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This paper examines the effect that voltage distortion has on the current distortion of eleven common 120 V single-phase loads. The study is conducted with a specially developed harmonics testing station in which feedback is applied to drive the load voltage to the desired target waveform. The results of 550 individual tests show that depending on load type, current distortion can vary dramatically with voltage distortion and depends on the individual voltage harmonic magnitudes and phase angles. Index Terms--Current distortion, harmonics, nonlinear loads, voltage distortion.

This paper develops a signal processing, time-frequency analysis-based analytic solution to locate transient capacitor switching disturbances. The flow of transient disturbance energy caused by the capacitor switching is determined by the time and frequency localized phase difference. Cross time-frequency analysis provides time-and frequency-localized phase difference between the transient voltage and current disturbance waveforms which determine the direction of transient disturbance energy flow. The time and frequency localization properties of the proposed scheme allows one to expand the application to complicated power distribution systems without knowledge of system parameters, capacitor size, and configuration. The proposed scheme has been verified by the Electromagnetic Transients Program simulation for all possible spatial locations of the capacitor switching. Index Terms--Capacitor switching disturbance, cross time-frequency analysis, direction finder, power quality, time-frequency analysis.

This paper develops a method using transient voltage and current measurements at the substation to determine which capacitor in a multicapacitor feeder switched on to cause a measured transient. The procedure is based upon time-domain analysis where a backward Kalman filter estimates the initial voltage of all feeder capacitors, and those estimates indicate which capacitor switched. The result is an automated procedure that can help electric utilities determine if their capacitors are switching properly, and also help pinpoint the source of capacitor switching-related power-quality problems. Index Terms--Backward Kalman filter, capacitor switching, power quality, switched capacitor estimation.

This paper presents a novel classification method for power distribution line disturbances using a rule-based method and a wavelet packet-based hidden Markov model (HMM). The rule-based method is utilized for the classification of time-characterized-feature disturbances, and the wavelet packet-based HMM is utilized for the frequency-characterized-feature power disturbances. This proposed method classifies six types of actual recorded power distribution disturbances, i.e., sag, interruption, fast capacitor switching, capacitor switching, normal variation, and impulse disturbance, and obtains 98.7 % correct classification rate for 670 actual disturbance events tested. Index Terms--Classifier, hidden Markov model (HMM), power disturbances, wavelet packet.

This paper investigates the effect of supply voltage harmonics on the excitation current of a typical 25 kVA single-phase distribution transformer. A complete analytical model is developed to calculate the time domain waveform and the harmonic components of the excitation current. The key findings are * The phase angles of the supply voltage harmonics determine whether or not those voltage harmonics increase or decrease the distortion of the input current (with respect to the sinusoidal supply voltage case). A peaked input voltage wave distorted by 3rd, 7th, 11th, ..., harmonic components, or a flattened input voltage wave distorted by 5th, 9th, 13th, ..., harmonics, creates a flattened current (i.e., decreases the current harmonics and distortion). A flattened input voltage wave distorted by 3rd, 7th, 11th, ..., harmonic components, or a peaked input voltage wave distorted by 5th, 9th, 13th,..., harmonics, creates a peaked current (i.e., increases the current harmonics and distortion). * The 3rd harmonic component in the supply voltage has the highest effect on the current harmonics and distortion. The effect of higher voltage harmonics gradually diminishes with frequency. The magnitudes of the individual current harmonics follow the same decreasing/increasing pattern of changes as does current distortion variation. The corresponding variations in harmonic current phase angles is negligible. Keywords - Single-phase transformer, transformer excitation current, nonsinusoidal supply voltage, harmonics.

In this paper we present a new approach to detect, localize, and investigate the feasibility of classifying various types of power quality disturbances. The approach is based on wavelet transform analysis, particularly the dyadic-orthonormal wavelet transform. The key idea underlying the approach is to decompose a given disturbance signal into other signals which represent a smoothed version and a detailed version of the original signal. The decomposition is performed using multiresolution signal decomposition techniques. We demonstrate and test our proposed technique to detect and localize disturbances with actual power line disturbances. In order to enhance the detection outcomes, we utilize the squared wavelet transform coefficients of the analyzed power line signal. Based on the results of the detection and localization, we carry out an initial investigation of the ability to uniquely characterize various types of power quality disturbances. This investigation is based on characterizing the uniqueness of the squared wavelet transform coefficients for each power quality disturbance. Keywords - Power quality disturbances, wavelet transform analysis, multiresolution signal decomposition, uniqueness search.

In this paper we use the results of simulations to predict the net harmonic currents produced by large numbers of single-phase desktop computers in a facility, such as a commercial office building. We take into account attenuation due to system impedance and voltage distortion, as well as diversity in harmonic current phase angles due to variations in power and circuit parameters. Using experimental and published data, we establish ranges of circuit parameters for an equivalent 120 V, 100 W 'base computer unit' and branch circuit, update our computer modeling code (described in previous papers) to iteratively handle the interaction between current and voltage harmonics, and use the code to predict the net harmonic injection currents at the point of common coupling (PCC) represented by a shared transformer connected to a stiff power system. The key contributions of this paper are 1. Providing estimates of the net harmonic current injection due to distributed single-phase computer loads in Amps/kW, as well as in percent of fundamental current, for a wide range of system loading and voltage distortion conditions, and 2. Illustrating that the reduction in harmonic currents due to phase angle diversity (expressed in Amps/kW) is relatively independent of system loading, whereas the reduction due to attenuation increases significantly with system loading. Keywords - Desktop computers, harmonic Amps/kW, harmonic attenuation, harmonic diversity, system loading, short circuit ratio.

The Variable Speed Air Conditioner (VSAC) is a large domestic distorting load. We investigate the impact of a large number of VSAC's on domestic harmonic levels. We present * a general method to build a harmonic numerical model of a passive filtered rectifier supplied by a distorted voltage, * a statistical method to assess the total harmonic currents produced by a large number of units running at various power levels and supplied by various distorted voltages. These two methods are applied to a rectifier used by many VSACS. We also present results for two other rectifiers. Index Terms--Analytical model, diversity, harmonic cancellation, single phase air conditioner, VSAC.

While existing techniques are capable of automatically identifying and classifying various types of distribution-level power quality disturbances, they do not provide any information about the locations of the disturbance sources. This paper shows that it is possible to use sampled voltage and current waveforms to determine on which side of a recording device a disturbance originates. This is accomplished by examining the energy flow and peak instantaneous power for both capacitor energizing and voltage sag disturbances. We demonstrate the technique by testing it on both ATP-generated waveforms and actual field disturbance data. In both cases, we are able to accurately determine on which side of a recording device the disturbance originates. If enough recording devices are available in a network, the individual readings can be collectively used to pinpoint the locations of disturbance sources. Index Terms--Capacitor switching, direction finder, disturbance locator, power quality, voltage sag.

A scalable event identification system for power quality events is proposed. Unlike ANN-based approaches where the system is not scalable and not 'debug-able' without retraining, the proposed approach is particularly advantageous compared to those of ANN's since it is scalable, debug-able and easily modified. This approach is adopted from artificial intelligence's rule-based approach and attempts to mimic power engineers thought process in identifying PQ events. This paper describes prerequisites in constructing such a scalable system. Examples of rules to identify power quality event are also presented. The prototype of the system is built and tested using 770 field-measured voltage waveforms which covers ten types of PQ events. The accuracy rate is nearly 95% with less than 6% of rejection rate. Potential applications of the proposed system in PQ community are also described. Index Terms--ANN, power quality, rule-based system, scalable.

It is the objective of this paper to present unique features that characterize power quality events and methodologies to extract them from recorded voltage and/or current waveforms using Fourier and wavelet transforms. Examples of unique features include peak amplitudes, RMS, frequency, and statistics of wavelet transform coefficients. These features are derived from well documented theories, power engineers' heuristics gained through long years of experience, and power quality data collected in recent years. Converter operation, transformer energization, and capacitor energization (which includes normal, back-to-back, and restrike on opening energization), representing three common power quality events at the distribution level, are presented. These examples provide the basis for further characterization of other power quality events. Index Terms--Fourier and wavelet transforms, identifying features, power quality.

A wavelet-based neural classifier is constructed and thoroughly tested under various conditions. The classifier is able to provide a degree of belief for the identified waveform. The degree of belief gives an indication about the goodness of the decision made. It is also equipped with an acceptance threshold so that it can reject ambiguous disturbance waveforms. The classifier is able to achieve the accuracy rate of more than 90% by rejecting less than 10% of the waveforms as ambiguous. Index Terms--Automatic classification and identification, Dempster-Shafer theory of evidence, power quality disturbance, voting scheme.

Existing techniques for recognizing and identifying power quality disturbance waveforms are primarily based on visual inspection of the waveform. It is the purpose of this paper to bring to bear recent advances, especially in wavelet transforms, artificial neural networks, and the mathematical theory of evidence, to the problem of automatic power quality disturbance waveform recognition. Unlike past attempts to automatically identify disturbance waveforms where the identification is performed in the time domain using an individual artificial neural network, the proposed recognition scheme is carried out in the wavelet domain using a set of multiple neural networks. The outcomes of the networks are then integrated using decision making schemes such as a simple voting scheme or the Dempster--Shafer theory of evidence. With such a configuration, the classifier is capable of providing a degree of belief for the identified disturbance waveform. Index Terms--Artificial neural networks, Dempster-Shafer theory of evidence, pattern recognition, power quality, voting scheme, wavelet transforms.

A power amplifier is used to supply sinusoidal currents of different frequencies for measuring eddy-current losses of a 25 kVA single-phase transformer under short-circuit condition. Measured data show that eddy-current loss is a linear function of frequency with power of 2 and the eddy-current loss co-efficient [P.sub.EC-Rlinear] is computed. New measurement techniques are applied to determine the derating of single-phase transformers with full-wave diode and thyristor rectifier loads. The derating of transformers has been defined such that for the (apparent, real) power transfer of a transformer the total losses are identical to the rated losses at rated temperature. A relation between apparent power, derating and K-factor is given taking into account iron-core and stray-power losses. Measured derating values are compared with computed results based on the eddy-current losses, iron-core losses, stray-power losses, and K-factors. The eddy-current loss co-efficient [P.sub.EC-Rnonlinear] is computed from harmonics caused by diode/thyristor bridge loads. Index Terms--Eddy-current loss, K-factor, nonlinear load, transformer derating.