Showing papers in "IEEE Transactions on Power Delivery in 2000"
TL;DR: In this paper, a linear optimal control based on LQR control is proposed for static compensators, which is shown to be superior in terms of response profile and control effort required.
Abstract: A static compensator (STATCOM) is a device that can provide reactive support to a bus. It consists of voltage sourced converters connected to an energy storage device on one side and to the power system on the other. In this paper the conventional method of PI control is compared and contrasted with various feedback control strategies. A linear optimal control based on LQR control is shown to be superior in terms of response profile and control effort required. These methodologies are applied to an example power system.
462 citations
TL;DR: In this paper, the results of the study carried out for the determination of the residential, commercial and industrial consumers daily load curves based on field measurements performed by the Utilities of Electric Energy of Sao Paulo State, Brazil.
Abstract: This paper presents the results of the study carried out for the determination of the residential, commercial and industrial consumers daily load curves based on field measurements performed by the Utilities of Electric Energy of Sao Paulo State, Brazil. A methodology for the aggregation of these loads to determine the expected loading in equipment of in a preset part of the distribution network by using the representative daily curves of each consumer's activity and the monthly energy consumption of the connected consumers is also presented.
406 citations
TL;DR: In this paper, the authors 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.
Abstract: 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 re-strike 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.
396 citations
TL;DR: In this paper, the analysis of voltage disturbance recordings in the time-frequency domain and in time-scale domain is discussed, where the discrete short-time Fourier transform (STFT) is used for the timefrequency domain; dyadic and binary-tree wavelet filters for the temporal domain; and the discrete STFT is also able to detect and analyze transients in a voltage disturbance.
Abstract: This paper discusses the analysis of voltage disturbance recordings in the time-frequency domain and in the time-scale domain. The discrete short-time Fourier transform (STFT) is used for the time-frequency domain; dyadic and binary-tree wavelet filters for the time-scale domain. The theory is explained with special emphases on the analysis of voltage disturbance data. Dyadic wavelet filters are not suitable for the harmonic analysis of disturbance data. Filter center frequencies and bandwidths are inflexible, and the results do not give easy insight in the time behavior of the harmonics. On the other hand, band-pass filter outputs from discrete STFT are well associated with harmonics and are thus more useful for power system analysis. With a properly chosen window size, the discrete STFT is also able to detect and analyze transients in a voltage disturbance. Overall, the STFT is more suitable than wavelet filters for the analysis of power system voltage disturbance data.
378 citations
TL;DR: The problem of capacitor allocation for loss reduction in electric distribution systems has been extensively researched over the past several decades as mentioned in this paper, and a comprehensive survey of all the literature in capacitor allocation can be found in this paper.
Abstract: The problem of capacitor allocation for loss reduction in electric distribution systems has been extensively researched over the past several decades. This paper describes the evolution of the research and provides an evaluation of the practicality and accuracy of the capacitor placement algorithms in the literature. The intent of this paper is not to provide a complete survey of all the literature in capacitor allocation, but to provide researchers and utility engineers further insight into the choices of available capacitor allocation techniques and their respective merits and shortcomings. Furthermore, this paper serves as a useful and practical guideline to assist in the implementation of an appropriate capacitor allocation technique.
368 citations
TL;DR: In this article, an adaptive fault detection/location technique based on a phasor measurement unit (PMU) for an EHV/UHV transmission line is presented.
Abstract: An adaptive fault detection/location technique based on a phasor measurement unit (PMU) for an EHV/UHV transmission line is presented. A fault detection/location index in terms of Clarke components of the synchronized voltage and current phasors is derived. The line parameter estimation algorithm is also developed to solve the uncertainty of parameters caused by aging of transmission lines. This paper also proposes a new discrete Fourier transform (DFT) based algorithm (termed the smart discrete Fourier transform, SDFT) to eliminate system noise and measurement errors such that extremely accurate fundamental frequency components can be extracted for calculation of fault detection/location index. The EMTP was used to simulate a high voltage transmission line with faults at various locations. To simulate errors involved in measurements, Gaussian-type noise has been added to the raw output data generated by EMTP. Results have shown that the new DFT based method can extract exact phasors in the presence of frequency deviation and harmonics. The parameter estimation algorithm can also trace exact parameters very well. The accuracy of both new DFT based method and parameter estimation algorithm can achieve even up to 99.999% and 99.99% respectively, and is presented in Part II. The accuracy of fault location estimation by the proposed technique can achieve even up to 99.9% in the performance evaluation, which is also presented in Part II.
348 citations
TL;DR: This paper's proposed recognition scheme is carried out in the wavelet domain using a set of multiple neural networks and is capable of providing a degree of belief for the identified disturbance waveform.
Abstract: 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 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.
346 citations
TL;DR: In this article, the authors describe the rationale for the DC Zonal system, characterize the stability issues, and discuss fault detection and load shedding problems in a stiffly-connected system.
Abstract: The US Navy is currently investigating the implementation of a DC zonal electric distribution system (DC ZEDS) for the next generation of surface combatant. In replacing the current AC radial distribution system, significant gains can be realized in terms of survivability, weight, manning and cost. DC ZEDS is predicated on having starboard and port DC buses feeding electrical zones delineated by watertight bulkhead compartments. The main bus DC voltage is stepped down within the zone and then converted to three-phase AC and lower voltage DC by additional power converters. Due to the large interconnection of tightly-regulated power converters in a stiffly-connected system, negative input impedance effects create the possibility of unwanted resonances. In this paper, the authors describe the rationale for the DC zonal system, characterize the stability issues, and discuss fault detection and load shedding problems.
331 citations
TL;DR: In this paper, a new approach for generating reference currents for an active filter and/or a static compensator is presented, where the compensators are connected to a load that may either be connected in star or in delta.
Abstract: This paper presents a new approach for generating reference currents for an active filter and/or a static compensator. It is assumed that the compensator is connected to a load that may either be connected in star or in delta. The load can be unbalanced and may also draw harmonic currents. The purpose of the compensating scheme is to balance the load, as well as make the supply side power factor a desired value. The authors use the theory of instantaneous symmetrical components to obtain an algorithm to compute three phase reference currents which, when injected to the power system, produce desired results. They also propose a suitable compensator structure that will track the reference currents in a hysteresis band control scheme. Finally, the feasibility of such a scheme is demonstrated through simulation studies.
322 citations
TL;DR: In this paper, a new method is proposed to determine the harmonic contributions of a customer at the point of common coupling, which can quantify customer and utility responsibilities for limit violations caused by either harmonic source changes or harmonic impedance changes.
Abstract: A new method is proposed in this paper to determine the harmonic contributions of a customer at the point of common coupling. The method can quantify customer and utility responsibilities for limit violations caused by either harmonic source changes or harmonic impedance changes. It can be implemented in current power quality monitors and digital revenue meters. The method makes it possible to develop fair and consistent billing schemes for harmonic distortion control.
294 citations
TL;DR: In this paper, the use of a continuous wavelet transform (CWT) was used to detect and analyze voltage sags and transients and a recursive algorithm was used and improved to compute the time-frequency plane of these electrical disturbances.
Abstract: This paper deals with the use of a continuous wavelet transform to detect and analyze voltage sags and transients. A recursive algorithm is used and improved to compute the time-frequency plane of these electrical disturbances. Characteristics of investigated signals are measured on a time-frequency plane. A comparison between measured characteristics and benchmark values detects the presence of disturbances in analyzed signals and characterizes the type of disturbances. Duration and magnitude of voltage sags are measured, transients are located in the width of the signal. Furthermore, meaningful time and frequency components of transients are measured. The whole method is implemented and tested over a sample representing recorded disturbances. Detection and measurement results are compared using classical methods.
TL;DR: In this paper, a wavelet transform based online voltage disturbance detection approach is proposed to identify voltage disturbances and discriminates the type of event which has resulted in the voltage disturbance, e.g. either a fault or a capacitor switching incident.
Abstract: This paper introduces a new online voltage disturbance detection approach based on the wavelet transform. The proposed approach: (1) identifies voltage disturbances; and (2) discriminates the type of event which has resulted in the voltage disturbance, e.g. either a fault or a capacitor-switching incident. The proposed approach is: (1) significantly faster; and (2) more precise in discriminating the type of transient event than conventional voltage-based disturbance detection approaches. The feasibility of the proposed disturbance detection approach is demonstrated based on digital time-domain simulation of a power distribution system using the PSCAD/EMTDC software package.
TL;DR: In this paper, a generalized dip model is built for all unbalanced voltage dips, taking into account the fault types, transformer types and load connections, and the characterization results in a so-called remaining complex voltage (a generalized magnitude phase angle shift) for balanced and unbalanced dip as well as a factor related to the rotating machine contribution to the source impedance for unbalanced dips.
Abstract: This paper analyzes the characteristic of voltage dips in power systems with special emphasis on unbalanced dips and electrical components analysis. A generalized dip model is built for all unbalanced dips, taking into account the fault types, transformer types and load connections. It shows the transformation for different types of unbalanced dips. The characterization results in a so-called remaining complex voltage (a generalized magnitude phase angle shift) for balanced and unbalanced dips as well as a factor, related to the rotating machine contribution to the source impedance for unbalanced dips. It is shown that the factor is close to unity, so that both balanced and unbalanced dips can be characterized with one phaser.
TL;DR: A wavelet-based neural classifier is constructed and thoroughly tested under various conditions and is able to provide a degree of belief for the identified waveform and is equipped with an acceptance threshold so that it can reject ambiguous disturbance waveforms.
Abstract: For pt.I see ibid., vol.15, no.1, p.222-8 (2000). 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.
TL;DR: In this article, the authors present the establishment of the linearized Phillips-Heffron model of a power system installed with a unified power flow controller (UPFC) and demonstrate the effect of UPFC DC voltage regulator on power system oscillation stability.
Abstract: For pt.II see ibid., vol.13, no.4, p.1355-62 (1998). This paper presents the establishment of the linearized Phillips-Heffron model of a power system installed with a unified power flow controller (UPFC). Two applications based on the Phillips-Heffron model are demonstrated: (1) study on the effect of UPFC DC voltage regulator on power system oscillation stability; and (2) selection of damping control signal for the design of UPFC damping controller.
TL;DR: In this article, the hysteresis loop of the core material in a test current transformer is simulated using the Jiles-Atherton theory and compared with recorded and simulated waveforms and it is found necessary to replace the modified Langevin function used by Jiles and Atherton.
Abstract: The hysteresis loop of the core material in a test current transformer is simulated using the Jiles-Atherton theory. Comparisons are made between recorded and simulated waveforms and it is found necessary to replace the modified Langevin function used by Jiles and Atherton. Using an alternative function described in the paper, good agreement is achieved between test and simulated waveforms.
TL;DR: In this paper, the authors present a Fourier algorithm to remove the DC offset in a voltage or current signal, which reduces the precision and convergence speed of the DFT and decomposes the accurate fundamental frequency components.
Abstract: Protecting transmission lines frequently involves adopting distance relays. Protective relays must filter their inputs to reject unwanted quantities and retain signal quantities of interest. Accuracy and convergent speed of the filter algorithm are essential for protective relays. A widely applied filter algorithm, the discrete Fourier transform (DFT) can easily erase harmonics using simple calculation. However, the voltage and current signals contain large harmonics and DC offset during the fault interval. The DC offset heavily influences the precision and convergence speed of the fundamental frequency signal from DFT. In this investigation, the authors present a novel Fourier algorithm to remove the DC offset in a voltage or current signal. Applying a full-cycle DFT (FCDFT) requires one cycle plus two samples to calculate and compensate for the DC offset. Half-cycle DFT (HCDFT) only requires half of a cycle plus two or three samples to accomplish the algorithm when the input signal has no even order harmonics. Adopting the proposed algorithm in distance relays effectively suppresses the DC offset and quickly decomposes the accurate fundamental frequency components.
TL;DR: In this paper, a method for determining a minimal-loss radial configuration for a power distribution network, using an exhaustive search algorithm, is proposed, deriving its efficiency from the use of graph-theoretic techniques involving semi-sparse transformations of a current sensitivity matrix.
Abstract: The authors suggest a method for determining a minimal-loss radial configuration for a power distribution network, using an exhaustive search algorithm. While exhaustive, the method is highly efficient, deriving its efficiency from the use of graph-theoretic techniques involving semi-sparse transformations of a current sensitivity matrix. The algorithm can he applied to networks of moderate size and has advantages over existing algorithms for network reconfiguration in that it guarantees a globally optimal solution (under appropriate modeling assumptions), and is easily extended to take account of phase imbalance and network operation constraints. A 33-bus example is used to demonstrate the operation of the algorithm.
TL;DR: In this article, a new timing device named "Global Synchronism Clock Generator, GSCG" including its hardware and software design is described in this paper, Experimental results show that the synchronized error of rising edge between the two GSCGs clock is well within 1 ps when the clock frequency is below 2.499 MHz.
Abstract: Part I of this paper set sets forth theory and algorithms for adaptive fault detection/location technique, which is based on phasor measurement unit (PMU). This paper is Part II of this paper set, A new timing device named "Global Synchronism Clock Generator, GSCG" including its hardware and software design is described in this paper, Experimental results show that the synchronized error of rising edge between the two GSCGs clock is well within 1 ps when the clock frequency is below 2.499 MHz. The measurement results between Chung-Jeng and Chang-Te 161 kV substations of Taiwan Power company by PMU equipped with GSCG is presented and the accuracy for estimating parameters of line is verified. The new developed DFT based method (termed as smart discrete Fourier transform, SDFT) and line parameter estimation algorithm are combined with PMU configuration to form the adaptive fault detector/locator system. Simulation results have shown that SDFT method can extract exact phasors in the presence of frequency deviation and harmonics, The parameter estimation algorithm can also trace exact parameters very well, The SDFT method and parameter estimation algorithm can achieve accuracies of up to 99.999% and 99.99%, respectively. The EMTP is used to simulate a 345 kV transmission line of Taipower System. Results have shown that the proposed technique yields correct results independent of fault types and is insensitive to the variation of source impedance, fault impedance and line loading. The accuracy of fault location estimation achieved can be up to 99.9% for many simulated cases, The proposed technique will be very suitable for implementation in an integrated digital protection and control system for transmission substations.
TL;DR: The ability to predict or confirm ferroresonance depends primarily on the correctness of the transformer model used by the computer simulation as mentioned in this paper, which is a general modeling approach and a general approach is given.
Abstract: The ability to predict or confirm ferroresonance depends primarily on the correctness of the transformer model used by the computer simulation. Ferroresonance is introduced and a general modeling approach is given. An overview of available literature and contributors to this area is provided. A simple ease of ferroresonance in a single phase transformer is used to illustrate this "phenomenon". Three phase transformer core structures are discussed. Ferroresonance in three phase grounded-wye distribution systems is described and illustrated with waveform data obtained from laboratory simulations. Representation of the study zone is discussed, modeling techniques are presented, and implementation suggestions are made. Three case studies are presented. Transformer representation is critical to performing a valid simulation. The direction of ongoing research is discussed, and the reader is advised to monitor the literature for ongoing rapid improvements in transformer modeling techniques.
TL;DR: A novel approach using approximate reasoning to determine suitable candidate nodes in a distribution system for capacitor placement using a fuzzy expert system containing a set of heuristic rules is presented.
Abstract: The problem of capacitor allocation in electric distribution systems involves maximizing energy and peak power (demand) loss reductions by means of capacitor installations. This paper presents a novel approach using approximate reasoning to determine suitable candidate nodes in a distribution system for capacitor placement. Voltages and power loss reduction indices of distribution system nodes are modeled by fuzzy membership functions. A fuzzy expert system (FES) containing a set of heuristic rules is then used to determine the capacitor placement suitability of each node in the distribution system. Capacitors are placed on the nodes with the highest suitability. Simulation results show the advantages of this approach over previous capacitor placement algorithms.
TL;DR: In this article, a series of precise digital algorithms based on discrete Fourier transforms (DFT) to calculate the frequency and phasor in real-time are proposed, which are called the Smart Discrete Fourier Transform (SDFT).
Abstract: A series of precise digital algorithms based on discrete Fourier transforms (DFT) to calculate the frequency and phasor in real-time are proposed. These algorithms, called the smart discrete Fourier transforms (SDFT) family, not only keep all of the advantages of DFT but also smartly take frequency deviation and harmonics into consideration. These make the SDFT family more accurate than the other methods. Besides, the SDFT family is recursive and very easy to implement, so it is very suitable for use in real-time. The authors provide the simulation results compared with conventional DFT method and second-order Prony method to validate the claimed benefits of SDFT.
TL;DR: In this article, a multiple line drop compensation (MLDC) voltage regulation method that determines tap positions of under-load tap changer (ULTC) transformers is proposed to maintain the customers' voltages within the permissible limits.
Abstract: This paper deals with an issue of voltage regulation for power distribution systems interconnected with dispersed storage and generation (DSG) systems. Since DSGs within power distribution systems impact on the conventional voltage regulation method, there is a possibility that customers' voltages violate the permissible limits. A multiple line drop compensation (MLDC) voltage regulation method that determines tap positions of under-load tap changer (ULTC) transformers is proposed to maintain the customers' voltages within the permissible limits. Several case studies indicate that the proposed MLDC voltage regulation method can be applied well to practical power distribution systems having DSGs and/or severely unbalanced load diversity on different feeders.
TL;DR: In this article, a number of mathematical models used to represent the nonlinear behavior of the magnetic core of instrument transformers are presented, and the transient response of the instrument transformer is compared to actual test results recorded in the laboratory.
Abstract: This paper reviews a number of mathematical models used to represent the nonlinear behavior of the magnetic core of instrument transformers. Models of instrument transformers using these core representations are presented. The transient response of the instrument transformer is compared to actual test results recorded in the laboratory. The paper provides practical guidelines as to which of the physical elements of instrument transformers are important to model during transient studies and which elements could be ignored without sacrificing the accuracy of the simulation results. The electromagnetic transients program (EMTP) data files used to generate the models are also provided in the appendix to help new EMTP users model instrument transformers for evaluation of high-speed protective relaying systems.
TL;DR: In this paper, a new approach to shunt capacitor placement in distribution systems having customers with different load patterns is presented, where the allocation of capacitors is considered in a system comprising a network of feeders fed from an upstream equivalent transmission system through a substation transformer.
Abstract: This paper presents a new approach to shunt capacitor placement in distribution systems having customers with different load patterns. The allocation of capacitors is considered in a system comprising a network of feeders fed from an upstream equivalent transmission system through a substation transformer. The benefits of capacitor placement, such as the system capacity release and reduction of overall power and energy losses, are considered. The fast method of total energy loss calculation based on the computation of the moments of normalized daily load curves is used to calculate the annual energy loss reduction. An example of optimal capacitor allocation in a distribution system is presented in which customers with commercial, urban residential, rural and light industrial load patterns are considered.
TL;DR: In this paper, it was shown that the Mayr-type arc models can be used to describe circuit breaker arc behavior before current zero exactly, and an improved version of the model with a constant time parameter and a cooling power dependent on the electrical power input was introduced.
Abstract: In this paper, it is shown that the Mayr-type arc models can be used to describe circuit breaker arc behavior before current zero exactly. Based on this analysis, the different types of 'modified' Mayr arc models can be explained. As a result of the theory, an improved Mayr-type arc model-with a constant time parameter and a cooling power which is dependent on the electrical power input-is introduced and used to reproduce current zero measurements successfully.
TL;DR: In this paper, an immune algorithm (IA) based optimization approach for solving the capacitor placement problem is proposed, in which the objective functions and constraints are represented as antigens through the genetic evolution, an antibody that most fits the antigen becomes the solution.
Abstract: An immune algorithm (IA) based optimization approach for solving the capacitor placement problem is proposed in this paper. In the capacitor placement problem, those practical capacitor operating constraints, load profiles, feeder capacities and allowable voltage limits at different load levels are all considered while the investment cost and energy loss are minimized. In the proposed method, objective functions and constraints are represented as antigens. Through the genetic evolution, an antibody that most fits the antigen becomes the solution. In this IA computation, an affinity calculation process is also embedded to guarantee the diversity. The process stagnation can be thus better prevented. The proposed method has been applied to a test system and the results are compared with other published techniques.
TL;DR: In this article, the lossless line model is modified to account for the series losses in the line, and the line model equations are then solved in the time domain to accurately locate the fault.
Abstract: Earlier work at Texas A&M University led to the development of transmission line fault location algorithms that were based on synchronized sampling of the voltage and current data from the two ends of the line. The line models used in the algorithms were based on lumped parameter models for electrically short lines, or lossless distributed parameter models for electrically long lines. In this paper, the lossless line model is modified to account for the series losses in the line. The line model equations are then solved in the time domain to accurately locate the fault. Testing of the modified algorithm is performed on a power system belonging to the Western Area Power Administration. Extensive EMTP based simulations are used to generate data that are supplied as inputs to the fault location algorithm. To make the testing as realistic as possible, detailed models of instrument transformers are used in the simulation of the various fault cases.
TL;DR: This paper presents a hybrid scheme using a Fourier linear combiner and a fuzzy expert system for the classification of transient disturbance waveforms in a power system which is much simpler than the recently postulated ANN or wavelet based approaches.
Abstract: This paper presents a hybrid scheme using a Fourier linear combiner and a fuzzy expert system for the classification of transient disturbance waveforms in a power system. The captured voltage or current waveforms are passed through a Fourier linear combiner block to provide normalized peak amplitude and phase at every sampling instant. The normalized peak amplitude and computed slope of the waveforms are then passed on to a diagnostic module that computes the truth value of the signal combination and determines the class to which the waveform belongs. Several numerical tests have been conducted using EMTP programs to validate the disturbance waveform classification with the help of the new hybrid approach which is much simpler than the recently postulated ANN or wavelet based approaches.
TL;DR: In this paper, the authors used sampled voltage and current waveforms to determine on which side of a recording device a disturbance originates by examining the energy flow and peak instantaneous power for both capacitor energizing and voltage sag disturbances.
Abstract: 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. The authors demonstrate the technique by testing it on both ATP-generated waveforms and actual field disturbance data. In both cases, they 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.