D. Gallo

On the Processing of harmonics and interharmonics: using Hanning window in standard framework

The harmonic and interharmonic analysis recommendations contained in the latest International Electrotechnical Commission (IEC) standards on power quality are considered. The spectral leakage problems due to synchronization errors of the analyzed waveforms with the window widths adopted are analyzed. Improvements of the signal processing recommended by the IEC, based on the utilization of the classical Hanning window in place of the rectangular window, are proposed and made compatible with the grouping technique introduced in the standards. Sensitivity analyses on simple case studies together with experimental results show the sensitivity of the signal processing recommended by the IEC to synchronization errors and the usefulness of the improvements proposed.

Desynchronized Processing technique for Harmonic and interharmonic analysis

A new desynchronized processing technique for harmonic and interharmonic analysis that has general validity and results fully compatible with the IEC standard is presented. This technique is based on a double-stage signal processing procedure: In the first stage, the harmonic components are accurately estimated via interpolations in frequency domain and filtered away from the original signal so that in the second stage, interharmonics can be evaluated without the spectral leakage due to harmonic tones. Since the procedure does not require synchronization, it allows adopting a fixed sampling frequency and, at the same time, the direct use of fast Fourier transform on the acquired samples, thereby reducing the computational burden. The procedure is successfully applied to both numerical tests and onfield measurements. The obtained results are as accurate as those of synchronized techniques.

On the processing of harmonics and interharmonics in electrical power systems

A recent IEC standard draft gives new definitions and methods for measurement and interpretation of results for harmonics and interharmonics, in particular introducing the concept of the harmonic and interharmonic groups. This paper analyses the spectral leakage problems due to a nonsynchronization of the analyzed waveforms with the window width, deriving from both fundamental frequency deviations and nonsynchronized interharmonics. Improvements of the signal processing recommended by IEC are introduced: the utilization of the classical Hanning Window, in place of the rectangular, and the doubling of the window width. In order to show the usefulness of the proposed improvements, the measurement results on a modern high power AC locomotive are reported and analyzed.

IEC flickermeter response to interharmonic pollution

The paper discusses the response of flickermeters to interharmonic voltage pollution from theoretical and experimental points of view. Light flicker can be caused by interharmonics because these components are able to introduce fluctuations both in rms and peak value of supply voltage. The IEC standard flickermeter was deigned, for historical reasons, only with reference to amplitude voltage modulation that is the first source of light flicker identified. Nevertheless, the instrument was expected to properly work and measure also the effects of interharmonics. The paper presents a test system able to perform the advanced calibration and performance verification of flickermeter also with reference to interharmonic pollution. The experimental results obtained testing a commercial instrument are shown and discussed.

On the effects of voltage subharmonics on power transformers: a preliminary study

In this paper the effects that voltage subharmonics have on power transformers are presented. The work tackles the basic case of a single phase transformer and the phenomenon of hysteresys loop asymmetrization and core saturation is focused on. Experimental results together with simulation results, both in time domain and frequency domain, are utilized for a first insight into the physical phenomenon and for sensitivity analyses.

On the effects on MV/LV component expected life of slow voltage variations and harmonic distortion

The effects of electrical stress on MV/LV component expected life due to slow voltage variations and harmonic distortion are considered in a realistic scenario characterized by multimodal distributions and the presence of correlations. A simplified approach based on peak voltage mean value, recently proposed, and a new proposal are tested with reference to case studies and field measurements. The slow voltage variations and harmonic distortion contributions to the peak voltage are separated. Field measurements, performed during a whole week on a distribution network, are used to compare the entities of slow voltage variations and harmonic distortion effects and to verify the negligibility of harmonic thermal stress.

Double stage harmonic and interharmonic processing technique

Measurement and analysis experiences have shown great difficulties in interharmonic detection and measurement due to their small amplitudes and their consequent vulnerability from harmonics spectral leakage. A new approach that has a general validity and results fully compatible with the IEC standard is presented. This approach is based on a double stage signal processing technique; in the first stage, the harmonic components are estimated and filtered away from the original signal, so that the second stage analysis can be performed for interharmonics estimation without harmonic tone spectral leakage. The procedure is successfully applied to both numerical and experimental tests.

Interharmonic measurements in IEC standard framework

The main problem for harmonic and interharmonic measurement is to reduce the effects of the spectral leakage of harmonics on interharmonic components: line frequency synchronization techniques or algorithms to compensate desynchronisation are necessary. In the paper, different proposals by the same authors are recalled and compared to each other. Numerous field measurements performed according to the IEC guidelines are reported and analysed.

High speed AC locomotives: harmonic and interharmonic analysis at a vehicle test room

The paper presents and analyzes the results of harmonic and interharmonic measurements performed at the vehicle test room of CRIS Ansaldo on the new high-speed locomotive ETR500. The adjustable speed drives of this locomotive utilize PWM-controlled converters to both rectify the voltage of the AC supply system and feed AC motors. These converters show advanced control characteristics, energy efficiency and currents distorted in terms of harmonics and interharmonics of reduced amplitude but with a wide range of frequencies. Harmonics and interharmonics are evaluated in different operating conditions. In particular, significant conditions are obtained tuning realistic resonance frequencies by means of variable power capacitors, properly designed. General problems such as test room flexibility and ability to reproduce realistic railway system conditions are discussed.

Comparison among techniques for distorted waveforms analysis in power system

Measurement and analysis experiences have shown great difficulties in interharmonic detection and measurement due to their small amplitudes and their consequent vulnerability from harmonics spectral leakage. The spectral leakage is due to lack of synchronization between the analyzed waveforms actual periods and the sampled window length, deriving from both fundamental frequency deviations and nonsynchronized interharmonics. This paper compares the techniques, that are introduced by the same authors in previous papers and that improve the IEC recommended signal processing: the utilization of the classical Hanning Window, in place of the Rectangular; the harmonic filtering and the self tuning signal processing. All the techniques are applied to numerical and experimental tests showing the different performances.