Nicola Locci

A Flexible GPS-based System for Synchronized Phasor Measurement in Electric Distribution Networks

Large-scale distributed measurement systems are the object of several applications and research. The goal of this paper is to develop, by employing global positioning system (GPS) receivers, measurement techniques that are suited to the continuous monitoring of the electrical quantities in distribution networks in terms of synchronized phasors. The proposed measurement procedures, differently from commercially available phasor measurement units, are based on general-purpose acquisition hardware and processing software, thus guaranteeing the possibility of being easily reconfigured and reprogrammed according to the specific requirements of different possible fields of application and to their future developments.

Evaluation of uncertainty in measurements based on digitized data

The paper deals with the uncertainty in measurement based on digital signal processing algorithms, like those achievable with the virtual instruments. The correct estimation of bias and uncertainty is discussed with reference to a simple case study. Three possible approaches to this question are examined and compared. It is shown how a Monte Carlo method, based on numerical simulations and implemented with commercial software packages, can allow virtual instruments to perform an auto-evaluation of both bias and uncertainty affecting their results. Some theoretical considerations, computer simulations and experimental tests are shown to support the proposed technique.

A PMU for the Measurement of Synchronized Harmonic Phasors in Three-Phase Distribution Networks

Owingtotheextension ofelectric distribution networks, monitoring andcontrol issues relyonlarge scale distributed measurement systems, abletocarry outsimultaneous measurements ofelectrical quantities inseveral points onthe monitored systems. Inthis papertheimplementation ofdigital procedures, suitable fortheevaluation ofthesynchronized harmonic phasors, inaflexible Phasor Measurement Unit(PMU) basedonPXImodular hardware ispresented. Someresults of experimental tests arepresented tocharacterize themeasurement systeminordertoevaluate thebehavior ofthedesigned instrument inrealoperating conditions onthree-phase electric distribution networks.

A numerical approach to the evaluation of uncertainty in nonconventional measurements on power systems

The application of the rules endorsed by the ISO Guide to the expression of uncertainty in measurement (GUM) can turn into a difficult task when quantities that characterize the operation of modern power systems are measured by means of DSP-based instruments. A numerical approach to easily tackle this task is proposed in this paper, as an alternative to the uncertainty evaluation based on the analytical solution of the uncertainty propagation law, as prescribed by the GUM. The validity of the numerical approach, which is based on a Monte-Carlo procedure, is first proved in the case of the spectral analysis of a periodic signal, which is the first step for many nonconventional measurements. Then the evaluation of the accuracy of a method for the measurement of the harmonic losses in a power transformer supplying nonsinusoidal load currents is dealt with as an application example.

GPS and IEEE 1588 synchronization for the measurement of synchrophasors in electric power systems

In modern transmission and distribution networks, monitoring, control and protection tasks are usually performed by Intelligent Electronic Devices (IEDs), that are often connected to each other by suitable communication links. Many of the procedures implemented require that the acquired data have an extremely accurate common time reference, with typical synchronization specifications ranging from milliseconds to a few hundreds of nanoseconds, according to the different use foreseen for the measured data. The strictest synchronization requirements lead to the need of highly accurate clock settings, such as the ones bases on satellite systems (e.g. the Global Positioning System, GPS). As an alternative, in situations where many devices are located in a geographically limited sub-area of the system, it could be advantageous to distribute the time reference to the remote stations through suitable network synchronization protocols. Between them, the PTP (Precision Time Protocol) defined in the Standard IEEE 1588 offers the best accuracy. This possibility is investigated in this paper, with special reference to one of the most challenging measurement problems, that is represented by the measurement of synchrophasors. Experimental results will be provided to evaluate the performance achievable with this solution.

Remote Didactic Laboratory “G. Savastano,” The Italian Experience for E-Learning at the Technical Universities in the Field of Electrical and Electronic Measurement: Architecture and Optimization of the Communication Performance Based on Thin Client Technology

The Remote Didactic Laboratory Laboratorio Didattico Remoto -LA.DI.RE. “G. Savastano” is an e-learning measurement laboratory supported by the Italian Ministry of Education and University. It provides the students of electric and electronic measurement courses with access to remote measurement laboratories, delivering different didactic activities related to measurement experiments. The core of the software architecture is the integration of the Learning Management System (LMS) with the remotely accessible measurement laboratories through web services and thin client paradigm, providing a new approach to remote experiments on measurement instrumentation. The overview of this paper is on the different solutions concerning the thin client technology, and the solution implemented is described. This solution takes into account the delivered services to students and teachers and permits optimization of the communication performances. The results of the comparison among the performances of different implementations of the thin client paradigm highlight the advantages of the adopted solution. As a consequence, the description of the thin client protocol implemented, together with the presentation of the LMS and delivered services given in a previous paper, makes an exhaustive analysis of the software architecture of the LA.DI.RE. “G. Savastano.”

Experimental comparison of MV voltage transducers for power quality applications

The paper presents a measurement campaign to compare the behavior of voltage transducers suitable for medium voltage (MV) networks in the measurement of power quality (PQ) parameters. In particular, high bandwidth resistive-capacitive dividers are compared to traditional magnetic core instrument transformers. Firstly, the main specifications of the compared transducers are recalled and the experimental setup used to perform the measurements is shown. Then, the results of laboratory characterization tests, performed with medium voltage signals, are presented, with the main purpose of comparing the harmonic behavior of the different kinds of transducers. Finally, the results of in-field measurements, performed in a node of a three phase MV network, are presented and discussed. These results are expected to provide useful indications about the accuracy achievable in the measurement of some important PQ parameters, such as the ones related to harmonics and transients, as well as in the measurement of harmonic synchrophasors.

Uncertainty estimation for DSP‐based power quality measurements

This paper deals with the uncertainty in digital measurement systems designed for power quality applications. The main goal of this work is to evaluate such uncertainty by means of a Monte Carlo method recently proposed in the literature. The accuracy of the measurement result obtained with a DSP‐based instrument for power quality metering depends on the behavior of the devices located in both the conditioning block and A/D conversion stage: it is thus necessary to consider the uncertainties introduced by each component of the system and the propagation of their effects through the measurement chain. Here, the uncertainty is estimated starting from the technical specifications provided by the manufacturers of these devices. Experimental results are reported to show the importance of some concerns about the practical implementation of the proposed methodology in a real instrument.

Modelling ADC nonlinearity in Monte Carlo procedures for uncertainty estimation

Monte Carlo procedures can be successfully employed to evaluate the uncertainty of measurements performed by digitally processing sampled data, provided that the uncertainties affecting the input samples are modelled correctly. The static nonlinearity is the most difficult error to be modelled, since the technical specifications afforded by the manufacturers of the acquisition systems usually are not sufficient to describe the nonlinearity curve over the entire input range. Thus, suitable assumptions are needed and approximations are unavoidable. This paper focuses on measurements systems based in plug-in data acquisition boards, which are generally based on successive approximation register A/D converters. A behavioural model is presented, according to which the overall nonlinearity is divided into two contributions: a smooth component, responsible for the macroscopic error trend in the output domain, and a component with sudden variation in the scale of values. Theoretical fundamentals of the methods are reported and experimental results highlighting the reliability of the proposed approach are discussed.

Converting specifications of DSP-based instruments into data suitable for Monte Carlo uncertainty estimation methods

This paper deals with the problem of convening the specifications of devices used in measurement systems based on digital signal processing into data that can be represented as probability density functions of the input quantities (samples) in a Monte Carlo procedure for uncertainty estimation. The attention is focused on data acquisition systems and input transducers. Authors proposals for facing this problem are based on the idea of considering separately the different uncertainty contributions, by defining for each of them appropriate pdfs and taking into account the correlation of their effects on the acquired samples to be processed. The advantages and limits of this approach are discussed with the help of experimental tests