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The stator ground fault location of large generators can guide rapid maintenance. In this paper, a location criterion without fault transition resistance is constructed by using the fundamental potential and the third harmonic potential of the faulty winding simultaneously. The above potentials of the faulty winding are corresponding to the fault position. To precisely locate the grounding fault, it is necessary to clarify the analytical relationship between the faulty winding potential and the fault position. However, the existing methods often take the coil potential as the unit to analyze the winding potential, which has theoretical errors for the generators with short-pitch winding. Aiming at this problem, a more precise analysis method for winding potential is established by taking the slot conductor potential as the unit. To solve the location criterion, the optimization model for each slot conductor of the faulty phase is constructed. The slot conductor with the smallest optimal objective function value is judged as the faulty slot conductor, and the corresponding decision variable is judged as the fault position. Simulation and experiments verify the effectiveness of the proposed method, which can still meet the needs of engineering applications under multiple adverse conditions. [ABSTRACT FROM AUTHOR]

With the development of HVdc transmission technology, the isolation of dc faults is becoming increasingly important. As the most effective solution, hybrid HVdc circuit breaker (CB) is not mature enough, which has restricted its engineering application. Accordingly, this paper proposes an auxiliary dc CB scheme suitable for HVdc grid. In this scheme, the traditional half-bridge modular multilevel converter (MMC) is partially innovated to have the ability of auxiliary breaking operation. With the effect of the MMC auxiliary breaking (MAB) operation at both ends of the fault line, the dc fault current can be easily interrupted and isolated by low-cost CB unit installed in the dc transmission line. The equivalent circuit under MAB process is analyzed, and the fault isolation sequences are designed. Furthermore, the economic comparative analysis among three schemes is performed. Finally, a four-terminal bipolar HVdc grid test model is built in PSCAD/EMTDC; in addition, an MMC prototype with proposed scheme is also developed. The simulation and experimental results validate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Some new methods, based on characterization of the dielectric response of transformer insulation in time and frequency domains, have been pointed out by CIGRE as suitable to assess moisture content in pressboard and paper. Measuring devices available today on the market are quite robust in field conditions; however there is a risk that undesired internal and external factors might influence the measurements. These influences can lead to mistaken interpretation of insulation wetness. Operators should therefore be aware of the risks appearing at different measuring conditions and of the precautions that can be taken to minimize their effects. This work presents a systematic investigation on the influence of some factors on the results of dielectric response measurements in field conditions. The errors that can be committed during the measurements if certain precautions are not taken, with different equipment connected in parallel, are evaluated. The influence of rain and electromagnetic disturbances are also analyzed proposing solutions to attenuate their effects. Finally, a discussion on the influence of temperature distribution follows. The work is concentrated on frequency response measurements, although some results from the use of polarization and depolarization current technique are also discussed. [ABSTRACT FROM AUTHOR]

Accurate computation of electromagnetic transients for underground cables and overhead transmission lines requires the frequency domain characterization of two matrix functions: propagation and characteristic admittance. The propagation function constitutes a high order Wideband system with inherent time delays. In this paper a weighted fitting technique is presented and advocated for the identification of the propagation function as a rational transfer function. The paper also contributes to theoretical clarifications on vector fitting and orthonormal vector fitting. The application of orthonormal vector fitting is demonstrated together with weighted vector fitting. Although the presentation is also applicable to transmission lines, the numerical examples are focused on underground cables where the frequency dependency problems are more complex. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach to the analysis of the interaction between induction motors (IMs) and voltage sags. The presented methodology enables quick assessment of the influence of IM on sag characteristics and avoids time-consuming transient simulations. The accuracy of the derived analytical formulae is verified through classical transient simulations using the PSCADIEMTDC package. This paper further proposes a simple, yet efficient transformation of resulting nonrectangular voltage sags, based on the loss of voltage index, into equivalent rectangular sags suitable for conventional voltage sag performance benchmarking. [ABSTRACT FROM AUTHOR]

In this paper, a linearized small-signal model for a six-pulse HVDC system is presented. In this paper, the effects of on and off states resistances, forward voltage drop, and snubber circuits of the thyristors and filter circuits are taken into account. RL series circuits are used for modeling of the converter transformer and ac system. To validate the model developed in this paper, a comparison is made with the PSCADIEMTDC time-domain simulation program. [ABSTRACT FROM AUTHOR]

In this paper, practical considerations for recursive Discrete Fourier Transform (DFT) implementation in numerical relays are presented. The DFT filter instabilities which would produce accumulated errors are emphasized. The aspects ruling error accumulation of the estimated magnitude and phase are highlighted. Novel solutions directed for the elimination of error accumulation are proposed and intensively tested. Digital signal processing (DSP) board based test set-up is utilized for the experimental verification. The paper results are valuable for the protection engineers particularly those concerned with the development and implementation of numerical relays. [ABSTRACT FROM AUTHOR]

The second part of this paper presents a practical implementation and application of the methodology for the stochastic assessment of the annual financial losses due to interruptions and voltage sags discussed in the first part of this paper. The costs of interruptions and voltage sags are determined separately and then combined in order to estimate the total financial losses in the network. The methodology is illustrated on a generic realistic distribution network with all relevant network components modeled appropriately. Finally, different network topologies are compared taking into account total financial losses in the network. It is shown that the inclusion of the financial losses due to voltage sags that may account for up to about 20% of the interruption costs may alter the network topology ranking. [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]

This paper analyzes four basic ground methods for personal protection during maintained distribution transformers considering reverse energy from end users. The test in this paper considers that no loads are connected at both the primary and secondary of the distribution transformer. The results are summarized to determine the effective grounding method of protecting distribution line workers on de-energized lines during accidental-line energization from the end users. The secondary voltage at the transformer was recorded with various configurations of temporary grounds, and the primary voltage is then computed by using the transformer turn ratio. As a result, the case of installing no temporary ground is considered lethal. Moreover, the cases of installing temporary ground with a short circuit at either the primary or secondary of the transformer are considered to be the effective means of protecting distribution line workers. [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]

The analysis of the three-phase transverse-electro- magnetic (TEM) line based on the Park approach represents, under the theoretical and the applicative point of view, an important analytical tool. For these reasons, this paper presents the analysis of lossy (quasi-TEM) three-phase transmission lines in terms of three-phase vectors, based on the Park transformation. The three-phase transmission-line transient analysis presented in this paper emphasizes the conceptual contents specific to the Park approach. Furthermore, applied to some examples, it gives very important results for the practical analysis of a lossy three-phase transmission line. [ABSTRACT FROM AUTHOR]

A few problems in the present calculation methods in the aspects of insulation flashover criteria, influence of operating voltages, induced overvoltage component, and shielding failure in China are briefly analyzed and discussed. Lightning performance of 500-ky double-circuit line schemes (nine tower types and thirteen schemes of insulation disposition) for the Three-Gorge Project is computed and compared with the existing operation experience of double-circuit lines. Different schemes are compared with each other. The cause of the remarkable increase of the total lightning outage rate of the usual unbalanced double-circuit lines, with one circuit insulation reduced, in the operation is analyzed. Different from the usual unbalanced insulation lines, a one-circuit insulation enhanced scheme is proposed in this paper. It is emphasized in the paper that the key of the lightning protection of double-circuit transmission lines is to reduce the double-circuit simultaneous trip-out rate and to keep a reasonable total trip-out rate at the same time. It can be achieved by choosing the proper insulation disposition scheme referring to the order of the weighted trip-out rate values. The viewpoints and methods in the paper would be useful to others working in this field. [ABSTRACT FROM AUTHOR]

This paper presents a detailed model for simulation of a Superconducting Magnetic Energy Storage (SMES) system. SMES technology has the potential to bring real power storage characteristic to the utility transmission and distribution systems. The principle of SMES system operation is reviewed in this paper. To understand transient and dynamic performance of a SMES system, a detailed SMES system benchmark model is given with extensive simulation results. This system is demonstrated using an electromagnetic transient program—PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

Air-magnetic circuit breakers are widely used for short-circuit protection in dc electric railways or industrial plants. The well-known drawbacks of these breakers are mainly a slow breaking action, a short lifetime, and high maintenance costs due to the destructive effects of the arc. The use of power semi-conductors in a full-static circuit breaker configuration allows the elimination of these disadvantages but is limited by excessive conduction losses. The paper will present the study of a so-called hybrid breaker, drawing its name from the combination of a high-speed mechanical switch and a bi-directional integrated gate-controlled thyristor assembly connected in parallel. The paper also includes experimental results from a prototype real scale. [ABSTRACT FROM AUTHOR]

The concepts of reactive power that originate from Buchholz's theory and are present in the IEEE Standard 1459 are important in compensation theory. It is shown in this paper that some misconceptions are present in the technical literature, in particular regarding the relationship between reactive power and power oscillation. In this paper, a number of examples are given to illustrate these misconceptions. [ABSTRACT FROM AUTHOR]

Conservation voltage reduction (CVR) and distributed-generation (DG) integration are popular strategies implemented by utilities to improve energy efficiency. This paper investigates the interactions between CVR and DG placement to minimize load consumption in distribution networks, while keeping the lowest voltage level within the predefined range. The optimal placement of DG units is formulated as a stochastic optimization problem considering the uncertainty of DG outputs and load consumptions. A sample average approximation algorithm-based technique is developed to solve the formulated problem effectively. A multiple replications procedure is developed to test the stability of the solution and calculate the confidence interval of the gap between the candidate solution and optimal solution. The proposed method has been applied to the IEEE 37-bus distribution test system with different scenarios. The numerical results indicate that the implementations of CVR and DG, if combined, can achieve significant energy savings. [ABSTRACT FROM AUTHOR]

This paper presents a novel time-domain fault location algorithm on HVDC transmission lines. The Bergeron line model is adopted to construct a time-domain fault location equation, considering unsynchronized two-end measurement and uncertain line parameters. The zero time reference point is set to the sample point of arrival at each end for the traveling wave-head. Time-tags of all sample points change with the zero time reference. So the time difference of two-end measurements has changed also, and equals the time difference between arrivals at two ends for the traveling wave-head. That makes it possible to mix the traveling wave theory with the Bergeron time-domain fault location method. Besides, the ratio coefficient of wave velocities between different frequencies and digital band-pass filter are presented for better performance of the proposed method. Simulations and tests demonstrate that the proposed method can locate faults accurately on the HVDC lines even in the case of loss of signals from GPS. [ABSTRACT FROM AUTHOR]

Aerial LiDAR survey is receiving wide application in transmission-line modeling due to its efficiency. The technique is particularly useful for modeling of existing lines for the purpose of thermal rating, upgrading, or vegetation management. An accurate modeling of an existing line depends largely on proper determination of the base conductor temperature, i.e. the conductor temperature at the time of the aerial light detection and ranging (LiDAR) survey. In this paper, an acceptable accuracy for the base conductor temperature is first established. Extensive parametric studies are then conducted to reveal the effects of all the potentially major factors: ambient air temperature, electrical load, solar radiation, wind, and conductor size on the base conductor temperature. As a result, recommendations are made on the proper practice of performing an aerial LiDAR survey and determining the base conductor temperature so that the resulting transmission line modeling is within an acceptable accuracy. It is demonstrated that a wide error can easily be introduced without following a proper procedure for the LiDAR survey. [ABSTRACT FROM AUTHOR]

The rapid growth of wind power systems worldwide will likely see the integration of large wind farms with electrical networks that are series compensated for ensuring stable transmission of bulk power. This may potentially lead to subsynchronous-resonance (SSR) issues. Although SSR is a well-understood phenomenon that can be mitigated with flexible ac transmission system (FACTS) devices, scant information is available on the SSR problem in a series-compensated wind farm. This paper reports the potential occurrence and mitigation of SSR caused by an induction-generator (IG) effect as well as torsional interactions, in a series-compensated wind farm. SSR suppression is achieved as an additional advantage of FACTS controllers which may already be installed in the power system for achieving other objectives. In this study, a wind farm employing a self-excited induction generator is connected to the grid through a series-compensated line. A static var compensator (SVC) with a simple voltage regulator is first employed at the IG terminal in addition to the fixed shunt capacitor for dynamic reactive power support. The same SVC is shown to effectively damp SSR when equipped with an SSR damping controller. Also, a thyristor-controlled series capacitor (TCSC) that is actually installed to increase the power transfer capability of the transmission line is also shown to damp subsynchronous oscillations when provided with closed-loop current control. While both FACTS controllers--the SVC and TCSC--can effectively mitigate SSR, the performance of TCSC is shown to be superior. Extensive simulations have been carried out using EMTDC/PSCAD to validate the performance of SVC and TCSC in damping SSR. [ABSTRACT FROM AUTHOR]

This paper presents a computational approach for an offline measurement-based design of an optimal damping controller using adaptive critics for a new type of flexible ac transmission system device--the gate-controlled series capacitor (GCSC). Remote measurements are provided to the controller to damp out system modes. The optimal controller is developed based on the heuristic dynamic programming (HDP) approach. Three multilayer-perceptron neural networks are used in the design--the identifier/model network to identify the dynamics of the power system, the critic network to evaluate the performance of the damping controller, and the controller network to provide optimal damping. This measurement-based technique provides an alternative to the classical linear model-based optimal control design. The eigenvalue analysis of the closed-loop system is performed with time-domain responses using the Prony method. An analysis of the simulation results shows potential of the HDP-based optimal damping controller on a GCSC for enhancing the stability of the power system. [ABSTRACT FROM AUTHOR]

This paper investigates issues related to practical implementation of the one-quarter of cycle-based estimation method [here called delayed signal cancellation (DSC)] for online detection of positive and negative sequence components of three-phase quantities. The detection error due to non-ideal sampling frequency is calculated. Furthermore, the effect of the DSC method on estimation when harmonic components are present in the input signal is analyzed. It is shown how harmonics transfer through the DSC and how a non-ideal sampling frequency affects the estimation of the harmonics. Experimental verification of the analytical results is presented. [ABSTRACT FROM AUTHOR]

Because traditional electric power distribution systems have been designed assuming the primary substation is the sole source of power and short-circuit capacity, DR interconnection results in operating situations that do not occur in a conventional system. This paper discusses several system issues which may be encountered as DR penetrates into distribution systems. The voltage issues covered are the DR impact on system voltage, interaction of DR and capacitor operations, and interaction of DR and voltage regulator and LTC operations. Protection issues include fuse coordination, feeding faults after utility protection opens, impact of DR on interrupting rating of devices, faults on adjacent feeders, fault detection, ground source impacts, single phase interruption on three phase line, recloser coordination and conductor burndown. Loss of power grid is also discussed, including vulnerability and overvoltages due to islanding and coordination with reclosing. Also covered separately are system restoration and network issues. [ABSTRACT FROM AUTHOR]

In this paper, a method for placement of distributed generation (DG) units in distribution networks has been presented. This method is based on the analysis of power flow continuation and determination of most sensitive buses to voltage collapse. This method is executed on a typical 34-bus test system and yields efficiency in improvement of voltage profile and reduction of power losses; it also may permit an increase in power transfer capacity, maximum loading, and voltage stability margin. [ABSTRACT FROM AUTHOR]

The role of a battery energy storage system in a unified power-flow control scheme is examined. Analysis shows that the capability of the storage system to support power transmission is governed by the state of discharge (SOD) of the battery. A changeover to a standby battery is necessary once the inservice battery SOD exceeds the level determined from the analytical method described in this paper. The method also permits, the battery changeover schedule to be evaluated for a given load demand profile. Furthermore, the capacity of the battery system is determined such that the resulting system operates under an optimal economic dispatch condition, while the transfer capability of the compensated transmission is maximized. [ABSTRACT FROM AUTHOR]

In the last decade, distributed generation, with its various technologies, has increased its presence in the energy mix presenting distribution networks with challenges in terms of evaluating the technical impacts that require a wide range of network operational effects to be qualified and quantified. The inherent time-varying behavior of demand and distributed generation (particularly when renewable sources are used), need to be taken into account since considering critical scenarios of loading and generation may mask the impacts. One means of dealing with such complexity is through the use of indices that indicate the benefit or otherwise of connections at a given location and for a given horizon. This paper presents a multiobjective performance index for distribution networks with time-varying distributed generation which consider a number of technical issues. The approach has been applied to a medium voltage distribution network considering hourly demand and wind speeds. Results show that this proposal has a better response to the natural behavior of loads and generation than solely considering a single operation scenario. [ABSTRACT FROM AUTHOR]

This paper investigates voltage and reactive power control in distribution systems and how the presence of synchronous machine-based distributed generation (DG) affects the control. A proper coordination among the onload tap changer (OLTC), substation switched capacitors and feeder-switched capacitors in order to obtain optimum voltage and reactive power control is proposed. It is assumed that there is no communication link between the OLTC and the capacitors, a normal case in distribution system operation these days. The results indicate that the proposed method decreases the number of OLTC operations, losses, and voltage fluctuations in distribution systems, with and without DG present. The power-flow reversal due to the lJG is shown not to interfere with the effectiveness of the OLTC operation. Further, it is also shown that as long as the available capacitors are enough to compensate the reactive power demand, the DG operation mode does not give a significant effect to the distribution system losses. However, DG operating at a constant voltage is beneficial for a significant reduction of OLTC operation and voltage fluctuation in the distribution system. [ABSTRACT FROM AUTHOR]

This paper describes the influence of induction motors (IMs) on voltage sag characteristics at low-voltage (LV) buses. This influence is particularly pronounced in case of low magnitude and long duration voltage sags. Even though the conventional magnitude duration representation of voltage sags in the presence of IMs is not completely accurate, it is very convenient as it can be directly linked to a standard way of recording/reporting voltage sags. The equivalent rectangular sags developed in this study take into account the effect of IMs and establish voltage sag performance more accurately at LV buses in the distribution network. The methodology developed is not limited to simulation-based voltage sag studies. It can be equally well applied as a "postprocessor" to finely tune the results of monitoring distribution systems as its inputs are "classical" voltage sag magnitude duration tables. The automated procedure for counting and characterization of voltage sags at LV distribution buses is illustrated on a 295-bus generic distribution network. [ABSTRACT FROM AUTHOR]

In this paper, a novel control strategy for subsynchronous resonance (SSR) mitigation using a static synchronous series compensator will be presented. SSR mitigation is obtained by increasing the network damping only at those frequencies that are critical for the turbine-generator shaft. This is achieved by controlling the subsynchronous component of the grid current to zero. Using the IEEE First Benchmark Model, the effectiveness of the proposed control algorithm when mitigating SSR due to torsional interaction and torque amplification effect will be shown. [ABSTRACT FROM AUTHOR]

This paper presents a harmonic analysis model for the Korean high-speed railway. Since the harmonic current flows through the catenary system, the catenary system must be modeled exactly to analyze harmonic current amplifications and the total harmonic distortion. In the present work, the line constants of five conductors in the catenary system were calculated by the reduction method, and each subsystem, which consisted of the Korean high- speed railway system, was modeled by the eight-port representation. Simulation results using the proposed model were compared to field test data of the Korean high-speed railway system, and the accuracy of the harmonic analysis model was verified. Also, the harmonic characteristics of the Korean high-speed railway system are presented. [ABSTRACT FROM AUTHOR]

This paper studies the behavior of a high-voltage direct current link based on voltage-source converters, which feeds a weak ac network with power produced from an offshore wind farm (WF) of induction generators. Its control system, which is based on adaptive fuzzy controllers, manages to offer very satisfactory performance, without the need for a detailed mathematical model, but just prior knowledge of the behavior of the electrical system. Using the simulation program PSCADIEMTDC, the study was performed under both steady-state and transient conditions. The results show that the link supplies the variable power of the WF to a weak grid, keeping the ac voltage fluctuations in the point of common coupling at an acceptable level. Moreover, due to the ability of the control system to adjust the stator frequency of the induction generators in relation to the wind velocity, maximum wind power acquisition is achieved. [ABSTRACT FROM AUTHOR]

The "318 Blackout Incident" at the Maanshan Nuclear Power Station on March 18, 2001, is considered to be the most serious event over the 24-year history of nuclear power generation in Taiwan. This paper simulates a special overvoltage phenomenon that occurred 4 h before the blackout event, which could have caused the incident. The simulation results almost coincide closely with the actual conditions recorded. We found two major low-frequency and ferroresonant overvoltages caused by the motors which acted as generators when they lost power supply, interacting with power-line capacitance and power transformers. Since overvoltages were present for a short period, the breaker insulation did not break down immediately but the defects were accumulated. A blackout eventually occurred 4 h later, when the power supplied to the 4.16-kV essential bus A changed over from the 161-kV system to the 345-kV system, due to damage in the incoming breaker insulation. [ABSTRACT FROM AUTHOR]

This paper presents a multiobjective approach for the design of electrical distribution networks. The objectives are defined as a monetary cost index (including installation cost and energy losses cost) and a system failure index. The true Pareto-optimal solutions are found with a multiobjective genetic algorithm that employs an efficient variable encoding scheme and some problem-specific mutation and crossover operators. Results based on 21- and 100-bus systems are presented. The information gained from the Pareto-optimal solution set is shown to be useful for the decision-making stage of distribution network evolution planning. [ABSTRACT FROM AUTHOR]

System reliability performance is usually based on average customer interruption information. These average values are valuable information, but provide only a single customer risk dimension without underlying probability distributions. The average annual indices give no insight on how reliability may vary from year to year as a result of the random behavior of bulk electric systems (BES). A significant advantage when utilizing sequential Monte Carlo simulation in bulk electric system reliability analysis is the ability to provide reliability index probability distributions in addition to the expected values of their indices. Parameter distribution analysis and its potential utilization are relatively new concepts in composite power system reliability analysis and decision making. This paper presents a technique to predict future reliability performance indices of the BES using a sequential simulation approach. The results obtained using the sequential software show that the system performance index probability distributions have unique characteristics that are basically dependent on the system topology and the operating philosophy. Operating policies involving load shedding procedures have a considerable impact on the system performance indices and their associated distributions. Two test systems are used to illustrate the concepts associated with the determination of system performance indices and their associated probability distributions. The results obtained using two different load shedding policies are presented and compared. [ABSTRACT FROM AUTHOR]

In this paper, a generalized leader inception model is proposed. It is based on an iterative geometrical analysis of the background potential distribution of an earthed structure to simulate the first meters of propagation of an upward connecting leader. By assuming a static field approach, the leader stabilization fields and the striking distances were computed for a lightning rod and for a building. The obtained results were compared with the existing leader inception criteria. Furthermore, in order to validate the model, the leader inception condition was computed for a triggered lightning experiment. Excellent agreement with the experimental results was obtained. The present model has several advantages in comparison with the existing leader inception criteria. One of them is related to the fact that the proposed model can be used to analyze the effect of the space charge on the upward leader inception. [ABSTRACT FROM AUTHOR]

This paper presents a study on losses in cables and transformers considering nonsinusoidal conditions in commercial facilities. A mathematical development based on classical definitions available in the literature supports the proposal of a factor that is suitable to indicate where losses are significant and must be compensated. A case study is also presented and meticulously analyzed in order to validate the theoretical assumptions. [ABSTRACT FROM AUTHOR]

This paper outlines the extension of harmonic domain modeling to flexible ac transmission system (FACTS) devices which contain series voltage injection elements. The proposed iterative technique is capable of modeling generic combinations of series and shunt converters; representing these elements as harmonic current and voltage sources, respectively. The harmonic performance of these converter combinations is characterized in terms of dc current mismatches, which are combined with fundamental frequency power-flow mismatches in an iterative Newton solution. This combination maintains modularity, allowing multiple converter FACTS devices, such as the unified power-flow controller (UPFC), and/or systems containing multiple FACTS devices to be studied. The proposed technique has been successfully validated against time-domain simulation for the UPFC and then used to highlight converter interactions within a UPFC. [ABSTRACT FROM AUTHOR]

This paper presents a generalized methodology for stochastic/probabilistic assessment of the annual financial losses due to interruptions and voltage sags. The costs of interruptions and voltage sags are treated separately and then combined in order to estimate the total financial losses in the network per annum. The methodology proposed is applicable to both assessment of individual customer losses and assessment of total network losses. It takes into account in a probabilistic manner all the uncertainties associated with the voltage sag calculation, sensitivity of customers' equipment to voltage sags, the interconnection of the equipment within an industrial process, and customer types and the location of the process in the network. [ABSTRACT FROM AUTHOR]

The "static" analysis (relevant to fixed load conditions) of current phase-shift effects on the magnetic field from ac double-circuit overhead transmission lines (Part I of this paper) becomes "dynamic" here by considering time-varying load conditions of an existing line, derived from a database recorded from 1994 to 2001, thereby showing that current phase shift plays a major role also when load changes. Indeed, often extreme field values over a time period are not associated with extreme current values, but with current phase shifts that, for given line geometry and conductor arrangement, yield the most effective field enhancement/reduction. An estimate of the mean/median phase-shift angle over a reference period is proposed that provides a good approximation, via one single static calculation, of the mean/median magnetic-field profiles calculated over that period (e.g., one year). It is confirmed that current phase shifts are fundamental for understanding the behavior of magnetic fields from ac double-circuit overhead transmission lines. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel power-quality (PQ) event detection and classification method using higher order cumulants as the feature parameter, and quadratic classifiers as the classification method. We have observed that local higher order statistical parameters that are estimated from short segments of 50-Hz notch-filtered voltage waveform data carry discriminative features for PQ events analyzed herein. A vector with six parameters consisting of local minimas and maximas of higher order central cumulants starting from the second (variance) up to the fourth cumulant is used as the feature vector. Local vector magnitudes and simple thresholding provide an immediate event detection criterion. After the detection of a PQ event, local maxima and minima of the cumulants around the event instant are used for the event-type classification. We have observed that the minima and maxima for each statistical order produces clusters in the feature Space. These clusters were observed to exhibit noncircular topology; hence, quadratic-type classifiers that require the Mahalanobis distance metric are proposed. The events investigated and presented are line-to-ground arcing faults and voltage sags due to the induction motor starting. Detection and classification results obtained from an experimentally staged PQ event data set are presented. [ABSTRACT FROM AUTHOR]

In this paper, a novel transformer structure is proposed in order to manufacture a high-power active filtering device. The novel transformer structure contains one primary and multiple secondary windings. The system configuration and compensation principle are addressed in detail. The fundamental magnetic flux compensation in the case of the transformer with multiple secondary windings is fulfilled. In addition, a three-phase active power filter topology consisting of three independent transformers with multiple secondary windings is presented so that the filter can run under unbalanced loads. The parameters of hysteresis current control are also analyzed in detail. A simple and practical fundamental detecting approach is discussed. Transient response and fault protection schemes are explained. A set of automatic three-phase active power filtering devices has been constructed and operated in the field. The field test results verify the validity of the novel transformer structure and the active power filtering system. [ABSTRACT FROM AUTHOR]

This paper studies the use of a voltage-source converter (VSC) with dc capacitors as an energy storage medium for the compensation of pulsating active and reactive power of the European Organization for Nuclear Research's (CERN's) proton synchrotron (PS) particle accelerator. The PS accelerator load demands periodic, active, and reactive power pulses of about 2-s duration and a magnitude of up to 45 MW and 65 Mvar. The proposed compensator is able to control both reactive and active power exchange with the network in order to eliminate network disturbances. The controllability study reveals that the best control strategy is to use a q-axis converter input for active power and a d-axis input for reactive power regulation. An analytical system model is created to study the system dynamics and to aid the controller design. The eigenvalue study with the MATLAB model reveals that with large energy storage units and small converter losses, there is only a small interaction between the control channels. The final testing is done with a detailed nonlinear model in PSCAD/EMTDC. The simulation results show that it is possible to fully compensate the active power exchange with the network during typical accelerator cycles and, at the same time, to achieve excellent ac voltage control. [ABSTRACT FROM AUTHOR]

For ferroresonant circuits, the sufficient condition for preventing fundamental ferroresonance (FF) from occuring is that there is no intersection between the voltage-current characteristic of the linear part of the circuit, and the saturated power frequency excitation characteristic of the nonlinear part. Based on this understanding, part II of this paper has presented a criterion for the possibility of FF in the form of an analytical expression which is composed of the essential parameters of the circuit. By giving the critical resistance value for damping FF, the expression clearly indicates not only the possibility of FF but also the methods for eliminating the FE The possibility of FF is judged by comparing the critical resistance value with the real value. In the meantime, the expression suggests how to adjust the essential parameters to suppress FE The criterion has been proven by both simulation results and field tests. With this criterion, the possibility and elimination of FF can be studied for the first time by a simple yet effective analytical method. [ABSTRACT FROM AUTHOR]

This paper has highlighted a major problem with the traditional excitation characteristic (TEC) of nonlinear inductors, in that the TEC contains harmonic voltages and/or currents, and has been used the way as if it were made up of pure fundamental voltage and current. In comparison to the TEC, a new concept, namely the power frequency excitation characteristic (PEC), which contains no harmonics, has been put forward. Two methods have been presented in obtaining the PEC. The first method is based on Electromagentic Transients Program simulation, resulting in discrete voltage and current pairs. This method essentially acts as a reference to validate the second one. The second method em- ploys Fourier and Maclaurin series approximation techniques, and brings forth a simple yet effective analytical expression. The expression is proven to have satisfactory precision in the saturated region of the PEC, especially in the extremely saturated region. [ABSTRACT FROM AUTHOR]

Potential applications of probabilistic modeling of current and voltage harmonics concern many aspects of power system engineering as accurate prediction of power system harmonic behavior provides important information to utility companies and equipment designers. In this paper, a method of reducing the expected value of the total voltage harmonic distortion for a specified range of source impedance values at different buses by using LC compensators, where it is desired to maintain a given power factor at a specified value, is presented. The criterion is based on mean value estimation of source and load characteristics, which are enabled by sampling measurements performed on the examined electrical plant as well as statistical analysis. [ABSTRACT FROM AUTHOR]

Distributed measurement architecture, due to its efficiency, is used to monitor the power quality in the electric systems. This paper introduces a novel algorithm to determine the optimum allocations of power quality monitors to reduce the cost of the distributed monitoring system taking into account the data redundancy. The optimization problem is formulated as a covering and packing one which can be manipulated by integer linear programm algorithms. The appropriate constraints are deduced by the electrical circuit topology independent of the load parameters. In addition, the problem is adopted to a general form which can be implemented by any optimization package. The proposed algorithm is applied to five different systems for validation. Then, the results are discussed in terms of the cost and data redundancy. [ABSTRACT FROM AUTHOR]

This paper describes an algorithm for calculating the direction to a flicker source with respect to a monitoring point. The proposed algorithm is based on sampling of both the voltage and current. The low-frequency fluctuations in voltage and current are recovered from the input signals by demodulation, and passed through a bandpass filter as described in IEC 61000-4-15. A new quantity—flicker power—defined from the output signals of the two filters. The direction to a flicker source is obtained from the sign of this flicker power. The proposed algorithm has been validated by simulations and several field measurements. [ABSTRACT FROM AUTHOR]

This paper introduces a small-signal dynamic model of a fixed-frequency (induction machine based) wind farm connected to an electrical power system. The model represents the system small-signal dynamics in the frequency range of a fraction of Hz to 50/60 Hz. The model includes the dynamics of the wind energy capturing mechanism, the rotating shaft system, the generator electrical system of each wind energy unit, the wind farm collector system, and the utility grid. Based on the proposed model, two performance indices are introduced to i) investigate sensitivity of the system modes, e.g., torsional modes, to the system parameters, and ii) evaluate the system capability to reject electrical and mechanical disturbances, e.g., a wind gust. The application of the model to the analysis of a system with two wind units is presented and the study results are validated based on comparison with the time-domain simulation results obtained in the PSCAD/EMTDC environment. [ABSTRACT FROM AUTHOR]

This paper discusses the uncertainty involved in the behavior of sensitive equipment used in various industrial processes and the methodology to incorporate this effect in quantifying the equipment trips due to voltage sags over a specified time period. The exact and more precise counting of equipment trips is essential for the accurate economic assessment of power quality. Existing standards and previously published test results on the sensitivity of this equipment against voltage sags are critically reviewed and possible ranges for variation in equipment sensitivity are investigated. Four different probable behaviors within respective ranges were considered for the stochastic assessment of equipment trips due to voltage sags. This study is performed on a generic power system. [ABSTRACT FROM AUTHOR]