Nicolino Locci

A digital compensation method for improving current transformer accuracy

This paper deals with error compensation in current transformers. Usually the manufacturer tries to limit these errors by stating a transformer nominal ratio slightly different from the turns ratio. On the other hand techniques have been developed that allow software current compensation. The proposed method requires acquisition of the instantaneous secondary current and its adjustment with magnetizing current, taking into account hysteresis effects. To do this, a preliminary procedure is performed for core and transformer parameter identification. The compensation method has been tested on a variety of instrument transformers, with sinusoidal primary current. Test results show in all examined cases, an improvement in primary current reproduction accuracy, compared with that achieved using CTs nominal ratio, even for core partial saturation. A further development of the compensation technique is in progress, with a view to eliminating some restrictive hypothesis introduced in the present study.

Hysteresis and eddy currents compensation in current transformers

In the paper a digital technique for improving the accuracy of instrument current transformers is presented. Since the exciting current can be considered as the main error source, its evaluation can allow the compensation of its detrimental effects to be obtained. The exciting current required by the transformer in every kind of steady state operation can be determined by simply acquiring the secondary current, provided that the examined CT has been preliminarily identified. A simple scalar model for the CTs magnetic core, taking into account saturation as well as hysteresis and eddy currents phenomena, has been implemented in a software compensation routine. This allows us to improve the accuracy in the reproduction of the primary current, in the case of both sinusoidal and distorted current waveforms (provided that DC components are not present). Many experimental tests, under different practical situations, have been performed. The results clearly show that the proposed technique is able to significantly reduce, in comparison with traditional methods, the errors introduced by current transformers.

Investigation on the accuracy of harmonic pollution metering techniques

The main goal of this paper is to investigate the robustness of some procedures recently proposed in the literature for harmonic pollution metering, in respect to the effects of the uncertainty sources present in the measurement chain. Both single point and multipoint methods are discussed. The research is based on computer simulations performed on an IEEE test system suitable for studies related to harmonics in power distribution networks. The estimate of the combined uncertainty affecting the measurement results is achieved by exploiting a Monte Carlo statistical approach. The results are discussed to highlight some important findings on the practical usability of these monitoring techniques.

Remote Didactic Laboratory “G. Savastano,” The Italian Experience for E-Learning at the Technical Universities in the Field of Electrical and Electronic Measurements: Overview on Didactic Experiments

The Remote Didactic Laboratory Laboratorio Didattico Remoto - LA.DI.RE. ldquoG. Savastanordquo is the e-learning measurement laboratory supported by the Italian Ministry of Education and University. It involves about 20 Italian universities and provides students of electric and electronic measurement courses with access to remote measurement laboratories delivering different didactic activities related to measurement experiments. In order to demonstrate the versatility for didactic use, the overview of some experiments is given. The didactic experiments summarized in this paper concern measurement characterization of instruments and communication systems, measurement devices for remote laboratories, basic electrical measurements, magnetic measurements, electromagnetic-interference measurements, and signal processing for measurement applications.

Comparative analysis between active and passive current transducers in sinusoidal and distorted conditions

Current measurements are a critical item in the monitoring of modern electrical power plants, since the quantities to be measured often show high harmonic content. The current transducers should therefore guarantee a good accuracy even when they operate with distorted waveforms. In this paper, the behavior of some devices commonly used for current measurement is examined, considering either sinusoidal or distorted conditions. Traditional current transformers, transducers based on the Hall effect, and resistive shunts combined with isolation amplifiers have been considered. The comparison is performed by evaluating a synthetic error index, called composite error, which allows all the main causes of uncertainty (amplitude errors, time shifts, and distortion) to be taken into account. The proposed investigation aims to find out the main characteristics that make each transducer suitable or unsuitable in different practical situations.

Remote Didactic Laboratory "G. Savastano": the Italian Experience for the E-learning at the Technical Universities in the Field of the Electrical and Electronic Measurements, Overview on Didactic Experiments

The Remote Didactic Laboratory Laboratorio Didattico Remoto - LA.DI.RE. G. Savastano is the e-learning measurement laboratory supported by the Italian Ministry of Education and University. It involves about twenty Italian universities and provides the students of electric and electronic measurement courses with the access to remote measurement laboratories delivering different didactic activities related to measurement experiments. In order to demonstrate the versatility for didactic use, the overview of same experiments is given. The didactic experiments summarized in the paper concern with: measurement characterization of instruments and communication systems, measurement devices for remote laboratory, basic electrical measurements, magnetic measurements, electromagnetic interferences measurements, and signal processing for measurement applications

On the Measurement of Power Quality Indexes for Harmonic Distortion in the Presence of Capacitors

Different techniques have been recently proposed in the literature for the identification of the sources of harmonic distortion in electric-distribution systems. Each of them has its own advantages and limitations as far as reliability, accuracy, and practical usability are concerned. In this paper, these techniques are grouped into three main fundamental criteria in order to investigate their performance in the presence of capacitors. A case study is analyzed by means of both experimental tests and computer simulations. The results put in evidence some major problems that may concern the information provided by the considered methodologies, in virtue of the interaction of the capacitors with the other network components.

Remote Didactic Laboratory "G. Savastano": the Italian Experience for the E-learning at the Technical Universities in the Field of the Electrical and Electronic Measurements, Architecture and Delivered Services

The Remote Didactic Laboratory Laboratories Didattico Remoto - LA.DI.RE. G. Savastano is the e-learning measurement laboratory supported by the Italian Ministry of Education and University. It provides the students of electric and electronic measurement courses with the access to remote measurement laboratories delivering different didactic activities related to measurement experiments. The paper describes the innovative aspects concerning the software and hardware architecture, and the delivered services to both the teachers and students. The core of the delivered services is the integration of the learning measurement system with the remotely accessible measurement laboratories through the Web. Moreover, the advantages of the proposed software and hardware architecture are highlighted in comparison with the traditional architectures

A tool to define the position and the number of irradiance sensors in large PV plants

Monitoring irradiance values is a critical issue for correct management and possible fault detection in large photovoltaic plants. In a previous work it was shown that the use of suitable spatial interpolation algorithms allows better accuracy in the estimation of the irradiance values, especially under partial shading conditions. At the same time, the number of irradiance sensors should be limited, for obvious economic reasons. In this paper a procedure is proposed to define the optimal placement of a fixed number of irradiance sensors and an analysis is performed to investigate the impact of the number of installed sensors on the quality of the estimated irradiance map. The proposed study is aimed to be a tool that supports the plant operator in the design of the most appropriate measurement infrastructure.

A distributed system for the synchronized acquisition of fast voltage transients

Voltage transients are the main causes of complaints for medium-voltage customers, and hence interest is focused on investigation techniques able to help in classifying and localizing such events in accordance with their origin. In this light of fact, a distributed measurement system for performing synchronized acquisition of fast voltage transients is presented in this paper. The system, designed to fulfill specific constraints about the reliability of the provided information, has been used in a one-year long measurement campaign performed in a medium voltage network. The main obtained results are presented.