Salvatore Nuccio

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 Chirp Z transform based synchronizer for power system measurements

Power system analyzers are required for performing an accurate evaluation of harmonic pollution, voltage and current synchronous sampling in order to limit leakage error and to assure reproducible results. Moreover, the increased interest about power and voltage quality, forced international working groups to define new standards for testing and measurement techniques. In particular, harmonic and interharmonic measurement and instrumentation standards require the correct voltage or current signal synchronization and the recognition of the same condition. In this paper a new synchronizer algorithm is proposed, able to respect in force and draft standards for its accuracy and characteristics. Theoretical aspects are discussed and different experimental tests are reported, comparing the proposed method with a similar well-known one based on interpolated fast Fourier transform.

A virtual instrument for measurement of flicker

All types of fluctuations of the r.m.s. voltage in power systems may be assessed by using a flickermeter which complies with the specification given in IEC-EN 60868. In this paper a digital flickermeter is presented based on the implementation in the frequency domain of the weighting filter block of the eye-brain simulation chain. The virtual instrument, implemented with an acquisition board inserted on a PC and with a software developed with the LabView tools, samples the voltage and furnishes the instantaneous flicker level and other severity coefficients. Results of simulated and actual data are reported to validate the performances of the developed flickermeter.

An induction motor speed measurement method based on current harmonic analysis with the chirp-Z transform

This paper presents a new method to measure motor speed by means of frequency estimation of rotor slot spectral components in the supply current of squirrel single-cage induction motors. The novelty of the method consists in the harmonic analysis of the supply current by means of the chirp-Z transform (CZT). The advantages are improved accuracy due to better spectral resolution and resolvability. Moreover, a shorter observation window is required, thus reducing errors related to nonstationary current signals. The experimental results are presented to validate the proposed method and to make a comparison with a similar method based on the fast Fourier transform (FFT).

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.

A Novel Approach to Current Transformer Characterization in the Presence of Harmonic Distortion

The current transformer (CT) performance under distorted waveform conditions is usually characterized by means of the frequency-response test. In this paper, a new way to characterize CTs, closer to real operation conditions, is proposed. The harmonic phase-angle and ratio errors are measured using a nonsinusoidal current composed of fundamental and one harmonic with adjustable phase shift. The new method was tested by determining the performance of two metering class CTs commonly used by the Italian power company. The errors measured using the proposed approach are larger than the ones obtained with the frequency response. This result suggests that the frequency-response approach for the evaluation of CT performance under distorted waveform conditions is not a reliable method.

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.

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.