Valentina Cosentino

A Phase-Locked Loop for the Synchronization of Power Quality Instruments in the Presence of Stationary and Transient Disturbances

Power quality instrumentation requires accurate fundamental frequency estimation and signal synchronization, even in the presence of both stationary and transient disturbances. In this paper, the authors present a synchronization technique for power quality instruments based on a single-phase software phase-locked loop (PLL), which is able to perform the synchronization, even in the presence of such disturbances. Moreover, PLL is able to detect the occurrence of a transient disturbance. To evaluate if and how the synchronization technique is adversely affected by the application of stationary and transient disturbing influences, appropriate testing conditions have been developed, taking into account the requirements of the in-force standards and the presence of the voltage transducer.

Synchronization techniques for power quality instruments

The measurement of voltage characteristics in power systems requires the accurate estimation of the power supply frequency and signal synchronization, even in the presence of disturbances. The authors developed and tested two innovative techniques for instrument synchronization. The first is based on signal spectral analysis techniques performed by means of the Chirp- transform analysis. The second is a phase-locked loop (PLL) software based on a time-domain coordinate transformation and an innovative phase-detection technique. To evaluate how synchronization techniques are adversely affected by the application of a disturbing influence, experimental tests were carried out, taking into account the requirements of the standards. The proposed techniques were compared with a standard hardware solution. In this paper, the proposed techniques are described, the experimental results are presented, and the accuracy specifications are discussed.

A virtual instrument for the measurement of IEEE Std 1459-2000 power quantities

In this paper, the authors present a PC-based instrument for the measurement of electrical-power quantities defined in IEEE Std. 1459. The instrument is based on a time-domain technique for the detection of the fundamental and harmonic components of voltages and currents. The time-domain strategy was originally developed by the authors for three-phase, three-wire systems. In that paper, the strategy had been extended to both three-phase, four-wire and single-phase systems. Simulation tests were carried out to assess the uncertainty contribution of the proposed strategy in the absence of the measurement transducers. Moreover, the accuracy of the PC-based instrument with its transducers was evaluated; the experimental tests were carried out by using a power calibrator.

A self-synchronizing instrument for harmonic sources detection in power systems

The energy markets deregulation holds a new contractual perspective between customers and utilities, in which energy price can depend on voltage quality and load characteristics, as well as on responsibility for disturbances caused on supply voltage in power systems. In this contest, harmonic sources detection is one of the most urgent problems, because of the proliferation of loads which draw nonsinusoidal currents. In this paper, the authors present a new instrument based on a time domain method for harmonic active power detection in three phase systems. Amplitude and sign of harmonic powers can be measured directly and no spectral analyses are required for the evaluation of amplitudes and phase angles of currents. Moreover, the instrument is able to synchronize itself to the input signal, to measure voltage and current total distortion factors and harmonic voltages amplitudes. Theoretical aspects are discussed, measurement accuracy is evaluated and experimental results are presented.

Transition of a distribution system towards an active network. Part II: Economical analysis of selected scenario

This paper outlines the economical issues related to the transition of the energy generation for a real MV/LV distribution system from a ‘fuel based’ one to a distributed and smart ‘renewables based’ one. It is the prosecution of a companion paper, which addressed the technical issues connected to such transition. The study has been carried out by University of Palermo and ENEA (Italy), on a portion of real MV/LV distribution system of the research center ENEA of Casaccia (Rome, Italy). The analysis is carried out for a specific scenario chosen among those proposed in the companion paper.

A New Measurement Method for the Detection of Harmonic Sources in Power Systems Based on the Approach of the IEEE Std. 1459–2000

In this paper, a novel single-point strategy is proposed for the detection of the harmonic sources in power systems. The method is an improvement of a strategy previously proposed by the authors; it is developed from the IEEE Std 1459-2000 approach and it can be entirely implemented in the time domain, thus simplifying the measurement system. The effectiveness of the proposed method is evaluated by introducing simple decision-making rules and by taking the presence of the measurement transducers into account. Several simulations and experimental tests are presented, showing that the enhanced strategy is able to give an useful information on the detection of the dominant harmonic source upstream or downstream the metering section.

Comparison of Nonactive Powers for the Detection of Dominant Harmonic Sources in Power Systems

This paper deals with an innovative technique for the detection of disturbing loads in distorted power systems. The technique is a single-point strategy based on a comparison among different ldquononactiverdquo power quantities already proposed in the literature, which are measured at the same metering section. In this paper, the effectiveness of the strategy is discussed, which also considered the errors of the measurement transducers; the analysis is supported by simulation tests, which were carried out on both a simple single-phase system and an IEEE standard three-phase test power system. The latter was used by other authors as a benchmark system for the analysis of multipoint measurement techniques for harmonic pollution monitoring.

A Time-Domain Strategy for the Measurement of IEEE Standard 1459-2000 Power Quantities in Nonsinusoidal Three-Phase and Single-Phase Systems

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.

The Measurement of Reactive Energy in Polluted Distribution Power Systems: An Analysis of the Performance of Commercial Static Meters

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.

Oil-Filled MV/LV Power-Transformer Behavior in Narrow-Band Power-Line Communication Systems

The aim of this paper is to characterize oil-filled power transformers in the narrow-band power-line communication (PLC) frequency range of 50-150 kHz. A new model is proposed for such type of a transformer, in the aforementioned frequency range of interest, in order to study its influence on the signal transmission and to investigate the possibility that the PLC signal can cross the power transformer itself. The new model is simpler than those previously proposed in literature, and it can be used in the whole frequency range available for NB PLC according to the CENELEC EN 50065-1 A-band. In order to validate the model, simulation and measurement results are compared for four oil-filled power transformers with different rated power values. A complete PLC system in the case of a medium-voltage (MV) power network is also simulated, in order to perform a preliminary evaluation of the influence of power transformers on the communication system. The MV overhead power line, the oil-filled power transformers, the MV signal coupling network, and two ST7540 frequency shift keying (FSK) power-line transceivers are included in the simulated system. The performances of the complete PLC communication system are evaluated in the case of both MV to low voltage (LV) and LV to MV transmissions. The analysis is carried out by evaluating the signal attenuation, which is computed as the ratio between the received and transmitted voltage signals, in the case of different line lengths and carrier frequency values.