Renato Sasdelli

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.

Low-cost DSP-based equipment for the real-time detection of transients in power systems

A novel solution for the real-time detection of transients in power systems is presented. It relies on a simple and robust algorithm, which analyzes the signal in the time domain, does not involve high computational burdens, does not require a high amount of memory, and has been implemented on a low-cost DSP. Experimental results showing the very good system performance are provided.

A VI-based measurement system for sharing the customer and supply responsibility for harmonic distortion

Owing to the proliferation of loads which draw nonsinusoidal currents, the current and the voltage distortion in public distribution systems is ever increasing. The usual online investigation methods cannot provide information about the responsibility for harmonic distortion in a given metering section. New methodologies are therefore searched for. Some recently proposed investigation techniques are recalled in this paper and the relevant measurement problems are discussed. A digital measurement system which is based on the virtual instrumentation (VI) technique and implements these methods, is described. The results of some experimental work are also presented.

Quality management for electricity as a processed material

The offer provided by an electric utility combines many characteristics of a service together with the continuous delivery of electricity as a product. The quality of electricity as a processed material, resulting from a continuous process and having immediate delivery in continuous flow can he adversely affected by the end-use processes of other customers, as well as by the continuous-process reliability. Hence, the guidelines endorsed by ISO Standard 9004-3 for the quality management of processed materials must be suitably tailored in the case of electricity. Problems that must be dealt with to control the characteristics critical to quality of electricity are discussed. In this connection, measurement activities oriented to quality management are considered, mainly to outline unsolved problems.

Compensable power for electrical systems in nonsinusoidal conditions

Power definitions are extended to electrical circuits where both loads and supply are harmonic generators and where a series source impedance is considered to provide a realistic representation of electrical power systems. A method is proposed whereby distortion is compensated and power-factor corrected by means of reactance one-ports inserted in series and parallel into the electrical circuit. The approach is applied to single-phase circuits. >

On the use of data from distributed measurement systems for correlating voltage transients to lightning

Voltage transients are the main causes of complaints from medium-voltage customers. For this reason, utilities and independent authorities are focusing their attention on investigation techniques capable of providing information useful for classifying voltage transients depending on their origin. Distributed measurement systems for power quality monitoring able to detect, measure, and classify impulsive transients can be used in coordination with lightning location systems to assess whether there is a relation between a given transient and a lightning event. In this paper, a criterion for evaluating the above correlation is proposed and a numerical example, which is based on real accuracy specifications, is presented. The results show that attempting a correlation between lightning events and induced transients is quite reasonable.

Measurement of harmonic losses in transformers supplying nonsinusoidal load currents

The spread of the load control techniques based on power electronics is causing the increase of harmonic losses in power distribution systems. A digital method for the evaluation of these losses in power transformers, which only requires measurements taken at the transformer output terminals, is discussed. The accuracy of the method, along with the performance of a virtual-instrumentation-based instrument implementing it, is also discussed. The results of some experimental work are reported.

On the uncertainty in wavelet-based signal analysis

The evaluation of uncertainty is a task usually neglected by people performing wavelet-based measurements. In this paper, the wavelet analysis aimed at gauging the synthesis of transient disturbances is considered, and a general expression of the uncertainty affecting this synthesis is provided. Simulations have been performed to validate the above expression, which holds no matter which mother wavelet is used and the kind of disturbance. Results of experiments on actual signals are also reported and discussed.

A Distributed Measurement System for Locating Transient-Voltage Sources

The use of a distributed measurement system to locate the source of transient voltages is discussed in this paper. The system implements a method based on the measurement of the starting instants of a transient in the nodes of the monitored network. The method performance is investigated by simulating the system operation. Results in the case of both faults and insertion of capacitors in an IEEE test network are presented and discussed

Electric-power quality measurements under distorted conditions:: Are they utopia or reality?

This paper discusses how distortion- and unbalance-dependent parameters can be used for assessing the electric-power quality. In particular, possible ways for the localization of the sources producing distortion are discussed. The information supplied by the different measurement procedures proposed in the literature or by the International Standards is compared, on the basis of experimental results. The discussion is aimed at outlining items that have not yet been studied in a satisfactory way.