Search

Accurate modeling and simulation of electric field transients in HVDC cables is an important support to optimize insulation system design and to evaluate the influence of voltage transients and steady-state conditions on accelerated ageing mechanisms and insulation reliability. Traditionally, field models considering time-independent permittivity and conductivity are used, but this approach neglects polarization mechanisms and charge trapping-detrapping phenomena. This article includes polarization dynamics in the field model and shows that its impact on transient electric field simulations in HVDC paper-insulated cables can be significant. A method is presented to infer the model parameters from experimental polarization and depolarization current measurements.

In Robot Assisted Minimally Invasive Surgery, discriminating critical subsurface structures is essential to make the surgical procedure safer and more efficient. In this paper, a novel robot assisted electrical bio-impedance scanning (RAEIS) system is developed and validated using a series of experiments. The proposed system constructs a tri-polar sensing configuration for tissue homogeneity inspection. Specifically, two robotic forceps are used as electrodes for applying electric current and measuring reciprocal voltages relative to a ground electrode which is placed distal from the measuring site. Compared to the other existing electrical bioimpedance sensing technology, the proposed system is able to use miniaturized electrodes to measure a site flexibly with enhanced subsurfacial detection capability. In this paper, we present the concept, the modeling of the sensing method, the hardware design, and the system calibration. Subsequently, a series of experiments are conducted for system evaluation including finite element simulation, saline solution bath experiments and experiments based on ex vivo animal tissues. The experimental results demonstrate that the proposed system can measure the resistivity of the material with high accuracy, and detect a subsurface non-homogeneous object with 100% success rate. The proposed parameters estimation algorithm is able to approximate the resistivity and the depth of the subsurface object effectively with one fast scanning.

Beam diagnostic and especially beam current measurements represent a key aspect in the production of a high-quality beam. Due to the known interplay between beam current and beam and plasma properties, many solutions have been addressed to solve this need. Although precise beam current measuring systems exist, they cannot provide noninvasive solutions for the measurement of very low-frequency currents in electron cyclotron resonance ion source (ECRIS) beamline, with a range from tens to hundreds of microamperes. To address the above-mentioned needs, this paper proposes an indirect measurement methodology based on the estimation of the magnetic field produced by target current exploiting a residence time difference fluxgate and a flux concentrator (a mechanical structure able to constrain produced magnetic field in a given area). The main advantage of this approach is related to the possibility to perform a noninvasive current measurement. An optimal geometry for the flux concentrator has been investigated by using a finite-element method analysis that has led to the definition of a minimum value of the magnetic field generated by the minimum value of the target current, around $5.0~\mu \text{A}$ , equal to 3.07 nT. To assess the solution, an experimental setup, miming real magnetic flux intensity inside ECRIS beamlines, has been realized. The measuring strategy has a magnetic resolution of 1 nT and a current resolution of $1.6~\mu \text{A}$ , that is, in line with requirements. Results obtained demonstrate the suitability of the measurement system for the specific application addressed in this paper, both in terms of operating range and resolution.

This paper investigates the influence of external radial load applied to the shaft on bearing fault detection based on vibration or current in induction motors operating under different conditions. This paper details the results of a laboratory trial comprising different test sets on the condition monitoring and fault diagnostic of a six-poles induction motor using a design of experiment (DOE) approach. The dedicated test setup comprises a custom-made fixture that allows us to dynamically vary the radial load applied to the output shaft. The aim is to investigate the effects of radial load on the fault diagnosis of shaft bearings and the interactions between other operating parameters, such as output torque. Specific scalar parameters have been proposed for the condition monitoring of the test motor from vibration and current data. The correct choice of the significant parameters is proven by the strong dependence on the damage returned by DOE results.

This paper is concerned with the development and the characterization of an ad hoc transducer for the contactless measurement of a high-intensity direct current (dc) for industrial applications. Specifically, the proposed transducer will be used to measure the oxidation process current in a continuous aluminum coil anodizing line (standard sulfuric acid anodizing). In this oxidation process, the current measurement is required to control the thickness of the obtained aluminum oxide, the most important parameter in determining the overall quality of the process. Starting from the features of the considered process, the transducer must measure, without contact, dc currents up to 13 kA in continuous aluminum strips, whose width and thickness can be up to 1600 and 5 mm, respectively; the mass of each coil can be greater than 4700 kg, and the length can be more than 800 m. The dc current is supplied by an ac/dc converter, but due to the features of the oxidation process, only a fraction of the supplied current flows in the aluminum strip and concurs to the oxidation process; the remaining current flows as a leakage current in the acid solution, creating undesired phenomena and energy losses. In this paper, we propose a low-cost current transducer, whose sensing element consists of an iron core equipped with two windings; the first excites the core, while the second is used to measure the variation in the magnetic saturation of the core due to the dc current to measure. The transducer output is conditioned by an electronic circuit that gives a continuous voltage proportional to the input current. A prototype of the proposed transducer has been designed and implemented; a series of characterization tests has been conducted, and the obtained results are discussed in this paper. The transducer is able to measure up to 13 kA, with an overall accuracy of 1.5% for currents over 11 kA.

Geomagnetically induced currents (GICs) are referred to the quasi-DC current flows in power networks, driven by complex space weather-related phenomena. Such currents are a potential threat to the power delivery capability of electrical grids. To mitigate the detrimental impacts of GICs on critical infrastructures, the GICs should be monitored in power systems. Being inherently DC from the power frequency point of view, the components of GICs are, however, challenging and costly to monitor in AC power grids. This paper puts forward a novel methodology for the real-time estimation of GICs in power transformers. Such aim is attained by means of an extended Kalman filter (EKF)-based approach, mounted on the nonlinear state-space model of the transformer, whose parameters can be derived from standard tests. The proposed EKF-based algorithm employs the available measurements for the transformer differential protection. The proposed approach, relying on the differential current, can properly deal with the external sources of interference like harmonic excitation and loading. The EKF-based estimator presented is validated by simulation and experimental data. The results verify the ability of the proposed approach to robustly estimate the GIC level during various operating conditions.

Penetration of DC networks is rapidly increasing in modern power systems. As transient behavior of DC grids is different from that of AC ones, AC grid protection schemes might not be applicable to protect DC networks. Exact fault location is vital for protection of DC networks to reduce repair cost and achieve fast power recovery. This paper proposes a novel topology independent multi-terminal DC scheme to identify fault section and location for DC transmission systems. Voltage and current signals measured at the terminals are analyzed by the least squares error (LSE) algorithm. Then, the proposed scheme uses low frequency components of the signals to locate DC faults offline. Unlike some other methods, it does not require sophisticated sensors and hardware to capture very high frequency content of the signals. Hence, the proposed scheme can be implemented in practice without additional measuring infrastructure. The performance of the proposed scheme is evaluated under various fault conditions for different topologies of DC networks in both overhead lines and cables. Numerous simulations carried out demonstrate that the proposed scheme is quite accurate and provides excellent performance under different fault resistances, sections, and locations.

This paper provides an approach to monitor oscillation status in tunnel diode measurement circuits-by,measuring the second derivative of the current-voltage (I-V) characteristic curve while doing I-V curve measurement. The method of using the second derivative to detect oscillations works even when the oscillation frequency is ultrahigh or the oscillation amplitude is very small, e.g., below 10 mV. In this paper, the experimental principle of the tunneling spectroscopy was extended to measurement circuits with the presence of internal oscillations, in contrast to the conventional tunneling spectroscopy, which normally does not deal with internal oscillation. The numerical relationships between the measured average values of transient derivatives and the derivatives of the average current are derived: The average values of the transient first and second derivatives are shown to equal the derivatives of the average current. These relationships serve as the foundation for the authors' experiments. The typical oscillation characteristics in the curves of the first and the second derivatives are used to detect the presence of oscillations and the bias voltage range of oscillation in the I-V curve. The monitor of oscillation status during measurements provides the tester the confidence in the measurement data and whether it is necessary to improve the test circuit further. Finally, benefited from free-of-oscillation, the indirect tunneling current contributions arising by 121-mV (TO + 0) two-phonon combination, 144-mV (TA + 0 + 0) and 181-mV (TO + 0 + 0) three-phonon combinations at the negative differential resistance region are observed from a silicon Esaki tunnel diode at 4.2 K.

This paper proposes a novel attack identification mechanism for internet-of-things-based (IoT-based) converter-composed DC grids, where each agent collects its own and neighbours' measurement data for output regulation to meet a preceding power-sharing consensus. Independent from model-free or average-model-based attack detection theories, this mechanism is mainly inspired by converter stitching behavior analysis. Correspondingly, when facing latent signal substitution or agent instigation attacks, through comparing estimated signals with received ones for signal source authentication, both self-sensors and neighbours will be inspected. Eventually, not only can such attacks be detected, but also will respective attack sources be identified. A simulation case of 4-agent 800V IoT-based DC grid on Simulink and a hardware case of 3-agent 90V IoT-based DC grid on dSpace testing platform were investigated. Experimental results revealed that the estimation ratio error kept lower than 3.9% and all attacks were successfully identified, verifying the effectiveness of the proposed mechanism.

Made available in DSpace on 2020-12-12T02:24:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 This paper presents an innovative method for fault location in distribution networks based on classical circuit analyses. Two synchronized and few nonsynchronized pre- and during-fault voltages are required at few buses along with the impedance matrix. A new impedance matrix manipulation procedure is proposed so that the distribution system is investigated in partitions across multiple subsystems. This procedure allows the fault location process to be performed by solving systems of determined equations, making the method more technically accessible. The fault is located by analyzing the voltage sag at the terminal-bus of each subsystem separately. The proposed method is validated on the IEEE 33-bus, 12.66 kV distribution system with/without distributed generation (DG). Simulation results show the robustness and accuracy of the method under several pre- and during-fault scenarios and measurements errors. Electrical Engineering, Sao Paulo State University-UNESP, Ilha Solteira, Sao Paulo Brazil (e-mail: ricardobuzo00@hotmail.com) Electrical engineering, Sao Paulo State University - UNESP, Ilha Solteira, So Paulo Brazil (e-mail: henrique1226@hotmail.com) Electrical Engineering, Sao Paulo State University-UNESP, Ilha Solteira, Sao Paulo Brazil 15385-000 (e-mail: bertequini@dee.feis.unesp.br)

Recent advances in Internet-of-Things technology have opened the doors to new scenarios for biosensor applications. Flexibility, portability, and remote control and access are of utmost importance to move these devices to people’s homes or in a Point-of-Care context and rapidly share the results with users and their physicians. In this paper, an innovative portable device for both quantitative and semi-quantitative electrochemical analysis is presented. This device can operate autonomously without the need of relying on other devices (e.g., PC, tablets, or smartphones) thanks to built-in Wi-Fi connectivity. The developed hardware is integrated into a cloud-based platform, exploiting the cloud computational power to perform innovative algorithms for calibration (e.g., Machine Learning tools). Results and configurations can be accessed through a web page without the installation of dedicated APPs or software. The electrical input/output characteristic was measured with a dummy cell as a load, achieving excellent linearity. Furthermore, the device response to five different concentrations of potassium ferri/ferrocyanide redox probe was compared with a bench-top laboratory instrument. No difference in analytical sensitivity was found. Also, some examples of application-specific tests were set up to demonstrate the use in real-case scenarios. In addition, Support Vector Machine algorithm was applied to semi-quantitative analyses to classify the input samples into four classes, achieving an average accuracy of 98.23%. Finally, COVID-19 related tests are presented and discussed.

In this paper, we report the first experimental demonstration of the Stretched A linearisation method. The theoretical framework of the method and related simulation studies have been presented in Part I of this work. Here, we apply the method on an 850 nm multimode vertical-cavity surface-emitting laser (VCSEL) specified for operation at 10 Gb/s and demonstrate good quality optical output waveforms with little non-linear distortion at 16 Gb/s using non-return-to-zero (NRZ) modulation. An experimental sensitivity analysis on the generation of the required modulating current components demonstrates large tolerance to parameter mismatch. In addition, it is shown that an adaptive gain scheme can improve the tolerance to the timing offset between the current components. Potential hardware implementations using either analog or digital electronics are also discussed.

Electrical impedance tomography (EIT) has the potential to be an alternative technique to microscopy for many biological applications. It is a novel approach to monitor cell viability, proliferation, or drug response with high temporal resolution in a label-free, non-toxic, and non-destructive way. To limit measurement errors, only time-difference EIT is currently used for biological imaging. Still, the need for constant background reference limits its uses in long-term imaging. A novel equivalent circuit model was developed to analyze the errors in frequency-difference EIT (FDEIT) measurements. Based on the circuit model, the calibrated FDEIT (CFDEIT) method has been derived to compensate the measurement errors. The simulation results show that the voltage variations introduced by the leakage current are correctly modeled by the equivalent circuit. Significant improvements in the image quality are observed in both simulation and experimental results after the application of CFDEIT. It indicates that this paper improves the accuracy of FDEIT and makes it feasible for 3D tissue culture monitoring.

Current transformers for ac power systems applications are usually calibrated by applying sinusoidal currents at different frequencies. The main limitation of this approach is that it does not take into account nonlinearities that may have a significant impact on harmonic current measurement. A more accurate characterization should be based on test currents that are similar to those found in normal working conditions. However, this demands a proper current generator able to generate multitone waveforms with proper accuracy, which is seldom available in laboratories. This paper proposes a simple approach to implement a current generator, based on a waveform generator, a power amplifier, and a transformer which allows boosting the output current capability. Its uneven input–output response can be compensated through linear prefiltering of the desired current waveform. When the generator is employed to reproduce a specific class of current waveforms, such as those typically found in ac distribution grids, an optimal compensation filter can be easily designed. This approach allows canceling systematic nonlinearities introduced by the transformer and the power amplifier, thus significantly increasing accuracy with respect to a conventional frequency response compensation, as confirmed by experimental results.

This paper reports on the electrical quality of liquid phase crystallized silicon (LPC-Si) on glass for thin-film solar cell applications. Spatially resolved methods such as light beam induced current (LBIC), microwave photoconductance decay (MWPCD) mapping, and electron backscatter diffraction were used to access the overall material quality, intra-grain quality, surface passivation, and grain boundary (GB) properties. LBIC line scans across GBs were fitted with a model to characterize the recombination behavior of GBs. According to MWPCD measurement, intra-grain bulk carrier lifetimes were estimated to be larger than 4.5 µs for n-type LPC-Si with a doping concentration in the order of 10$^{16}$ cm$^{−3}$. Low-angle GBs were found to be strongly recombination active and identified as highly defect-rich regions which spatially extend over a range of 40–60 µm and show a diffusion length of 0.4 µm. Based on absorber quality characterization, the influence of intra-grain quality, heterojunction interface, and GBs/dislocations on the cell performance were separately clarified based on two-dimensional (2-D)-device simulation and a diode model. High back surface recombination velocities of several 10$^5$ cm/s are needed to get the best match between simulated and measured open circuit voltage (V$_{o c}$), indicating back surface passivation problem. The results showed that V$_{o c}$ losses are not only because of poor back surface passivation but also because of crystal defects such as GBs and dislocation.

Gallium nitride (GaN) devices are suitable for high-frequency power converters due to their excellent switching performance. To maximize the performance of GaN devices, it is necessary to study the switching characteristics, which requires measuring the switching current. However, GaN devices have a fast switching speed and are sensitive to parasitic parameters, so the current measurement should have a high bandwidth and should not introduce excessive parasitic inductance into the power converters. Traditional current measurements are difficult to meet these requirements, especially for fast GaN devices. This paper presents a high-bandwidth integrated current measurement for detecting the switching current of fast GaN devices. By effectively utilizing the parasitic inductance in the circuit, a single-Turn coil is embedded in the printed circuit board. This coil could pick up a sufficiently strong voltage signal, which is then processed to reconstruct the switching current. Moreover, corrections are carried out to further improve the accuracy. The current measurement has a small insertion impedance and a high bandwidth with a small influence on the parasitic inductance of the converter. The accuracy of the current measurement is experimentally verified by a 40 V GaN-based double pulse test circuit with a load current up to 25 A.

Integrated magnetic components are key elements of the power supply on chip modules. Due to the application requirements, these magnetic devices work at very high frequency and have low inductances. Conventional small-signal tests do not provide all the required information about the magnetic device. Hence, it is important to develop new setups to apply large signals to accurately measure the performance of devices under realistic operating conditions, including nonlinear core effects. The proposed experimental setup is suitable to measure the device impedance under different large-signal test conditions, similar to those in the actual converter, since the excitation current can be configured through every winding: ac current up to 0.5 A at frequencies up to 120 MHz and dc bias current up to 2 A through one or both windings. Voltage and current are measured using commercial instrumentation. Due to the characteristics of the probes and the high frequency of the test, the attenuation and delay due to the probes and the experimental setup have to be taken into account when processing the voltage and current waveforms to calculate the impedances. The compensation test to calculate this attenuation and delay is described. Finally, the proposed setup is validated by measuring a two-phase coupled inductor microfabricated on silicon. This work was supported in part by the European Union through FP7 (Project: PowerSwipe) under Grant 318529, in part by the Science Foundation Ireland through the Investigators Programme under Grant 15/IA/3180, and in part by the Spanish Ministry of Economy and Competitiveness and FEDER funds under Project DPI2014-53685-C2-1-R and Project DPI2017-88062-R. This paper was recommended for publication by Associate Editor Matthew A. Wilkowski.

The main obstacle to a wide use of dc-Decay tests lies in the necessity to align the rotor with the $d$ - or $q$ -axis, which is very difficult to perform for high-power units. The goal of this paper is to propose and validate standstill dc-Decay measuring methods for a rotor in arbitrary position, which consist of generalizations of the existing methods with the rotor aligned with one axis. The first new method (dc-Decay I) delivers the equivalent circuit with a few measurements. The second new method (dc-Decay II) permits to determine the full equivalent circuit of both axes by performing only one measurement, which is unique and a breakthrough in parameter identification. The field current measurement enables obtaining the characteristic reactance $x_{c}$ . A new method (dc-Decay III) is used to get the rotor angle. To extract the time constants and the reactances, an enhancement of the existing parameter identification algorithms using curve fitting is presented (used for the dc-Decay I method). Simulation and experimental results validate as good as possible the new methods and show their accuracy as well as their drawback.

International Standards IEC 61936-1 and EN 50522 define a global earthing system (GES) as the earthing network, created by the interconnection of local earthing systems that should guarantee the absence of dangerous touch voltages. Despite that, standards do not provide any official practical guidelines for its identification. The official classification of GES areas would lead to a simplification of the design and verification procedures of medium voltage/low voltage (MV/LV) substations grounding systems with associated economical savings for both distribution system operators and MV users. To overcome this regulatory vacuum, several teams of researchers proposed methods to identify the presence of a GES. In this paper, the main methods developed to identify a GES are presented. The different methodologies are applied to a real urban scenario and compared.

International audience; In the electromagnetic compatibility (EMC) behavior of power electronic converters, magnetic parasitic couplings between components are one of the main causes of dysfunctions or bad filtering (e.g., in EMC filter). These couplings could be as conducted or near-field interferences. In order to handle interaction problems, a complete knowledge of these magnetic couplings is then necessary. Our study is focused on near magnetic field's interferences. Indeed, the characterization of electromagnetic field in power electronics is still in active research. This paper details a predictive method that calculates accurately and efficiently the near magnetic field coupling between two sources. By using the near-field multipolar expansion in spherical harmonics of electromagnetic sources, the close magnetic coupling between two sources is determined from their equivalent model. It is shown that the increase in degree up to the fourth provides a more precise representation of the elements and thus a better accuracy of the near-field coupling prediction. Also, theoretical and experimental developments will be presented. The coupling between two complex sources will be considered to validate the predictive method.

This paper presents a comparative investigation of two versatile error-mitigation techniques, applicable to general antenna near-field measurement scenarios with echo signals of unknown origin. Both techniques are based on spatial filtering of the measured field, taking advantage of a priori knowledge of the antenna's size. The first approach takes advantage of the spatial-filtering properties of the spherical-wave expansion of the measured field. The second approach is based on the reconstruction of equivalent currents, and implements the spatial filtering as a direct consequence of the selected size and shape of the reconstruction surface. The investigation was performed using measured data on two different horns in both planar and spherical near-field scanning geometries. The presence and levels of echo pollution in the measurements were controlled by introducing known scattering objects in the anechoic chambers, and comparing with reference situations without disturbance.