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The article presents a list of power system relaying references. The bibliography include references to the subjects of service restoration, testing and methods of calculations. The references include the title, author, publication information and a brief summary of the subject matter. A list of section titles is provided.

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]

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]

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]

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]

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]

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 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]

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]

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]

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]

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]

Adjustable Speed Drives (ASDs) have become the primary choice for most new and retrofit precision motor-control applications, offering major improvements in system efficiency. The significant increase in the use of ASDs makes it important to understand the compatibility issues between ASDs and their electrical environment in order to appropriately design the electrical systems. Even though there have been numerous studies addressing ASD effects on power systems, models for predicting the effect of the source voltage sags or unbalance have been limited. This paper is devoted to the analysis of utility-side input current harmonics under input voltage unbalance and sag conditions and the effects of these harmonics on the distribution transformer K-factor for practical ASD systems. The relationships between the unbalanced input voltages, the resulting input current harmonics, the input inductance, and the required transformer K-factor are explored for 5 hp, 100 hp, and 600 hp power distribution systems with ASDs. The results can be used as a design guide for power distribution system design with ASDs. Theoretical derivations are accompanied by both simulations and experimental results to provide verification of key conclusions. [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 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]

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 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]

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 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]

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 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]

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]

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]

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]

In order to remove the present IEC 60060-1 and IEEE Standard 4 ambiguities in the evaluation of the test voltage when oscillations and/or an overshoot appear superimposed in a lightning impulse, at the end of the 1990s, a European Project within the Standard, Measurement and Testing (SMT) program was developed by KEMA (Netherlands), Schering Institute (Germany), LCOE (Spain), and NGC (United Kingdom) in coordination with the CIGRE Working Group 33.03. The conclusion of this European Project is a new evaluation method called test voltage function K(f) derived on the breakdown behavior of different dielectric media, that removes the standard ambiguity to determine the test voltage of an impulse with oscillations and/or an overshoot. This paper presents the experimental results of the project and deals in depth with the definition of K(f). [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]

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]

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]

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 presents system modeling and control design for fast load voltage regulation using static compensators (STATCOMs). The modeling strategy gives a clear representation of load voltage magnitude and STATCOM reactive current on an instantaneous basis. The particular coordinate transformation employed here also facilitates extraction of linearized system dynamics in conjunction with circuit simulators. It is rigorously shown that the control problem of load voltage regulation using reactive current is nonminimum phase. Linear and nonlinear controllers for the regulation problem are designed and compared via simulation results. Internal dynamics of the STATCOM are modeled using the same strategy. Lyapunov based adaptive controllers are designed for controlling the STATCOM reactive current while maintaining its dc bus voltage. Simulation results of the controlled STATCOM integrated with the load bus voltage controller are presented to show efficacy of the modeling and control design. [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]

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]

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]

The measurement of real and apparent power derating of three-phase transformers is important for transformers feeding nonlinear loads. This paper presents a new digital data-acquisition method for measuring derating and reactive power demand of three-phase transformers under full or partial load conditions. The accuracy requirements of the instruments employed (potential, current transformers, shunts, voltage dividers, optocoupIers volt- and current meters) are addressed. Application examples demonstrate the usefulness of this new digital data-acquisition method. [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]

This paper presents the application of a combined adaptive Fourier filtering technique and fault detector to fast distance protection of transmission lines. The filtering technique is extended from the Fourier filters and can be applied under arbitrary data window length. The proposed filtering technique possesses the advantage of recursive computing, and a decaying dc offset component is removed from fault signals by using an adaptive compensation method. A variable data window scheme is embedded in the technique to adaptively speed up its transient response under various system and fault conditions. A fault detector is developed to initiate the process of the technique. For the sake of speed and security, two phasor estimation methods based on the proposed technique are designed to achieve fast distance protection. An algorithm consisting of the two methods is used to detect internal faults by "OR" logic. Extensive simulation studies show that the algorithm significantly reduces tripping time of a distance relay and provides better protection performance than that of the conventional filters with fixed data windows. [ABSTRACT FROM AUTHOR]

This paper proposes an agent-based paradigm for self-healing protection systems. Numerical relays implemented with intelligent electronic devices are designed as a relay agent to perform a protective relaying function in cooperation with other relay agents. A graph-theory-based expert system, which can be integrated with supervisory control and a data acquisition system, has been developed to divide the power grid into primary and backup protection zones online and all relay agents are assigned to specific zones according to system topological configuration. In order to facilitate a more robust, less vulnerable protection system, predictive and corrective self-healing strategies are implemented as guideline regulations of the relay agent, and the relay agents within the same protection zone communicate and cooperate to detect, locate, and trip fault precisely with primary and backup protection. Performance of the proposed protection system has been simulated with cascading fault, failures in communication and protection units, and compared with a coordinated directional overcurrent protection system. [ABSTRACT FROM AUTHOR]

Wide area measurements have been widely used in the energy management systems (EMS) of power systems for monitoring, operation, and control. In recent years, the advent of synchronized phasor measurements has added another dimension to the field of wide-area measurements. At the same time, the field of protection systems has been dominated by computer based relays, which make it relatively easy to communicate with relays and thus include them in many innovative protection systems. Special Protection Systems (SPS) or Remedial Action Schemes (RAS) are one example of integration of communication and protection systems. In recent years-due to operational demands imposed on transmission networks by deregulation it has become clearer that wide-area measurements and their integration in protection and control systems is a necessity. This paper documents the state-of-the-art in modem sensor, communication, and protection technologies which show great potential for innovations in protection and control systems for the future. [ABSTRACT FROM AUTHOR]