Daniele Gallo

Power-Quality Monitoring Instrument With FPGA Transducer Compensation

In this paper, the design and the prototype implementation of a power-quality (PQ) measuring and monitoring instrument based on an embedded controller with reconfigurable I/O are described. The instrument performs the calculation of main PQ indexes according to the latest standards, and it can be reconfigured for future standard developments. It is properly implemented to operate in stand-alone mode, and it is interfaced with hardware modules to exchange information and data, locally, with RS-232 connection or, remotely, with Transmission Control Protocol/Internet Protocol communication. The design includes enhancing of transducer performances through the correction of systematic errors with digital filters implemented by a field-programmable gate array module. This instance allows better performance without increasing cost. Finally, the whole accuracy of the proposed measurement system is evaluated by experimental tests that were performed in agreement with the specification of a class-A instrument for some of the main PQ indexes. The tests are performed, including the transducers, although that component is not required by the standard, to evaluate the behavior of compensated transducers. The test results are compared with those obtained by a commercial PQ instrument and show a good agreement.

Real-Time Digital Compensation of Current Transformers Over a Wide Frequency Range

The advance in power electronics causes, over the years, an increasing diffusion of nonlinear loads. Moreover, electrical generation systems are going to include a growing amount of solar and wind energy, characterized by time-variant flow of energy and, very often, with a relevant distortion. These aspects give more and more emphasis to the monitoring of conducted disturbances on power systems over a wide frequency range, and consequently, voltage and current transducers adopted for this aim must have a proper frequency bandwidth. Voltage transformers (VTs) and current transformers (CTs), which are the most installed transducers in electrical power systems, are typically constructed to operate only at the industrial frequency, i.e., 50/60 Hz, but it is clear that their substitution would require an unsustainable cost. Therefore, in this paper, a method for real-time digital compensation of the CT frequency response over a wide range is presented. An implementation of the proposed method is shown, and the compensated CT is characterized and tested in some practical situations, with waveforms affected by typical power quality disturbances.

A New Methodological Approach to Quality Assurance of Energy Meters Under Non-Sinusoidal Conditions

In this paper the authors propose a methodology to guide verification of energy meters under sinusoidal and non sinusoidal conditions. At first, it is presented a brief review about definitions of the quantities that should be measured or monitored for revenue purposes and their relationship with electrical quantities that are recognized to be important in terms of metering accuracy. Then, a design of experiment that allows testing meters under a combination of disturbances showing positive and negative correlation is described. Finally, a hardware and software system to perform verification procedures in complex situation is presented with some preliminary analyses

Implementation of a test system for advanced calibration and performance analyses of flickermeters

This paper presents an implementation of a test system for advanced calibration and performance analysis of flickermeters. Tests include not only the complete set of test points reported in IEC Standard 61000-4-15, but also an array of different voltage fluctuations - related to common power quality issues - that may be encountered in actual use. This is done because it can be shown that different flickermeter implementations fully meeting the performance tests defined in IEC Standard can still disagree significantly in some actual measurements. After the description and the performance analysis of the test system, a commercial instrument is tested and its response is presented.

Light flicker prediction based on voltage spectral analysis

The paper shows how flicker prediction can be achieved by means of a harmonic and interharmonic analysis of voltage. Weighting the spectral components in inverse proportion to the flicker perceptibility threshold is the main concept of such an approach, which also takes advantage of the use of the interharmonic grouping introduced by IEC. In this way more comprehensive results in terms of limit definition and compliance seem to be obtainable. The results of the application of this approach to both numerical and experimental data is discussed and analyzed.

Advanced Instrument For Field Calibration of Electrical Energy Meters

Calibration of electrical energy meters is coming up as a metrological concern. The latest European Union (EU) directives about measuring instruments adopted for commercial transactions state that their accuracy has to be verified in actual operating conditions. This requirement is leaving all laboratories involved in energy meter calibration in serious difficulty because this kind of metrological verification is, at the moment, still not fully developed or even clarified in all involved aspects. In this paper, a measurement equipment for the calibration of energy meters is presented. Its structure and metrological characterization are discussed. To improve its performances without increasing its costs, two online digital compensation procedures have been realized and are shown: one increases the spectral purity of test signals and one corrects the transducer frequency response. Experimental results relating metrological characterization have shown that the so-realized calibrator is suitable for the onsite calibration of energy meters.

Accuracy Analysis of Algorithms Adopted in Voltage Dip Measurements

This paper analyzes the accuracy of algorithms commonly adopted in instruments devoted to the detection and characterization of voltage dips (which are also called sags). This analysis is particularly interesting, because the results of dip measurements are utilized for calculation of severity levels and site indexes, which are important parameters not only in the assessment of the quality level of power supply but also in the selection of equipment with proper intrinsic immunity. Instruments for dip measurement still have unresolved technical and theoretical issues related to the characterization of their metrological performances, so it can be found that different instruments are significantly in disagreement in some actual measurements. This paper moves a step into the direction of deepening the knowledge about the measurement of voltage dips, pointing out the limits incident to the adoption of the detection algorithms indicated in the standards. It starts with a discussion about parameters that characterize voltage dips, in agreement with the standard. Then, analytical calculations of some systematic deviations in the event characterization, which are introduced by the most diffused dip detection algorithms, in simplified measurement situations, are presented, underlining their remarkable impact. The obtained relations are experimentally verified on a commercial power quality instrument, forecasting its systematic deviations.

Design and Calibration of an Objective Flickermeter

Measurement of light flicker according to current standard EN ISO 61000-4-15 is performed through measurement of voltage variations filtered by a model of a 60 W/230 V incandescent lamp. Hence, differences in current illumination systems technology can determine discrepancies between light flicker measurements performed under the same voltage flicker. In the paper, a method to measure light flicker with a low cost digital device, based on light intensity measurements, is proposed, thus including the lamp itself in the measurement process. In this way an objective measurement of light flicker is obtained. The metrological characterization of the device has been implemented by means of an automatic testing station which includes a standard IEC flickermeter (Norma D6000) as reference instrument. Thanks to its portability, the instrument can be used to measure light flicker no matter the illumination system used, over a wide range of environments spanning from home/office to industrial locations, and including the environmental condition (i.e., ambient light and reflection by walls and objects) in the measurement process

Collaborative multisensor network architecture based on smart Web sensors for power quality applications

In this paper, the aim of the authors is to propose a multisensor network architecture for distributed power quality measurements, based on the use of low cost smart Web sensors and on a collaborative mobile agent mechanism that allow an easy remote access, for a generic user, to the measurement results. The network has a full decentralized processing architecture in which the sensors can collaborate in the signal analysis. A low cost smart Web sensor is also presented. It is mainly characterized by an architecture, both hardware and software, modular and adaptable to specific requirement that allows an easy integration into distributed measurement systems. Finally, in-field measurements, conducted on low voltage sub-networks, are reported for some of the main power quality disturbances.

On the Use of the Flickermeter to Limit Low-Frequency Interharmonic Voltages

The possibility of using the IEC flickermeter for the assessment of the limits of low frequency interharmonic voltages is critically analyzed. The response of flickermeters to interharmonic components is analytically investigated, obtaining approximation formulas for the calculation of Pst in the presence of couples of components at frequencies that are symmetric with reference to the fundamental and in the presence of one or more single components. The instrument characteristics and limitations are also highlighted, using the results obtained from a numerical implementation of the IEC flickermeter. Finally, the general problem of the limits of low frequency interharmonic voltages is discussed and practical solutions are proposed.