A Method for the Measurement of Digitizers’ Absolute Phase Error

A lot of engineering applications, from telecommunications to power systems, require accurate measurement of phase angles. Some of them, like synchrophasor measurement and calibration of instrument transformers with digital output, in order to reach high phase measurement accuracy, require the knowledge of phase error of digitizers. Therefore, in this paper a method for the measurement of digitizers’ absolute phase errors is proposed. It adopts a sinewave and two square waves, that are the digitizer sample clock and a phase reference signal. Combining the measurements of the relative phase differences between the adopted signals it is possible to accurately evaluate the absolute phase error of a digitize

Accuracy Type Test for Rogowski Coils Subjected to Distorted Signals, Temperature, Humidity, and Position Variations

Low-Power Instrument Transformers (LPITs) are becoming the first choice for distributed measurement systems for medium voltage networks. However, there are still a lot of challenges related to their operation. Such challenges include their accuracy variation when several influence quantities are acting on them. Among the most significant influence quantities are temperature, electromagnetic field, humidity, etc. Another aspect that increases the importance of studying the LPITs’ accuracy behavior is that, once installed, they cannot be calibrated for several years; hence, one cannot compensate for in-field conditions. Hence, this work aims at introducing a simple type test for a specific LPIT, the Rogowski coil. First, an experimental setup to assess the effect of temperature, humidity, and positioning on the power quality accuracy performance of the Rogowski coil is described. Second, from the results and the experience of the authors it has been possible to design a specific type test. The test has the aim of finding the limits of the accuracy variations of a single Rogowski coil. Afterwards, such limits can be used to compensate for the in-field measurements, obtaining an overall higher accuracy. The results of this work may contribute to the alwaysevolving standardization work on LPITs

Numerická analýza a simulace Rogowského cívky

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 práce ilustruje analýzu rogowských cívek pro energetické aplikace při provozu v podmínkách bez ideálního měření. Vyvinutý numerický model, ověřený porovnáním s jinými metodami a experimenty, umožňuje zkoumat vliv geometrických a konstrukčních parametrů na chování měření cívky a také studujeme chování rogowských cívek spojených s tyčovými vodiči za kvazi-statických podmínek . Pomocí analýzy konečných prvků (FEM) odhadujeme rozložení proudu přes tyč a tok spojený snímačem pro různé polohy primárního vodiče a pro různé provozní frekvence. Simulační a experimentální výsledky jsou uvedeny v textu.410 - Katedra elektroenergetikydobř

Compensation of Nonlinearity of Voltage and Current Instrument Transformers

partially_open11This paper aims at characterizing and improving the metrological performances of current and voltage instrument transformers (CTs and VTs) in harmonic measurements in the power system. A theoretical analysis is carried out to demonstrate that, due to the iron core nonlinearity, CT and VT output signal is distorted even when the input signal is a pure sine wave. Starting from this analysis, a new method for CT and VT characterization and compensation is proposed. In a first step, they are characterized in sinusoidal conditions and the harmonic phasors of the distorted output are measured; in the second step, these phasors are used to compensate the harmonic phasors measured in normal operating conditions, which are typically distorted. The proposed characterization and compensation techniques are called SINusoidal characterization for DIstortion COMPensation (SINDICOMP). Several experimental tests, using high-accuracy calibration setups, have been performed to verify the proposed methods. The experimental results showed that the SINDICOMP technique assures a significant improvement of CT and VT metrological performances in harmonic measurements.restrictedopenCataliotti, Antonio; Cosentino, Valentina; Crotti, Gabriella; Femine, Antonio Delle; Cara, Dario Di; Gallo, Daniele; Giordano, Domenico; Landi, Carmine; Luiso, Mario; Modarres, Mohammad; Tine, GiovanniCataliotti, Antonio; Cosentino, Valentina; Crotti, Gabriella; Femine, Antonio Delle; Cara, Dario Di; Gallo, Daniele; Giordano, Domenico; Landi, Carmine; Luiso, Mario; Modarres, Mohammad; Tine, Giovann

Contactless measurement of electric current using magnetic sensors

We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields

Theory and Experimental Validation of Two Techniques for Compensating VT Nonlinearities

Inductive instrument transformers (ITs) are still the most used voltage and current sensors in power systems. Among the numerous applications that require their use, one of the most important is surely represented by harmonics measurement. In this case, the recent literature shows that, since they suffer from both a filtering behavior due to their dynamics and from nonlinear effects produced by their iron core, they can introduce errors up to some percent. This article wants to deeply investigate, in the very same experimental conditions, about the performance of two digital signal processing techniques, recently introduced for the improvement of harmonics measurements performed through ITs, namely, SINusoidal characterization for DIstortion COMPensation (SINDICOMP) and compensation of harmonic distortion through polynomial modeling in the frequency domain (PHD). These methods have been applied to two different voltage transformers, having different specifications, by using two measurement setups based on different architectures. The impact of the voltage generator employed during the identification on the achieved accuracy is theoretically and experimentally evaluated. Modified versions of SINDICOMP and PHD compensation, which are more robust against nonidealities of the measurement setup, are presented. The performances of the techniques are evaluated by adopting voltage waveforms similar to those that can be encountered during the normal operation in a real distribution grid

FPGA-based real time compensation method for medium voltage transducers

open5noSince the increase of the distributed power connected to the medium voltage networks, a capillary monitoring of the power quality becomes essential. This entails the spread of transducers with suitable frequency bandwidths, as required by the relevant standards. The paper describes a real time compensation method for the extension of the frequency bandwidth of medium voltage dividers whose performances do not allow to perform measurements over a wide frequency range. This approach will contribute to keep the costs of this innovation lowopenCrotti, Gabriella; Gallo, Daniele; Giordano, Domenico; Landi, Carmine; Inrim, Mario Luiso2 1Crotti, Gabriella; Gallo, Daniele; Giordano, Domenico; Landi, Carmine; Inrim, Mario Luiso2