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This paper presents a novel philosophy to compensate the load-reactive power demand through a three-phase unified power quality conditioner (UPQC). Most of the UPQC-based applications show the dependency on shunt inverter for load-reactive power compensation, whereas the series inverter is always looked as controlled voltage source to handle all voltage-related problems. This paper proposes a new functionality of UPQC in which both the shunt and series APFs supply the load-reactive power demand. This feature not only helps to share the load-reactive power demand, but also helps to reduce the shunt APF rating, and hence, the overall cost of UPQC. This results in better utilization of the existing series inverter. The theory and complete mathematical analysis termed as "power angle control (PAC)" is presented. The simulation results based on MATLAB/Simulink are discussed in detail to support the concept developed in the paper. The proposed approach is also validated through experimental study. [ABSTRACT FROM AUTHOR]

This paper presents a new method for online real-time detection and classification of voltage events in power systems. The method proposed simultaneously uses the results obtained in the application of the discrete wavelet transform and an extended Kalman filtering to the voltage waveform. Wavelet analysis is used for detection and estimation of the time-related parameters of an event and the extended Kalman filtering is used for confirmation of the event and for computation of the voltage magnitude during the event. The paper presents different experimental results showing the improved performance of this combined approach. [ABSTRACT FROM AUTHOR]

Industries that produce flicker are often placed close to each other and connected to the same power grid system. This implies that the measured flicker level at the point of common coupling (PCC) is a result of contribution from a number of different flicker sources. In a mitigation process it is essential to know which one of the flicker sources is the dominant one. Therefore this paper proposes a method to determine the flicker propagations and trace the flicker sources by using flicker power measurements. Flicker power is considered as a quantity containing both sign and magnitude. The sign determines if a flicker source is placed downstream or upstream with respect to a given monitoring point and the magnitude is used to determine the propagation of flicker power throughout the power network and to trace the dominant flicker source. This paper covers the theoretical background of flicker power and describes a novel method for calculation of flicker power that can be implemented in a power network analyzer. Also a conducted field test based on the proposed method is described in the paper. [ABSTRACT FROM AUTHOR]

Voltage fluctuations and interharmonics have an inherent relationship. The magnitude of voltage waveform can fluctuate if it contains interharmonics. Although the impact of voltage fluctuation caused by a single interharmonic has been understood due to recent research activities, little knowledge is available on the impact of a pair of interharmonics. In reality interharmonics often appear in pairs. The objective of this paper is to investigate voltage fluctuations caused by a pair of interharmonics. Using rms and peak values as indices, the amount of voltage fluctuations caused by a pair of interharmonics is determined. Analytical formulas to estimate the impact are developed. One of the interesting findings of this work is that the voltage fluctuation impact of a pair of interharmonics can be equivalenced into that produced by one interharmonic component. This paper also presents potential applications of the findings. [ABSTRACT FROM AUTHOR]

This paper presents a new technique for voltage sag state estimation. The proposed method is based on estimating the number of voltage sags occurring at nonmonitored buses from the number of sags recorded at a limited number of monitored buses. This problem, contrary to the traditional state estimation where redundant measurements are available, is formulated as an underdetermined system of equations. In this paper, linear integer programming techniques are employed to solve this estimation problem. The performance of the proposed method is tested by means of several case studies applied in the IEEE 24-bus Reliability Test System (RTS) and in the IEEE 118-bus Test System. [ABSTRACT FROM AUTHOR]

A generalized approach for the assessment and description of compatibility levels between the power supply system and electrical equipment is proposed in this paper. The proposed approach is an alternative to the existing, widely used concept of electromagnetic compatibility (EMC). The existing EMC concept uses only two general stages for description and quantification of all possible interactions between power supply system and connected electrical equipment. This paper, on the other hand, discusses different types of power quality disturbances, as well as situations in which equipment has multiple malfunction criteria. The subject of the EMC is analyzed here from the equipment point of view. [ABSTRACT FROM AUTHOR]

This paper presents a method for stochastic prediction of voltage sags caused by faults in a power system. The area of vulnerability must be determined to estimate the expected sag frequency (ESF) at a sensitive load site. However, the area of vulnerability is not easy to identify in a large meshed network. In the paper, the residual phase voltage equations for balanced and unbalanced faults are presented, and an efficient method to determine the area of vulnerability in a large meshed network is described. An ESF estimation method based on Information Technology Industry Council (ITIC) curve is also described. The developed method was applied to the IEEE 30-bus test system. [ABSTRACT FROM AUTHOR]

This paper proposes a method for analyzing measurements of voltage transients in three-phase systems. The method is based on the Clarke transform introduced in 1950 for calculations of travelling waves along three-phase transmission lines. The proposed method also shows close similarities with the classification of three-phase unbalanced voltage dips. After extracting the actual transient (e.g., by using a notch filter centered on the power-system frequency), the three signals are decomposed into seven components. From the relation between these seven components, the dominant component is identified. The method is successfully applied to a number of measured transients. The paper also identifies the limitations of the method and gives suggestions for future work. [ABSTRACT FROM AUTHOR]

The definitions for the measurement of electrical power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions are established in IEEE Standard 1459–2000. Measured magnitudes, such as apparent powers or effective quantities, are evaluated considering the frequency spectrum of voltage and current signals (fundamental, nonfundamental, and combined magnitudes). Previous papers implement these definitions in the frequency domain (DFT) and in the time domain (Clarke-Park Transformations). In the time domain, low-pass filters (LPFs) must be applied to obtain the fundamental magnitudes but, in this case, the quality of the measurements depends on the LPFs orders and their cutoff frequencies. This paper proposes a time-domain implementation of the standard definitions without LPFs and employs a recursive averaging algorithm which improves the measurements precision and reduces the computational burden. Simulation and experimental tests showing the proposed method performance are included. [ABSTRACT FROM AUTHOR]

Voltage dips and interruptions may cause major economic damage, not only can they create considerable loss of production (manufacturing) or data (ICT), there is also loss of market, the loss of client trust, comfort, etc. that incite energy consumers to implement certain forms of protection for their systems. However, the selection of the most cost-effective mitigation method is difficult because of the wide range in available protection devices and the mostly unknown and variable interruption cost. In this paper, the theoretical selection method is compared with the currently used selection methods in industry, showing a discrepancy between theory and practice. Using an alternative selection method, an optimal mitigation method can be found. This paper describes this method and its use by means of a practical example. The case examined is the protection of a 250 kVA installation, sensitive to voltage dips (ICT load). The proposed method makes a cost-benefit analysis of several proposed mitigation solutions resulting in an overview giving the optimal solution for a certain interruption cost interval. It enables to clearly interpret the investment costs and to compare completely different mitigation methods, only using data available to an industrial customer. [ABSTRACT FROM AUTHOR]

This paper proposes a new connection for a unified power quality conditioner (UPQC) to improve the power quality of two feeders in a distribution system. A UPQC consists of a series voltage-source converter (VSC) and a shunt VSC both joined together by a common dc bus. It is demonstrated how this device is connected between two independent feeders to regulate the bus voltage of one of the feeders while regulating the voltage across a sensitive load in the other feeder. Since the UPQC is connected between two different feeders (lines), this connection of the UPQC will be called an interline UPQC (IUPQC). The structure, control and capability of the IUPQC are discussed in this paper. The efficacy of the proposed configuration has been verified through simulation studies using PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

This paper presents an improved design method for a novel transformer inrush current reduction scheme. The scheme energizes each phase of a transformer in sequence and uses a neutral resistor to limit the inrush current. Although experimental and simulation results have demonstrated the effectiveness of the scheme, the problem of how to select the neutral resistor for op- timal performance has not been fully solved. In this paper, an analytical method that is based on nonlinear circuit transient analysis is developed to solve this problem. The method models transformer nonlinearity using two linear circuits and derives a set of analytical equations for the waveform of the inrush current. In addition to establishing a set of formulas for optimal resistor determination, the results also reveal useful information regarding the inrush behavior of a transformer and the characteristics of the sequential energization scheme. This paper also proposed a method, the use of surge arrester, to solve the main limitation of the sequential phase energization scheme—the rise of neutral voltage. Performance of the improved scheme is presented. [ABSTRACT FROM AUTHOR]

This paper introduces the details of an intelligent adaptive fuzzy system—with self-learning functions—that could be installed to monitor electrical equipment or systems, and self-learn the trend of events leading to the failure of the monitored system. If any of the learned trends is repeated, the intelligent fuzzy system will predict the eventual failure of the monitored system in case of either human or automatic nonintervention. This paper presents the design details of the new intelligent fuzzy predictor. The self-learning process is accomplished using adaptive neuro-fuzzy techniques. Full details of the development of the new tool and the results of several test cases based on various practical applications and real-site data are included. Wavelet denoising is also used as the filtering technique for pre-preparation of the data before introducing it to the fuzzy predictor. [ABSTRACT FROM AUTHOR]

This paper is the second part of a joint paper aimed at predicting the voltage sag performance of distribution net- works by estimating voltage sag indices. This part explores the characteristics of voltage sags caused by faults in a distribution network considering the effect of the protective devices installed in the network. The work is based on a Monte Carlo procedure implemented in a time-domain simulation tool. Several scenarios with a different coordination between protective devices have been analyzed. As expected, the main conclusions are that the protection system can have a significant influence on voltage sag characteristics and proper coordination between protective devices can reduce voltage sag impact on end-user equipment. [ABSTRACT FROM AUTHOR]

This paper is the first part of a work aimed at predicting the voltage sag performance of distribution networks using digital simulation and an EMTP-like tool. The paper discusses modeling guidelines for representing power distribution components in voltage sag simulations and details the approaches selected in this work. Different models for representing some components can be used to obtain voltage sag characteristics with similar accuracy. Test results are included to illustrate the performance of the developed models and support the selection of different modeling approaches. [ABSTRACT FROM AUTHOR]

Power quality indices have been developed to assess the performance of a single site or an entire system. They can guide utilities to improve their systems and can be used by manufacturers to decide about equipment immunity. This paper is the third part of a joint paper aimed at predicting the voltage sag performance of distribution networks by estimating voltage sag indices. Two types of indices are analyzed in the present paper, they give, respectively, the average number of events and the average interruption duration of each kilovolt ampere served at the low-voltage level over the assessment period. Their values are obtained from a stochastic prediction using a time-domain simulation tool. The methodology used to obtain these indices and the analysis of the influence of the protective devices are the main contributions of this paper. The limitations of the present work are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a systematic algorithm to locate the power-quality (PQ) event source in the distributed monitoring system. Firstly, this paper proposes an improved realization of a distributed monitoring scheme for PQ diagnosis. The algorithm utilizes the topology of power system and the direction of PQ events. As a result, the coverage matrix and the direction matrix are constructed. The algorithm determines the candidate areas for an event source by manipulating these two matrices. For more accurate results, it calculates the distance from the PQ monitor to the location of the PQ event source. It is explained with an illustrative example and is applied to IEEE test feeder in order to validate the accuracy. The proposed algorithm can replace the expert's analysis on the PQ event source with an automated computer program. [ABSTRACT FROM AUTHOR]

Power insulated-gate bipolar transistor (IGBT) and other gate turnoff switches have allowed to analyze, in a previous paper, four new circuits for onload-tap-changing ac stabilizers that typically permit to make up to 7 or 45 (depending on the particular circuit solution) changes per half cycle of the mains voltage. This second and last paper considers the synthesis aspects of these sub- cyclic stabilizers giving design rules, and a synthesis calculus sheet actualized in a 100-kVA numeric example. A comparative table for the four circuit solutions, involving both technical and economical figures, is given as the final step of the iterative analysis and synthesis cost comparative method performed along the research. Preliminary experimental results are obtained from a 1-kVA prototype and a first evaluation of the possibilities of reducing voltage distortions is demonstrated in the fields of voltage low harmonics and flicker by means of a high-accuracy graphic simulator. [ABSTRACT FROM AUTHOR]

The rate of change in classic thyristor-based onload tap-changing ac stabilizers is limited to that of the load current zero crossing (once per half cycle) due to the natural turnoff method involved. The growth of the power rate of insulated-gate bipolar transistor and other gate turnoff switches allows exploring of stabilizers that are able to change taps several times in a half cycle of the mains wave (subcyclic commutation). This paper analyzes the best four solutions for the power circuit of this new class of tap-changers in the multitap version, developed through an iterative analysis and synthesis cost comparative method that moves the tap-changing stabilizers over to the world of low-frequency voltage harmonics, oscillations, flicker, and instability phenomena attenuators. These topologies allow changing times as low as 150 μs by using a multicoil inductance to perform current limitation and voltage clamping tasks during the switching operation, as it shall be shown in a second paper dedicated to the synthesis and experimental aspects. [ABSTRACT FROM AUTHOR]

Transformers are essential elements, which facilitate the transmission of electric power at high voltages over long distances and transformer energization is a common occurrence. The energization can lead to excessive transient inrush current, especially when the transformer core has remnant flux that adds to the flux build-up after switching. Inrush current sags the system voltage, thereby affecting the power quality of the network in proximity of the transformer. The extent to which power quality is degraded depends on short circuit MVA at the source bus, and the magnitude and decay time constant of the transient current. Present day thyristor-controlled machinery used in mining, pulp and paper industries and semiconductor manufacturing require high quality power. Some of these industries even pay a premium price for high quality power. It is, therefore, necessary to first assess the impact of energizing a large transformer on power quality and then develop a technique to limit this impact. This paper presents results from field tests and simulations using Electromagnetic Transients Program a 138 kV 315 MVA transformer energization in the BC Hydro system. The transformer is situated close to a pulp and paper mill with voltage sensitive loads. Methods to assess and to limit the voltage sags during energization are discussed. [ABSTRACT FROM AUTHOR]

Phase sequence is an important attribute of voltages and currents in three phase power systems. This paper investigates the sequence characteristics of interharmonic components. Three common cases involving interharmonics are analyzed. These are variable frequency drives (VFD), motors with fluctuating mechanical loads and general fluctuating impedance loads. The results reveal that interharmonics can have either positive or negative sequence and are rarely zero sequence. Its sequence cannot be determined by examining the interharmonic frequency alone. The general rule is that the sequence of interharmonics is the same as that of the supply system harmonic components being modulated. If the resulting interharmonic frequency produced by the modulation process is negative, the sequence of the interharmonic component will change from positive to negative or vice versa. The findings of this paper will help to improve our understandings on the characteristics of interharmonics and can be useful for the development of interharmonic simulation programs. [ABSTRACT FROM AUTHOR]

The aim of this paper is to introduce a novel real-time digital signal processing technique for power quality disturbance detection. The proposed technique is inspired on the Divide and Conquer Principle and on the Innovation Concept. Essentially, the Divide and Conquer Principle is applied in splitting the monitored disturbance event into stationary and nonstationary components, allowing localized individual signal analysis. Thereafter, the Innovation Concept is introduced for revealing new information not previously observed in the energy of the nonstationary signals and so detecting a new event. In addition, this paper demonstrates a straightforward and feasible way to evaluate the Total Harmonic Distortion (THD) or a distortion measure for voltage signals. Simulation results indicate that the proposed technique is able to accurately detect a variety of voltage disturbances. [ABSTRACT FROM AUTHOR]

This paper presents an inverter-interfaced distributed generation (DG) device, dubbed the premium power supply (PPS), which is designed to provide reliable electric power, and to improve power quality. This paper proposes an effective configuration for the PPS, using inverters, an inter-tie breaker, and a small generating unit. When the DGs are operated in parallel with the utility systems, some problems occur due to interconnections on such categories as reverse power flow and island protection. This paper advances both an operating strategy and a control scheme for the PPS, with respect to the interconnection standard, IEEE Standard 1547. Simulation results demonstrate the efficacy of the PPS. [ABSTRACT FROM AUTHOR]

Data storage and data communication currently pose a major problem for all parties involved with power quality and power systems monitoring. The problem arises from the tremendous amount of data involved. There is a common desire in the power industry to find new techniques for high-accuracy data compression and data storage. This paper introduces the details of a novel data compression technique that is very suitable for application to power-quality waveforms, in particular, and to power system disturbance waveforms in general. The new technique is developed using adaptive neuro-fuzzy techniques. The paper. ex- plains the mechanics of the new technique. Full technique implementation details are given, and test cases based on power-quality, waveforms are analyzed. [ABSTRACT FROM AUTHOR]

In contrast to most other power-quality phenomena, it requires several years of measurements to obtain a good insight of the voltage sag problems at a given grid connection point. In some countries, sag measurements at high- or medium-voltage level of several years are available. This paper analyzes how to calculate the sag characteristics at lower voltage levels if the sags measured at higher voltage levels are only characterized as the largest value of the voltage drop in each phase. Whether these values are based on phase-to-phase or phase-to-neutral voltages turns out to be an important parameter and is therefore analyzed in detail. Based on this analysis, this paper gives guidelines on how new sag meters should preferably be connected (measuring phase-to-phase or phase-to-neutral voltages). [ABSTRACT FROM PUBLISHER]

This paper presents a theory to explain the characteristics of a sequential phase energization based inrush current reduction scheme. The scheme connects a resistor at the transformer neutral point and energizes each phase of the transformer in sequence. It was found that the voltage across the breaker to be closed has a significant impact on the inrush current magnitude. By analyzing this voltage using steady-state circuit theory, the simulation and experimental results presented in a companion paper are explained. The results lead to the establishment of a guide to select the optimal value of the neutral resistor. The applicability of the proposed scheme to different transformer configurations has also been investigated in this paper. It is shown that the idea of sequential phase energization leads to a new class of techniques for limiting switching transients. [ABSTRACT FROM PUBLISHER]

This paper investigates the challenges in developing a performance index that will reflect the level of power quality at a site based on the actual field data obtained from the site via power-quality (PQ) monitors. For the index, each observed voltage variation is assessed in terms of its potential to impact the customers served from the site. The paper considers the substation level PQ monitoring and adopts a procedure that is similar to one of the methods being proposed in the emerging IEEE guide 1564. [ABSTRACT FROM AUTHOR]

Envelope tracking has many important applications in electrical distribution systems for either flicker meters or flicker compensators. This paper presents a novel control technique for flicker mitigation. This technique is based on the instantaneous tracking of the measured voltage envelope. The ADAptive LINEar neuron (ADALINE) algorithm, and the Recursive Least Square (RLS) algorithm are introduced for the flicker envelope tracking. The ADALINE algorithm is characterized by a light computational demand, unlike that of existing techniques; the RLS algorithm outperforms the ADALINE algorithm by its fast con- vergence and robust tracking performance. Both the ADALINE and the RLS algorithms give accurate results even under rapid dynamic changes. The paper investigates the effects of different parameters on the performance of the ADALINE algorithm and that of the RLS algorithm. Extensive simulations of the proposed flicker tracking algorithms are conducted to evaluate their performance for the tracking and mitigation of voltage flicker. The ADALINE and the RLS algorithms are examined by tracking and mitigating the flicker produced by a resistance welder and an arc furnace in a simple distribution system simulated in the PSCAD/EMTDC package. [ABSTRACT FROM AUTHOR]

This paper focuses on voltage sag phenomena and their impact on customer satisfaction. In order to derive a unique power quality of service index, information from both the supply network (according to standards in use) and the customer (defined in terms of load sensitivity and interruption cost) are merged. The well-known CREMA power acceptability curve is revisited with definitions from the WEE Standard 1159 superimposed. This depiction suggests a way to assign a cost or index of power quality events. Although individual cost assignments used in the calculation are subject to question, once the assignments are made, the calculation is consistent and gives a useful measure of quality of service. The method is illustrated factoring severity of the events based on the CEEMA curve and IEEE 1159 classified power quality events. The paper addresses the elusive issue of the cost of power quality disruption. [ABSTRACT FROM AUTHOR]

Classification of power-quality (PQ)-related voltage and current waveform disturbances is a key task for power system monitoring. A new method based on the optimized time-frequency representation (TFR) has been proposed in the first paper [1] of this two-paper series. This paper (the second paper) presents a case study of PQ event classification with the proposed method. The classification algorithm has been successfully tested with $60 real world PQ events that cover five classes, achieving a recognition rate of 98%. The algorithm is implemented on a digital signal processor (DSP) based hardware system and optimized according to the DSP architecture to meet the hard real-time constraints. The DSP-based system is capable of processing a five-cycle (83.3 ms) PQ waveform within 11.2 ms. The real-time computing capability of the algorithm has been verified with this result. The scalability of this method is also discussed. [ABSTRACT FROM AUTHOR]

Better software and hardware for automatic classification of power quality (PQ) disturbances are desired for both utilities and commercial customers. Existing automatic recognition methods need improvement in terms of their capability, reliability, and accuracy. This paper presents the theoretical foundation of a new method for classifying voltage and current waveform events that are related to a variety of PQ problems. The method is com- posed of two sequential processes: feature extraction and classification. The proposed feature extraction tool, time-frequency ambiguity plane with kernel techniques, is new to the power engineering field. The essence of the feature exaction is to project a PQ signal onto a low -dimension time-frequency representation (TFR), which is deliberately designed for maximizing the separability between classes. The technique of designing an optimized TFR from time-frequency ambiguity plane is for the first time applied to the PQ classification problem. A distinct TFR is designed for each class. The classifiers include a Heaviside-function linear classifier and neural networks with feedforward structures. The flexibility of this method allows classification of a very broad range of power quality events. The performance validation and hardware implementation of the proposed method are presented in the second part of this two-paper series [1]. [ABSTRACT FROM AUTHOR]

Symmetrical components as well as harmonic tracking are of great importance in many applications in power systems such as power quality and protection. This paper introduces a novel Adaptive linear combiner (ADALINE) structure for symmetrical components estimation. This structure is capable of dealing with multi-output systems for parameter tracking/estimation rather than the existing ADALINE, which deals only with single output systems. As the new topology deals with Multi-Output systems, it is called MO-ADALINE. Moreover, the paper presents a new processing unit, which can estimate sym- metrical and harmonic components from the measured current signals. The advantages of this proposed unit are its independence of the voltage waveform and its ability to give information about the reactive component of the resolved current Simulation results are given to validate the proposed algorithms. [ABSTRACT FROM AUTHOR]

This paper deals with the analysis of transients initiated by the switching of shunt capacitors in power networks. These transients will propagate through the network along the transmission elements and will, accordingly, be felt at other locations far from the capacitors, such as load terminals. This can lead to adverse effects on the supply quality at those load buses. Based on a typical radial system, the distributed-parameter analysis will give analytical expressions for the expected transient voltages at the load terminals in terms of both the size and location of the switched capacitor. In its second part, this paper presents simple closed-form expressions for the accurate identification of the shunt capacitor's size and location, in terms of easily measurable parameters of the voltage signal at the load terminals. [ABSTRACT FROM AUTHOR]

Conventionally, control system of a static transfer switch (STS) is designed based on the assumption that the STS terminal voltages are in-phase. This paper investigates the impact of phase difference of the STS terminal voltages on the STS transfer time and cross current. The phase difference is assumed to be a result of the difference of the feeder impedances. The paper shows that phase differences of even up to 4.5°, which are accompanied by up to 5% voltage drop at the STS terminal, can noticeably increase the transfer lime and the cross current magnitude. The studies are conducted on the IEEE STS-1 benchmark system using the PSCAD/EMTDC software. [ABSTRACT FROM AUTHOR]

An interline dynamic voltage restorer (IDVR) is a new device for sag mitigation which is made of several dynamic voltage restorers (DVRs) with a common dc link, where each DVR is connected in series with a distribution feeder. During the sag period, active power can be transferred from a feeder to another one and voltage sags with long durations can be mitigated. IDVR compensation capacity, however, depends greatly on the load power factor, and a higher load power factor causes lower performance of IDVR. To overcome this limitation, a new idea is presented in this paper which enables reducing the load power factor under sag conditions and, therefore, the compensation capacity is increased. The proposed IDVR employs two cascaded H-bridge multilevel converters to inject ac voltage with lower total harmonic distortion and eliminates the necessity to low-frequency isolation transformers in one side. The validity of the proposed configuration is verified by simulations in the PSCAD/EMTDC environment. Then, experimental results on a scaled-down IDVR are presented to confirm the theoretical and simulation results. [ABSTRACT FROM AUTHOR]

The Navy's future and near-term high-energy sensors and energy weapons will consume a large portion of the resources of the intended ship platform. Many of these new systems will have extreme dynamic power profiles, including both periodic and aperiodic characteristics. These dynamics can cause sudden changes in power at the prime power system that can be stressing to platform systems, both to the generators and prime movers as well as other loads sharing the common distribution bus. This paper presents the use of a new adaptive power system (APS) to mitigate the negative impacts levied on the platforms resulting from large dynamic loads. A notional size of the hardware required to implement the APS design is presented along with simulation results verifying the concept. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for automated disturbance analysis and fault location on electric power distribution systems using a combination of modern techniques for network analysis, signal processing, and intelligent systems. New algorithms to detect, classify, and locate power-quality disturbances are developed. The continuous process of detecting these disturbances is accomplished through statistical analysis and multilevel signal analysis in the wavelet domain. The behavioral indices of the current and voltage signals are extracted by employing the discrete wavelet transform, multiresolution analysis, and the concept of signal energy. These indices are used by a number of independent Fuzzy-ARTMAP neural networks, which aim to classify the fault type and the power-quality events. The fault location is performed after the classification process. A real life three-phase distribution system with 134 nodes—13.8 kV and 7.065 MVA—was used to test the proposed algorithms, providing satisfactory results, attesting that the proposed algorithms are efficient, fast, and, above all, intelligent. [ABSTRACT FROM AUTHOR]

This paper presents a new single-event characteristic, sag severity index (SSI), derived with respect to equipment sensitivity to voltage sags. It is more inclusive of associated uncertainties/variation in equipment response to voltage sags than existing single-event characteristics. By changing parameter settings, the index appropriately accounts for sag duration and adequately addresses the variation in equipment sensitivity. The value of the index changes continuously at the joining regions of different sag severity levels and reflects realistically the sensitivity trend of equipment embedded in voltage tolerance curves. The properties of the SSI are analyzed and discussed through comparison with characteristics of five previously reported single-event indices including four numerical indices and one fuzzy voltage sag index. [ABSTRACT FROM PUBLISHER]

The dynamic voltage restorer (DVR) is a series compensator for distribution system applications, which protects sensitive loads against voltage sags by fast voltage injection. The DVR must estimate the magnitude and phase of the measured voltages to achieve the desired performance. This paper proposes a phasor parameter estimation algorithm based on a recursive variable and fixed data window least error squares (LES) method for the DVR control system. The proposed algorithm, in addition to decreasing the computational burden, improves the frequency response of the control scheme based on the fixed data window LES method. The DVR control system based on the proposed algorithm provides a better compromise between the estimation speed and accuracy of the voltage and current signals and can be implemented using a simple and low-cost processor. The results of the studies indicate that the proposed algorithm is insensitive to noise, harmonics, interharmonics, and dc offset unlike the LES method, while both methods estimate the phasor parameters within 5 ms. The performance of the control scheme based on the proposed method is evaluated by multiple case studies in the PSCAD/EMTDC environment and experimentally validated based on a laboratory setup. [ABSTRACT FROM AUTHOR]

This paper introduces a stochastic methodology to assess annual performance of distribution network and individual customers with respect to voltage sags, long duration interruptions, equipment trips, and process trips. These values are then used to evaluate financial losses in the entire distribution network. For each of the large number of simulated faults throughout the network, a probability of sag and long duration interruption occurrences is evaluated at each network bus. The methodology then includes for the first time the concept of process immunity time in order to assess as accurately as possible the resulting financial loss due to process interruption. To increase the accuracy of the assessment of financial loss, the methodology also considers the possibility of equipment and process restart, reliability, and type of fault. The methodology is illustrated on a real distribution network and it shows that inclusion of PIT in financial loss assessment results in a reduction of about 25% in estimated financial loss. [ABSTRACT FROM AUTHOR]

This paper presents a new method for the classification and characterization of voltage dips and swells in electricity networks. The proposed method exploits unique signatures and parameters of three-phase voltage signals extracted from the polarization ellipse in 3-D coordinates. Five ellipse parameters, which include azimuthal angle, elevation, tilt, semi-minor axis, and semi-major axis, are used to classify and characterize voltage dips and swells. Seven types of voltage dips, which include a total of 19 groups of dips incorporating different kinds of balanced (three-phase dips) and unbalanced (single-phase or double-phase) dips, are identified and successfully classified using the 3-D polarization ellipse parameters. Two types of voltage swells, which include a total of 6 groups, are also classified using the proposed method. The proposed method is validated using real measurement data, recorded waveforms provided by the IEEE 1159.2 working group, and the data of unbalanced dips associated with phase-angle jumps, voltage drops, and rotations due to loading effects. [ABSTRACT FROM AUTHOR]

This paper presents measurements of harmonic and interharmonic current (with 5-Hz frequency resolution) in the complex plane. The complex currents are spread around a center point. For interharmonics, this center corresponds to the origin of the complex plane. For integer harmonics, this center is offset from the origin. A goodness-of-fit test reveals that phase angles of most interharmonics are uniformly distributed. A Monte Carlo simulation based on the measurements has been performed to study the aggregation of the emission from individual turbines to the public grid. Low-order integer harmonics show less cancellation compared to high-order harmonics. Interharmonics aggregate close to the square-root rule for uniform phase angles. [ABSTRACT FROM AUTHOR]

This paper proposes a new algorithm to generate reference voltage for a distribution static compensator (DSTATCOM) operating in voltage-control mode. The proposed scheme exhibits several advantages compared to traditional voltage-controlled DSTATCOM where the reference voltage is arbitrarily taken as 1.0 p.u. The proposed scheme ensures that unity power factor (UPF) is achieved at the load terminal during nominal operation, which is not possible in the traditional method. Also, the compensator injects lower currents and, therefore, reduces losses in the feeder and voltage-source inverter. Further, a saving in the rating of DSTATCOM is achieved which increases its capacity to mitigate voltage sag. Nearly UPF is maintained, while regulating voltage at the load terminal, during load change. The state-space model of DSTATCOM is incorporated with the deadbeat predictive controller for fast load voltage regulation during voltage disturbances. With these features, this scheme allows DSTATCOM to tackle power-quality issues by providing power factor correction, harmonic elimination, load balancing, and voltage regulation based on the load requirement. Simulation and experimental results are presented to demonstrate the efficacy of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper introduces an optimum method to design a unified power-quality conditioner (UPQC) system with the minimum possible VA rating based on the compensation requirements. A set of generalized VA loading equations for the UPQC is derived, which are valid for all of the UPQC control approaches (such as UPQC-P, UPQC-Q, and UPQC-VA\min). The variation in series and shunt inverters VA loadings of UPQC for the given compensation requirements is analyzed for all existing control approaches. A novel design method and the corresponding algorithm are proposed to size the major components in an UPQC, such as the series inverter, shunt inverter, and series transformer corresponding to the minimum possible overall VA rating. The VA rating and the utilization of power-electronic converters using the proposed design method are compared with those of UPQC-P, and UPQC-VA\min approaches to show the effectiveness of the proposed design method. [ABSTRACT FROM AUTHOR]

This paper presents a probabilistic harmonic simulation method to study the power-quality impact of electric vehicles (EVs). The proposed method takes into account the random operating characteristics of the vehicles, such as random charging time, charging duration, and vehicle locations. A multiphase model of the primary and secondary systems is used to represent the study system. Extensive case studies have been conducted using the method and the measured EV data. The results reveal that the current versions of plug-in hybrid EVs have no significant harmonic impact on power systems. However, the Level 1 charger can increase the neutral-to-earth voltage at homes which could lead to increased stray voltage incidents. [ABSTRACT FROM AUTHOR]

Monitoring of voltages and currents at system buses gives the network operators information about the performance of their network, both for the system as a whole and for individual locations and customers. There is also demand from the customers and the regulatory agencies to provide information on the actual power-quality (PQ) level. Developments in enabling technology have made it possible to monitor at a large scale and to record virtually any PQ parameter of interest. While many network operators are installing monitoring equipment and while more and more monitors are available, there is a lack of knowledge and agreement on a number of aspects of the monitoring process and on processing the recorded data. As a response to this lack of uniformity in approach, data acquisition, and processing, in February 2011, CIGRE and CIRED established the Joint Working Group C4.112: “Guidelines for Power quality monitoring—measurement locations, processing and presentation of data.” In order to identify the current international industry practice on PQ monitoring, the group carried out a survey in 43 countries across the world. This paper summarizes the key findings from 114 responses to the questionnaire and identifies prevalent industrial practice in PQ monitoring around the world. [ABSTRACT FROM AUTHOR]

The nonstationary nature of power-quality (PQ) waveforms requires a tool that can accurately analyze and visually identify the instants of transitions. One of the recently reported tools available to analyze nonstationary complex waveforms with a very good time resolution is the Hilbert Huang Transform (HHT). However, HHT has difficulty in resolving waveforms containing components with close frequencies with a ratio of less than two, and similar to other waveform classification techniques, it has difficulty in resolving the instants of sudden changes in the waveform. To overcome the problem with components containing close frequencies, a novel Iterative Hilbert Huang transform (IHHT) is proposed in this paper. To overcome the problem in identifying instants of sudden changes in the waveform, a new method using the Symbolic Aggregate ApproXimation (SAX) method is proposed. SAX converts the signal into symbols that can be utilized by a pattern detector algorithm to identify the boundaries of the stationary signals within a nonstationary signal. Results from IHHT and SAX method to analyze and visually identify simulated and measured nonstationary PQ waveforms will be provided and discussed. The proposed method is particularly useful when investigating the behavior of the harmonic components of a particular PQ waveform of interest in a given interval of time, following a data-mining search of a large database of PQ events. It can be used to both identify, and later isolate unique signatures within a provider's distribution system. [ABSTRACT FROM AUTHOR]

A fault-location method for radial distribution systems is proposed in this paper. The proposed method uses voltage and current phasors from feeder root and voltage sags measured at sparse nodes along the feeder, and pinpoints faults to the nearest node. Decision-tree (DT)-based fault segment identification is introduced before the process of node selection to reduce the computational complexity and improve fault-location accuracy. The method has been implemented on a practical distribution system and tested under a large number of fault scenarios. Test results are compared with those from the traditional voltage-sag-based fault-location algorithm using the same inputs, and the conclusion is that the proposed method can achieve more reliable results while maintaining computational simplicity. A quantitative method to suggest the optimal placement of measurement units based on the DT variable importance is proposed at the end. [ABSTRACT FROM PUBLISHER]

The method presented in this paper addresses the problem of voltage sag state estimation. The problem consists in estimating the voltage sags frequency at nonmonitored buses from the number of sags measured at monitored sites. Usually, due to limitations on the number of available voltage sag monitors, this is an underdetermined problem. In this approach, the mathematical formulation presented is based on the fault positions concept and is solved by means of the singular value decomposition technique. The proposed estimation method has been validated by using the IEEE 118 test system and the results obtained have been very satisfactory. [ABSTRACT FROM PUBLISHER]

This paper investigates the voltage sag caused by distributed generation anti-islanding protection. This is a new power-quality concern associated with distributed generation expansion. Anti-islanding protection aims to disconnect distributed generators immediately after the opening of a recloser. As a consequence, after the reclosing operation, voltage sag will occur in some parts of the distribution system, since the loads are energized immediately but the generators are no longer present. In this context, this work presents the findings on our investigations about this problem. The results show that the resulting voltage sag level can violate power-quality limits. Thus, a set of indices has been introduced to characterize the severity of the voltage sag, and a load flow-based method has been proposed to predict the phenomenon. Sensitivity studies are also conducted in order to identify some key factors that influence this type of voltage depression. [ABSTRACT FROM PUBLISHER]