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19 pages, 3257 KiB

Open AccessArticle

A Simple Method for Compensating Harmonic Distortion in Current Transformers: Experimental Validation

by Christian Laurano, Sergio Toscani and Michele Zanoni

Sensors 2021, 21(9), 2907; https://doi.org/10.3390/s21092907 - 21 Apr 2021

Cited by 15 | Viewed by 2099

Abstract

Conventional current transformers (CTs) suffer from nonlinearities due to their ferromagnetic cores. On one hand, it is well-known that severe core saturation may occur because of large overcurrents or unidirectional transient components: this may substantially impact the operation of relays. On the other [...] Read more.

Conventional current transformers (CTs) suffer from nonlinearities due to their ferromagnetic cores. On one hand, it is well-known that severe core saturation may occur because of large overcurrents or unidirectional transient components: this may substantially impact the operation of relays. On the other hand, weaker nonlinear effects are also present during regular working conditions. In particular, the spectral content of typical current waveforms is characterized by a strong fundamental term responsible for harmonic distortion affecting the frequency components at the secondary side. In turn, this has a significant impact on the accuracy that can be reached as long as current harmonics must be monitored. The target of this work is implementing a simple signal processing technique that allows compensating for this effect. The method, characterized by extremely low computational complexity, is first introduced and validated using numerical simulations. After this, it was tested experimentally to improve the harmonic measurement capability of inductive CTs. The achieved results highlight a noticeable reduction of errors at low-order harmonics over a wide range of primary current amplitudes. It is worth noting that the black-box approach makes the technique suitable also for compensating nonlinearities introduced by current transducers based on different operating principles. Thanks to this peculiarity and to the low computational complexity, the proposed method is suitable to be employed in power quality analyzers and merging units. In this way, high-accuracy monitoring of current harmonics in power systems can be achieved, opening the way to advanced power quality management and to the location of disturbing users. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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13 pages, 4411 KiB

Open AccessCommunication

A Low-Cost IoT Sensors Network for Monitoring Three-Phase Induction Motor Mechanical Power Adopting an Indirect Measuring Method

by Fabrizio Ciancetta, Edoardo Fiorucci, Antonio Ometto, Andrea Fioravanti, Simone Mari and Maria-Anna Segreto

Sensors 2021, 21(3), 754; https://doi.org/10.3390/s21030754 - 23 Jan 2021

Cited by 6 | Viewed by 3098

Abstract

Three-phase induction motors are widely diffused in the industrial environment. Many times, the rated power of three-phase induction motors is not properly chosen causing incorrect operating conditions from an energetic point of view. Monitoring the mechanical dimension of a new motor is helpful, [...] Read more.

Three-phase induction motors are widely diffused in the industrial environment. Many times, the rated power of three-phase induction motors is not properly chosen causing incorrect operating conditions from an energetic point of view. Monitoring the mechanical dimension of a new motor is helpful, should an existing motor need to be replaced. This paper presents an IoT sensors network for monitoring the mechanical power produced by three-phase induction motors, adopting an indirect measuring method. The proposed technique can be easily adopted to monitor the mechanical power using only one line of current transducer, reducing the cost of the monitoring system. The proposed indirect measurement technique has been implemented on a low-cost IoT system, based on a Photon Particle SoC. The results show that the proposed IoT system can estimate the mechanical power with a relative error of within 8%. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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21 pages, 6740 KiB

Open AccessArticle

Precise Amplitude and Phase Determination Using Resampling Algorithms for Calibrating Sampled Value Instruments

by Yeying Chen, Enrico Mohns, Michael Seckelmann and Soeren de Rose

Sensors 2020, 20(24), 7345; https://doi.org/10.3390/s20247345 - 21 Dec 2020

Cited by 3 | Viewed by 2611

Abstract

Sampling-based calibration systems for calibrating “Sampled Value” (SV)-based instruments for substation automation require synchronised and time-aligned sampling processes. As the signal frequency of the power grid is always asynchronous to the standardised sampling frequencies according to IEC 61869-9, the sampled waveforms of the [...] Read more.

Sampling-based calibration systems for calibrating “Sampled Value” (SV)-based instruments for substation automation require synchronised and time-aligned sampling processes. As the signal frequency of the power grid is always asynchronous to the standardised sampling frequencies according to IEC 61869-9, the sampled waveforms of the calibration system and of the SV-based device under test can be resampled to be synchronised and to allow better accuracy in the following measurements based on the Discrete Fourier Transform (DFT) of the resampled waveforms. The paper presents simulations and results for different resampling algorithms. A modified sinc interpolation method with a finite impulse response (FIR) is presented. The deviation of the results for the root mean square (RMS) and phase angle is in the order of 10⁻⁸V/V (or rad) for normalised frequencies of up to 20% of the sampling frequency. No practical degradation in the presence of noise and harmonics could be observed. In addition, laboratory experiments demonstrate the realization of the proposed resampling process in the future SV-based calibration systems for SV-based instrumentation. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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20 pages, 8424 KiB

Open AccessArticle

Methodology for the Accurate Measurement of the Power Dissipated by Braking Rheostats

by Domenico Giordano, Davide Signorino, Daniele Gallo, Helko E. van den Brom and Martin Sira

Sensors 2020, 20(23), 6935; https://doi.org/10.3390/s20236935 - 4 Dec 2020

Cited by 7 | Viewed by 2222

Abstract

The energy efficiency of transportation is a crucial point for the rail and metro system today. The optimized recovery of the energy provided by the electrical braking can lead to savings of about 10% to 30%. Such figures can be reached by infrastructure [...] Read more.

The energy efficiency of transportation is a crucial point for the rail and metro system today. The optimized recovery of the energy provided by the electrical braking can lead to savings of about 10% to 30%. Such figures can be reached by infrastructure measures which allow the recovery of the breaking energy that is not directly consumed by the rail system and dissipated in rheostat resistors. A methodology for the accurate estimate of such energy is valuable for a reliable evaluation of the cost–benefit ratio associated with the infrastructural investment. The energy can be estimated by measuring a braking current flowing in the rheostats. The varying duty-cycle associated with the high dynamic variation, from zero to thousands of amperes, makes the current measurement very challenging. Moreover, the digitization of such waveforms introduces systematic errors that affect the energy estimation. To overcome these issues, this paper proposes a technique to measure the power and energy dissipated by the rheostat of a DC operated train with high accuracy. By means of an accurate model of the electrical braking circuit (chopper and rheostat) and the frequency characterization of the current transducer, a correction coefficient as a function of the duty-cycle is estimated. The method is then applied to data recorded during a measurement campaign performed on-board a 1.5 kV train of Metro de Madrid during normal operation. Using the proposed technique, the estimation of the dissipated braking energy is improved by 20%. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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30 pages, 3495 KiB

Open AccessArticle

Stray Current Protection and Monitoring Systems: Characteristic Quantities, Assessment of Performance and Verification

by Andrea Mariscotti

Sensors 2020, 20(22), 6610; https://doi.org/10.3390/s20226610 - 18 Nov 2020

Cited by 15 | Viewed by 6940

Abstract

Electrified transportation systems (ETSs) are affected by stray current problems impacting within and outside the right of way on reinforcement, buried metal structures and foundations. Stray current protection systems have recently been integrated in the track structure. Track electrical quantities are, thus, usually [...] Read more.

Electrified transportation systems (ETSs) are affected by stray current problems impacting within and outside the right of way on reinforcement, buried metal structures and foundations. Stray current protection systems have recently been integrated in the track structure. Track electrical quantities are, thus, usually measured to assess track insulation and protection efficiency but should be backed up by additional measurements at the affected structures and installations, in order to assess their exposure and risk of corrosion. Ideally, a stray current monitoring system proceeds from the measurement of these quantities, to data collection and archival, to data presentation, analysis and prediction. Feasible sensors and probes, the impact of environmental conditions and uncertainty are considered for the measurement at the physical level. Data analysis is critically reviewed considering the variability of operating conditions and the effectiveness of each quantity as indicator of track insulation and protection efficiency. Given the normal spread of values, for data presentation and interpretation, suitable techniques are considered based on averaging, curve similarity and feature extraction, and also for the task of assessing compliance to limits or reference values and establishing a trend that may drive informed maintenance decision. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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27 pages, 4717 KiB

Open AccessArticle

PQ and Harmonic Assessment Issues on Low-Cost Smart Metering Platforms: A Case Study

by Giovanni Artale, Giuseppe Caravello, Antonio Cataliotti, Valentina Cosentino, Dario Di Cara, Nunzio Dipaola, Salvatore Guaiana, Nicola Panzavecchia, Marilena G. Sambataro and Giovanni Tinè

Sensors 2020, 20(21), 6361; https://doi.org/10.3390/s20216361 - 7 Nov 2020

Cited by 17 | Viewed by 2995

Abstract

This paper presents a feasibility study on how to implement power quality (PQ) metrics in a low-cost smart metering platform. The study is aimed at verifying the possibility of implementing PQ monitoring in distribution networks without replacing existing smart metering devices or adding [...] Read more.

This paper presents a feasibility study on how to implement power quality (PQ) metrics in a low-cost smart metering platform. The study is aimed at verifying the possibility of implementing PQ monitoring in distribution networks without replacing existing smart metering devices or adding new modules for PQ measurements, thus zeroing the installation costs. To this aim, an electronic board, currently used for remote energy metering, was chosen as a case study, specifically the STCOMET platform. Starting from the specifications of this device, the possibility of implementing power quality metrics is investigated in order to verify if compliance with standard requirements for PQ instruments can be obtained. Issues related to device features constraints are discussed; possible solutions and correction algorithms are presented and experimentally verified for different PQ metrics with a particular focus on harmonic analysis. The feasibility study takes into account both the use of on-board voltage and current transducers for low voltage applications and also the impact of external instrument transformers on measurement results. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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18 pages, 6675 KiB

Open AccessArticle

Laboratory Calibration of Energy Measurement Systems (EMS) under AC Distorted Waveforms

by Daniela Istrate, Abderrahim Khamlichi, Soureche Soccalingame, Jorge Rovira, Dominique Fortune, Martin Sira, Pascual Simon and Fernando Garnacho

Sensors 2020, 20(21), 6301; https://doi.org/10.3390/s20216301 - 5 Nov 2020

Cited by 3 | Viewed by 2771

Abstract

Current standard EN 50463-2 indicates the tests and the requirements to be satisfied for an energy measurement system of a traction unit for railway applications. Some of these tests are to be done with several harmonics superposed on the rated voltage, respectively current. [...] Read more.

Current standard EN 50463-2 indicates the tests and the requirements to be satisfied for an energy measurement system of a traction unit for railway applications. Some of these tests are to be done with several harmonics superposed on the rated voltage, respectively current. However, no calibration systems satisfying the standard requirements were available few years ago. The work performed in the EURAMET project “MyRailS” leads to the development of fictive power sources and reference measurement systems described in this paper. Therefore, it is possible to generate distorted 25 kV-50 Hz voltages with harmonics up to 5 kHz and 90° phase-fired currents up to 500 A with harmonics up to 5 kHz. The generated power is measured by developed traceable reference systems with accuracy better than 0.5%. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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Other

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13 pages, 3206 KiB

Open AccessLetter

On the Long-Period Accuracy Behavior of Inductive and Low-Power Instrument Transformers

by Alessandro Mingotti, Lorenzo Bartolomei, Lorenzo Peretto and Roberto Tinarelli

Sensors 2020, 20(20), 5810; https://doi.org/10.3390/s20205810 - 14 Oct 2020

Cited by 17 | Viewed by 2166

Abstract

The accuracy evaluation of instrument transformers is always a key task when proper control and management of the power network is required. In particular, accuracy becomes a critical aspect when the grid or the instrumentation itself is operating at conditions different from the [...] Read more.

The accuracy evaluation of instrument transformers is always a key task when proper control and management of the power network is required. In particular, accuracy becomes a critical aspect when the grid or the instrumentation itself is operating at conditions different from the rated ones. However, before focusing on the above non-rated conditions, it is important to fully understand the instrument transformer behavior at rated conditions. To this end, this work analyzed the accuracy behavior of legacy, inductive, and low-power voltage transformers over long periods of time. The aim was to find patterns and correlations that may be of help during the modelling or the output prediction of voltage transformers. From the results, the main differences between low-power and inductive voltage transformers were pointed out and described in detail. Full article

(This article belongs to the Special Issue Advanced Transducers and Systems for Voltage and Current Measurement)

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