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This paper reports the performance of clamp-on current transformers under nonsinusoidal conditions. A set of experimental measurements helped to determine the ratio and the phase errors under two conditions: 1) sinusoidal excitation with frequencies from 45 to 1000 Hz and 2) nonsinusoidal excitation using the fundamental frequency and one harmonic, with adjusted phase shift. It was found that ratio and phase errors are affected by the phase angle between the harmonic and the fundamental and the harmonic amplitude. The effects of conductor location in the current transformer's window and of the air-gap width were also investigated. It was concluded that harmonic phase and ratio errors measured in nonsinusoidal conditions can be higher than the ones determined by the frequency response. Index Terms--Clamp-on current transformers, current transformers (CTs), frequency response, power system harmonics, transducers.

The aim of this paper is the development of a theoretical model of medium-voltage (MV) cables in the frequency range of 25-200 kHz, which can be easily implemented in the Simulink enviroment. Two transmission-line configurations: 1) line-ground and 2) line-line were considered. The model requires the knowledge of the transmission channel parameters in the frequency domain. Thus, a characterization of MV cables in the two transmission-line configurations by means of experimental measurements was performed on commonly used MV cables, RG7H1R, of different sections, 95 [mm.sup.2] and 185 [mm.sup.2] with an aluminum core and copper shielded. To validate the model, a comparison between the attenuation constant [alpha] measured and the one simulated for both configurations under study was carried out. Index Terms--Attenuation constant, medium-voltage (MV) cables, power-line communication (PLC), transmission line.

This paper describes a time domain technique for the detection of fundamental and harmonic components of voltages and currents, which is able to evaluate all the quantities required by IEEE Standard 1459-2000. The technique does not require any spectral analysis to separate the fundamental positive-sequence components from harmonic, negative-sequence and zero-sequence ones. In the paper the development of the proposed technique is presented for three-phase systems, both three-wires and four-wires, as well as for single-phase systems. The implementation of the proposed technique on a PC-based instrument is also described and experimental results are presented. Finally, accuracy specifications are investigated in the presence of the measurement transducers. Index Terms--Harmonic distortion, IEEE Standard 1459-2000, phase-locked loops (PLLs), power measurement, power quality (PQ).

The aim of this paper is to illustrate the development of a theoretical and experimental study on the characterization of medium voltage (MV) cables in the frequency range 25-200 kHz. Two transmission line configurations, line-ground and line-line, were considered in order to evaluate the main parameters, such as the characteristic impedance and the attenuation constant [alpha]. A simplified model of the line-ground configuration is proposed which allows one to evaluate the characteristic impedance and the attenuation constant by means of geometrical dimensions. The model was verified by experimental measurements on commonly used MV cables, RG7HIR, with an aluminium core of different sections, 95 [mm.sup.2] and 185 [mm.sup.2]. Moreover, the experimental tests were carried out for the line-line configuration. Index Terms--Attenuation constant, characteristic impedance, medium voltage cables, power line communication, power system communication.

This paper presents a comparative analysis of the performances of both a traditional induction meter and various types of commercial static meters for reactive energy in the presence of harmonic distortion. This is a topical issue, since there are several types of static meters on the market, based on different principles of construction. In accordance with current standards, these meters are designed to operate in sinusoidal conditions and their performance is not tested in the presence of harmonic distortion. However, with the increase of pollution levels in power systems, the meters may be used even in the presence of distorted voltages and/or currents; in such cases, their accuracy may be very different from the nominal conditions, and the various meters may lead to different measurements of energy for the same load conditions. In this paper, the analysis is supported by several experimental tests, performed by means of a power calibrator. Index Terms--Energy measurements, induction meters, power systems harmonics, reactive power, static meters.

The aim of this paper is to present the operating principle of a new resonant device, called the fault decoupling device (FDD), able to improve power quality in electrical distribution systems. In low-voltage networks, this device can be employed in order to mitigate voltage dips due to faults or large induction motor startup. Moreover, in the presence of distributed-generation (DG) units, the FDD allows one to obtain various benefits such as a reduction of the fault current in each node of the network and an increase in the voltage at the DG unit node. In order to show the performances of the FDD, analytical studies and computer simulations were carried out which took into account various working operation conditions. Finally, the prototype of the FDD as well as the preliminary experimental results are presented. Index Terms--Distributed generation (DG), fault decoupling device, power generation, power quality (PQ), voltage dips.

In this paper, a new approach is proposed for the detection of harmonic sources in polluted power systems. It is a single-point strategy, based on a comparison among different 'nonactive' power quantities proposed in literature that, in the same working conditions, assume different values at the same metering section. Some simulations tests were carried out on a standard IEEE test system proposed by other authors as a benchmark system for the analysis of multipoint measurement techniques for harmonic pollution monitoring. The obtained results show that the proposed single-point approach is in agreement with other strategies already proposed in the literature and can provide useful indications for the detection of the dominant harmonic source upstream or downstream the metering section also in some critical cases. Index Terms--Detection of harmonic sources, harmonic distortion, power quality, power system harmonics, reactive power.

This paper presents a new approach in realizing various carrier-based pulsewidth-modulation techniques by a generalized control algorithm, which is referred to as the universal control algorithm and is obtained via unequal sharing of null states. The flexibility of such an approach allows one to easily and quickly control two-level inverters. Furthermore, this approach may be also extended with few changes to the control of multilevel inverters. The algorithm that is presented here for two-level voltage-source inverters (VSIs) also obtains efficient detection and management of both the linear and overmodulation ranges. In the overmodulation range, which is treated by using the [alpha]-[beta] components of the reference-voltage space vector, the algorithm shows the advantage of lower calculation time, thus allowing one, if required, to increase the switching frequency. Several simulation runs have been performed, aiming to test the proposed procedure for both two-level and multilevel VSIs. Finally, the new algorithm was experimentally validated in the case of two-level inverters by using it in a VSI workbench that can carry out several experimental tests. Index Terms--Multilevel inverter, overmodulation, pulsewidth modulation (PWM), space-vector modulation (SVM), voltage-source inverter (VSI).

Grid-connected photovoltaic systems are increasingly used in electrical distribution systems. However, they inject distorted currents. Therefore, special attention must be paid to harmonic and interharmonic measurements. The new edition of IEC 61000-4-7 introduces the concept of harmonic and interharmonic groups, which implies new expressions for total harmonic distortion (THD) factors. In this paper, a theoretical and experimental comparison is made between the different THD factors in order to show which of the currently defined distortion factors is best suited to detect harmonic and interharmonic pollution. Experimental tests were carried out first by means of a calibrator and subsequently in a single-phase grid-connected photovoltaic system. In both cases, measurements were carried out with a PC-based instrument developed by the authors and able to calculate the distortion factors according to IEC 61000-4-7. Index Terms--Grid-connected photovoltaic systems, harmonic and interharmonic analysis, IEC 61000-4-7 Ed 2002.