boundary characteristics of the problem. A commercial software is then used to perform numerical dosimetry. Specifically, two realistic anatomical models, both in a driving position and in a standing posture, are considered, and the chassis of the EV is modeled either as a currently employed aluminum alloy and as a futuristic carbon fiber composite panel. Aligned and misaligned coil configurations of the WPT system are considered as well. The analysis of the obtained results shows that the International Commission on Non-Ionizing Radiation Protection (ICNIRP) reference levels are exceeded in the driving position, especially for the carbon fiber chassis, whereas the system is compliant with the basic restrictions, at least for the considered scenarios
Mitigation Solutions for the Magnetic Field Produced by MFDC Spot Welding Guns
Full text linkAmong the different welding technologies, portable welding guns are one of the most critical devices in relation to human exposure to electromagnetic fields. This paper focuses on medium frequency (MF) direct current guns proposing two actions aimed to the mitigation of the magnetic field generated during the welding process. The first action consists in the adoption of a passive shield for the on-board MF transformer. The analysis points out that the transformer alone produces a magnetic field that can exceed the prescribed limits. Therefore, a suitable mitigation system is identified. The second action aims to mitigate the predominant magnetic field that is generated by the electrodes of the welding gun. The analysis of the field waveforms shows that the rise time of the welding current pulse is the main parameter affecting the exposure index. The effect of the increase of the rise time is investigated through experimental and numerical analyses. The results prove that a small increase of the rise time causes a significant reduction of the exposure level. It is noteworthy that the two mitigation actions can be adopted on both existing and newly developed welding guns as they do not require any structural modification of the welding device
Influence of posture and coil position on the safety of a WPT system while recharging a compact EV
Full text linkIn this study, the human exposure to the magnetic field emitted by a wireless power transfer (WPT) system during the static recharging operations of a compact electric vehicle (EV) is evaluated. Specifically, the influence of the posture of realistic anatomical models, both in standing and lying positions, either inside or outside the EV, is considered. Aligned and misaligned coil configurations of the WPT system placed both in the rear and front position of the car floor are considered as well. Compliance with safety standards and guidelines has proven that reference levels are exceeded in the extreme case of a person lying on the floor with a hand close to the WPT coils, whereas the system is always compliant with the basic restrictions, at least for the considered scenarios
Uncertainty quantification in energy management procedures
Full text linkComplex energy systems are made up of a number of components interacting together via different energy vectors. The assessment of their performance under dynamic working conditions, where user demand and energy prices vary over time, requires a simulation tool. Regardless of the accuracy of this procedure, the uncertainty in data, obtained both by measurements or by forecasting, is usually non-negligible and requires the study of the sensitivity of results versus input data. In this work, polynomial chaos expansion technique is used to evaluate the variation of cogeneration plant performance with respect to the uncertainty of energy prices and user requests. The procedure allows to obtain this information with a much lower computational cost than that of usual Monte-Carlo approaches. Furthermore, all the tools used in this paper, which were developed in Python, are published as free and open source software
Real-time optimization of active loops for the magnetic field minimization
Full text linkThis paper deals with the design and the final implementation of a low-cost active shielding system for the mitigation of magnetic fields generated by electrical installations like power lines or substations. In this paper a new working prototype is built and tested. It is shown that the developed control strategy is effective also for field sources with complex geometries. Moreover, a real-time optimizer is added to the control strategy in order to guarantee the minimization of the source field at any working conditions of the source (i.e. different from the rated power). The control algorithm and the real-time optimizer are fully described in the paper, moreover, their behavior is verified through simulations and experimental tests
High-performance magnetic shielding solution for extremely low frequency (ELF) sources
Full text linkSome particular aspects related to open shields with high performance are presented. The magnetic flux density targets related to the protection of sensitive devices are quite low, <0.2 μT. The problem to reach high magnetic field attenuation is more complicated by the fact that open shields have to be adopted instead of closed solutions. After some general considerations about open shields two practical examples are presented and discussed
On the use of the HMCPL shielding system in renewing the underground HV power lines in big cities
No full textUsing underground cables in big cities, one of the most important acceptability issues is the magnetic field mitigation. This paper focuses on the joint bays, which are a critical part of the buried power lines regarding the magnetic field generation. For technical reasons, within a joint bay cables have to be arranged in flat configuration with an increment of the cable distances which cause a higher magnetic field generation compared to the trefoil arrangement. For a standard buried power line the magnetic field above a joint bay can be 10 times higher than the one of the trefoil. Joint bays are usually mitigated by means of passive shields. The literature covers comparisons of flat metallic shields, passive loops and passive loops with improved magnetic coupling (called HMCPL). In the renewal of the HV grid of Torino, from 2010 to 2014 sixteen new 220 kV lines were laid. The total length is about 50 km. The cables were provided from three different manufacturers. A total of 70 joint bays were installed. 20 of 70 joint bays required, for their position, a mitigation action. In 14 of them, HMCPL system has been used; in the others 6, the classical passive loops system has been installed. In this paper the results of measurement data concerning a sample of the joint bays are presented. The measurement results serve to compare the magnetic field with joint bays without a mitigation system and also to compare the HMCPL with the classical passive loops. Regarding the innovative HMCPL shielding system, in Torino it has been made the more extensive application; furthermore, the results are very satisfactory: the average value measured at the reference point is reduced of about ten times. We also experienced that the site assembly of the system is fast and flexible
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