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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]

In locations exposed to freezing conditions over the station service life, additional measures for selecting adequate station insulators at distribution and transmission voltage levels should be taken. This second part of the paper describes the selection process and mitigation options, based on the environmental parameters, as discussed in Part I. These include insulator size, shape, surface material, surface quality, electric field improvement, and orientation. [ABSTRACT FROM AUTHOR]

Directional relays use voltage as the polarizing quantity. When three-phase faults occur close to the relay bus, the available voltage becomes nearly zero and this creates a problem in estimation of the fault direction. The capacitor coupling voltage transformer subsidence transients add to this problem. The memory voltage used as the polarizing quantity at these situations is a compromise. This paper highlights these issues and proposes a simple solution using the power-flow direction in addition to other information. The performance of the technique is evaluated through simulation in Power System Computer Aided Design. [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]

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]

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]

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]

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]

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]

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 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]

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 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]

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]

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 presents a systematic approach to develop a dynamic model for a matrix converter. The matrix converter interfaces two three-phase ac systems that can be at different voltages and/or frequencies, e.g., a high-speed micro-turbine generator and a utility distribution system. The model is developed by (i) transferring the abc frame equations to a newly defined switching reference frame and then (ii) transferring the resultant equations to a rotating dqo frame. The model is then linearized and the concept of "sequential loop closing" is used to design a controller for the matrix converter as a multi-input multi-output system. The accuracy of the developed model and performance of the controller are evaluated based on comparing the study results with those obtained from digital time-domain simulations in the PSCAD/EMTDC software environment. [ABSTRACT FROM AUTHOR]

This paper describes the development and implementation of a tool for the diagnosis of faults in power transformers through the analysis of dissolved gases in oil. The computational system approach is based on the combined use of some traditional criteria of the dissolved gas analysis published in standards, an artificial neural network, and a fuzzy logic system. The objective of the tool is to provide the user with an answer obtained from analysis not only of the traditional methods already consolidated in the technical literature, but also via artificial-intelligence techniques, reaching a higher degree of reliability with respect to each technique individually. The results obtained with this tool are promising in the diagnosis of incipient faults in transformers, reaching success levels of more than 80%. [ABSTRACT FROM AUTHOR]

In Japan during the 20th century, developments of high voltage transmission and distribution apparatus advanced tremendously and circuit breakers were the center of these developments. And as a result, 1100 kV SF6 gas insulated switchgear (GIS) for ac transmission systems and also 500 kV dc GIS for dc transmission systems have become available. Vacuum circuit breakers (VCBs) have also been actively developed and a 168 kV two break VCB and 100 kA VCB are already available. This paper describes these developments and future trends in technology. [ABSTRACT FROM AUTHOR]

Spring mechanisms have demonstrated their high reliable performance by operating thousands of circuit breakers (CBs) safely all over the world for decades under the most severe conditions. This well-known technology could be improved, when merged with a servo motor system. The result is a hybrid drive, which offers the accuracy and flexibility of servomechanisms and the reliability of spring operating mechanisms. The paper starts with a reminder of the state of the art of operating mechanisms, followed by an overview of spring mechanisms with the aim of identifying potential improvements. The remaining part is dedicated to the first evolution of the hybrid drive. The architectural description emphasizes the reliability aspects, especially due to the application of redundant tripping circuits, allowing the tripping operation without either an auxiliary power supply or electronic support. Test results are discussed. The conclusion illustrates that if technical benefits are obtained, the cost of some critical components still remains high. The applications of such a hybrid technology are restricted today to specific applications. As the prices of electronic systems decrease with time and, hopefully, the cost of low inertia motors, the architecture of operating mechanisms could be dramatically modified and tightly merged with the CB. The advantages of hybrid drives could be decisive for the long-term future. [ABSTRACT FROM AUTHOR]

In this paper, three element-oriented models based on simplified Bayesian networks with Noisy-Or and Noisy-And nodes are proposed to estimate the faulty section of a transmission power system. The three models are used to test if any transmission line, transformer, or busbar within a blackout area is faulty. They can deal with uncertain or incomplete data and knowledge relating to power system diagnosis, so they are flexible. The structures and initial parameters of the Bayesian networks depend on the prior knowledge of the domain experts. The parameters can be revised by using an error back propagation algorithm similar to the back- propagation algorithm for artificial neural networks. The fault diagnosis models do not vary with the change of the network structure, so they can be applied to any transmission power system. Furthermore, they have clear semantics, rapid reasoning, powerful error tolerance ability, and no convergence problem during the diagnosing procedure. Experimental tests show that the approach is feasible and efficient, so the prototype program based on the approach is promising to be used in a large transmission power system for online fault diagnosis. [ABSTRACT FROM AUTHOR]

This paper presents a new algorithm for locating faults on two-terminal power transmission lines. Unsynchronized two-end voltages and currents are processed for determining the sought distance to fault and the synchronization angle. The calculations are performed initially for the lumped model of a transmission line. Then, these results are used as the initial data for the Newton-Raphson method-based iterative calculations, in which the distributed parameter line model is utilized. The delivered fault location algorithm has been tested and evaluated with the fault data obtained from versatile ATP-EMTP simulations. The sample results of the evaluation are reported and discussed. [ABSTRACT FROM AUTHOR]

It is essential to extract the stray parameters accurately and efficiently in analyzing impulse responses of a power apparatus. In this paper the stray capacitances and stray inductances of a 500-kV dc transmission-line voltage divider are extracted by the hybrid finite element-analytical approach, and the corresponding equivalent circuit for analyzing the impulse voltage response of the voltage divider is established. According to the discussion of the results of the extracted stray parameters of the voltage divider, reasonable simplification of the equivalent circuit of the voltage divider is made. In addition, the influence of the insulating housing and the electrical insulation oil on the stray capacitances of the voltage divider is discussed. [ABSTRACT FROM AUTHOR]

A dynamic model which describes the impulse behavior of concentrated grounds at high currents is described in this paper. This model is an extension of previous models in that it can successfully account for the surge behavior of concentrated grounds over a much wider range of current densities. It is able to describe the well known effect of ionization of soil as well as the observed effect of discrete breakdowns and filamentary arc paths at much higher currents. Results of verification against experimental results are also presented. [ABSTRACT FROM AUTHOR]

Fault arc tests showed that the three-phase fault arc currents depend on the arrangement of electrodes at the fault site and vary stochastically. Up to now, experimental investigations have mainly been carried out for the medium-voltage switchgears, and the fault arc currents are either recognized by the experimental results or derived by the probability method. A calculation method used for the determination of the three-phase fault arc currents is introduced in this paper, which can be expressed accurately by mathematics according to the characteristics of the three-phase internal faults. [ABSTRACT FROM AUTHOR]

Harmonic amplification and interaction of the PV plant which contains multiple parallel inverters influence the renewable power generation and operation seriously. In this article, the resonance mechanism and characteristics of a real large-scale PV plant are explored based on its plant-level circuit model. The component and system models are established first. The distribution rules of wideband resonance frequency from the perspective of the point of common coupling (PCC) and the inverter are respectively determined. Two different resonance bands excited by LCL filter and underground cable are further identified. At last, the practical case of harmonic resonance in the studied PV plant is investigated. Both the measured data and the simulation results support the analytical conclusions. This article combines the theoretical study with the engineering practice, which provides beneficial guidance on the resonance prevention. [ABSTRACT FROM AUTHOR]