A. Prudenzi

A survey on power quality cost in industrial customers

The problem of the power quality (PQ) cost in industrial customers is particularly important at present in the new scenery of competitive electricity markets. In fact, it represents the added value that the electric suppliers can provide to the users for improving their productivity and the reliability of their industrial process. The industry must compare the cost of the PQ services provided by the utilities with the cost derived from damage to the production output and/or to the plants. While this latter is easy to define because it is related to the physical replacement of some equipment, the cost of production losses is not simple to monetize. The paper refers to a survey that has been conducted on medium-large factories in Italian industrialized areas, with the goal to identify the type of disturbances that generate productivity losses and to estimate the relevant damage.

Experimental characterization of personal computers harmonic impact on power quality

Abstract The paper reports some experimental measurement results concerning harmonic content of current absorbed by Personal Computers (PC). The measurements provided different samples of PCs being monitored at short time interval lengths (2 s). The relatively large quantity of measurement results has permitted a statistical characterization of the harmonic content with both different modes of operation and various upstream system characteristics. Curves obtained from the measurement results processing have been proposed which give a parametrical estimate of the mutual influence between harmonics produced by PCs and the supply system characteristics at the point of common coupling.

IEC Std. 61000-3-2 harmonic current emission limits in practical systems: need of considering loading level and attenuation effects

The paper deals with the harmonic emission limits provided by International Electrotechnical Commission (IEC) Std. 61000-3-2 for appliances with current absorption less than or equal to 16 Amps. To this aim attention is focussed on personal computers (PC) as a sample of the wide nonlinear appliance class D as regulated by the Standard. Results of some laboratory tests on a PC supplied from the low voltage (LV) grid show that: (1) EEC limits expressed to mA/W are exceeded by actual PCs operating In practical systems; and (2) the IEC limits are stated for nominal load even though lower loading conditions produce higher specific (mA/W) harmonic contents. The problems are assessed by means of a testing activity performed in the laboratory. To this aim, an experimental layout providing harmonic monitoring of a PC supplied from a system with variable impedance has been implemented in the laboratory.

Power quality costs and upgrading solutions: the energy centre

Voltage sags and interruptions originating on primary and secondary sides of facilities are among the most concerning issues for industrial customers. In the paper a classification approach to costs involved by the mentioned power quality (PQ) disturbances in industrial end-use segment is illustrated. To this aim some of the most diffuse mitigation techniques have been considered. Finally, a case study concerning a novel approach adopted for solving PQ problems in a semiconductor factory has been illustrated and discussed.

The continuous harmonic monitoring of single-phase electronic appliances: desktop PC and printers

The paper reports some experimental measurement results concerning harmonic current drawn by PCs and printers. Several samples of equipment have been continuously monitored during their typical operation. For the purpose a custom monitoring system has been used. The continuous harmonic monitoring has permitted an interesting characterization of harmonic spectrum variability that reveals very useful information for penetration studies based upon a bottom-up approach.

Surveying PQ aspects in Italian industrial customers

The paper has the objective to identify levels of power quality (PQ) at industrial customers in the various areas of Italian electric system. To this aim, the results of two different questionnaire based surveys performed so far in different Italian Districts have been analyzed in comparison in order to derive general rules and guidelines concerning PQ aspects. The surveys have involved, as a whole, a sample of about 200 industrial customers located in central and northern areas of the country. The surveys have concerned even some aspects relevant to costs of PQ problems. The main results as obtained from either the surveys are reported and discussed.

Harmonics monitoring survey on office LV appliances

The paper reports some experimental measurement results concerning current harmonics and power consumptions associated to some single phase non-linear loads supplied in low voltage. In particular some office equipments and florescent lamps have been monitored during their typical operation phases. For the purpose a custom monitoring system has been used. The harmonic monitoring survey has permitted an interesting characterization of harmonic spectrum variability that is very useful for penetration studies based upon a bottom-up approach.

Harmonics and PQ events monitoring in an electrified metro-transit system

The paper illustrates some results of a wide power quality (PQ) survey performed on the power supply installations of the metro-transit system serving the city of Rome, in Italy. The system currently includes two railway lines supplied at 1,500 V DC through several AC/DC 3.7 MW rated converters. The power supply of the system is provided at medium voltage (20 kV) from five different connections to the public grid. Fourteen electrical substations provide the total demand of about 20 MW of the system. The survey, currently still in progress, involves monitoring activities aimed at identifying possible PQ problems of various nature. Identification of typical daily patterns of harmonics distortion due to the system is even a task of the current survey.

A Knowledge Based System for Medium Term Load Forecasting

The paper reports a new methodology for the medium term load forecasting providing monthly energy consumption and monthly maximum demand for a municipal utility. To this aim a modular procedure, based on an artificial neural network (ANN), which is a multi-layer perceptron using a back-propagation feed-forward algorithm, is implemented. The monthly forecasts are obtained through some knowledge based activities from the output of stage providing annual energy forecast. The choice of the prediction stage is reported by illustrating the results of a comparison with canonical statistical methods, such as exponential smoothing and ARIMA. The whole knowledge based procedure is illustrated in due detail and some best forecasting performances are reported thus demonstrating validity of the proposed approach

Harmonic analysis procedures: a comparison between IEEE and IEC guidelines

The goal of the paper is the comparison between two guidelines for harmonic analysis evaluation given by international standards on quality of power: the IEEE 519, mainly related to the American market, and the IEC 1000, mainly adopted in the European market. The comparison is made considering an industrial plant where nonlinear loads and large motors are present. Comments and discussion are made on the suggested models and harmonic summation methods.