G. Crotti

INRIM Istituto Nazionale di Ricerca Metrologica, Torino, Piedmont, Italy

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Publications (50)31.54 Total impact

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    ABSTRACT: Similar to low-voltage power systems, also in medium voltage networks there is a growing need for power quality (PQ) analyses, required by the increasing diffusion of distributed generation sources equipped with switching converters. This leads to the employment of transducers and measurement techniques able to convert and acquire voltage signals with better accuracy on a wider frequency range than conventional voltage and current instrument transformers. Voltage dividers (VDs) are expected to become the most used transducers in PQ assessments, since, with respect to conventional voltage transformers, they show higher frequency bandwidth and better linearity. The main disadvantage of the VDs is the absence of galvanic insulation between the transducer and the measurement/protection devices. Therefore, in this paper, a prototype of a VD for phase-to-ground connection with an insulating transmission system is presented. It is constituted by a high-impedance resistive-capacitive VD and by an analog electronic insulation interface. Such an electronic interface, inserted between the output of the divider and the input of a measuring instrument, realizes the galvanic insulation by means of an optical transmission system ensuring, simultaneously, wide frequency bandwidth and high accuracy. The design, simulation, and characterization of the realized insulated equipment are presented. Its performance well fit the prescription of the international standards about instrument transformers for PQ measurements.
    IEEE Transactions on Instrumentation and Measurement 10/2014; 63(10):2349-2357. · 1.71 Impact Factor
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    ABSTRACT: Due to the increasing presence of renewable energies and advances in power electronics, the power systems are nowadays working with more and more disturbing sources. Increasing performances are then required to voltage and current instrument transformers, in terms of both accuracy and frequency bandwidth. With reference to these requirements, low power non-conventional instrument transformers, which typically show better performances than the conventional inductive instrument transformer, are expected to rapidly diffuse in power system monitoring applications. Because of the low level of their output, the calibration of such instruments cannot be performed with the classical set-ups designed for conventional instrument transformers. In the paper, a test set for the calibration of non-conventional current instrument transformer working with current down to the 0.1 mA level, is presented. The considered set-up, intended for use in industrial environment, allows calibration from DC to 4 kHz with target uncertainties within 100 µA/A and 100 µrad. The working principle and the configuration of the developed test set are discussed and preliminary experimental results related to its characterization are shown.
    AMPS 2014; 09/2014
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    ABSTRACT: The increasing interest in the use in medium and high voltage networks as well as in the low voltage ones of non-conventional low power instrument measurement transformers entails the availability of dedicated calibration set-up, equipped with flexible and accurate measurement systems. The paper presents a measurement system for the calibration of both inductive and low power voltage and current transformers, which includes a low cost and digital acquisition and measurement equipment. It is based on a portable data acquisition system composed of various current and voltage data acquisition boards. The proposed system can be used for the calibration of transducers with analog output from DC up to tens of kilohertz and allows the comparison of signals of different kind and order of magnitude.
    2014 IEEE International Instrumentation and Measurement Technology Conference (I2MTC); 05/2014
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    ABSTRACT: This paper is focused on the uncertainty estimate of a hybrid experimental-numerical procedure for the evaluation of the electric field induced in a human model radiated by a low-frequency magnetic field produced by unknown sources. The procedure is based on magnetic field measurements in a limited number of points around the field source and makes use of the boundary element method. The uncertainty contribution due to the measurement operations is taken into account by evaluating its propagation through the computational process using a Monte Carlo approach coupled to a discrete numerical technique. The procedure is then applied to the case of a body exposed to the field generated by a Helmholtz coil system. The results show that the relative standard uncertainty of the estimated induced electric field is within a few percent.
    IEEE Transactions on Instrumentation and Measurement 01/2013; 62(6):1436-1442. · 1.71 Impact Factor
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    ABSTRACT: Voltage dividers are expected to become the most used transducers in power quality assessments, since, with respect to conventional voltage transformers, they show higher frequency bandwidth and better linearity. Anyway, the main disadvantage of the VDs is the absence of galvanic insulation, which, especially in MV grids, is an absolute necessity. Therefore, in this paper a new medium voltage insulated divider is presented. It is constituted by a high impedance resistive-capacitive voltage divider and by an electronic insulation interface. Such an electronic interface, inserted among the output of the VD and the input of a measuring instrument, realizes the galvanic insulation by means of an optical fiber; at the same time, it has a wide frequency bandwidth and a high accuracy.
    Applied Measurements for Power Systems (AMPS), 2013 IEEE International Workshop on; 01/2013
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    ABSTRACT: Features and performances of a calibration system for both conventional and electronic measurement transformers with analog output are described. The calibration circuit includes standard current/voltage transformers as reference transducers and two synchronised digitizers which enable measurement of signals with amplitude that can differ up to three orders of magnitude. Best measurement uncertainty at power frequency (confidence level 95%) is estimated to be within a few hundreds of ppm and microradians for the ratio and phase error respectively. By making use of different acquisition strategies the same set-up can be employed for the frequency response measurement of transducers up to tens of kilohertz with enlarged uncertainty.
    Applied Measurements for Power Systems (AMPS), 2013 IEEE International Workshop on; 01/2013
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    ABSTRACT: It is shown that the chemical composition data published by Carpinteri et al. in the article "Compositional and Microchemical Evidence of Piezonuclear Fission Reactions in Rock Specimens Subjected to Compression Tests" [Strain 47 (Suppl. 2), 282 (2011)] cannot be the result of independent measurements as claimed by the authors. Therefore, no conclusion can be drawn from them about compositional modifications induced in the stone by hypothetical piezonuclear reactions taking place during catastrophic failure of the material at fracture.
    05/2012;
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    Article: Comment on
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    ABSTRACT: It is shown that the chemical composition data published by Carpinteri et al. in the article "Compositional and Microchemical Evidence of Piezonuclear Fission Reactions in Rock Specimens Subjected to Compression Tests" [Strain 47 (Suppl. 2), 282 (2011)] cannot be the result of independent measurements as claimed by the authors. Therefore, no conclusion can be drawn from them about compositional modifications induced in the stone by hypothetical piezonuclear reactions taking place during catastrophic failure of the material at fracture.
    05/2012;
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    ABSTRACT: The paper is focused on the estimate of the uncertainty of the results obtained by a hybrid experimental/numerical procedure for the evaluation of the electric field induced in a human body radiated by a LF magnetic field produced by unknown sources. The procedure is based on magnetic field measurements in a limited number of points around the field source and makes use of the Boundary Element. A method for the evaluation of the uncertainty contributions due to both the measurement process and the use of a discrete numerical technique is presented.
    Precision Electromagnetic Measurements (CPEM), 2012 Conference on; 01/2012
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    ABSTRACT: The paper focuses on the calibration techniques of non-conventional voltage and current measurement transformers. Calibration circuits set up at INRIM are described, which makes use of digital acquisition and numerical analysis of the transducer output. Examples of calibration of non-conventional instruments to be used as on-site references are discussed, which include a system based on Rogowski coil for live-on-site check of measuring current transformers with rated voltages up to 380 kV.
    Precision Electromagnetic Measurements (CPEM), 2012 Conference on; 01/2012
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    ABSTRACT: The paper describes techniques and results of a measurement survey for the electromagnetic characterization of a magnetic resonance imaging device (MRI) and the evaluation of medical staff exposure who might stay close to the patient. The investigation is performed under different operating sequences. The paper describes the human exposure evaluation techniques recommended by the International Commission on Non-Ionising Radiation Protection (ICNIRP). A comparison between the compliance with limits published in 1998 and with the new ones, published in 2010, is discussed. (Language: Italian). L’articolo descrive tecniche e risultati di una campagna di misura per la caratterizzazione elettromagnetica di un tomografo a risonanza magnetica finalizzata alla valutazione dell’esposizione elettromagnetica del personale sanitario in prossimità della macchina. La memoria include la descrizione delle tecniche di valutazione dell’esposizione raccomandate dall’International Commission on Non-Ionizing Radiation Protection (ICNIRP) e una valutazione della conformità dell’esposizione riscontrata ai limiti emessi dall’ICNIRP nel 1998 e, relativamente alla gamma 1 Hz-100 kHz, a quelli pubblicati nel 2010.
    Tutto Misure. 04/2011; vol. 4:pp. 263-266.
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    M. Chiampi, G. Crotti, A. Morando
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    ABSTRACT: This paper investigates the effects of some influence quantities on the measurement of power frequency sinusoidal currents by means of flexible Rogowski coil sensors. The analysis is carried out through a numerical model, which is specifically developed and allows both the prediction of the circuital and coil parameter effects and the improvement of the coil design. The estimate of the measurement uncertainty associated with the on-site use of a flexible and openable Rogowski coil is finally given by assuming relatively controlled operating conditions.
    IEEE Transactions on Instrumentation and Measurement 04/2011; · 1.71 Impact Factor
  • Gabriella Crotti, Domenico Giordano, Angelo Sardi
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    ABSTRACT: The development and the characterization of a resistive-capacitive divider, intended for indoor calibrations and measurements at medium voltage level, are described. A numerical tool is developed and largely used in the design phase to optimize the divider performances with respect to frequency behavior and insulation strength. The divider, with a coupled matching stage, is laboratory characterized both at low and high voltage, taking into account the expected operating conditions. The estimated measurement uncertainty associated with its on-site use as a reference is within 550 ppm for the ratio error and 310 µrad for the phase displacement. Results of the first tests performed in MV/LV substations confirm that it can be effectively used in the calibration of medium voltage measurement transformers.
    01/2011;
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    ABSTRACT: The results of a magnetic and electromagnetic measurement survey are presented, which was carried out around a Magnetic Resonance Imaging device. The investigation is performed with the twofold aim of characterising the field source under the different operating sequences and evaluating the exposure of workers both to the static and time-varying magnetic field. The exposure levels are estimated, as a function of the position of the workers and the field characteristics, and their compliance with both the existing and possible new limits is discussed. Critical situations are put in evidence in relation to both the exposure limits and the performance of the available measuring instruments
    17th Imeko TC4 Symposium, Kosice; 09/2010
  • G. Crotti, D. Giordano, A. Sardi
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    ABSTRACT: The design and the characterization of a medium voltage resistive-capacitive divider for on-site calibrations and measurements are described. Measurements of voltage linearity up to 10 kV, temperature and frequency behavior performed on the air-insulated divider are found compliant with the design requirements.
    01/2010;
  • Y. Hu, M. Chiampi, G. Crotti, A. Sardi
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    ABSTRACT: A system is developed to evaluate the performances of partial discharge (PD) measuring instruments that implement complex analysis functions such as PD pattern classification and identification. In addition to impulse current sequences, the system can reproduce PD patterns, obtained from mathematical model based on the PD mechanism or from experiments. The capabilities of the system are discussed and examples of its application to digital PD measuring instruments are given.
    01/2010;
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    ABSTRACT: This paper focuses on the performances of TEM cells when used in the calibration of power frequency environmental electric field meters. The spatial non-uniformity of the electric field inside a TEM cell is analyzed through experimental investigations and three-dimensional Boundary Element modeling to evaluate the field experienced by the sensing elements of actual 3D meter probes. The perturbation caused by the probe support is also taken into account. The uncertainty component associated with the spatial non-uniformity in the volume taken up by typical power and low frequency field probes is estimated. The field non-uniformity is also evaluated in relation to the use of TEM cells of reduced size. Finally, the field non-uniformity is exploited to predict the performance of an actual field meter operating in significant field gradients.
    Measurement. 01/2010;
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    ABSTRACT: Contactless electromagnetic temperature sensors are analyzed and compared, under a number of configurations, for applications in spinning devices. Their working principle is based on the variation of electrical or magnetic properties with temperature. By a preliminary study, carried out through finite element modeling, a number of effective solutions have been identified and a few of them have then been selected for testing in the laboratory. Two significant experimental examples are here discussed.
    IEEE Transactions on Magnetics 11/2009; · 1.42 Impact Factor
  • G Crotti, D Giordano
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    ABSTRACT: The paper analyses some critical situations in the assessment of the compliance with the human exposure limits to the low-frequency magnetic fields. The study is focused on non-sinusoidal and transient waveforms in the frequency range from 8 Hz to 65 kHz. It is carried out by combining measurements and numerical evaluations, starting from actual magnetic flux density behaviours. The results show that inconsistent indications of compliance with the exposure limits may arise not only because of the evaluation method adopted, but also as a result of the used time or frequency windows in relation to the investigated magnetic field waveform.
    Radiation Protection Dosimetry 10/2009; 137(3-4):227-30. · 0.91 Impact Factor
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    ABSTRACT: We report an experimental and modeling analysis of ferroresonance phenomena in a series inductance-capacitance-resistance circuit with a saturable inductor. The nonlinear reactor core is made of a nanocrystalline ribbon whose magnetic properties can be modified by suitable thermal treatments. This choice of core allows us to investigate the influence of the magnetization curve on the evolution of the ferroresonance phenomenon. We detected different ferroresonance modes experimentally and reproduced them by simulation. We gave particular attention to the longitudinally field-annealed alloy, whose magnetization characteristic is close to a step ideal curve; this feature enables us to analytically interpret the ferroresonance mechanism and predict the conditions that lead to a stated evolution of the phenomenon.
    IEEE Transactions on Magnetics 10/2009; · 1.42 Impact Factor